Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
ICS 91.100.30 ISBN 0-626-10153-0
SABS 0100-2*
*This standard references other standards
Edition 2
1992 (As amended 1994)
SOUTH AFRICAN STANDARD Code of practice
The structural use of concrete Part 2: Materials and execution of work
Reprint 1994 Published by THE SOUTH AFRICAN BUREAU OF STANDARDS
Gr 15
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
SABS 0100-2 Ed. 2
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
SABS 0100-2 Ed. 2
ICS 91.100.30
(As amended 1994)
SOUTH AFRICAN BUREAU OF STANDARDS CODE OF PRACTICE THE STRUCTURAL USE OF CONCRETE PART 2: MATERIALS AND EXECUTION OF WORK
Obtainable from the South African Bureau of Standards Private Bag X191 Pretoria Republic of South Africa 0001 Telephone Fax E-mail Website
: (012) 428-7911 : (012) 344-1568 :
[email protected] : http://www.sabs.co.za
COPYRIGHT RESERVED Printed in the Republic of South Africa by the South African Bureau of Standards
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
SABS 0100-2 Ed. 2
Notice This part of SABS 0100 was approved in accordance with SABS procedures on 20 February 1992. NOTE 1 In terms of the Standards Act, 1993 (Act 29 of 1993), no person shall claim or declare that he or any other person complied with an SABS standard unless a) such claim or declaration is true and accurate in all material respects, and b) the identity of the person on whose authority such claim or declaration is made, is clear. NOTE 2 It is recommended that authorities who wish to incorporate any part of this standard into any legislation in the manner intended by section 31 of the Act consult the SABS regarding the implications.
This part of SABS 0100 will be revised when necessary in order to keep abreast of progress. Comment will be welcome and will be considered when this part of SABS 0100 is revised.
Foreword This second edition (first revision) cancels and replaces SABS 0100-2:1980. Annex A (Concrete subjected to wet conditions - aggressiveness of the water, and countermeasures) forms an integral part of this part of SABS 0100. Annex B (Curing), annex C (Technical data for prestressed structural elements required in a contract), annex D (Recommended specialist literature on massive concrete) and annex E (Bibliography) are for information only.
Reprint incorporating Amendment No. 1: 12 September 1994
Attention is drawn to the normative references given in clause 2 of this standard. These references are indispensable for the application of this standard.
ISBN 0-626-10153-0
ii
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
SABS 0100-2 Ed. 2
Contents Page Notice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ii
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ii
Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
x
1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3.1 3.2 3.3 3.4 3.5 3.6
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conditions of exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete, general characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete, strength characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prestressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 3 3 4 5 5
4 Materials for concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
4.1 4.1.1 4.1.2 4.2 4.3 4.3.1 4.3.2 4.3.3 4.3.4 4.3.5 4.3.6 4.3.7 4.3.8 4.3.9 4.4 4.4.1 4.4.2 4.4.3 4.5
Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Properties of concrete made with a blend of cement and cement extenders . . . Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aggregate classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Natural aggregates covered by SABS 1083 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aggregates not covered by SABS 1083 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nominal maximum size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aggregates for high-strength concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aggregates and fire resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aggregates and concrete density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Use of "plums" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Admixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air-entraining agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deteriorated material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 6 7 7 7 7 7 8 8 8 8 8 8 9 9 9 10 10 10
5 Plant for concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
5.1 5.2 5.3 5.4
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Batching plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mixing plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vibrators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10 10 10 11
iii
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
SABS 0100-2 Ed. 2 (As amended 1994) 6 Proportioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 6.1.1 6.1.2 6.1.3 6.1.4 6.1.5 6.1.6 6.1.7 6.1.8 6.1.9 6.1.10 6.2 6.2.1 6.2.2 6.2.3 6.2.4 6.2.5 6.2.6 6.3 6.3.1 6.3.2 6.3.3 6.3.4
11
Quality of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Density of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Consistence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Workability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bleeding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chloride content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulfates in concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alkali-silica reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drying shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Durability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Exposure to freezing and thawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Exposure to aggressive chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Exposure to salt-laden air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Exposure to corrosive fumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Exposure to polluted air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mix proportions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . High cement content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete exposed only to mild conditions . . . . . . . . . . . . . . . . . . . . . . . . . . Deleted by Amendment No. 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deleted by Amendment No. 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11 11 11 11 12 12 12 12 13 13 13 14 14 14 15 16 17 17 17 17 17 17 17
7 Production of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
Amdt 1, Sept. 1994
7.1 7.1.1 7.1.2 7.1.3 7.1.4 7.2 7.2.1 7.2.2 7.3
Batching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Admixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mixing on site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ready-mixed concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18 18 18 18 18 18 18 20 20
8 Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
8.1 8.2 8.3 8.3.1 8.3.2 8.4 8.4.1 8.4.2 8.4.3 8.5 8.5.1 8.5.2 8.5.3 8.5.4 8.5.5 8.5.6
iv
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cover to reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preheating prior to bending or straightening . . . . . . . . . . . . . . . . . . . . . . . . . Fixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steel reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Zinc-coated (galvanized) reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . Epoxy-coated reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Use of welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Location of welded joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strength of structural welded joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Welded lapped joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21 21 22 22 22 22 22 24 24 24 24 24 24 25 25 25
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
SABS 0100-2 Ed. 2 9 Formwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1 9.2 9.2.1 9.2.2 9.2.3 9.2.4 9.3 9.4 9.5 9.5.1 9.5.2 9.5.3
25
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design and construction of formwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Form accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Temporary openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of formwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Re-use of formwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Removal of formwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Formwork removal time for cast-in-situ concrete . . . . . . . . . . . . . . . . . . . . . . . . . Reshoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25 26 26 26 26 26 26 26 27 27 27 28
10 Placing and protection of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
10.1 10.2 10.3 10.4 10.4.1 10.4.2 10.4.3 10.4.4 10.4.5 10.5 10.5.1 10.5.2 10.5.3 10.6 10.7 10.8 10.8.1 10.8.2 10.8.3 10.8.4 10.9 10.9.1 10.9.2 10.9.3 10.10
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Placing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Embedded items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Waterstops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pipes and conduits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete for water-retaining structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete in saturated ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Protection and curing of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concreting in hot weather or in windy conditions . . . . . . . . . . . . . . . . . . . . . . . . Concreting in cold weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concreting during rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Surface finish of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Upper surfaces of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete surfaces cast against forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Repair of surface defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29 29 30 31 31 31 31 32 32 33 33 33 33 34 34 34 34 35 36 36 36 36 36 37 37
11 Massive concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
12 Prestressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
38
12.1 12.1.1 12.1.2 12.1.3 12.1.4 12.1.5 12.1.6 12.1.7
Prestressing tendons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Handling and storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Surface condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Straightness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cutting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Formwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
38 38 38 38 39 39 39 39
v
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
SABS 0100-2 Ed. 2 12.2 12.2.1 12.2.2 12.2.3 12.2.4 12.2.5 12.3 12.4 12.5 12.5.1 12.5.2 12.5.3 12.5.4 12.5.5 12.5.6 12.5.7 12.5.8 12.5.9
Tensioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Safety precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tensioning apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pre-tensioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Post-tensioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Positioning of tendons and sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tensioning procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grouting of prestressing tendons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grouting equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strength of grout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Injection of grout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grouting during cold weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Protection and bond of prestressing tendons . . . . . . . . . . . . . . . . . . . . . . . . . . .
40 40 40 40 41 41 42 43 44 44 44 44 45 45 45 45 46 46
13 Precast concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47
13.1 13.2 13.3 13.4 13.4.1 13.4.2 13.4.3 13.4.4 13.4.5 13.4.6
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Permissible deviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prestressed units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Handling and erection of precast concrete units . . . . . . . . . . . . . . . . . . . . . . . . . Lifting equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Handling and transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Assembly and erection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Temporary supports during construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forming structural connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47 47 48 48 48 48 49 49 49 51
14 Testing and acceptance of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
51
14.1 14.2 14.2.1 14.2.2 14.2.3 14.2.4 14.2.5 14.3 14.3.1 14.3.2 14.3.3 14.4 14.4.1 14.4.2 14.4.3
vi
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Testing services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basic testing services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Testing services required by the engineer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Additional services when required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Test reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Responsibilities and duties of the contractor . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strength tests of concrete during construction . . . . . . . . . . . . . . . . . . . . . . . . . . General procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Evaluation of strength test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acceptance criteria for strength test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strength tests of concrete in place . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Non-destructive testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Core tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acceptance of concrete on the basis of core strengths . . . . . . . . . . . . . . . . . . . .
51 51 51 51 52 52 52 52 52 53 53 54 54 54 54
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
SABS 0100-2 Ed. 2 (As amended 1994) 15 Load tests
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55
Individual precast units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Non-destructive test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Destructive test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Special test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structures and parts of structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Age at test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Test loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Measurements during the tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Assessment of results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
55 55 55 55 55 55 55 55 56 56 56
16 Procedure in the event of failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
57
15.1 15.1.1 15.1.2 15.1.3 15.1.4 15.2 15.2.1 15.2.2 15.2.3 15.2.4 15.2.5
Tables 1 2 3 4 5 6 7 8
Limits of chloride content of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Total air content for various sizes of coarse aggregate for normal-density concrete . . . . Cement/water ratio and cement content for normal-density reinforced concrete and low-density reinforced concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement/water ratio and cement content for normal-density unreinforced concrete . . . . . Minimum cover for various conditions of exposure and cement/water ratios for normal-density concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum cover for various conditions of exposure and cement/water ratios for lowdensity concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Removal of formwork: minimum time in days . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Permitted tolerance in the location of tendons and sheathing . . . . . . . . . . . . . . . . . . . . . .
13 14 17 17 21 21 28 42
Annexes A Concrete subjected to wet conditions - aggressiveness of the water, and countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.1 A.2 A.3 A.4
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Analytical tests required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Assessment of the aggressiveness of water, using the Basson Index (BI) . . . . . . . Recommended anti-corrosion measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
58 58 58 59 61
Tables A.1 A.2 A.3 A.4 A.5 A.6 A.7 A.8 A.9 A.10
Ionic characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculation of water properties indices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculation of environmental indices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Classification of water in terms of Basson Index BI . . . . . . . . . . . . . . . . . . . . Countermeasures against leaching corrosion . . . . . . . . . . . . . . . . . . . . . . . . . Countermeasures against spalling corrosion . . . . . . . . . . . . . . . . . . . . . . . . . Countermeasures against chloride corrosion . . . . . . . . . . . . . . . . . . . . . . . . . Concretes for aggressive chemical environments . . . . . . . . . . . . . . . . . . . . . Cements recommended for the making of concretes for aggressive waters . Coatings for concretes in aggressive waters . . . . . . . . . . . . . . . . . . . . . . . . . .
58 59 60 60 61 63 63 64 65 66
Amdt 1, Sept. 1994
vii
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
SABS 0100-2 Ed. 2 Blank
viii
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
SABS 0100-2 Ed. 2 B Curing
...........................................................
67
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strength of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Distortion and cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Durability and appearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
67 67 67 68
C Technical data for prestressed structural elements required in a contract . . . . . . . . . . . .
69
B.1 B.2 B.3 B.4
C.1 C.2
Data for pre-tensioned elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Data for post-tensioned elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
69 70
D Recommended specialist literature on massive concrete . . . . . . . . . . . . . . . . . . . . . . . . .
72
E Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
72
ix
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
SABS 0100-2 Ed. 2
Committee South African Bureau of Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VJ Woodlock (Chairman) I Jablonski (Standards writer) E Coetzee (Committee clerk)
CSIR Division of Building Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
BG Lunt
Portland Cement Institute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
BJ Addis
South African Federation of Civil Engineering Contractors . . . . . . . . . . . . .
HH Meier
The South African Association of Consulting Engineers . . . . . . . . . . . . . . .
GJ de Ridder
The South African Institute of Civil Engineers . . . . . . . . . . . . . . . . . . . . . . .
AE Goldstein
x
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
CODE OF PRACTICE
SABS 0100-2 Edition 2
The structural use of concrete Part 2: Materials and execution of work
1 Scope 1.1 This part of SABS 0100 covers the materials and execution of work related to the structural use of concrete in buildings and structures where the design of reinforced, prestressed and precast concrete is entrusted to appropriately qualified structural or civil engineers and the execution of the work is carried out under the direction of appropriately qualified supervisors.
1.2 This part of SABS 0100 does not cover the structural use of concrete made with high-alumina cement.
2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this part of SABS 0100. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of SABS 0100 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Information on currently valid national and international standards may be obtained from the South African Bureau of Standards. PCI. TM 9.28. SABS 82:1976, Bending dimensions of bars for concrete reinforcement. SABS 471:1971, Portland cement (ordinary, rapid-hardening and sulphate-resisting). SABS 626:1971, Portland blastfurnace cement. SABS 831:1971, Portland cement 15 (ordinary and rapid-hardening). SABS 878:1983, Ready-mixed concrete. SABS 920:1985, Steel bars for concrete reinforcement.
1
Copyright protected. This standard may only be used and printed by subscribers to the SABS’ Complete Collection of Standards and Related Documents in accordance with a formal copyright agreement.
SABS 0100-2 Ed. 2 SABS 1024:1974, Welded steel fabric for concrete reinforcement. SABS 1083:1976, Aggregates from natural sources. SABS 1200 G:1982, Standardized specification for civil engineering construction: Concrete (structural). SABS 1466:1988, Portland fly ash cement. SABS 1491-1:1989, Portland cement extenders - Part 1: Ground granulated blastfurnace slag. SABS 1491-2:1989, Portland cement extenders - Part 2: Fly ash. SABS 1491-3:1989, Portland cement extenders - Part 3: Condensed silica fume. SABS 0100-1:1980, Structural use of concrete - Part 1: Design. SABS 0109:1969, Floor finishes on concrete. SABS 0144:1978, Detailing of steel reinforcement for concrete. SABS 0155:1980, Accuracy in buildings. SABS method 11:1990, Water - pH value. SABS method 202:1983, Chloride content of water. SABS method 212:1971, Sulphate content of water. SABS method 213:1990, Water - Dissolved solids content. SABS method 216:1990, Water - Calcium content. SABS method 217:1990, Water - Free and saline ammonia content. SABS method 218:1971, Albuminoid ammonia content of water. SABS method 856:1976, Bulking of fine aggregates. SABS method 861:1976, Sampling of freshly mixed concrete. SABS method 862:1976, Slump of freshly mixed concrete. SABS method 863:1976, Compressive strength of concrete (including making and curing of the test cubes). SABS method 865:1982, The drilling, preparation, and testing of concrete cores. SABS method 1071:1990, Water - Magnesium content. SABS method 1085:1985, Initial drying shrinkage and wetting expansion of concrete.
3 Definitions For the purposes of this part of SABS 0100, the following definitions apply:
2
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SABS 0100-2 Ed. 2 3.1 General 3.1.1 acceptable/approved: Acceptable to/approved by the engineer. 3.1.2 cement: Portland cement; blends of portland cement and portland cement extenders as covered in SABS 1491. 3.1.3 concrete cover: The thickness of concrete between the face of the concrete, as cast, and the outer face of reinforcing steel, prestressing steel, steel used for binding the reinforcing, or any embedded steel. 3.1.4 contractor: The individual who, or the organization that, has entered into an agreement to carry out the work specified. 3.1.5 engineer: The representative appointed by the owner to administer the requirements of a project specification for specific concrete work.
3.1.6 formwork: All the temporary aids and material required to support, and to provide the shape of, the concrete in a structure (while the concrete is in the fresh state). 3.1.7 ready-mixed concrete: Concrete that complies with the relevant requirements of the project specification and as further defined in SABS 878.
3.2 Weather 3.2.1 adverse weather: Cold weather or a combination of a high ambient temperature, low relative humidity and high wind velocity, which may tend to impair the quality of fresh or hardening concrete or otherwise cause hardened concrete to have undesirable properties.
3.2.2 cold weather: Weather in which the ambient temperature is 5 °C or less. 3.2.3 cool weather: Weather in which the ambient temperature exceeds 5 °C but does not exceed 15 °C.
3.2.4 hot weather: Weather in which the ambient temperature exceeds 32 °C. 3.2.5 normal weather: Weather in which the ambient temperature exceeds 15 °C but does not exceed 32 °C.
3.3 Conditions of exposure NOTE - For the definitions of - non-aggressive to mildly aggressive water, - mildly to fairly aggressive water, and - highly aggressive water, see table A.4 of annex A, and for an explanation of wet conditions, see the commentary below.
3.3.1 mild conditions: The concrete is exposed generally to unpolluted air. For example:
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SABS 0100-2 Ed. 2 - indoors (but not including industrial areas); or - out of doors in arid rural areas (Karoo).
3.3.2 moderate conditions: The concrete is a) sheltered from severe rain; b) buried in non-aggressive soil; or c) subject to polluted air (but not corrosive fumes). For example: - indoors in industrial areas; or - out of doors in rural Highveld areas.
3.3.3 severe conditions: The concrete is exposed to a) wet conditions in which the water is mildly to fairly aggressive; b) corrosive fumes; or c) salt-laden air. For example: - out of doors in industrial areas; - out of doors in marine atmospheric conditions (i.e. up to 15 km from the sea); or - out of doors in the Cape winter-rainfall area.
3.3.4 very severe conditions: The concrete is exposed to a) wet conditions in which the water is mildly to fairly aggressive; b) abrasive action under any wet conditions; or c) highly corrosive fumes.
3.3.5 extreme conditions: The concrete is exposed to wet conditions in which the water is highly aggressive. COMMENTARY - Conditions are considered wet if the concrete is exposed to water continuously or intermittently. The effect on the concrete of exposure to water depends on the aggressiveness of the water, the period of time during which the concrete is wet, and the frequency of the wet-dry cycling. It is not possible to propose definite limits in this regard. However, it should be kept in mind that highly aggressive water can have a seriously detrimental effect on concrete even if the period of time during which the concrete is exposed to such water is short.
3.4 Concrete, general characteristics 3.4.1 consistence: The extent (usually measured by the slump test) to which fresh concrete flows or can be deformed.
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SABS 0100-2 Ed. 2 (As amended 1994)
3.4.2 grade of concrete: An identifying number for a particular concrete, which is numerically equal to the characteristic strength at 28 d, expressed in megapascals.
3.4.3 high-density concrete: Concrete made of a high-density aggregate complying with SABS 1083 and that usually has a density in the range 2 500 kg/m3 to 3 600 kg/m3.
Amdt 1, Sept. 1994
3.4.4 low-density concrete: Concrete intentionally made to have low density by the use of low-density aggregate or a mixture of low-density and normal-density aggregates, and usually required to have an air-dry density not exceeding 2 000 kg/m3.
3.4.5 normal-density concrete: Concrete made with aggregates complying with SABS 1083 and that usually has a density in the range 2 200 kg/m3 to 2 500 kg/m3.
3.4.6 precast concrete: Concrete that consists of units cast and cured in a position other than their final position, and placed in position to form an integral part of the structure.
3.4.7 prescribed-mix concrete: Concrete for which the engineer has prescribed the mix proportions. 3.4.8 strength concrete: Concrete designed primarily for strength considerations and designated by its characteristic strength in conjunction with the maximum nominal size of stone used in its manufacture, e.g. 30 MPa/19 mm.
3.4.9 target slump: The average value for the slump of concrete aimed for to ensure compliance with the slump required.
3.4.10
workability: The property of fresh concrete that determines the ease of placing and compacting the concrete without segregation of its constituent materials.
3.5 Concrete, strength characteristics 3.5.1 characteristic strength: The value for the compressive strength of concrete, below which not more than 5 % of the valid test results obtained on cubes of concrete of the same grade fall.
3.5.2 specified strength: The characteristic strength required by the engineer. 3.5.3 target strength: An average value of the strength of concrete that is higher than the specified strength, and that is aimed for to ensure that the characteristic strength is attained. 3.5.4 valid test result: The average result obtained from three test cubes of concrete that have been tested in accordance with SABS method 863, with the additional requirement that curing water be maintained at a temperature between 22 °C and 25 °C.
3.6 Prestressing 3.6.1 anchorage: A device used to anchor a tendon to the concrete member. 3.6.2 bonded tendon: A prestressing tendon that is bonded to the concrete throughout its effective length, either directly (by being cast into the concrete) or by grouting. 3.6.3 coating: Material applied to unbonded tendons to protect them from corrosion, or material applied to either bonded or unbonded tendons to lubricate them during stressing.
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SABS 0100-2 Ed. 2 3.6.4 coupler: A device designed to transfer the prestressing force from one tendon to another. 3.6.5 sheathing: An enclosure in which tendons intended to be post-tensioned are encased, to
prevent bonding during concrete placement (e.g. a paper or plastics jacket for unbonded tendons, or metal conduit for bonded tendons).
3.6.6 tendon: An assemblage of steel elements (e.g. wire, bar or strand) used to impart prestress to concrete when the assemblage is tensioned.
3.6.7 unbonded tendon: A tendon that is not bonded to the concrete.
4 Materials for concrete 4.1 Cement 4.1.1 General 4.1.1.1 SABS specifications cover the following: a) portland cements: these cements shall comply with SABS 471, Portland cement (ordinary, rapid-hardening, and sulphate-resisting); b) cements containing ground granulated blastfurnace slag or fly ash: these cements shall comply with the applicable of the following specifications: - SABS 831, Portland cement 15 (ordinary and rapid-hardening); - SABS 626, Portland blastfurnace cement; or - SABS 1466, Portland fly ash cement. NOTE - Any type of cement other than those referred to in 4.1.1.1 may be used when so required in terms of the project specification or when specifically authorized by the engineer.
4.1.1.2 Cement extenders shall comply with the applicable of the following specifications: - SABS 1491-1, Ground granulated blastfurnace slag (GGBS); - SABS 1491-2, Fly ash (FA); or - SABS 1491-3, Condensed silica fume (CSF). NOTE - It is recommended that users of cement extenders consult producers of the extender or appropriate publications of recognized institutions (Portland Cement Institute or CSIR).
4.1.1.3 Cements for sulfate-resisting concrete shall be chosen in accordance with the procedures given in annex A, taking into account the factors described in 6.2.3. Sulfate-resisting cements may have a lower resistance to chloride-ion migration than other cements. 4.1.1.4 For particular regions, or where it is suspected that alkali-silica reaction may occur, it may be necessary to use cement of low alkali content (Na2O + 0,658 K2O) or aggregate of low potential alkali-silica reactivity. 4.1.1.5 The type of cement to be used in each part of the structure shall be specified by the engineer, and the cement used in the structure shall correspond to that specified. The type and source of cement may not be changed during the duration of a contract without the approval of the engineer.
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SABS 0100-2 Ed. 2 4.1.1.6 Separate storage facilities shall be provided on the site for each type of cement used, and cement shall be stored in weatherproof conditions. Storage of cement in bulk is permissible provided that the cement drawn for use is measured by mass and not by volume. Provision shall be made to ensure that different types of cement are stored in suitable silos. Cement shall be stored in such a manner that the oldest cement is used first. Cement extender on its own or masonry cement shall not be used as cement for concrete works.
4.1.2 Properties of concrete made with a blend of portland cement and cement extenders 4.1.2.1 Strength 28 d strengths (under standard curing conditions) of GGBS or FA or CSF cement concretes comparable with 28 d strengths of ordinary portland cement concretes can be obtained in many cases, although adjustments in the concrete mix proportions may be necessary. Generally, as the cement extender content is increased, the early rate of strength development is reduced, particularly at lower temperatures. At ages exceeding 28 d, water-cured GGBS, FA and CSF concretes show an increase in strength over ordinary portland cement concretes of equivalent 28 d strengths. 4.1.2.2 Other properties Provided sufficient GGBS or FA or CSF is incorporated and the concrete is properly cured, there is likely to be increased resistance to some forms of chemical attack and reduction of early heat of hydration.
4.2 Water 4.2.1 Water shall be clean and free from injurious amounts of acids, alkalis, chlorides, organic matter and other substances that could impair the strength or durability of concrete or metal embedded in the concrete. (It should be noted that sea water contains injurious amounts of chlorides and alkalis.)
4.2.2 Should the suitability of water be in doubt, particularly in remote areas or where water is derived from sources not normally utilized for domestic purposes, such water shall be tested.
4.3 Aggregates 4.3.1 Aggregate classification Aggregates can be classified in terms of their density, as follows: a) normal density: aggregates that have a particle density exceeding 2 000 kg/m3 but not exceeding 3 000 kg/m3; b) low density: aggregates that have a porous structure and a particle density not exceeding 2 000 kg/m3; c) high density: aggregates that have a particle density exceeding 3 000 kg/m3.
4.3.2 Natural aggregates covered by SABS 1083 4.3.2.1 Normally, both coarse aggregate (stone) and fine aggregate (sand) should comply with the requirements of SABS 1083.
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SABS 0100-2 Ed. 2 4.3.2.2 Acceptable variations to the requirements of SABS 1083 in the project specifications shall be clearly specified. 4.3.2.3 Appendices to SABS 1083 identify characteristics of certain fine and coarse aggregates that are normally not acceptable but are nonetheless suitable for use in particular circumstances and may be preferred on the grounds of economy. Such aggregates shall be clearly specified, and may only be used after tests have verified their particular characteristics and if guidance for their use is provided. 4.3.2.4 SABS 1083 specifies additional optional requirements for aggregates to be used for specific purposes or where specific properties such as resistance to alkali-silica reaction, fire resistance, low shrinkage, or general durability are of significant importance.
4.3.3 Aggregates not covered by SABS 1083 Where aggregates other than those covered by SABS 1083 are to be used, such aggregates and requirements for their quality shall be clearly specified.
4.3.4 Nominal maximum size The preferred nominal maximum sizes of coarse aggregate are 37,5 mm; 26,5 mm; 19 mm; 13,2 mm and 9,5 mm. The nominal maximum size of coarse aggregate should not exceed a) one-quarter of the minimum thickness of the concrete cross-section, and b) the cover of reinforcement specified. In elements with closely spaced reinforcement, the use of a nominal maximum size of 9,5 mm or 13,2 mm should be considered.
4.3.5 Aggregates for high-strength concrete Where high-strength concrete is required, both the source and the type of aggregate may need careful selection, based on results of previous use or of trial mixes.
4.3.6 Aggregates and fire resistance It may be necessary to use an aggregate that behaves satisfactorily when exposed to high temperatures, e.g. low-density aggregates or limestone.
4.3.7 Aggregates and concrete density The density of the aggregates used influences the density of the concrete. If a high-density concrete is required, a high-density aggregate (see 4.3.1) may need to be specified. If a low-density concrete (see 3.4.4) is required, a low-density aggregate (see 4.3.1) may need to be specified.
4.3.8 Use of "plums" In plain concrete of thickness at least 300 mm, hard, clean, stone "plums" of mass 15 kg to 55 kg may, if approved, be used to displace concrete to a maximum of 20 % of the volume of the concrete, provided that a) such plums have no adhering films or coatings,
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SABS 0100-2 Ed. 2 b) no plum has a dimension exceeding 300 mm or one-third of the smallest dimension of the concrete element, whichever is less, c) each plum is surrounded by at least 80 mm of concrete, and d) the strength of the rock that makes up the plums (as indicated by the aggregate crushing value or the 10 % fines aggregate crushing test) is at least that specified for coarse aggregate in SABS 1083.
4.3.9 Storage 4.3.9.1 Aggregates of different nominal sizes shall be stored separately and in such a way that a) segregation of particles of the same size is minimized, b) contamination by foreign matter is prevented, and c) intermixing of aggregates is minimized. 4.3.9.2 Where aggregates of different chloride content are stockpiled on the same site, strict control shall be exercised over their use in different classes of concrete. 4.3.9.3 Stockpiles of natural or manufactured sand shall be free-draining to ensure a relatively uniform moisture content throughout the stockpile.
4.4 Admixtures 4.4.1 General 4.4.1.1 Admixtures are added to a concrete mix to change certain properties of concrete by their chemical effect or physical effect (or both). In changing certain properties, an admixture can significantly affect other properties. 4.4.1.2 Admixtures that may impair the durability of the concrete, or combine with the ingredients to form harmful compounds, or increase the risk of corrosion of the reinforcement shall not be used. When an admixture is used in concrete that is made with any type of cement and that is to contain prestressing tendons, reinforcement and embedded metal, the chloride content of the admixture, expressed as chloride ions (by mass), should not exceed 2 % (m/m) of the admixture or 0,03 % (m/m) of the cement. 4.4.1.3 Admixtures shall not be used without the approval of the engineer, who may require tests to be conducted before admixtures are used. To facilitate approval, the following information should be available: a) the trade name of the admixture, its source and the manufacturer's recommended method of use; b) typical dosages and possible detrimental effects of underdosages and overdosages; c) whether compounds likely to cause corrosion of the reinforcement or deterioration of the concrete (such as those containing chloride in any form as an active ingredient) are present and, if so, the chloride content of admixtures, expressed as chloride ions (by mass) or expressed as equivalent anhydrous calcium chloride (by mass); and d) the average expected air content of freshly mixed concrete containing an admixture that causes air to be entrained (see 4.4.2) when the admixture is used at the manufacturer's recommended dosage.
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SABS 0100-2 Ed. 2 4.4.1.4 If two or more admixtures are to be used simultaneously in the same concrete mix, all available data should be used to assess the interaction of the admixtures and to ensure their compatibility. 4.4.1.5 Admixtures used in the work shall be of the same composition as those used in establishing the concrete mix proportions. 4.4.1.6 The effect of an admixture can be highly specific to the combination of ingredients in the mix. It is therefore important that trial mixes be made before an admixture is used in concrete for construction and if any mix ingredient is changed during the course of the project.
4.4.2 Air-entraining agents An air-entraining admixture shall be of such a type and the dosage of sufficient quantity that the air content (see table 2) is maintained at the point of placing. When another admixture (or cement extender) is present in the concrete mix, a different dosage of the air-entraining admixture may be required. The entrainment of air tends to reduce the strength of concrete. Trial mixes should be made to determine the extent of strength reduction, and mix proportions adjusted if necessary.
4.4.3 Storage Admixtures shall be stored in a manner that will prevent contamination, evaporation or damage. For admixtures used in the form of suspensions or non-stable solutions, agitating equipment shall be provided to ensure thorough distribution of the ingredients. Liquid admixtures shall be protected from temperature changes that would adversely affect their characteristics.
4.5 Deteriorated material Cement or any other material that has deteriorated or that has been contaminated or otherwise damaged shall not be used in concrete and shall be removed from the site without delay.
5 Plant for concrete 5.1 General All plant shall be maintained in good working order.
5.2 Batching plant 5.2.1 Regular examination, calibration and tests shall be carried out at frequencies that will ensure that the batching system functions effectively and accurately and that hoppers and cement containers are kept dry and clean. 5.2.2 The batching plant shall be such that the batching accuracy complies with 7.1. 5.2.3 In the case of an automatic plant, the mass batching scales shall be so interlocked that a new batch of materials cannot be delivered until the hoppers have been completely emptied of the previous batch and the scales are in balance. Where discharge of materials from the hoppers is manually controlled, a method of signalling shall be employed to ensure that ingredients are not omitted, or added more than once, when a batch of concrete is being made up.
5.3 Mixing plant 5.3.1 The type and capacity of mixing machines shall be such that the rate of output of concrete is suitable for the rate of concreting. Each machine shall be capable of producing a uniform distribution
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SABS 0100-2 Ed. 2 of the ingredients throughout the batch within the time specified by the manufacturer. Worn or bent blades and paddles shall be replaced. The inner surfaces of the mixer shall be clean and shall have no hardened concrete adhering to them.
5.3.2 It is recommended that an agreement be reached between the contractor and the engineer if the mixer to be used a) has unusual mixing characteristics, or b) it is claimed that effective mixing can be consistently achieved in mixing periods shorter than those specified in 7.2.1.
5.4 Vibrators Where compaction by vibration is specified, vibrators shall be capable of fully compacting each layer of concrete. It is recommended that at least one standby vibrator be available for every three (or lesser number of) vibrators necessary to maintain the rate of placing.
6 Proportioning 6.1 Quality of concrete 6.1.1 General Concrete for all parts of the work shall be of the specified quality and capable of being placed and compacted without excessive segregation. When hardened, concrete should have developed all the properties required by this part of SABS 0100 and by the project specification. The engineer shall ensure that samples of the constituent materials of the concrete, together with evidence that they comply with the provisions of clause 4, are supplied for approval in good time before concreting of the works commences. Evidence shall be in the form of either a) a statement, from an approved laboratory, of the results of tests, or b) an authoritative and acceptable report or record of previous use of, and experience with, the material concerned.
6.1.2 Strength 6.1.2.1 Compressive strength The specified compressive strength of concrete should be based on the 28 d characteristic compressive strength fcu, unless a different test age is specified. 6.1.2.2 Maximum cement content Cement content should normally not exceed 550 kg per cubic metre of concrete.
6.1.3 Density of concrete For certain purposes, e.g. to provide radiation shielding, a high-density concrete may have to be specified. In other cases, e.g. to provide thermal insulation, a low-density concrete may have to be specified. These densities are normally achieved by selecting suitable aggregates (see 4.3.7).
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SABS 0100-2 Ed. 2 (As amended 1994)
6.1.4 Consistence Unless otherwise dictated by the general workability of the concrete, the method of transportation or conditions of placement, or unless otherwise specified by the engineer, slump values for different types of construction should normally not exceed 150 mm for hand-placed concrete and 100 mm for vibrated concrete.
6.1.5 Workability The concrete shall be of such workability that it can be readily compacted into the corners of the formwork and around reinforcement without the materials in the mix segregating.
6.1.6 Bleeding The concrete shall be so proportioned with suitable materials that bleeding (i.e. the upward migration of water in compacted fresh concrete) is not excessive. It is not possible to put quantitative limits to bleeding. To assess the bleeding behaviour of concrete, the consequences of bleeding should be borne in mind. Note that initially, bleeding is accompanied by the settlement of solid particles (i.e. cement and aggregates). Where this settlement is prevented by reinforcement or by changes in cross-section, differential settlement occurs and cracks and voids are formed in the concrete. This phenomenon is especially troublesome in columns, in T and I beams, and in beams and slabs with top reinforcement. On the other hand, a film of bleed water on the surface of an element such as a slab will prevent or retard plastic shrinkage of the concrete and is therefore beneficial. Methods of dealing with the detrimental consequences of bleeding and settlement are discussed in 10.3.8. Amdt 1, Sept. 1994
6.1.7 Chloride content The presence of chloride ions in concrete increases the risk of corrosion of embedded metal. Chlorides could be present in concrete as a result of inclusion in the raw materials; or they could become present at a later stage by ingress, especially via cracks and when the concrete is highly absorbent or permeable. To reduce the likelihood of corrosion of embedded metal owing to the ingress of chlorides from an external source, it is essential to ensure adequate cover to reinforcement (see table 5), an appropriate cement/water ratio (minimum class 2 of table A.8 (see annex A)), good compaction and thorough curing of the concrete. In particularly severe exposure conditions, alternative methods of reinforcement protection such as the use of surface coatings or more resistant reinforcement may be necessary.
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SABS 0100-2 Ed. 2 (As amended 1994) To minimize the chloride content in reinforced or prestressed concrete:
Amdt 1, Sept. 1994
a) the chloride content of the mixing water shall not exceed 500 mg/L (sea water shall not be permitted as mixing water); b) calcium chloride and chemical admixtures that contain chlorides shall not be permitted; and c) the chloride content of fine aggregate obtained from river estuaries, the sea or other sources likely to be contaminated by chlorides shall not exceed the limiting values given in SABS 1083. Table 1 - Deleted by Amendment No. 1.
6.1.8 Sulfates in concrete Although sulfates are present in most cements and in some aggregates, excessive amounts of sulfate in mix constituents can cause expansion and disruption of concrete. To prevent this, the total water-soluble sulfate content of the concrete mix, expressed as SO3, should not exceed 4 % (m/m), of the cement in the mix. The sulfate content shall be calculated as the total from the various constituents of the mix.
6.1.9 Alkali-silica reaction 6.1.9.1 Some aggregates containing particular varieties of silica may be susceptible to attack by alkalis (Na2O and K2O) originating from the cement or other sources, producing an expansive reaction that can cause cracking and disruption of concrete. This is likely to happen only when all the following are present together: a) a high moisture level within the concrete; b) a cement that has a high alkali content, or another source of alkali; and c) aggregate containing an alkali-reactive constituent. 6.1.9.2 When the materials are unknown and precautions based on the preceding three conditions are judged to be necessary, these can take the following form: a) limiting the alkali content of the concrete mix to 2,1 kg per cubic metre of Na2O equivalent; or b) use of GGBS or FA or CSF as composite cements or replacement materials in order that at least 40 % of GGBS or 20 % of FA or 10 % of CSF, by mass, of the combined material is introduced in the mix.
6.1.10 Drying shrinkage All concretes shrink when they dry out after the cessation of moist curing. Where this shrinkage is restrained, tensile stresses develop and may cause cracking. Factors in the proportioning of concrete that influence shrinkage are: water content, paste content, and elastic properties of aggregates. Potential drying shrinkage may be determined by SABS method 1085.
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SABS 0100-2 Ed. 2 6.2 Durability 6.2.1 General A concrete element is durable if, when subjected to potentially destructive exposure (other than wear or loading), it protects the embedded metal from corrosion and performs satisfactorily for the life-time of the structure. 6.2.1.1 Impermeability One of the main characteristics that enhances the durability of any concrete is its impermeability. Suitable impermeability is achieved with normal-density aggregates if there is a sufficiently high cement/water ratio (see 6.3), complete compaction of the concrete, and sufficient hydration of the cement through proper curing methods. 6.2.1.2 Cement content The cement in the concrete is the component most vulnerable to attack by aggressive substances and thus the cement type and the cement content of the concrete will determine the degree of resistance of the concrete to attack by such substances. 6.2.1.3 Detailing Since many processes of deterioration of concrete occur only in the presence of free water, the details of shape and design of exposed structural elements shall be such as to promote good drainage of water and to prevent standing pools. Minimum covers to reinforcement to meet the durability requirements for normal-density concrete and low-density concrete are given in 8.2.
6.2.2 Exposure to freezing and thawing 6.2.2.1 Normal-density concrete that is likely to be subjected to freezing-and-thawing action under wet conditions should contain entrained air and should conform to the air-content limits given in table 2. Table 2 - Total air content for various sizes of coarse aggregate for normal-density concrete 1
2
Nominal maximum size of coarse aggregate
Total air content
mm
% (V/V)
9,5 13,2 19 37,5
6-10 5-9 4-8 3-6
The cement/water ratio shall be at least 1,9 by mass. 6.2.2.2 Low-density concrete that is likely to be subjected to such freezing-and-thawing action shall contain 6 % ± 2 % total air when the nominal maximum size of aggregate exceeds 9,5 mm, or 7 % ± 2 % total air when the nominal maximum size is 9,5 mm or less. Proportions shall be so selected that a characteristic strength fcu of 20 MPa or more is attained.
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SABS 0100-2 Ed. 2 6.2.3 Exposure to aggressive chemicals NOTE - See annex A for additional information.
Deterioration of concrete by chemical attack can occur by contact with gases or solutions of many chemicals, but is generally the result of exposure to acidic solutions or to solutions of sulfate salts. Concrete made with portland cement is not recommended in persistently acidic conditions (pH 5,5 or less). Solutions of naturally occurring sulfates of sodium, potassium, calcium or magnesium, as may be present in some soils and groundwaters, can cause expansion and disruption of concrete. In extreme conditions, some form of lining such as those listed in table A.10 of annex A should be used to prevent access by deleterious solutions. Corrosive attack by water is one of the most serious conditions of exposure. All the materials found in concrete are to some extent soluble in water. The aggregates normally used are generally more resistant to attack than is the cementitious binder, which is the most vulnerable constituent owing to its greater chemical activity. (Steel reinforcement is also susceptible, if embedded in a pervious concrete or if corrosive attack on an initially impervious concrete has reached a relatively advanced stage and the corrosive agents have penetrated to the depth where reinforcement is embedded.) The two properties of water that contribute most towards its high corrosiveness are the following: - water is an extremely effective solvent; and - water is able to dissociate dissolved salts and enable them to participate in ion-exchange and ion-addition reactions. The corrosiveness of water depends on the rate of dissolution of concrete in the water, which is influenced by the factors given in 6.2.3.1 to 6.2.3.7. 6.2.3.1 The concentration gradient between the solid phase (concrete) and the liquid phase (water) In the case of concrete wetted by water, the concentration of calcium compounds in the concrete is usually many orders of magnitude higher than that of these compounds in the water. In the case of distilled or very soft water, the concentration of dissolved calcium salts in the water is almost zero and the concentration gradient becomes very large. The resultant dissolution rate can consequently be very high and rapid attack will take place. It is this mechanism that is responsible for the extremely aggressive behaviour of distilled water and very soft water towards concrete, which can result in the rapid leaching-out of the components of the concrete, especially calcium hydroxide, the presence of which is essential for maintaining the integrity of the binder. On the other hand, where water already contains a high concentration of the compounds present in the concrete, the concentration gradient is lower and can disappear when saturation of the aqueous phase is achieved. 6.2.3.2 The acidity of the water The materials normally found in concrete have a higher solubility in acidic than in alkaline water. 6.2.3.3 The temperature of the water Warm water is usually more aggressive than cold water.
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SABS 0100-2 Ed. 2 (As amended 1994) 6.2.3.4 The movement of the water relative to the concrete Corrosion rates proceed much more rapidly if the water is in motion and the interface layer is constantly replenished. (Thus wave movements in tidal zones or turbulent flow in pipelines are accelerating agents by virtue of their effective mixing action.) 6.2.3.5 The volatility of reaction products Ammonium compounds present in the water in contact with the concrete, become part of the reaction products resultant from the corrosive attack on the concrete and may, under certain conditions, volatilize and be lost to the atmosphere as ammonia. The net result is the formation of voids in the concrete and a loss of alkalinity (rise in acidity) of the water, which then becomes even more corrosive. 6.2.3.6 The mobility of ions The mobility of ions is an important factor in the control of the rate of penetration of the ions into the concrete. 6.2.3.7 The presence of dissolved gases The presence of dissolved gases is required for certain corrosion reactions to proceed and the concentration of the gases in the water influences the corrosion rate. In the case of many concrete structures in contact with water, the water level is variable and certain areas of the concrete are subjected to cycles of wet and dry conditions. The following factors can influence the corrosion rate in such areas: a) enhanced concentration of dissolved salts: if the water level drops, previously wetted areas dry off as a result of evaporation of the surface layer of water. Any salts present in this layer become more and more concentrated as evaporation proceeds and eventually crystallize out of solution. A coat of variably concentrated salts can therefore be created, with all the implications that this may hold for the concrete; b) exposure to gases present in the atmosphere: in heavily polluted industrial atmospheres, gases may be significant corrosion accelerators. Amdt 1, Sept. 1994
6.2.4 Exposure to salt-laden air In coastal environments, concrete structures are exposed to wind-driven, salt-laden air. When a critical concentration of free chlorides is reached, depassivation of the reinforcement could occur, leading to corrosion and to subsequent spalling of the concrete. Salts that enter the pore structure of the surface concrete could also crystallize on drying. This process sets up expansive forces which could cause the concrete to crack and spall, allowing the rate of chloride ingress to increase. The degree of aggressiveness of coastal environment depends on the salt content of the air and the atmospheric relative humidity. In areas where the salt content and relative humidity of the air are high, it may be necessary to undertake protective measures similar to those for concretes in marine environments (see table A.8 of annex A).
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SABS 0100-2 Ed. 2 (As amended 1994) 6.2.5 Exposure to corrosive fumes
Amdt 1, Sept. 1994
The deterioration of concrete as a result of exposure to corrosive fumes is usually associated with a high relative-humidity environment which presents a special case of concrete deterioration caused by aggressive water. Corrosive fumes are often characterized by a high concentration of corrodants, and special protection measures are usually required for the concrete. Depending on the degree of aggressiveness of the fumes, protective measures could range from the provision of a high-strength, low-permeability concrete to the application of a chemically resistant barrier to isolate the concrete from the aggressive fumes. A careful assessment of the degree of aggressiveness of the fumes, together with specialist advice, is essential in determining the most effective protection method. 6.2.6 Exposure to polluted air
Amdt 1, Sept. 1994
The deterioration of concrete in heavily polluted industrial areas is caused by a number of mechanisms, depending on the nature of the atmospheric pollutant; for example, in areas around coal-burning power stations where emission of sulfates results in the precipitation of sulfuric acid, both acid attack and sulfate attack could cause concrete deterioration. The minimum requirements for concrete that is exposed to heavily polluted air are given in class 1 of table A.8 (see annex A).
6.3 Mix proportions 6.3.1 High cement content A cement content in excess of 550 kg per cubic metre of concrete should normally not be used because such a cement content tends to make concrete sticky and difficult to handle, place and compact.
6.3.2 Concrete exposed only to mild conditions (see 3.3) Specified strength shall be determined by structural design considerations. If the concrete is to include embedded metal, the characteristic strength shall not be less than 20 MPa. There is no requirement for minimum cement/water ratio or for minimum cement content.
6.3.3 Deleted by Amendment No. 1. 6.3.4 Deleted by Amendment No. 1.
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SABS 0100-2 Ed. 2 (As amended 1994)
7 Production of concrete 7.1 Batching 7.1.1 Cement The mass of cement in a standard sack is 50 kg. All cement taken from bulk storage containers and from partially emptied bags shall be batched by mass to an accuracy of 2 % (or better) of the mass required.
7.1.2 Water Mixing water for each batch shall be measured and the amount of water adjusted to allow for the moisture content of the aggregates (see 7.1.3). The true quantity shall be measured to an accuracy of 2 % (or better).
7.1.3 Aggregates If batching is by mass, the mass of the aggregates of each size shall be measured and a correction made for the moisture content of the aggregates. The true mass shall be measured to an accuracy of 3 % (or better). If batching is by volume, the fine and coarse aggregates shall be measured separately in suitable measuring boxes of known volume and of such capacity that the quantities of aggregates for each batch are suitable for direct transfer into the mixer. Bulking tests on the fine aggregate (or moisture determination if the relation between bulking and moisture content of the specific fine aggregate is known) shall be conducted at least daily (in accordance with SABS method 856) and the results used to adjust the batch volume of fine aggregate to give the true volume required. Additional tests for bulking shall be carried out after rain has fallen or if there has been any other reason for variation in the moisture content of the aggregate.
7.1.4 Admixtures The amount of admixture to be used shall be measured to an accuracy of 2 % (or better). Daily calibration of the measuring device is imperative, and after each day's use, the measuring device shall be uncoupled from the supply and cleaned. The person responsible for batching shall be fully conversant with the effects of the admixture and the consequences of underdosage or overdosage. Amdt 1, Sentence deleted by Amendment No. 1. Sept. 1994
7.2 Mixing 7.2.1 Mixing on site 7.2.1.1 General 7.2.1.1.1 Mixing of materials for concrete shall be conducted by an experienced operator.
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SABS 0100-2 Ed. 2 7.2.1.1.2 The total volume of material per batch shall not exceed the rated capacity of the mixer. 7.2.1.1.3 Concrete shall only be mixed in quantities required for immediate use. Concrete that has set shall be discarded. In the event of delay in the concreting operations, concrete may be retained in the mixer for a maximum period of 2 h, provided that only just enough water is added to the mixer to maintain the target slump. During this time, the mixer shall be restarted and run for about 2 min every 15 min. The period of 2 h shall be reduced if the ambient temperature, or any other factor, tends to produce early setting. 7.2.1.1.4 At the commencement of each concrete production run and before any concrete is mixed, the inner surfaces of the mixer shall be cleaned and all hardened concrete removed. Sand, cement and water, proportioned as for the concrete to be made, shall then be introduced into the cleaned mixer in sufficient quantity to cover the entire inside surface of the mixer. The mixer shall then be operated (to mix these materials and to coat the interior surfaces of the mixer with the mixture) and discharged immediately prior to charging of the mixer with the first batch. 7.2.1.1.5 Instructions for the sequence of charging the particular mixer shall be given before operations commence. Control systems shall be introduced to ensure that the batch is not discharged until the required mixing time has elapsed. At least three-quarters of the required mixing time shall take place after the last of the mixing water has been added. 7.2.1.1.6 The period of mixing shall be measured from the time when all the materials are in the drum or pan, to the commencement of discharge. Subject to the exception given in 7.2.1.1.7, mixing shall take place for at least 1,5 min or 1 min, for drum-type and pan-type mixers respectively, for each batch of 1,5 m3 or less, and the mixing time shall be increased by 20 s or 15 s respectively, for each additional cubic metre or part of a cubic metre. During this period, the drum or pan shall be rotated at the speed recommended by the manufacturer of the mixer. To prevent attrition, continuous mixing periods shall not exceed 10 min or 6 min per batch, for drum-type and pan-type mixers respectively, at the recommended mixing speeds. 7.2.1.1.7 If a mixer of the type described in 5.3.2(b) is used, shorter mixing periods may be used if approved by the engineer. 7.2.1.1.8 The mixed concrete shall be so discharged that there is no significant segregation of the materials in the mix. 7.2.1.2 Control of admixtures 7.2.1.2.1 Air-entraining admixtures, calcium chloride and other chemical admixtures shall be charged into the mixer as solutions, and shall be measured by means of an acceptable mechanical dispensing device, the liquid being considered a part of the mixing water. Admixtures that cannot be added in solution may be weighed or may be measured by volume if so recommended by the manufacturer. 7.2.1.2.2 If two or more admixtures are used in the concrete, they shall be added separately to avoid possible interaction that could interfere with the effectiveness of either admixture or that could adversely affect the concrete. 7.2.1.2.3 Addition of retarding admixtures shall be completed within 1 min after addition of the water has been completed, or prior to the beginning of the last three-quarters of the required mixing, whichever occurs first. 7.2.1.3 Tempering and control of mixing water When concrete delivered at the place of operation has a slump below that suitable for placing, as indicated by the project specifications, water may be added, provided that the cement/water ratio is not reduced to below the minimum permissible for strength and durability and the maximum slump is not
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SABS 0100-2 Ed. 2 exceeded. The water shall be incorporated by additional mixing equal to at least half of the total mixing time required. Any addition of water in excess of that permitted by the limitation on the cement/water ratio shall be accompanied by a quantity of cement sufficient to maintain the proper cement/water ratio. The approval of the engineer (or of his representative) for such addition shall be obtained before the water is added. 7.2.1.4 Adverse weather 7.2.1.4.1 Cold weather The required concrete temperature from the time of mixing until the concrete has hardened (see 10.8.3) may be obtained in several ways, such as by: a) heating the mixing water and the aggregate (if water or aggregate is heated above 60 °C, combine the water with the aggregate in the mixer before adding the cement. Cement shall not be mixed with water or mixtures of water and aggregate of temperatures exceeding 60 °C); b) increasing the cement content in the mix; c) using a cement that hardens more rapidly; or d) incorporating an accelerator. (Chloride-free accelerators should be used when the concrete contains reinforcement or other embedded metal.) NOTE - If insulation is used, its effect on the temperature of concrete should be taken into consideration.
7.2.1.4.2 Hot weather When the temperature of the fresh concrete is likely to exceed the permissible maximum (see 10.8.2), the concrete can be cooled by a) cooling the mixing water or substituting flaked or well-crushed ice for part or all of the mixing water; ice particles have to be small enough to melt completely during the mixing process; b) cooling the aggregates, for example by shading the stockpiles and by wetting the stone to cause evaporative cooling; or c) injecting liquid nitrogen into the mix during mixing.
7.2.2 Ready-mixed concrete Where concrete is delivered to the site ready mixed, the requirements of SABS 878 shall apply.
7.3 Transportation The mixed concrete shall be discharged from the mixer and transported as rapidly as practicable to its final position by means that will prevent segregation, adulteration, loss of ingredients and ingress of foreign matter or water and that will maintain the required workability at the point of placing. Concrete may only be conveyed through pipes made with materials that are non-reactive with cement. Aluminium pipes shall be suitably protected. The capacity of conveying equipment shall be sufficient to ensure that placed concrete does not set before adjacent concrete of the same pour is placed. Conveying equipment shall be cleaned at the end of each operation or work day.
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SABS 0100-2 Ed. 2 (As amended 1994)
8 Reinforcement 8.1 General Reinforcement should comply with the relevant requirements of SABS 82, SABS 920 and SABS 1024. NOTE - See also the relevant section of SABS 0100-1.
8.2 Cover to reinforcement The minimum cover to reinforcement for normal-density concrete and low-density concrete is given in Amdt 1, table 5 for various conditions of exposure (see 3.3). Sept. 1994 Detailing of reinforcement shall allow for fire resistance (see SABS 0100-1), dimensional tolerances in cutting, bending and fixing of reinforcement (see 4.13 and 5.1.5 of SABS 0144:1978), and permissible deviations in dimensions of concrete work (see SABS 0155). Table 5 — Minimum cover for normal-density and low-density concrete for various conditions of exposure
1
2
3
4
5
Amdt 1, Sept. 1994 6
Minimum cover mm
Concrete
Conditions of exposure Mild
Moderate
Severe
Very severe
Extreme
Normal-density concrete
20
30
40
50
60
Low-density concrete
20
40
50
60
70
NOTE - This table should be used in conjunction with table A.8 of annex A.
Table 6 — Deleted by Amendment No. 1.
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SABS 0100-2 Ed. 2 8.3 Bending 8.3.1 General The following provisions shall apply: a) all reinforcement shall be bent to the dimensions shown on the drawings and in accordance with the requirements of SABS 82; b) all reinforcement shall be bent cold unless otherwise permitted (see 8.3.2); c) bending shall be carried out slowly, using a steady, even pressure without jerk or impact; d) it is permissible to bend grade 250 reinforcement protruding from concrete elements, provided that care is taken to ensure that the radius of bend is not less than that specified in SABS 82. 450 MPa bars shall not be bent, rebent or straightened without the engineer's approval; e) where it is necessary to reshape steel previously bent, this shall only be done with the engineer's approval and each bar shall be inspected for signs of fracture.
8.3.2 Preheating prior to bending or straightening Provided that the bars do not depend on cold working for their strength, they may be bent or straightened hot, in accordance with the following provisions: a) the preheating procedure shall be such as not to harm the bar material (or to cause damage to the concrete in the case of bars already cast-in); b) the preheat shall be applied to a length of bar equal to at least five bar diameters in each direction from the centre of the bend. The temperature of the bar at the concrete interface shall not exceed 260 °C; c) the preheat temperature shall not exceed 650 °C; d) the preheat temperature shall be maintained until bending or straightening is complete; e) heated bars shall be cooled slowly in air. (Hot bars shall not be quenched with water.)
8.4 Fixing The grade of accuracy for cover over reinforcement shall comply with the requirements of SABS 1200 G. Reinforcement shall not be subjected to mechanical damage, rough handling, dropping from a height, or shock loading.
8.4.1 Steel reinforcement 8.4.1.1 All reinforcement, at the time of placing of the concrete, shall be free from rust, scale, oil and other coating that may reduce the bond between the steel and surrounding concrete, or initiate corrosion of the reinforcement. The reinforcement shall not be contaminated by any substance used as a release agent for the formwork. All reinforcement shall be well and cleanly rolled. Rust, seams, surface irregularities and mill scale shall not be cause for rejection, provided that the mass per metre, dimensions, cross-sectional area and tensile properties of a test specimen comply with the applicable requirements for the specified bar.
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SABS 0100-2 Ed. 2 8.4.1.2 Reinforcement shall be placed as shown on the drawings and shall be maintained in that position within the specified tolerances. Reinforcement shall be tied with annealed wire of diameter 1,6 mm or 1,25 mm or by acceptable clips, at sufficient intersections to avoid displacement of bars. It may also similarly be secured by welding if permitted by the engineer. Reinforcement shall be supported in its correct position by hangers or saddles, and aligned by means of chairs and spacers of approved design. Spacers of such materials and designs shall be durable, shall not lead to corrosion of the reinforcement and shall not cause spalling of the concrete cover. Spacer blocks made from cement and sand shall be made of the cement and sand used for the surrounding concrete. Proportions shall be 1 volume of cement (loose), 1 volume of sand (dry and loose) and sufficient water to produce a mix that can be thoroughly compacted. Spacer blocks shall be cured in water for at least 14 d before being used. Concrete spacer blocks made on the construction site shall not be used unless they are made under strictly controlled conditions. Spacers and chairs shall be placed at the spacing recommended in 5.2.2 of SABS 0144:1978. 8.4.1.3 The clear distance between reinforcing bars shall be determined in accordance with 3.11 of SABS 0100-1:1980. 8.4.1.4 In the detailing and dimensioning of bars (in particular bends, hooks and stirrups), the designer should take into account the diameters of all the bars intersecting at any point, the sweep or curve of bends, the need for the use of ties to fix steel, the shuttering and reinforcement tolerances, the cover specified for various exposure conditions and the tolerances permitted for the fabrication of reinforcement and erection of formwork. The concrete cover specified is equally applicable to the upper layer of reinforcing steel in floors and slabs. For any slab, cognizance shall be taken of the specified concrete cover, and the detail dimensions and diagrams of the reinforcing bars to which the steel is to be bent shall be such that the specified concrete cover can be achieved. 8.4.1.5 The design of the laps and the lengths of main bars in vertical reinforcement shall be such as to suit the position of construction joints shown on the drawings or as specified. It is particularly important that where a kicker or starter stub for a wall is specified or shown on the drawings or will be permitted, that the lap in the vertical reinforcement start above the kicker. A lap shall not start below a joint at the top of a kicker and shall not finish above it. 8.4.1.6 Templates should be furnished for placement of all column dowels, unless otherwise permitted. 8.4.1.7 Welded wire fabric for slabs on grade shall extend to within 100 mm of the concrete edge. Welded wire fabric shall be adequately supported during placing of concrete, to assure proper positioning in the slab. 8.4.1.8 Where exposed-aggregate, ribbed or patterned finishes are to be achieved, the detail dimensions of reinforcing bars shall be such that the specified concrete cover can be maintained after the texture, ribbing or pattern is applied. NOTE - The contractor cannot provide the specified cover unless the outside dimensions of reinforcement cages and the like provide for greater cover than would be provided for plain finishes of concrete.
8.4.1.9 Supporting steel should be included in the reinforcing schedule by the engineer. The use of other supporting materials is subject to the approval of the engineer. 8.4.1.10 Laps and joints of reinforcing bars shall be formed only as and where shown on the drawings or as approved by the engineer. Bars left exposed for bonding of future extensions to the structure shall be well protected from corrosion, using suitable means.
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SABS 0100-2 Ed. 2 8.4.1.11 Reinforcement in elements cast on ground shall rest on precast concrete blocks at least 100 mm square, and having a compressive strength at least equal to the specified compressive strength of the concrete being placed. Other means of support may be used if approved by the engineer.
8.4.2 Zinc-coated (galvanized) reinforcement Zinc-coated reinforcing bars supported away from formwork shall rest on zinc-coated wire bar-supports or on wire bar-supports made of dielectric material or other acceptable materials. All other reinforcement and embedded steel items in contact with zinc-coated reinforcing bars, or within a minimum clear distance of 50 mm from zinc-coated reinforcing bars, shall be zinc-coated, unless otherwise approved. Zinc-coated reinforcing bars shall be fixed with zinc-coated tie wire or non-metallic-coated tie wire or other acceptable material.
8.4.3 Epoxy-coated reinforcement Epoxy-coated reinforcing bars supported away from formwork shall rest on epoxy-coated wire bar-supports, or on bar-supports made of dielectric material or other acceptable materials. Wire bar supports shall be coated with dielectric material for a minimum distance of 50 mm from the point of contact with the epoxy-coated reinforcing bars. All reinforcing bars used as support bars or as spreader bars shall be epoxy-coated or coated with dielectric material. Epoxy-coated reinforcing bars shall be fastened with nylon-coated, epoxy-coated or plastics-coated tie wire, or with other acceptable materials.
8.5 Welding 8.5.1 General Generally, all welding should be carried out under controlled conditions in a factory or workshop and welding on site should be avoided if possible. Welding on site may be undertaken when required and permitted by the engineer, provided that suitable safeguards and techniques are employed and the types of steel (including high-yield steels to SABS 920) have the required welding properties. The competence of the operators shall be demonstrated prior to, and periodically during, welding operations.
8.5.2 Use of welding Welding may be used for: a) fixing in position; for example, by welding between crossing or lapping reinforcement, or between bars and other steel elements (metal-arc welding or electric resistance welding may be used on suitable steels); or b) structural welds involving transfer of load between reinforcement or between bars and other steel elements. Butt welds may be carried out by flash butt welding or metal-arc welding. For lapped joints, metal-arc welding or electric resistance welding may be used.
8.5.3 Types of welding 8.5.3.1 Flash butt welding Flash butt welding shall be carried out with the correct combination of flashing, heating, upsetting and annealing, and with the use of only those machines that automatically control this cycle of operations.
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SABS 0100-2 Ed. 2 8.5.3.2 Metal-arc welding Metal-arc welding of reinforcement shall be carried out in accordance with the recommendations of the reinforcement manufacturer, as approved by the engineer. 8.5.3.3 Electric resistance welding Electric resistance welding is done by the use of welding machines that can be adequately controlled but that require the correct preparation of the bars to be welded. 8.5.3.4 Other methods Other methods of welding may be used, subject to their satisfactory performance in trial joints.
8.5.4 Location of welded joints Structural welds shall not occur at bends in reinforcement. Unless otherwise agreed by the engineer, joints in parallel bars of the principal tensile reinforcement shall be staggered in the longitudinal direction. For joints to be regarded as staggered, the distance between them shall be at least equal to the end anchorage length for the bar.
8.5.5 Strength of structural welded joints The strength of all structural welded joints shall be assessed by means of testing trial joints.
8.5.6 Welded lapped joints The length of run deposited in a single pass shall not exceed five times the diameter of the bar. If a longer length of weld is required, it shall be divided into sections and the space between runs shall be at least five times the diameter of the bar.
9 Formwork 9.1 General 9.1.1 Materials that have a deleterious effect on concrete (e.g. untreated timber) shall not be used for formwork.
9.1.2 Forms shall have sufficient strength to withstand the pressure resulting from placement and compaction of the concrete and shall have sufficient rigidity to maintain specified tolerances, the required shapes, finishes, positions, levels and dimensions shown on the drawings.
9.1.3 Tolerances shall comply with the relevant requirements of SABS 0155. 9.1.4 Forms shall be sufficiently tight to prevent loss of grout. 9.1.5 The formwork shall be capable of being dismantled and removed from the cast concrete without shock, disturbance or damage to the concrete. 9.1.6 Earth cuts shall not be used as forms for vertical surfaces, unless permitted or unless so required. 9.1.7 Shop drawings for formwork, including the location of shoring and reshoring, shall be submitted for review as required by the contract documents.
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SABS 0100-2 Ed. 2 9.1.8 Where formwork is to be erected over a road, a street or a railway, the formwork shall be so designed that the full clearances required for the free movement of traffic are maintained to the satisfaction of the authority controlling such road, street or railway. It is recommended that, prior to the commencement of erection, the approval of such authority be obtained for the design of the formwork.
9.2 Design and construction of formwork 9.2.1 Loads The forms shall be designed to withstand the worst combination of self-weight, wet concrete weight, concrete pressure, construction loads and wind loads, together with all incidental dynamic effects caused by placing and compacting the concrete.
9.2.2 Deflection To maintain the specified tolerances, the formwork shall be cambered to compensate for anticipated deflections in the formwork prior to hardening of the concrete.
9.2.3 Form accessories NOTE - Recommendations for spacers are given in 8.4.
Form accessories such as ties and hangers shall be of a commercially manufactured type. Non-fabricated wire shall not be used. Form ties and spacers left in situ should not impair the desired appearance or durability of the structure, e.g. by causing spalling or rust staining or by allowing the passage of moisture. After the ends or end fasteners of form ties have been removed, any embedded portion of the tie shall terminate at a distance of not less than the specified minimum cover from the formed surface of the concrete. Runways for moving equipment during concreting shall be provided with struts and legs, shall be supported directly on the formwork or structural member, and shall not rest on the reinforcing steel.
9.2.4 Temporary openings Temporary openings shall be provided at the base of column forms and wall forms and at other points where necessary to facilitate cleaning and observation immediately before concrete is placed. Subsequently, the openings shall be so closed as to provide the finish specified and to conform to the applicable tolerances given.
9.3 Preparation of formwork All matter that could contaminate or adulterate the concrete, including rubble and dust, shall be removed from the interior of the forms before the concrete is placed. Surfaces that are to be in contact with fresh (wet) concrete shall be clean and covered with an acceptable coating material that will effectively prevent absorption of moisture, will prevent bond with the concrete, and will not stain the concrete surfaces. A mineral oil or other approved material may be used.
9.4 Re-use of formwork Before re-use, all formwork shall be reconditioned, and all form surfaces that are to be in contact with the concrete shall be thoroughly clean.
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SABS 0100-2 Ed. 2 9.5 Removal of formwork 9.5.1 General 9.5.1.1 Forms and shoring in the formwork shall remain in place until the concrete has reached at least the strength (which should be specified in the contract documents) necessary to prevent plucking of the surface during removal of the formwork and to support its own weight and any loads that may be imposed on it. 9.5.1.2 Due regard shall be given to curing methods to be employed before formwork is removed. 9.5.1.3 Formwork shall be removed carefully so that shock and damage to the concrete are avoided. Sudden removal of wedges is equivalent to an impact load on the partially hardened concrete. 9.5.1.4 The quality of formwork shall be such that the finished surface of the concrete is as shown on the drawings or as required in terms of the project specification. Requirements for surface finishes are given in 10.9.
9.5.2 Formwork removal time for cast-in-situ concrete 9.5.2.1 Recommended periods before removal of forms (see table 7) Forms may not be removed within periods shorter than those specified by the designer. Table 7 should not be used if accelerating curing methods or sliding forms are used or in cases such as in 9.5.2.2. 9.5.2.2 Shorter periods before removal of forms It may be possible to remove formwork within periods shorter than normal if the early strength of the concrete is assessed. This strength may be assessed by tests on cubes of equal maturity, and cured, as far as possible, at the same temperature as the concrete in the element. Formwork for columns, walls, sides of beams, and other parts not supporting the weight of the concrete, may be removed as soon as the concrete has hardened sufficiently to resist damage from removal operations.
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SABS 0100-2 Ed. 2 Table 7 - Removal of formwork: minimum time in days1) 1
2
3
4
5
6
7
8
9
10
Minimum time d Type of cement used Type of structural member or formwork
Ordinary portland cement and portland cement 15
Rapid-hardening portland cement2) and rapid-hardening portland cement 153)
Cements containing more than 15 % of GGBS or FA
Weather (see 3.2) Normal Beam sides, walls and unloaded columns
0,75
Slabs with props left in place
4
Beam soffits with props left in place, and ribs of a ribbed floor construction
7
Slab props ) )including cantilevers Beam props )
10
Cool 4) 4)
4) 4)
Cold
Normal
1,5
0,5
7
2
12
3
17
5
4)
14
Cool 4) 4)
4) 4)
Cold
Normal
1
2
4
6
5
10
9
10
4)
21
7
Cool
Cold
4) 4)
4) 4)
4 10 17 17
4)
12
14
21
1) The time of removal of formwork allowing for the surface finish is to be decided by the designer. This table should be regarded as a guide only. 2) Shorter periods may be used for sections having a thickness of 300 mm or more. 3) Only if rapid-hardening cement is used as a direct replacement for ordinary portland cement. Shorter removal times for formwork do not apply if mixes are designed with rapid-hardening cement to achieve the same 28-d strength. 4) In cool weather, stripping times are to be determined by interpolation between the periods specified for normal and cold weather.
9.5.3 Reshoring When reshoring is permitted or required, it shall be planned in advance and shall be subject to approval by the engineer. The following recommendations are given as guidance: a) floors that are supported by shores under newly placed concrete shall have their original supporting shores left in place or shall be reshored. The reshoring system shall have a capacity sufficient to resist expected loads and in all cases shall have a capacity equal to at least one-half of the capacity of the shoring above; b) the shores shall be located directly under a shore position above, unless other locations are acceptable; c)
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in a multistorey building, the reshoring shall extend over a sufficient number of storeys to distribute the weight of newly placed concrete, forms and construction live loads in such a way that the design superimposed loads on the shores that support floors are not exceeded.
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SABS 0100-2 Ed. 2
10 Placing and protection of concrete 10.1 General All placing and compacting should be carried out under suitable supervision; the engineer shall be given adequate notice of the intention to place concrete. Concrete shall be placed continuously, or in layers of such thickness that no concrete will be placed on concrete that has so hardened as to cause planes of weakness within the section. If a section cannot be placed continuously, construction joints (see 10.4) shall be located as indicated in the contract documents or as permitted. Concrete that has hardened to the extent that it no longer responds plastically to compactive effort or has been contaminated by foreign matter shall not be placed.
10.2 Placing 10.2.1 The concrete shall be placed within 1 h from the time of discharge from the mixer. Re-tempering by the addition of water or other material shall not be permitted. 10.2.2 Placing shall be carried out at such a rate that the concrete that is being integrated with fresh concrete is still plastic. 10.2.3 Wherever practicable, the concrete shall be placed vertically into its final position to avoid segregation and displacement of reinforcement and other items that are to be embedded. 10.2.4 Placed concrete shall not be so reworked (whether by means of vibrators or otherwise) as to cause it to flow laterally in such a way that segregation occurs. Where practicable, the concrete shall be placed in horizontal layers of compacted thickness not exceeding 450 mm, to avoid "heaping". Use of vibrators to move concrete laterally within forms shall not be allowed.
10.2.5 Where a chute is used to convey the concrete, its slope shall be such that it will not cause segregation; a suitable spout or baffles shall be provided for the discharge of the concrete. Generally, the chute should be at an angle exceeding 30° to the horizontal.
10.2.6 Unless permitted by the engineer, the concrete shall not be allowed to fall freely through a height of more than 3 m. 10.2.7 Placing of concrete in an element that is supported shall not be commenced until the concrete previously placed in supporting elements (columns, walls, beams) is no longer plastic and has been in place for at least 2 h. When elements that are supported and supporting elements are placed in one operation, the concrete in the vicinity of the junction between these elements shall be revibrated shortly before it sets. This procedure is necessary to eliminate defects such as cracks caused by the settlement of solids in the fresh concrete.
10.2.8 When a closed circuit is being concreted, work shall commence at one or more points in the circuit and shall so proceed in opposite directions at the same time that, at completion of the circuit, the junctions are formed with freshly placed concrete. 10.2.9 No concrete shall be placed in flowing water. When the placing of concrete underwater is permitted owing to exceptional circumstances because, in the opinion of the engineer, it is not practicable to dewater before placing, it shall be placed by means of a tremie. During placing, the lower end of the
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SABS 0100-2 Ed. 2 (As amended 1994) tremie shall be continuously so immersed in the concrete being placed that the fresh concrete enters the mass of previously placed concrete from within, causing water to be displaced with minimum disturbance at the surface of the concrete. Amdt 1, The mix proportion of the concrete shall be adjusted to provide a concrete suitable for placing by tremie. Sept. 1994 Full details of the method proposed and of the adjusted concrete mix proportions shall be submitted for
approval before placing commences. During and after concreting underwater, pumping or dewatering operations in the immediate vicinity shall be suspended if there is any danger that such operations will interfere with the freshly placed concrete before it has set and gained adequate strength.
10.2.10 In any section of the works, the placing of concrete by pumping is subject to approval. Full details shall be furnished regarding the mix proportions of concrete intended to be placed by pumping. 10.2.11 The lift height to be concreted at any one time shall be agreed between the contractor and the engineer. In massive sections, it will be necessary to consider the effect of lift height on the temperature rise because of the heat of hydration.
10.3 Compaction 10.3.1 All concrete shall be so compacted (by vibration, spading, rodding, etc.) during and immediately after placing, that the concrete is thoroughly worked around the reinforcement, around embedded items and into corners of formwork and forms a solid void-free mass having the required surface finish. Where compaction is only by means other than vibration, approval should be sought.
10.3.2 The concrete shall be free from honeycombing and planes of weakness. Successive layers of the same lift shall be thoroughly worked together. To achieve this, the compaction tool shall be permitted to penetrate through the new layer into the lower layer, which shall be sufficiently plastic to permit interknitting.
10.3.3 Vibration shall be applied continuously during the placing of each batch of concrete until the expulsion of air has virtually ceased. Over-vibration that results in segregation, surface laitance or leakage, or any combination of these, shall be avoided.
10.3.4 Immersion vibrators shall be inserted vertically into the concrete to be compacted, at regular spacings not exceeding 0,6 m or 10 times the diameter of the vibrator, whichever is less. Systematic spacing of insertions of the vibrator at the recommended intervals is essential to ensure that no concrete remains outside the sphere of energy released by the vibrator. As soon as a water sheen is visible on the surface, the vibrator shall be slowly withdrawn from the concrete, care being taken to avoid the formation of voids.
10.3.5 When external vibrators are used, the design of formwork and the disposition of vibrators shall be such as to ensure efficient compaction and to avoid surface blemishes. 10.3.6 The rate of concrete placing shall be commensurate with the available compaction equipment, and compaction by vibration shall be executed by skilled operators only. The number of vibrators used shall be compatible with the rate at which concrete is placed. Standby vibrators shall also be made available.
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SABS 0100-2 Ed. 2 10.3.7 Where permanent formwork is incorporated in the structure, its energy absorption should be taken into account when the method of vibration to be used is being decided upon. Extra care is required to ensure full compaction of the concrete, since this cannot be checked as usual when the formwork is removed.
10.3.8 To overcome the detrimental effects of bleeding (see 6.1.6) and settlement, the technique of "revibration" or "recompaction" should be used. The technique consists of recompacting the concrete at a time that is as long as possible after initial compaction but while the concrete retains sufficient workability to respond plastically to compactive energy. In practice, this energy is normally applied by means of immersion vibrators. Recompaction is especially necessary in upper zones of columns, forms that have abrupt changes in cross-section (such as T and I beams and coffered slabs), elements that have horizontal reinforcing bars placed near the top of the concrete, liquid-retaining structures, and structures exposed to aggressive conditions.
10.4 Construction joints NOTE - See also 3.11 of SABS 0100-1:1980.
10.4.1 General The number of construction joints should be kept to the minimum necessary for the execution of the work. Their type and locations shall be acceptable to the engineer. The concrete at the joint shall be bonded with that subsequently placed against it, without provision for relative movement between the two. To ensure that the load-bearing capacity of the concrete in the area is not impaired, high quality workmanship is necessary when the joints are being formed.
10.4.2 Location 10.4.2.1 In general, joints should be located near the middle of the spans of slabs, beams and girders, unless a beam intersects a girder at this point, in which case the joint in the girder should be offset at a distance equal to twice the width of the beam. Joints in walls and columns should be at the underside of floors, slabs, beams or girders and at the tops of footings or floor slabs. Joints should be perpendicular to the main reinforcement. 10.4.2.2 The term "unforeseen joint" is used to identify a joint formed during concreting when plant failure, inclement weather or some other unforeseen event has enforced a halt in the placing of concrete and thus created a situation in which a construction joint has to be made in a location that was not approved prior to the commencement of concreting. If an unforeseen joint occurs at a critical section (e.g. at a section of maximum shear), it may be possible to remove part of the fresh concrete in order to place the joint in a less critical section. The face of the joint should be trimmed to a suitable shape.
10.4.3 Bonding When so required or permitted, bonding shall be achieved by means of one of the methods given in 10.4.3.1 to 10.4.3.4. 10.4.3.1 The use of an adhesive Joints to which an adhesive is applied shall be prepared, and the adhesive applied, in accordance with the manufacturer's recommendations, prior to the placing of fresh concrete.
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SABS 0100-2 Ed. 2 10.4.3.2 The use of a retarder Surfaces of joints that have been treated with a chemical retarder shall be prepared in accordance with the manufacturer's recommendations, prior to the placing of fresh concrete. 10.4.3.3 Roughening and dampening the surface of the concrete Roughening the surface of the concrete in an acceptable manner shall uniformly expose the aggregate and shall not leave laitance, loosened particles of aggregate or damaged concrete on the surface. The hardened concrete of construction joints and of joints between footings and walls or columns, between walls or columns and beams or floors they support, and joints in other elements not mentioned above shall be dampened (but not saturated) immediately prior to the placing of fresh concrete. The hardened concrete of horizontal construction joints a) in exposed work, or b) in the middle of beams, girders, joists and slabs, or c)
in work designed to contain liquids
shall be dampened (but not saturated) and then thoroughly covered with a thin coat of cement grout of similar proportions to the mortar in the concrete. Alternatively, application of a concrete layer of thickness approximately 250 mm, and made richer by reducing the amount of coarse aggregate by 25 %, may be considered. The fresh concrete shall be placed before the grout or the intermediate layer of concrete has attained its initial set. 10.4.3.4 Alternative methods to roughening the surface of the concrete Alternatively, mesh or expanded metal stop ends (not extending into the cover zone) may be used, if approved, to provide a rough face to the joint.
10.4.4 Reinforcement All reinforcement shall be continued across construction joints. If a kicker or starter stub is used, it shall be at least 70 mm high and carefully constructed. It is sometimes necessary and, in the case of columns, it is normally necessary, that a kicker stub be cast with the previous concrete.
10.4.5 Construction 10.4.5.1 Construction joints shall be formed in accordance with a) the details shown on the drawings, or b) the applicable requirements of the project specification. 10.4.5.2 In the case of an unforeseen joint (see 10.4.2.2), concrete shall be finished off at the place of stoppage in a manner that will least impair the durability, appearance and proper functioning of the concrete. The engineer's instructions shall then be followed. 10.4.5.3 In the case of a joint not covered by 10.4.5.1 or 10.4.5.2, one of the methods given in 10.4.5.3.1 to 10.4.5.3.4 shall apply.
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SABS 0100-2 Ed. 2 10.4.5.3.1 Construction joints when concrete is less than 24 h old The surface of the concrete shall be brushed with a steel wire brush before new mortar and concrete are placed as specified in 10.4.5.3.2. 10.4.5.3.2 Construction joints when concrete is more than 24 h and less than 3 d old The surface of the concrete shall be sand-blasted, or chipped with a light hammer, and swept clean. The surface dry concrete shall then be brushed with a thin layer of mortar composed of cement and sand mixed in the same ratio as the cement and sand in the concrete mixture, or a thin layer of cement/water mix of creamy consistence. This mortar or mix shall be freshly mixed and placed immediately before the new concrete is placed. It shall not be allowed to dry out before new concrete is poured. 10.4.5.3.3 Construction joints when concrete is more than 3 d old The old surface shall be cleaned as in 10.4.5.3.2 and kept continuously wet for at least 24 h and then allowed to become surface dry before the mortar or cement/water mix (as in 10.4.5.3.2) and new concrete are placed. 10.4.5.3.4 Construction joints at tops of columns The procedure for brushing or cleaning specified in 10.4.5.3.1 or 10.4.5.3.2, as applicable, shall be followed before the steel reinforcement of the slab or floor to be cast on the columns is placed in position.
10.5 Embedded items 10.5.1 General Expansion joint material, waterstops, pipes and conduits, and other embedded items shall be positioned accurately and supported against displacement. Voids shall be filled temporarily with readily removable material to prevent the entry of concrete into the voids. All contractors whose work is related to the concrete (or has to be supported by the concrete) should be given ample notice and opportunity to introduce or furnish (or both) embedded items before the concrete is placed.
10.5.2 Waterstops The material and design of waterstops and their location in joints shall be as indicated in the contract documents. Each piece of premoulded waterstop shall be of maximum practicable length in order to keep the number of end joints to a minimum. Joints at intersections and at ends of pieces shall be made in the manner most appropriate to the material being used. Joints shall develop effective watertightness fully equal to that of the continuous waterstop material, shall permanently develop at least 50 % of the mechanical strength of the parent section, and shall permanently retain their flexibility.
10.5.3 Pipes and conduits No pipes or conduits, other than shown on the drawings, may be permanently embedded in the concrete without prior approval.
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SABS 0100-2 Ed. 2 10.6 Concrete for water-retaining structures 10.6.1 Special care shall be taken when concrete for structures intended to retain water is being cast. The details of the drawings shall be followed meticulously, especially regarding the quality of concrete to be used, construction joints, the making good of holes used for formwork fixing purposes, and the grouting of pipes and other accessories. 10.6.2 For purposes of impermeability, durability, and the protection of steel, the cement/water ratio of the concrete mix shall be more than 2,0. (But see also clauses 6 and 7.) 10.6.3 When so required in terms of the project specification, tests for watertightness shall be carried out to verify that the intended degree of watertightness of the structure has been achieved. Should the degree of watertightness not be approved, an investigation should be carried out to ascertain what remedial steps are required.
10.7 Concrete in saturated ground Where concrete is to be placed in saturated ground, shallow drains shall be excavated in the ground, filled with broken stone, and connected to suitably placed sumps. A concrete blinding layer the top of which will form the foundation level for the structural concrete, shall then be laid. The layout and dimensions of the dry-stone drainage channels and the thickness of the blinding should have been included in the detailed drawings. If this is not the case, or if the engineer considers the project specification inappropriate, the channels and blinding shall be constructed as directed by the engineer.
10.8 Protection and curing of concrete 10.8.1 General 10.8.1.1 Beginning immediately after it has been placed, concrete shall, as far as is practicable, be protected from moisture loss and maintained at a temperature suitable for continued hydration for the period necessary for hydration of the cement and hardening of the concrete. Concrete shall be so protected and so cured that it is not exposed to any of the following: a) premature drying out, particularly as a result of solar radiation and wind; b) excessively high or low temperatures; c)
erosion by rain and flowing water;
d) rapid cooling (during the first few days after placing); e) high internal thermal gradients; f)
frost (see 10.8.3);
g) mechanical damage; h) contamination; and i)
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vibration and impact that could disrupt the concrete and interfere with its bond to the reinforcement.
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SABS 0100-2 Ed. 2 10.8.1.2 In the case of concrete surfaces not in contact with forms, one of the following procedures shall be adopted as soon as practicable after completion of placement and compaction, subject to the provisions of 10.8.2 and 10.8.3: a) ponding or continuous sprinkling of the exposed surfaces with water; b) covering the concrete with sand, or with mats made of a moisture-retaining material, and keeping the covering continuously wet; c)
the continuous application of steam (not exceeding 60 °C) or mist spray;
d) covering the concrete with waterproof or plastics sheeting firmly anchored at the edges; e) the use of an approved curing compound, applied in accordance with the manufacturer's recommendations. NOTE - Some curing compounds inhibit bond of finishes, such as toppings, plasters or paints, applied to the hardened concrete. The compound used should therefore be suitable for the intended finish.
10.8.1.3 Moisture loss from surfaces placed against wooden forms shall be minimized by keeping the forms wet until they are removed. After form removal, the concrete shall be cured by one of the methods given in (a) to (e) above, for the duration of time prescribed below. Whichever method of curing is adopted, its application shall not cause staining, contamination or marring of the surface of the concrete and the water used shall be in accordance with 4.2. When the ambient temperature is 15 °C and higher, the curing period shall be at least 7 d for concrete made with ordinary portland cement or portland cement 15 slag or portland cement 15 fly ash, and at least 10 d for concrete made with portland blastfurnace cement, and with blends of portland cement and more than 15 % of GGBS or FA. When the ambient temperature is below 5 °C, the curing periods shall be doubled. When the ambient temperature is between 5 °C and 15 °C, the curing period shall be determined by interpolation between the above times.
10.8.2 Concreting in hot weather or in windy conditions (see also 7.2.1.4.2) High temperatures and loss of moisture may cause thermal and plastic shrinkage (and possible cracking) and a reduction in strength and durability. The rate at which the concrete stiffens can be reduced slightly by the use of a retarder or of a cement with a low rate of hydration or by replacing of a part of the portland cement with GGBS or FA. When the ambient temperature exceeds 30 °C, the temperature of the concrete, when placed, shall not exceed 30 °C. The following procedures may be adopted to reduce the placing temperature of the concrete: a) shielding aggregate stockpiles (and all metal surfaces in contact with aggregates) from the direct rays of the sun; b) cooling aggregate (stone) stockpiles by spraying with water; c)
using chilled water or ice flakes for mixing water; and
d) injecting liquid nitrogen into the concrete during mixing.
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SABS 0100-2 Ed. 2 The protection of newly placed concrete against rapid drying, and consequent plastic shrinkage and possible cracking, is especially important in hot, windy conditions. Protection consists essentially of preventing evaporation from exposed concrete surfaces as soon as concrete has been placed and compacted. A combination of shading the concrete and spraying it or covering it with plastics sheeting may be used. Covers shall be such that they do not mark the surface of the concrete and shall be firmly anchored at the edges to prevent air movement over the concrete.
10.8.3 Concreting in cold weather (see also 7.2.1.4.1) Concrete shall not be placed during falling temperatures when the ambient temperature is below 7 °C or during rising temperatures when the ambient temperature is below 3 °C. When the concrete is placed at ambient temperatures below 5 °C, the temperature of the concrete shall not be below 10 °C, for which purpose heating of the water or of the aggregate (or of both) shall be permitted. Heated water and aggregate shall first be mixed and the cement added only while the temperature of the mixture is below 30 °C. The temperature of placed concrete shall not be allowed to fall below 5 °C until the concrete has attained a strength of at least 5 MPa.
10.8.4 Concreting during rainfall Concrete shall not be placed during periods of heavy or prolonged rainfall unless the materials, plant and the concreting operation are all well covered.
10.9 Surface finish of concrete 10.9.1 Upper surfaces of concrete Refer to SABS 0109.
10.9.2 Concrete surfaces cast against forms 10.9.2.1 General Surfaces cast against forms may be left as-cast (plain or profiled), or the initial surface may be removed (by tooling or sand-blasting), or the concrete may be covered (by painting or tiling). When the type of external finish is being selected, consideration should be given to the viewing distance, the weather pattern at the particular location, any impurities in the air and the effect of the shape of the structure upon the flow of water across the surface. 10.9.2.2 As-cast finishes 10.9.2.2.1 Rough form finish No selected form facing-material shall be specified for rough form finish surfaces. Tie holes and defects shall be patched. Fins exceeding 6 mm in height shall be chipped off or rubbed off; otherwise, surfaces shall be left with the texture imparted by the forms. 10.9.2.2.2 Smooth form finish The form facing-material shall be such as to produce a smooth, hard, uniform texture on the concrete. Facing-material may be plywood, tempered concrete-form-grade hardboard, metal, plastics, paper, or
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SABS 0100-2 Ed. 2 other acceptable material capable of producing the required finish. Tie holes and defects shall be patched. All fins shall be completely removed. 10.9.2.3 Unspecified finish If the finish is not designated in the project specification, the following finishes shall be used, as applicable: a) rough form finish: for all concrete surfaces not exposed to public view; or b) smooth form finish: for all concrete surfaces exposed to public view.
10.9.3 Repair of surface defects If, after removal of the forms or after finishing of concrete surfaces, the concrete shows any defect, no patching or remedial work shall be undertaken without authorization by the engineer who will, after thorough inspection and investigation of the quality and strength of the defective work, and after due consideration of the possible consequences of such defect, specify the extent and method of repair, or order the demolition and reconstruction of the whole of the defective work to the extent that he considers necessary. All repair, remedial and reconstruction work is subject to approval.
10.10 Records Written records shall be maintained that provide the following information in relation to each part of the works: a) the date on which each element was concreted, the time taken to place the concrete, and the position of the element in the works; b) the weather; and c)
the nature of samples taken, the dates on which they were taken, and the means of identification by which the results of tests on such samples may be correlated with the section of work to which they pertain.
11 Massive concrete 11.1 General 11.1.1 Portions of the structure that are to be treated as massive concrete under the provisions of this clause shall be stated in the project specification. Such massive concrete shall be subject to the provisions of this clause in addition to all other applicable provisions of this part of SABS 0100. 11.1.2 Concrete is said to be massive when the size and proportions of an element placed in one operation are such that temperature increases (caused by heat of hydration) in the concrete are high enough to result in potentially harmful effects. High temperatures in the concrete can lead to temperature gradients within the concrete; if these gradients are steep enough to cause differential strain that exceeds the concrete's tensile strain capacity, the concrete will crack. The critical dimension of an element with regard to heat of hydration is normally the least dimension. Concrete may usually be regarded as massive if the least dimension exceeds 0,5 m to 1,0 m, but the critical value is specific to each situation.
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SABS 0100-2 Ed. 2 11.2 Construction The construction of massive concrete elements should be done in such a way that the likelihood of cracking due to thermal effects is minimized. Possible steps include: a) using aggregates that produce concrete with the lowest possible coefficient of thermal expansion; b) using low cement contents; c)
cooling the aggregate and the mixing water, or installing cooling pipes;
d) replacing part of the portland cement with a cement extender such as FA; e) reducing the placing temperature of the concrete; and f)
insulating the placed concrete to minimize internal temperature gradients.
The subject of massive concrete cannot be dealt with in detail in this part of SABS 0100 and reference should be made to specialist literature (see annex D).
12 Prestressing NOTE - See also the appropriate clause of SABS 0100-1.
12.1 Prestressing tendons 12.1.1 General Prestressing tendons should comply with specialist documentation. NOTE - BS 4486 and BS 5896 may also be referred to.
12.1.2 Handling and storage All prestressing tendons shall be stored clear of the ground and protected from the weather and from splashes from any other materials, and from welding sparks or electric ground currents. The sheathing shall also be protected from any physical damage.
12.1.3 Surface condition 12.1.3.1 At the time of incorporation in the structural member, all bonded prestressing tendons and internal and external surfaces of sheathing or ducts shall be free of loose millscale, loose rust, oil, paints, grease, soap or other lubricants (except for the lubricant used in the drawing process), or other harmful matter. A uniform film of slight rust is not necessarily harmful and may improve the bond. It may, however, also increase the losses due to friction. 12.1.3.2 Cleaning of the tendons may be carried out by wire brushing or by passing the tendons through a pressure box containing carborundum powder. Solvent solutions shall not be used for cleaning without the approval of the engineer.
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SABS 0100-2 Ed. 2 12.1.4 Straightness 12.1.4.1 Wire Low relaxation and normal relaxation wire shall be in coils of diameter sufficiently large to ensure that the wire plays off reasonably straight. 12.1.4.2 Bars Prestressing bars, as delivered, shall be straight. Any small adjustments necessary for straightness shall be made on site, by hand, under the supervision of the engineer. Bars bent in the threaded portion shall be rejected. Any straightening of bars shall be carried out at ambient temperature. If the ambient temperature is less than 5 °C, any necessary heating shall be by means of steam or hot water to raise the temperature of the bars above 5 °C.
12.1.5 Cutting The following points shall be taken into consideration: a) any special requirements by the supplier of the prestressing system shall be met; b) all cutting to length and trimming of ends shall be by means of either 1) a high-speed abrasive cutting wheel, guillotine, friction saw or any other mechanical method approved by the engineer; or 2) an oxyacetylene cutting flame, excess oxygen being used to ensure a cutting rather than a melting action. Care should be taken that neither the flame nor splashes come into contact with either the anchorage or other tendons. The oxyacetylene method shall not be used on unbonded tendons; c)
in post-tensioning systems, the cutting action as in (1) and (2) above shall be at least one diameter from the anchor.
12.1.6 Formwork Formwork shall not be such as to restrain any elastic shortening, deflection or camber of the structure that results from application of the prestressing force. Form supports shall not be removed until sufficient prestressing force has been applied to support the self-weight load, the formwork and the anticipated construction loads, and shall be done to the engineer's approval.
12.1.7 Sheathing 12.1.7.1 Sheathing for bonded tendons 12.1.7.1.1 Sheathing or duct-formers shall be of a material that will not react with alkalis in cement and that is strong enough to retain its shape and resist damage during construction. It shall prevent the intrusion of cement paste from the concrete. Sheathing material left in place shall not cause electrolytic action or deterioration. 12.1.7.1.2 The sheathing shall have an internal cross-sectional area at least twice that of the net steel area of the tendon.
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SABS 0100-2 Ed. 2 12.1.7.1.3 Sheathing shall have injection pipes fitted at each end and vent pipes at all high points except where curvature is small and the sheathing is relatively level, such as in continuous slabs. Drain holes shall be provided at all low points if the tendon may be subject to freezing after placing and before grouting. 12.1.7.2 Sheathing for unbonded tendons The sheathing shall have sufficient tensile strength and weather resistance to prevent irreparable damage or deterioration during transportation, storage on site, and installation. The sheathing shall be a continuous tube and shall continue over the unbonded length of the tendon. The sheathing shall prevent the intrusion of cement paste and loss of lubricant.
12.2 Tensioning 12.2.1 General 12.2.1.1 Tendons may be stressed either by pre-tensioning or by post-tensioning, according to the particular needs of the form of construction. In each system, different procedures and types of equipment are used and these govern the method of tensioning, the form of anchorage and, in post-tensioning, the protection of the tendons. 12.2.1.2 Where possible, all wires or strands to be stressed in one operation shall be taken from the same parcel of prestressing steel. Each tendon shall be tagged with its number and the coil number(s) of the steel used. Tendons shall not be kinked or twisted and individual wires and strands shall be readily identifiable at each end of a member. A strand that has become unravelled shall not be used.
12.2.2 Safety precautions A tendon, when tensioned, contains a considerable amount of stored energy, which, in the event of any failure of a tendon, anchorage or jack, may be released violently. All possible precautions shall be taken (both during and after tensioning) to safeguard persons from injury and to safeguard equipment from damage that may be caused by the sudden release of this energy.
12.2.3 Tensioning apparatus Hydraulic jacks are the normal means for tensioning tendons. The tensioning apparatus shall meet the general provisions given in 12.2.3.1 to 12.2.3.4. 12.2.3.1 The means of attachment of the tendon to the jack or tensioning device shall be safe and secure. 12.2.3.2 Where two or more wires or strands are stressed simultaneously, they shall be of approximately equal length between anchorage points at the datum of force and extension measurement. The degree of variation in individual extensions shall be small in comparison with the expected extension. 12.2.3.3 The tensioning apparatus shall be such that the controlled total force is imposed gradually and no dangerous secondary stresses are induced in the tendons, anchorage or concrete. 12.2.3.4 The force in the tendons during tensioning shall be measured by direct-reading load cells or obtained indirectly from gauges of minimum diameter 150 mm fitted into the hydraulic systems to determine the pressure in the jacks. When pressure gauges are used, they shall be calibrated together with the jack to allow for jack friction. Facilities shall be provided for the measurement of the extension of the tendon and of any movement of the tendon in the gripping devices. The force measuring device shall be calibrated to an accuracy of ± 2 % (or better) and checked at frequent intervals. Elongation of the tendon shall be measured to an accuracy of ± 2 % (or better), or 2 mm, whichever is the more accurate.
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SABS 0100-2 Ed. 2 12.2.4 Pre-tensioning Where pre-tensioning methods are used, positive means shall be used to maintain the full force during the period between tensioning and transfer. The force shall be transferred slowly to minimize shock, which would adversely affect the transmission length. 12.2.4.1 Straight tendons 12.2.4.1.1 In the long-line method of pre-tensioning, sufficient locator plates shall be distributed along the length of the bed to ensure that the wires or strands are maintained in their proper position during concreting. Where a number of units are made in line, they shall be free to slide in the direction of their length and thus permit transfer of the prestressing force to the concrete along the whole line. 12.2.4.1.2 In the individual mould system, the moulds shall be made sufficiently rigid to provide the reaction to the prestressing force without distortion. 12.2.4.2 Deflected tendons 12.2.4.2.1 Where practicable, the mechanisms for holding down or holding up of tendons shall be such that the part in contact with the tendon is free to move in the line of the tendon in order to eliminate frictional losses. If, however, a system is used that develops a frictional force, this force shall be determined by testing, and due allowance made. 12.2.4.2.2 For a single tendon, the deflector in contact with the tendon shall have a radius of at least 5 times the tendon diameter for wire, or 10 times the tendon diameter for a strand, and the total angle of deflection shall not exceed 15°. 12.2.4.2.3 The transfer of the prestressing force to the concrete in conjunction with the release of hold-down and hold-up forces shall be so effected that any tensile stresses in the concrete that result during the process, do not exceed permissible limits.
12.2.5 Post-tensioning 12.2.5.1 Arrangement of tendons 12.2.5.1.1 Where wires, bars or strands in a tendon are not stressed simultaneously, spacing members shall be made so rigid that they are not displaced during the successive tensioning operations. 12.2.5.1.2 Tendons, whether in anchorages or elsewhere, shall be so arranged that they do not pass round sharp bends or corners likely to provoke rupture when the tendons are under stress. 12.2.5.2 Anchorages 12.2.5.2.1 The adequate performance of anchorages shall be demonstrated before prestressing. NOTE - Suitable tests for checking prestressing tendon anchorage performance are described in BS 4447 and in the FIP recommendation for acceptance and application of post-tensioning systems (March 1981).
12.2.5.2.2 The anchorage system in general comprises the anchorage itself and the arrangement of tendons and reinforcement designed to act with the anchorage. The form of anchorage system shall be such as to facilitate the even distribution of stress in the concrete at the end of the member and shall be capable of maintaining the prestressing force under sustained and fluctuating load and under the effect of shock.
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SABS 0100-2 Ed. 2 12.2.5.2.3 Split-wedge-and-barrel type anchors shall be of such material and construction that a) under the forces imposed during the tensioning operation, the strain in the barrel does not allow such movement of the wedges that the wedges reach the limit of their travel before sufficient lateral force is developed to grip the tendon, and b) at or before the limit of travel, the wedges do not cause an excessive force in the tendon. 12.2.5.2.4 If a proprietary form of anchorage is used, the anchoring procedure shall be strictly in accordance with the manufacturer's instructions and recommendations. 12.2.5.2.5 All bearing surfaces of the anchorages, of whatever form, shall be cleaned prior to the tensioning operation. 12.2.5.2.6 Any allowance for draw-in of the tendon during anchoring shall be in accordance with the engineer's instructions, and the actual slip occurring shall be recorded for each individual anchorage. 12.2.5.2.7 After the tendons have been anchored, the force exerted by the tensioning apparatus shall be gradually and steadily so decreased as to avoid shock to the tendon or the anchorage. 12.2.5.2.8 Provision shall be made for the protection of the anchorage against corrosion. 12.2.5.2.9 Intermediate anchorages, if bearing against hardened concrete at a construction joint, shall have design features permitting efficient transfer of prestressing force to the hardened concrete and shall have adequate corrosion protection by epoxy-tar painting of anchor parts. 12.2.5.3 Deflected tendons 12.2.5.3.1 Where practicable, a deflector in contact with a tendon shall have a radius of at least 50 times the diameter of the tendon, and the total angle of deflection shall not exceed 15°. 12.2.5.3.2 Where the radius is less than 50 times the diameter of the tendon or the angle of deflection exceeds 15°, the loss of strength of the tendon shall be determined by testing, and due allowance made.
12.3 Positioning of tendons and sheathing 12.3.1 The tendons and sheathing shall be accurately located and maintained in position both vertically and horizontally as shown on the drawings. Unless otherwise shown on the drawings, the permitted tolerance in the location of the tendon or sheathing shall be as given in table 8. Table 8 - Permitted tolerance in the location of tendons and sheathing Dimensions in millimetres 1
2
3
4
Vertical tolerance
Width of beam
Horizontal tolerance
< 200 200 - 1 000 > 1 000 (incl. slabs)
±5 ± 10 ± 30
Depth of member d < 200 200 - 1 000 > 1 000
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± d /40 ±5 ± 10
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SABS 0100-2 Ed. 2 12.3.2 The method of supporting and fixing the tendons (or the sheathing) in position shall be such that they will not be displaced by heavy or prolonged vibration, by pressure of the wet concrete, by workmen, or by construction traffic. The means of locating prestressing tendons shall not unnecessarily increase the friction when they are being tensioned. 12.3.3 Sheathing should retain its correct cross-section and profile and shall be handled carefully to avoid damage. 12.3.4 Joints in sheathing shall be securely taped to prevent penetration of the duct by concrete or cement paste, and ends of ducts shall be sealed and protected after the stressing and grouting operations. Joints in adjacent sheathing shall be staggered at least 300 mm. 12.3.5 As damage might occur during the concreting operation, and if the tendon is to be inserted later, the duct shall be protected during the concreting operation to ensure a clear passage for the tendon.
12.4 Tensioning procedure 12.4.1 All tendons shall be free to move in the ducts before being tensioned. Tensioning shall be so carried out under competent supervision that the stress in the tendons increases at a gradual and steady rate. Tensioning shall not be carried out at a temperature below 0 °C without the approval of the engineer. 12.4.2 The supervisor in charge of stressing shall be provided with particulars of the required tendon force and expected extensions. During stressing, allowance shall be made for the friction in the jack and in the anchorage, although allowance for the former is not necessary when load cells are used. 12.4.3 Stressing shall be continued until the required tendon force is reached. The measured extension shall allow for any draw-in of the tendon occurring at the non-jacking end, but measurement shall not commence until any slack in the tendon has been taken up. A comparison between the measured extension and the calculated extension provides a check on the accuracy of the assumptions made for the frictional losses at the design stage. If the difference exceeds 8 %, corrective action shall be taken, but only with prior approval. Full records shall be kept of all tensioning operations, including the measured extensions, pressure-gauge or load-cell readings, and the amount of draw-in at each anchorage. 12.4.4 Where a large number of tendons or tendon elements are being tensioned and the full force cannot be achieved in an element because of breakage, slippage or blockage of a duct, and if the replacement of that element is not practicable, the engineer may have to determine whether a change in the stress levels is still within the relevant limit state requirements.
12.4.5 In the case of curved tendons, or tendons made up of a number of constituent elements, or tendons loaded in stages, the engineer shall specify the order of loading and the magnitude of the force for each component of the tendon.
12.4.6 Tensioned tendons, anchorages, and duct forms shall be effectively protected from corrosion during the period between stressing and covering with grout, concrete or other permanent protection. Ducts shall be plugged at their ends and at their vents.
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SABS 0100-2 Ed. 2 12.5 Grouting of prestressing tendons 12.5.1 General 12.5.1.1 The two main objectives when the ducts of post-tensioned concrete elements are grouted are a) to protect the prestressing tendons from corrosion, and b) to provide bond between the prestressing tendons and the concrete element in order to control the spacing of cracks at heavy overload and to increase the ultimate moment of resistance of the element. 12.5.1.2 Both of the objectives in 12.5.1.1 make it essential to ensure that the whole of the void space within the ducts is filled. The success of this operation will be dependent on the production of a grout mix that has the desired properties, together with efficient equipment for its injection, and careful workmanship and supervision on site. 12.5.1.3 The important properties of a satisfactory grout for the injection of ducts in a post-tensioned member are good fluidity and low sedimentation or bleeding in the plastic state, and durability and density with low shrinkage in the hardened state in order that the grout will bond with the steel and the sides of the duct and provide protection for the prestressing tendon. The methods to be adopted should be such that they can be carried out on site effectively and reasonably easily. 12.5.1.4 Grouting trials shall be undertaken when required by the engineer.
12.5.2 Grouting equipment 12.5.2.1 A high-pressure water supply of sufficient volume shall be provided before grouting commences. Sheathing shall be cleaned of dirt and other foreign matter by thorough flushing with water immediately prior to grouting. 12.5.2.2 The mixing equipment shall be of a type that is capable of producing a grout of colloidal consistence by means of high local turbulence while imparting only a slow motion to the body of the grout. 12.5.2.3 The injection equipment shall be capable of continuous operation with little variation of pressure and shall include a system for agitating the grout while actual grouting is not in progress. Compressed air shall not be used to agitate or inject the grout. 12.5.2.4 Normally, equipment should have a delivery pressure of 1 MPa. Piping to the grout pump shall have a minimum of bends, valves and changes in diameter, and connections shall be air-tight. All baffles to the pump shall be fitted with sieve strainers of aperture size 3 mm. All equipment, especially piping, shall be thoroughly flushed with clean water after every series of operations and more frequently if necessary. Intervals between washings shall not exceed 3 h.
12.5.3 Materials 12.5.3.1 General All materials shall be measured by mass. 12.5.3.2 Cement Only portland cement that complies with SABS 471 or SABS 831 and that has not been stored in paper sacks on site for more than 1 month, shall be used. The temperature of the cement shall be less than 35 °C.
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SABS 0100-2 Ed. 2 12.5.3.3 Sand Sand should only be used when the diameter of the duct exceeds 150 mm. Sand shall be of particle size not exceeding 0,6 mm. 12.5.3.4 Admixtures Admixtures should only be used when experience has shown that their use will improve the quality of the grout. Admixtures shall not contain chlorides, nitrates, sulfides or sulfites. When aluminium powder is used, the total expansion shall not exceed 6 % by volume.
12.5.4 Ducts 12.5.4.1 Air vents of diameter at least 10 mm shall be provided at any crests present in the duct profile, since it is important that the whole volume of the duct be filled with grout. Horizontal ducts of length not exceeding 30 m shall be grouted from one end, without intermediate vents. 12.5.4.2 Threaded entries to the duct or anchorage to permit the use of a screwed connector from the grout pump may be used with advantage. 12.5.4.3 Before the concrete is placed, duct linings shall be inspected for continuity, correct alignment, secure fixing, dents, splits and holes, and any defects shall be rectified; particular attention should be paid to joints between ducts and anchorages and joints between adjacent precast units. 12.5.4.4 Lined ducts should be kept dry before grouting to prevent corrosion of the tendon, possible frost damage or excess water, but they may be flushed with water immediately before grouting. If the tendon is to remain unstressed for more than 28 d from the time of tendon placement, temporary corrosion protection should be provided. Vertical ducts shall be sealed at all times before grouting, to prevent the ingress of rain and debris.
12.5.5 Mixing 12.5.5.1 The cement/water ratio of the mix shall be at least 2,3 by mass. The quantity of sand or filler used should not exceed 30 % of the mass of the cement. 12.5.5.2 Water shall be added to the mixer first, then two-thirds of the cement. When these are thoroughly mixed, any admixture or sand and the remainder of the cement shall be added. Mixing shall continue for not less than 2 min and not more than 5 min, until a uniform consistence is obtained. Mixing by hand is not permissible.
12.5.6 Strength of grout The compressive strength of 100 mm cubes of grout, made in conditions similar to those of the injected grout and cured in a moist atmosphere for the first 24 h and thereafter in water at 22 °C to 25 °C, shall exceed 20 MPa at 7 d.
12.5.7 Injection of grout 12.5.7.1 Grout should be used within 60 min of mixing unless it contains a retarder. Grout that has partially set shall be discarded. Injection shall be continuous and slow enough (6 m to 12 m per minute) to avoid segregation of the grout. The method of injecting grout shall be such as to ensure complete filling of the ducts and complete surrounding of the steel. The volume of the spaces to be filled by the injected grout should be compared with the quantity of grout injected. Grout shall be allowed to flow from the free end of a duct until its consistence is equivalent to that of the grout injected. The opening shall then be firmly closed. Any vents shall be similarly closed, one after another, in the direction of the flow.
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SABS 0100-2 Ed. 2 12.5.7.2 Grouting shall be carried out as soon as is practicable but not later than 7 d after the tendons have been stressed. 12.5.7.3 Vertical and inclined ducts should be grouted from the lowest point, the maximum length grouted in one operation being 50 m. 12.5.7.4 In the event of a blockage or an interruption of grouting, all grout shall be flushed from the duct with water.
12.5.8 Grouting during cold weather 12.5.8.1 When the weather is cold, accurate records shall be kept of maximum and minimum air temperatures, and the temperatures of the members to be grouted. Any materials in which snow, frost or ice is present shall not be used, and the ducts and equipment shall be completely free from frost and ice. 12.5.8.2 Unless the member is so heated as to maintain the temperature of the placed grout above 5 °C for at least 48 h, no grout shall be placed when the temperature of the member is below 5 °C or is likely to fall below 5 °C during the following 48 h. 12.5.8.3 Unless accompanied by general external heating of the member or structure, ducts shall not be warmed with steam. 12.5.8.4 The grout materials shall be warmed within the limits recommended for concrete (see 7.2.1.4).
12.5.9 Protection and bond of prestressing tendons 12.5.9.1 General It is essential to protect prestressing tendons from both mechanical damage and corrosion. Protection may also be required against fire damage. 12.5.9.2 Protection and bond of internal tendons Internal tendons may be protected and bonded to the element by either cement grout or sand cement grout in accordance with 12.5.3 and 12.5.5. Alternatively, the tendons may be protected by other materials based on bitumen, epoxy resins, rubber and the like, provided that the effects on bond and on fire resistance are investigated. 12.5.9.3 Protection and bond of external tendons 12.5.9.3.1 A tendon is considered to be external when, after stressing and incorporation in the work but before protection, it is outside the structure. It does not apply, for example, to a floor comprising a series of precast beams that are themselves stressed with external tendons and subsequently so concreted or grouted that the prestressing tendons are finally contained in that filling together with adequate cover. 12.5.9.3.2 Protection of external prestressing tendons against mechanical damage and corrosion from the atmosphere or other environment should generally be provided by an encasement of dense concrete or dense mortar of adequate thickness. It may also be provided by other materials hard enough and stable enough for the particular environment.
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SABS 0100-2 Ed. 2 12.5.9.3.3 When the type and quality of the material to be used for the encasement are being determined, full consideration should be given to the differential movement between the structure and the applied protection that arises from changes of load and stress, creep, relaxation, drying shrinkage, humidity and temperature in either. If the applied protection is dense concrete or dense mortar, and investigations show the possibility of undesirable cracking, a primary corrosion protection that will be unimpaired by differential movement should be used. 12.5.9.3.4 If external prestressing tendons are to be bonded to the structure, this shall be achieved by suitable reinforcement of the concrete encasement to the structure.
13 Precast concrete 13.1 General Precast units, whether of plain, reinforced or prestressed concrete, shall have been designed in accordance with the provisions of SABS 0100-1 and the quality and workmanship shall be in accordance with the applicable provisions of this part of SABS 0100.
13.2 Permissible deviations For permissible deviations, see SABS 0155. Allowances for construction inaccuracies are given in SABS 0100-1.
13.2.1 While dimensional variations are inevitable, precast concrete units can be manufactured to comparatively small permissible deviations. Manufacturing to such fine tolerances, however, will materially increase the cost of the units.
13.2.2 Permissible deviations shall only be specified for those dimensional characteristics that are important to the correct assembly, performance and appearance of the structure, and shall be as large as is practicable. The permissible deviations for other dimensional characteristics shall be left to the discretion of the manufacturer, but shall be reasonable for the conditions of production and use. The manufacturer shall, when so requested, make these permissible deviations known.
13.2.3 The permissible deviations for the units shall be consistent with any variation in the position of the adjoining elements in the building. 13.2.4 The permissible deviations are a general guide. In exceptional cases, it may be possible to reduce certain permissible deviations even further by means of specially designed moulds, but such reductions should be made with considerable caution.
13.2.5 It is strongly recommended that the manufacturer's advice be obtained at the early design stages when very small permissible deviations are likely to be required, since those that can be achieved in practice depend on a number of factors, including the following: a) the shape of the unit, particularly since this affects the stiffness of the mould; b) the mould materials and the method of assembly; c)
the number of castings from each mould; and
d) the position and shape of any projections through the moulded faces.
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SABS 0100-2 Ed. 2 13.2.6 For irregular, curved or specially shaped units, the necessary dimensions and permissible deviations shall be clearly defined in the project specification and shown on the drawings.
13.2.7 Particular attention is drawn to the fact that deviations can be cumulative, i.e. adjoining edges of two floor panels nominally at the same level can differ by the sum of the positive deviations on bow and thickness on one unit, and the same negative deviations on the next unit. 13.2.8 Where appropriate, permissible deviations shall be given as both plus and minus values on a specific dimension, rather than as a deviation from a maximum or minimum value; working drawings to be used by the manufacturer shall give dimensions and permissible deviations as required.
13.3 Prestressed units 13.3.1 When permissible deviations for prestressed units are being specified, the creep, shrinkage and elastic shortening of the concrete, the eccentricity of the steel and other significant factors shall be taken into account. 13.3.2 At a given age, and by the use of factors appropriate to that age applied to the method recommended in SABS 0100-1, a camber can be predicted. This predicted camber, the age and other controlling conditions (e.g. when supported at the ends and subjected to self-weight only) shall be stated on the drawings or in the project specification. The actual camber shall not exceed the predicted camber by more than 50 %. 13.3.3 Where variation in camber between closely associated units (e.g. floor panels laid side by side and practically touching, and receiving plaster or topping, or both) is critical, it shall not exceed 6 mm for units of up to 4,5 m in length, or 9 mm for longer units. 13.3.4 Where variation in camber is not critical (e.g. in the case of closely associated units that have a false ceiling and thick top screed, or units not closely associated with one another), variations in camber in excess of those stated above may be acceptable to the engineer, and should be judged in relation to the conditions the units have to fulfil.
13.4 Handling and erection of precast concrete units 13.4.1 Lifting equipment Lifting equipment shall comply with safety regulations, and the method of support during lifting and placing shall be in accordance with approved procedures.
13.4.2 Handling and transportation 13.4.2.1 Precast units shall be designed to resist, without permanent damage, all stresses induced by handling, storage and transport. The minimum age for handling and transporting shall be specified by the engineer or designer, and is related to the concrete strength, the type of unit and other factors. 13.4.2.2 The position of lifting and supporting points, the method of lifting, and the type of equipment and transport to be used shall be as specified by the engineer or as agreed by him, and shall be practical and safe to use, and such that no damage is likely to result from the lifting equipment. 13.4.2.3 Units shall be marked with indelible identity, location and orientation marks as and where necessary. 13.4.2.4 The engineer shall, in all cases, specify the points of support during storage, and shall ensure that these are so chosen as to prevent unacceptable permanent distortion of the units; resilient supporting
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SABS 0100-2 Ed. 2 arrangements that permit small settlements without inducing stresses in the units are preferred. The engineer shall also ensure that, when a stack is several units high, the units are vertically above one another to prevent bending stresses in any unit. Where disfigurement would be detrimental, packing pieces shall not discolour or otherwise permanently damage the units. 13.4.2.5 Trapped water and dirt shall not be allowed to accumulate in the units. NOTE - The freezing of trapped water can cause severe damage.
13.4.2.6 Where necessary, precautions shall be taken to prevent projecting reinforcement from causing rust stains, and to minimize efflorescence. 13.4.2.7 During transportation, the following additional factors shall be considered: a) overloading of the transporting vehicle; b) centrifugal force resulting from cornering; c)
oscillation (a slim unit might flex (vertically or horizontally) sufficiently to cause damage); and
d) the possibility of damage due to chafing.
13.4.3 Assembly and erection The method of assembly and erection specified as part of the design, shall be strictly adhered to on site. Immediately a unit is in position and before the lifting equipment is removed, temporary supports or temporary connections shall be provided between units, as necessary. The final structural connections shall be completed as soon as is practicable.
13.4.4 Temporary supports during construction 13.4.4.1 When temporary supports are being provided, all construction loads (including wind) likely to be encountered during the completion of joints between any combination of precast units and in-situ concrete structural elements shall be taken into account. Temporary supports (when relevant) shall take movements into account, including those caused by shrinkage of concrete and any post-tensioning. In addition, the arrangement and design of temporary supports shall be such that, if a unit breaks or accidentally strikes against another during erection, the temporary supports of adjacent units will be sufficient to prevent any local collapse from becoming progressive. 13.4.4.2 The supports shall be arranged in a manner that will permit the proper finishing and curing of any in-situ concrete, mortar or grout. Temporary supports shall not be removed or released until the required strength is attained in the in-situ portion of a construction. NOTE - Attention is directed to the requirements of various Acts and regulations governing temporary works, stagings, scaffolding, and lifting equipment.
13.4.5 Forming structural connection 13.4.5.1 General requirements 13.4.5.1.1 The precast units shall be inspected to ensure that the design requirements of the structural connection are met. 13.4.5.1.2 The precast units shall be free from irregularities of such size and shape as to lead to damaging stress concentrations. When reliance is placed on bond between the precast units and in-situ concretes, the contact surface of the precast unit shall have been suitably prepared in accordance with
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SABS 0100-2 Ed. 2 SABS 0100-1. If frictional resistance is assumed to have developed at a bearing, the construction shall be such that this resistance can be realized. Particular attention shall be given to checking the accurate location of reinforcement and any structural steel sections in the ends of precast units and to the introduction of any additional reinforcement needed to complete a connection. 13.4.5.2 Packing requirements The packing of joints shall be carried out in accordance with assembly instructions. 13.4.5.2.1 Concrete or mortar packing The following points shall be taken into consideration: a) when joints between units, particularly the horizontal joints between successive vertical lifts, are load-bearing and are to be packed with mortar or concrete, tests shall be carried out to prove that the material is suitable for the purpose and that the proposed method of filling results in a solid joint; b) the composition and cement/water ratio of the in-situ concrete or mortar used in any connection shall be as specified by the engineer; and c)
care shall be taken to ensure that in-situ material is thoroughly compacted. The use of an expanding agent may be considered advantageous.
13.4.5.2.2 Other packing materials The following points shall be taken into consideration: a) packing materials other than grout, mortar or concrete (e.g. resinous adhesives, lead, bituminous compounds, etc.) may be used, provided that they fulfil all the necessary requirements and are compatible in all respects with the concrete components being joined together; b) the manufacturer's recommendations as to the methods of application shall be strictly followed; and c)
levelling devices, such as nuts and wedges, that have no load-bearing function in the completed structure, shall be slackened, released or removed, as necessary.
13.4.5.3 Fixing by welding Where precast units are fixed by welding, it should be noted that the expansion of cast-in plates may cause cracking of the precast section. Heat may be reduced by a) the use of low-heat welding rods of small size, b) the use of intermittent welds, and c)
the use of smaller welds.
Plates should not be less than 10 mm thick. Welding should preferably not be done where connections are galvanized, unless steps are taken to re-instate the zinc layer, e.g. with zinc-rich epoxy paint. Where galvanizing is used, consideration should be given to using a chromate passivator in the concrete, to prevent interaction of the zinc with the alkali in the cement. Welding shall not be done near prestressing cables or anchorages.
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SABS 0100-2 Ed. 2 13.4.6 Protection At all stages, and until completion of the work, precast concrete units and any other concrete associated with them shall be properly protected. The degree and extent of the protection to be provided shall be sufficient for the surface finish and profile being protected, the position and importance of the units being borne in mind. This is particularly important in the case of permanently exposed concrete surfaces, especially arrises and decorative features. The protection can be provided by timber strips, hessian, etc., but shall be such as will not damage, mark or otherwise disfigure the concrete.
14 Testing and acceptance of concrete 14.1 General Concrete materials and operations shall, as the work progresses, be tested and inspected in accordance with the methods referred to in the project specification or in accordance with such other methods as specified by the engineer. Failure to detect any defective work or material shall not in any way prevent later rejection when such defect is discovered nor shall it obligate the engineer to final acceptance. Site testing shall be carried out by a competent technician or by a person deemed by the engineer to be sufficiently experienced. Laboratory testing shall be carried out by a recognized testing authority or an accredited laboratory or a firm approved by the engineer.
14.2 Testing services 14.2.1 Basic testing services The following testing services shall be performed by an approved testing authority: a) reviewing or testing (or both) the contractor's proposed materials for compliance with the relevant specification; b) collecting samples of materials at plants or stockpiles during the course of the work and testing them for compliance with the relevant specification; c)
during construction, conducting strength tests of the concrete in accordance with 14.3;
d) conducting tests to monitor mix characteristics such as cement/water ratio and cement content where these have been specified; and e) conducting tests to monitor in-situ cover to reinforcement.
14.2.2 Testing services required by the engineer The following services shall, when so required by the engineer, be performed by the approved testing authority: a) reviewing or testing (or both) the contractor's proposed mix design; b) inspecting concrete batching, mixing and delivery operations to the extent deemed necessary by the engineer; c)
sampling concrete at the point of placement, and carrying out the required tests;
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SABS 0100-2 Ed. 2 d) reviewing the manufacturer's report for each shipment of cement, reinforcing steel and prestressing tendons, or conducting laboratory tests or spot checks of the materials as received (or both), for compliance with relevant specifications; and e) other testing or specification services as required.
14.2.3 Additional services when required The following services shall be performed by the approved testing authority when necessary: a) additional testing and inspecting when changes in materials or proportions are proposed by the contractor; and b) additional testing of materials or concrete occasioned by their failure by test or inspection to meet specification requirements.
14.2.4 Test reports All test reports shall include the exact location in the work where the batch of concrete represented by a test was placed. Reports of strength tests shall include detailed information on storage and curing of specimens prior to testing.
14.2.5 Responsibilities and duties of the contractor 14.2.5.1 The contractor shall submit to the engineer his proposals for the concrete materials and the concrete mix designs. These shall include the results of the tests performed on the materials and the tests to establish the mix designs. No concrete should be placed in the works until the contractor has received the approval of the engineer. 14.2.5.2 To facilitate testing and inspection, the contractor shall ensure that the following test equipment, in good condition, is available: a) slump test apparatus as specified in SABS method 862; b) moulds for compressive strength testing in accordance with the requirements of SABS method 863, and in sufficient quantity to permit the frequency of sampling and testing in terms of 14.3; c)
apparatus for curing strength specimens;
d) equipment to permit the measurement of entrained air, if air-entraining admixtures or any other admixtures are used (see 4.4); and e) any other test equipment specified.
14.3 Strength tests of concrete during construction 14.3.1 General procedures During construction, strength tests of the concrete shall be conducted in accordance with the procedures in 14.3.1.1 to 14.3.1.5. 14.3.1.1 During the time when concrete of a particular grade is being placed, samples shall be taken in accordance with SABS method 861 and in accordance with a predetermined programme. The programme shall be worked out taking the following into account:
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SABS 0100-2 Ed. 2 (As amended 1994) a) each sample (one sample being sufficient for three cubes for each testing age) shall be taken from a different batch of concrete chosen on a random basis: the numbers of batches to be selected as the test batches shall be determined before commencement of concrete placement; b) at least one sample shall be taken from each day's placing and from at least every 50 m3 of concrete of each grade placed; c)
the frequency of sampling shall be determined by the importance of the work, e.g. a critical part of the structure may require that additional samples be taken;
d) when the batch size is less than 2 m3, the first sample of each grade shall be taken after at least Amdt 1, three batches of this grade have been mixed and discharged. Sept. 1994 e) Deleted by Amendment No. 1. 14.3.1.2 The slump of the concrete sample shall be determined in accordance with SABS method 862 for each strength test and whenever the consistence of the concrete appears to vary. 14.3.1.3 The cubes shall be cast and cured in accordance with SABS method 863. Cubes cured on site shall be cured in water at a temperature between 22 °C and 25 °C.
Amdt 1, Sept. 1994
14.3.1.4 The cubes shall be tested in accordance with SABS method 863. Three cubes shall be tested for acceptance at the age specified, which is usually 28 d. For prestressed concrete, sets of three cubes shall be tested at 3 d. Sets of three cubes may be tested at other ages for information. 14.3.1.5 In the case of low-density concrete, the air content and unit mass of a concrete sample shall be determined for each strength test.
14.3.2 Evaluation of strength test results Test results for test cubes shall be evaluated separately for each grade of concrete. Such evaluation is only valid if tests have been conducted in accordance with procedures specified in 14.3.1.
14.3.3 Acceptance criteria for strength test results NOTE - The specified strength referred to below is the characteristic strength shown on the drawings or otherwise specified.
14.3.3.1 The strength test results shall meet both of the following acceptance criteria: a) no individual test result shall be more than 3 MPa below the specified characteristic strength; and
Amdt 1, Sept. 1994
b) the mean of any group of three consecutive and overlapping results shall exceed the specified characteristic strength by at least 2 MPa. 14.3.3.2 If the test results fail to meet the acceptance criteria given in 14.3.3.1, the following apply: a) the mix design shall be adjusted to ensure compliance with the acceptance criteria, due cognizance being taken of available 7 d/projected 28 d cube results;
Amdt 1, Sept. 1994
b) in relation to the part of the structure in which concrete represented by the test results has been used, 1)
an assessment of the stress level in the structure should be carried out; or
2)
tests should be carried out in accordance with 14.4 or clause 15, or both;
c) if the acceptance criterion given in 14.3.3.1(a) is not met, the amount of concrete represented by the test should be limited to the lesser of 50 m3 and that represented by the actual testing frequency; and d) if the acceptance criterion given in 14.3.3.1(b) is not met, it shall be assumed that the concrete represented by the test includes the batches represented by the first and the last samples, together with all intervening batches. 14.3.3.3 Should a concreting operation of the same concrete mix be of such magnitude or the sampling Amdt 1, of such frequency that 30 or more valid test results have become available within three months, the con- Sept. 1994 tractor may choose to have results assessed statistically. In such a case, the average of overlapping sets
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SABS 0100-2 Ed. 2 (As amended 1994) of 30 valid test results for a specific grade of concrete shall exceed the specified strength by at least 1,7 times the standard deviation, and no individual result shall fall below the value specified in 14.3.3.1(a). In the event of strength failure, 14.3.3.2 shall apply.
14.4 Strength tests of concrete in place NOTE - For load tests, see clause 15.
14.4.1 Non-destructive testing Testing by rebound hammer, sonoscope or other non-destructive device may be permitted by the engineer to determine relative strengths at various locations in the structure as an aid in evaluating the strength of concrete in place or for selecting areas to be cored. Such tests, unless properly calibrated and correlated with other test data, shall not be used as a basis for acceptance or rejection.
14.4.2 Core tests Where so required, drilled cores shall be obtained and tested in accordance with SABS method 865. Cores should be drilled and tested when the age of the concrete is as close as possible to the age for strength acceptance according to cubes. At least three representative cores shall be taken from each member or predetermined volume of concrete in locations that are considered potentially deficient. The location of cores shall be determined by the engineer, to cause the least impairment to the strength of Amdt 1, the structure. The lesser of the top 300 mm and top 20 % of the depth of the concrete member shall not Sept. 1994 be used for core testing unless unavoidable (e.g. thin slabs). If, before testing, one or more of the cores shows evidence of having been damaged subsequent to or during removal from the structure, it shall be replaced with a new core. If a core contains reinforcing steel, the measured compressive strength of the core shall be corrected in accordance with SABS method 865. Core holes shall be filled with low-slump concrete or mortar (see 10.9.3). Amdt 1, Sept. 1994
14.4.3 Acceptance of concrete on the basis of core strengths 14.4.3.1 If the average core strength is at least 80 % of the specified strength (see 14.3.3), and if no single core strength is less than 70 % of the specified strength, the concrete shall be accepted. 14.4.3.2 If the concrete in a certain area fails to comply with 14.4.3.1 because a single core result falls below 70 % of the specified strength, a further set of three cores may be taken from the same area, to determine the extent of deficient concrete. If the new set of three cores complies with the requirements of 14.4.3.1, the area represented by this second set of cores shall be considered acceptable. If the new set of cores fails to comply with the requirements of 14.4.3.1, 14.4.3.3 applies. 14.4.3.3 If the core strength does not meet the acceptance criteria of 14.4.3.1 or 14.4.3.2, the following should be considered in relation to the deficient part of the structure: a) strength requirements for the member(s); b) performance of a full-scale load test as in clause 15; c) strengthening the deficient part of the structure; and d) removal and replacement of the deficient part of the structure.
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SABS 0100-2 Ed. 2
15 Load tests 15.1 Individual precast units 15.1.1 General The load tests described in this clause are intended as checks on the quality of the units, and are not to be used as a substitute for normal design procedures. Where units require special testing, such special testing procedures shall be in accordance with the project specification. Test loads are to be applied and removed incrementally.
15.1.2 Non-destructive test 15.1.2.1 Support the unit at its designed points of support, and load it for 5 min with a load equal to the sum of the nominal self-weight plus 1,25 times the nominal imposed load. Record the deflection. Ensure that the maximum deflection measured after application of the load is in accordance with the requirements defined by the engineer. 15.1.2.2 Measure the recovery 5 min after the removal of the applied load and then re-impose the load. Ensure that the recovery after the second loading is not less than that after the first loading and not less than 90 % of the deflection recorded during the second loading. At no time during the test shall the unit show any sign of weakness or faulty construction as defined by the engineer in the light of a reasonable interpretation of relevant data.
15.1.3 Destructive test Support the unit at its designed points of support and load it. The unit shall not fail at its ultimate load within 15 min of the time when the test load (see 15.2.3) becomes operative. Regard a deflection exceeding 1/40 of the span as failure of the unit.
15.1.4 Special test In the case of very large units or units not readily amenable to the above tests, such as columns, the precast parts of composite beams, and units designed for continuity of fixity, the testing arrangements should be agreed upon before such units are cast.
15.2 Structures and parts of structures 15.2.1 General The tests described in this clause are intended as a check on structures other than those covered by 15.1, where there is doubt regarding serviceability or strength. Test loads are to be applied and removed incrementally.
15.2.2 Age at test 15.2.2.1 Carry out the test as soon as possible after expiry of the 28 d from the time of placing the concrete. The test may be carried out earlier, if the test is for any reason other than uncertainty in respect of the quality of the concrete in the structure, and provided that the concrete has already reached its specified strength. 15.2.2.2 When testing prestressed concrete, make allowance for the effect of prestress being above its final value at the time of testing.
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SABS 0100-2 Ed. 2 15.2.3 Test loads 15.2.3.1 The test loads to be applied for the limit states of deflection and for local damage are the appropriate loads, i.e. the self-weight plus the nominal imposed load. When the ultimate limit state is being considered, ensure that the test load, maintained for a period of 24 h, is the greater of a) the sum of the self-weight plus 1,25 times the nominal imposed load, or b) 1,125 times the sum of the self-weight plus the nominal imposed load. If any of the final self-weight loads is not in position on the structure, add compensating loads as necessary. 15.2.3.2 Where only part of a structure is to be tested, special precautions may be necessary to ensure that all the elements actually under test are subjected to the full test load, with proper allowance being made for load sharing between elements.
15.2.4 Measurements during the tests Examine the structure before loading, and record the location and width of any cracks present. Take measurements of deflection and crack width as follows: a) immediately after the application of load; b) in the case of the 24 h sustained load test, at the end of the 24 h period of loading; c) after removal of the load; and d) after a 24 h recovery period. Record ambient temperature and weather conditions during the test.
15.2.5 Assessment of results 15.2.5.1 In assessing the serviceability of a structure or part of a structure after a loading test, consider the possible effects of variation in ambient temperature and humidity during the period of the test. 15.2.5.2 The following criteria shall apply: a) in the case of reinforced concrete structures and class 3 prestressed concrete structures (see SABS 0100-1), the maximum width of any crack measured immediately on application of the test load for local damage shall not exceed two-thirds of the value for the limit-state requirement (see SABS 0100-1). In the case of class 1 and class 2 prestressed concrete structures, no visible cracks shall have occurred under the test load for local damage; b) in the case of elements spanning between two supports, the deflection measured immediately after application of the test load for deflection shall not exceed 1/500 of the effective span. Agreement on limits shall be reached before cantilevered portions of structures are tested; c) if the maximum deflection, in millimetres, occurring during a period of 24 h under load test, does not exceed 40 L 2/h (where L is the effective span, in metres, and h is the overall depth of construction, in millimetres), the recovery need not be measured, and the criteria given in (d) and (e) below will not apply;
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SABS 0100-2 Ed. 2 d) if, within 24 h of the removal of the test load calculated in accordance with 15.2.3 for the ultimate limit state, a reinforced concrete structure or class 3 prestressed concrete structure does not show a recovery of at least 75 % of the maximum deflection occurring during the 24 h under load, repeat the loading. Consider the structure to have failed the test if the recovery after the second loading is less than 75 % of the maximum deflection shown during the second loading; e) if, within 24 h of the removal of the test load calculated in accordance with 15.2.3 for the ultimate limit state, a class 1 or class 2 prestressed concrete structure does not show a recovery of at least 85 % of the maximum deflection occurring during the 24 h under load, repeat the loading. Consider the structure to have failed the test if the recovery after the second loading is less than 85 % of the maximum deflection occurring during the second loading.
16 Procedure in the event of failure Concrete work judged (by structural analysis or by results of a test) to be inadequate shall be replaced or shall be strengthened by additional construction or other means approved by the engineer. The procedure shall apply to a) each section that failed or contains concrete that failed, as relevant, and b) any other section, irrespective of strength, the functional purpose of which is affected by the section or concrete referred to in (a) above.
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SABS 0100-2 Ed. 2
Annex A (normative)
Concrete subjected to wet conditions - aggressiveness of the water, and countermeasures1) A.1 General Where concrete is subjected to wet conditions, the water in contact with the concrete should be assessed for aggressiveness, and appropriate measures taken to ensure the durability of the concrete.
A.2 Analytical tests required Unless it is known with certainty that the water contains no more than trace quantities of any of the ionic characteristics listed in table A.1, all the corresponding tests (or other tests that give equivalent results) should be carried out. Additional tests may be specified in special circumstances at the discretion of the engineer, e.g. brines in salt pans, and water from hot mineral springs. Table A.1 - Ionic characteristics 1
2
Ionic characteristics
Test method
pH value
SABS method 11
Calcium-carbonate-saturated pH value
PCI TM 9.28
Calcium hardness
SABS method 216
Total ammonium ion content
SABS method 217 SABS method 218
Magnesium ion content
SABS method 1071
Total sulfates
SABS method 212
Chloride ion content*)
SABS method 202
Total dissolved solids
SABS method 213
)
* This determination is necessary only in the case of reinforced-concrete or prestressed-concrete structures and may be omitted if plain concrete only is at issue.
1) For more information, see the Portland Cement Institute publication, Deterioration of concrete in aggressive waters measuring aggressiveness and taking countermeasures by JJ Basson.
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SABS 0100-2 Ed. 2
A.3 Assessment of the aggressiveness of water, using the Basson Index (BI) A.3.1 Basson Index The Basson Index BI is a measure of the total aggressiveness of water, and is calculated as follows: BI = Na + Nb where Na is a factor representing the water properties; and Nb is a factor representing environmental factors (e.g. temperature, flow).
A.3.2 Calculations A.3.2.1 Factors Na and Nb A.3.2.1.1 The water properties factor Na is calculated as the sum of the indices N1 to N6, each of which is calculated as shown in table A.2. A.3.2.1.2 The environmental factor Nb is calculated as the sum of the indices N11 to N14 (each of which is calculated as shown in table A.3) for whichever conditions are being taken into account. Table A.2 - Calculation of water properties indices 1
2
3
Property
Symbol
Units
4 Index Nx
pH value
V1
1/log[H+]
N1 = 200 x (9,5 - V1)
Calcium carbonatesaturated pH value
V2
1/log[H+]
N2 = - 2 000 x (V1 - V2)
Calcium hardness (as CaCO3)
V3
mg/L
N3 = 2,2 x (500 - V3)
Total ammonium ions (as NH4)
V4
mg/L
N4 = 10 x V4
Magnesium ions (as Mg)
V5
mg/L
N5 = 0,6 x V5
Total sulfates (as SO4)
V6
mg/L
N6 = 0,3 x V6
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SABS 0100-2 Ed. 2 Table A.3 - Calculation of environmental indices 1
2 Index
Property Nx Flow - turbulent
N11 = 0,75
- stagnant
N12 = -0,5
Temperature t, °C
N 13 = 0,05 x (t - 20)
Wet-dry cycles: d = dry time fraction c = cycles per year s = total dissolved solids, mg/L
N14 = 0,16 x 10-6 x d x c x s
A.3.2.2 Other indices The subindex for leaching corrosion LSI, and the subindex for spalling corrosion SSI, are calculated as follows:
LSI =
SSI =
(N1 + N2 + N3) 3
(N4 + N5 + N6) 3
A.3.3 Classification After the Basson Index BI has been calculated as shown in A.3.1 and A.3.2.1, the water is classified as in table A.4. Table A.4 - Classification of water in terms of Basson Index BI
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1
2
3
Basson Index BI
Water aggressiveness
Recommendation
Under 350
Non-aggressive to mildly aggressive
Use concrete class as required for structural design, but see remarks in table A.6.
350 to 750
Mildly to fairly aggressive
Good concrete design and construction essential. See remarks in table A.6.
750 to 1 000
Highly aggressive
Identify dominant corrosion subindex and follow applicable recommendations.
Over 1 000
Very highly aggressive
Do not use in contact with unprotected concrete unless recommended anti-corrosion measures can be carried out in full.
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SABS 0100-2 Ed. 2
A.4 Recommended anti-corrosion measures A.4.1 Identification of suitable countermeasures A.4.1.1 Identify the dominant mode of attack by establishing which one of the leaching or spalling corrosion subindices, as calculated, is the greater. If leaching-corrosion subindex LSI is the greater, use table A.5. If spalling-corrosion subindex SSI is the greater, use table A.6. Use table A.5 or table A.6, as appropriate, to determine what anti-corrosion measures are applicable to the case under consideration.
A.4.1.2 Repeat this procedure for the subdominant mode of attack, to ensure that all the anti-corrosion measures that may be required have been taken into consideration. As a result of the fortuitous and beneficial overlap of treatments, a second or third anti-corrosion treatment will seldom be required unless very unusually aggressive conditions are present. A.4.1.3 When reinforcing or prestressing steel is present in the concrete, it should be remembered that the degree of protection provided by the concrete to such steel is related to cover thickness. See the recommendations given in table A.7. Table A.5 - Countermeasures against leaching corrosion 1
2
3
4
5
Limits of leachingcorrosion subindex LSI
Other applicable factors
Recommended class of concrete*)
Recommended type of coating**)
Remarks
Spalling-corrosion subindex SSI less than 300
1
Spalling-corrosion subindex SSI 300 to 500
2
None or A
High turbulence or temperature corrections (or both) may necessitate extra sacrificial inorganic coating allowance, depending on anticipated service life of concrete structure
Below 350
350 to 750
Spalling-corrosion subindex SSI not exceeding 500
750 to 1 000
Above 1 000
3 or 4 3 or 4
B C D E
3 or 4
B D E
Obtain coating manufacturer's advice on best coating type for specific conditions of exposure
*) See table A.8. **) See table A.10.
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SABS 0100-2 Ed. 2 A.4.2 Materials to be used A.4.2.1 Concrete See tables A.5, A.6, A.7 and A.8.
A.4.2.2 Cement Table A.9 lists the cements that may be used in concrete intended for exposure to aggressive waters.
A.4.2.3 Aggregates See 4.3.
A.4.2.4 Mixing water See 4.2.
A.4.2.5 Mix proportions Table A.8 summarizes the classes of concrete considered suitable for use under aggressive water conditions and indicates the proportions in which the various components should be mixed in order to achieve the desired properties.
A.4.2.6 Anti-corrosion coatings for concrete See table A.10.
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SABS 0100-2 Ed. 2 Table A.6 - Countermeasures against spalling corrosion 1
2
3
4
5
Limits of spallingcorrosion subindex SSI
Other applicable factors
Recommended class of concrete*)
Recommended type of coating**)
Remarks
Below 350
350 to 750
Leaching-corrosion subindex LSI less than 300
Leaching-corrosion subindex LSI 300 to 500
High turbulence and/or temperature and/or wet-dry cycling corrections may necessitate an additional thickness allowance, depending on anticipated service life of concrete structure
1 or 2
3 or 4
None or A
or 5 750 to 1 000
Above 1 000
Preferred type if attack is mainly because of sulfates
Sulfate subindex N6 less than 800
3 or 4
B C D E
Sulfate subindex N6 exceeding 800
or 5
B D E
Obtain coating manufacturer's advice on best coating type for specific conditions of exposure
*) See table A.8. **) See table A.10. Table A.7 - Countermeasures against chloride corrosion 1
Chloride ion content (as Cl)
2
Other applicable factors
3
Recommended class of concrete
4
5
Recommended type of coating
Recommended minimum cover of concrete over reinforcement mm
Below 350
25
350 to 750 750 to 1 000
35 As determined for dominant and subdominant corrosion subindices (or for both) (see tables A.3 and A.4)
Above 1 000
50 75 (greater in tidal zones)
NOTE -This table is only applicable if reinforcing or prestressing steel is present.
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SABS 0100-2 Ed. 2 (As amended 1994) Table A.8 - Concretes for aggressive chemical environments 1
Class
2
3
4
Cement code*)
Minimum cement content**) 3
kg/m
1
2
OPC RHPC PC 15 (SL) RHPC 15 (SL) PC 15 (FA) PC 45 (SL) 50/50 PC/GGBS PC 30 (FA) 90/10 PC/CSF OPC RHPC PC 15 (SL) RHPC 15 (SL) PC 15 (FA) PC 45 (SL) 50/50 PC/GGBS PC 30 (FA) 90/10 PC/CSF
Minimum cement/water ratio**)
5 Characteristic strength
Amdt 1, Sept. 1994 6
Remarks
MPa
340
1,8
30
Minimum quality recommended for use under freshwater conditions and in heavily polluted air
420
2,2
40
Minimum quality recommended for use under marine or saline conditions and in salt-laden air
3
PC 45 (SL) 50/50 PC/GGBS
420
2,2
40
Improved protection of steel under marine or saline conditions, because of chloride-binding ability
4
PC 30 (FA) 90/10 PC/CSF
420
2,2
40
Improved denseness and impermeability of concrete and also improved resistance to leaching attack, because of pozzolanic pore-refinement properties
5
SRPC***)
420
2,2
40
Moderately resistant to some sulfates because of low tricalcium aluminate content
*) See table A.9 for explanation. Note that the cement types grouped together for any one class of concrete do not necessarily produce concrete of the same strength. **) Refers to total quantity of all binders. ***) In cases where low strength is acceptable, a site blend of 20 parts of OPC and 80 parts of ground granulated blastfurnace slag may be considered as an alternative.
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SABS 0100-2 Ed. 2 Table A.9 - Cements recommended for the making of concretes for aggressive waters 1
2
3
Code
Applicable standard
Description
OPC
SABS 471
Ordinary portland cement
RHPC
SABS 471
Rapid-hardening portland cement
PC 15 (SL)
SABS 831
Portland cement with not more than 15 % ground granulated blastfurnace slag
RHPC 15 (SL)
SABS 831
Rapid-hardening version of PC 15 (SL)
PC 15 (FA)
SABS 831
Portland cement with not more than 15 % fly ash
RHPC 15 (FA)
SABS 831
Rapid-hardening version of PC 15 (FA)
PC 45 (SL)*)
SABS 626
Portland cement with 45 % to 55 % ground granulated blastfurnace slag
50/50 PC/GGBS
PC 30 (FA)
Site blend of portland cement with 50 % ground granulated blastfurnace slag SABS 1466
90/10 PC/CSF SRPC
Portland cement with 30 % fly ash Site blend of portland cement with 10 % condensed silica fume
SABS 471
Sulfate-resistant portland cement
)
* To be used in preference to portland blastfurnace cement (PBC) in which the slag content is allowed to vary over a wide range of 15 % to 70 % (see SABS 626). In the case of PC 45 (SL), the manufacturer guarantees a slag content in the range 45 % to 55 %.
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SABS 0100-2 Ed. 2 Table A.10 - Coatings for concretes in aggressive waters 1
2
3
4
5
Type
Category
Some examples
Minimum coating thickness required
Remarks
A
Extra thickness of base concrete as sacrificial allowance Plaster coats
20 mm to 50 mm
Preformed polymeric liners
Polyethylene Polyvinyl chloride Polychloroprene
0,2 mm to 1 mm
C
Emulsion-based waterborne organics
Polyacrylics Polyacrylonitriles
150 µm
Tolerant of wet surfaces
D
Solvent-based organics
Chlorinated rubbers Vinyls Vinylidenes
150 µm
High-build, thixotropic types available
Catalysed organics
Epoxy tars Solventless and water-based epoxies*) Polyurethanes
B
E
Inorganic
150 µm to 300 µm
Use under mild to moderate leaching conditions only Available in light, regular and heavyduty gauges
Accurate mixing and time-scheduling required
*) Aggregate-filled, solventless epoxy systems, applied in film of thicknesses 2 mm to 5 mm have proved to be very effective on surfaces of oil rigs.
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SABS 0100-2 Ed. 2
Annex B (informative)
Curing B.1 General The principal requirements for curing concrete are given in 10.8. The following notes are intended to amplify the factors that should be considered in complying with these requirements. The recommendations are based on the assumption that the temperature of the concrete during the curing period will not fall below 5 °C. Particular precautions that have to be taken when concreting at low ambient temperatures are given in 10.8.3.
B.2 Strength of concrete A rough guide to the development of strength at early ages at different temperatures can be obtained by using the concept of "maturity", which may be defined as the area under a curve of the temperature of the concrete (in degrees Celsius), plotted against time (in hours). Once the maturity is known, the corresponding age of concrete cured at normal temperatures can be estimated and the strength then found from data relating to the strength of that type of concrete to age at that temperature. Such calculations are only applicable if the concrete is kept constantly moist for the period under consideration.
B.3 Distortion and cracking B.3.1 The concrete should be so cured that internal stresses within the element, whether owing to differences in temperature or differences in moisture content within the concrete, are not sufficient to cause distortion or cracking. The disposition of reinforcement will affect the restraint to the strains and hence will also have an effect on any distortion and cracking. B.3.2 When the likely temperature variation within the concrete is being assessed, the following factors apply: a) rate of heat evolution (related to rate of development of strength); b) size and shape of element; c) different insulation values of curing media (e.g. wooden moulds or water spray); and d) ambient temperature. For example, surface cracking may occur as a result of variation in temperature when cold water spray is applied to a relatively massive element immediately after the moulds have been stripped and while the concrete is still hot.
B.3.3 When the likely variation in moisture content within the concrete is being assessed, it should be kept in mind that the rate of evaporation from unprotected concrete will be higher in the case of a) atmospheric conditions that encourage evaporation (e.g. low relative humidity, high wind speed, concrete surface hotter than the air) especially if the rate of migration of water through the concrete exceeds the rate of evaporation from the surface,
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SABS 0100-2 Ed. 2 b) members of high surface/volume ratio, c) early age concrete, and d) lower grades of concrete. For example, cracking may occur as a result of varying shrinkage in elements when sudden changes in section affect the surface/volume ratio appreciably, especially if the more massive section is reinforced and the more slender section is not.
B.3.4 If the shrinkage of precast units after they have been built into the structure is likely to cause undesirable cracking at the ends of the unit, curing aimed at preventing the loss of water from the unit should be continued no longer than is necessary to obtain the desired durability and strength. The concrete should then be given the maximum opportunity of drying out to an extent consistent with the limitation of the variation in moisture content as already outlined. For example, cracks may occur at the ends of precast concrete lintels that were moist-cured but were not allowed to dry sufficiently before they were built into the structure.
B.4 Durability and appearance B.4.1 As deterioration is most likely to occur if the concrete provides inadequate protection for the reinforcement, all vulnerable surfaces of newly cast concrete should be protected from excessive loss of water by evaporation, which would result in a weak, porous surface layer. The factors given in 10.8 therefore apply. B.4.2 Where it is important that the formation of lime bloom be prevented, especially in cold weather, the atmosphere adjacent to the surface of the concrete should be maintained at a constant relative humidity approaching 100 % for as long as is practicable. Concrete should be protected from the wetting and drying cycles produced by rain or condensation and drying winds.
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SABS 0100-2 Ed. 2
Annex C (informative)
Technical data for prestressed structural elements required in a contract C.1 Data for pre-tensioned elements The following technical data in a contract in respect of pretensioned structural elements shall be given on the construction drawings:
C.1.1 Tendon alignment A diagrammatic layout showing the centroid of the tendons in both the horizontal and vertical planes, together with the ordinates and offset dimensions.
C.1.2 Tendons The tendons on which the design is based, designated by the number and nominal diameter of the bars, wires or strands and the type of prestressing steel, expressed in that order, e.g. 15 x 12,5 mm 7-Hi strand.
C.1.3 Tensioning force The maximum tensioning force and the corresponding stress level in the prestressing steel, for each tendon or group of tendons. The forces shall be given in kilonewtons (kN) and the stress levels shall be expressed as a percentage of the characteristic strength, the 0,2 % proof stress or the yield stress of the prestressing steel, as relevant.
C.1.4 Prestressing losses in tendons The losses allowed for in the design shall be given as follows: a) elastic deformation of concrete: the "elastic factor", which, when multiplied by the average compressive stress in the concrete adjacent to the tendon, will give the loss due to elastic deformation of the concrete; b) creep of concrete: the "creep factor", which, when multiplied by the average compressive stress in the concrete adjacent to the tendon, will give the loss due to the creep of the concrete; c) shrinkage of concrete: the stress loss, in megapascals (MPa), due to shrinkage of the concrete; and d) relaxation of prestressing steel: the stress loss, in megapascals (MPa), at a stress level of 70 % of the characteristic strength of the prestressing steel due to relaxation of the prestressing steel.
C.1.5 Bursting reinforcement The bursting reinforcement for the prestressing system on which the design is based.
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SABS 0100-2 Ed. 2 C.1.6 Precamber The precamber at intervals not exceeding 0,25 times the span length.
C.2 Data for post-tensioned elements The following technical data in a contract in respect of post-tensioned structural members shall be given on the construction drawings.
C.2.1 Tendon alignment A diagrammatic layout showing the centroid of the tendons in both the horizontal and vertical planes, together with the ordinates, offset dimensions and curve equations of the centroid of the tendons.
C.2.2 Tendon system The tendon system on which the design is based, designated by the number and nominal diameter of the bars, wires or strands per tendon and the type of prestressing steel, expressed in that order, e.g. 12 x 12,7 mm 7-Hi strand.
C.2.3 Tensioning force The initial jacking force and the effective force at the live anchorage(s) after transfer, as well as the corresponding stress level in the prestressing steel, for each tendon or group of tendons. The forces shall be given in meganewtons (MN) and the stress levels shall be expressed as a percentage of the characteristic strength, the 0,2 % proof stress or the yield stress of the prestressing steel, as relevant.
C.2.4 Draw-in The draw-in or intended release (or both) of the tendons or group of tendons, in millimetres (mm).
C.2.5 Prestressing losses in tendons The losses allowed for in the design shall be given as follows: a) friction loss: the formula used to determine the tendon/duct friction loss together with the values adopted for the friction coefficient (u) due to curvature and the wobble factor (k) due to unintentional variation from the specified alignment; b) elastic deformation of concrete: the "elastic factor", which, when multiplied by the average compressive stress in the concrete section, will give the loss due to elastic deformation of the concrete; c) creep of concrete: the "creep factor", which, when multiplied by the compressive stress in the concrete adjacent to the tendon, will give the loss due to the creep of the concrete; d) shrinkage of concrete: the stress loss, in megapascals (MPa), due to shrinkage of the concrete; and e) relaxation of prestressing steel: the stress loss, in megapascals (MPa), at a stress level of 70 % of the characteristic strength of the prestressing steel due to relaxation of the prestressing steel.
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SABS 0100-2 Ed. 2 C.2.6 Anchorages The positions where loop type or fan type dead end anchorages may be used.
C.2.7 Concrete cover The minimum depth of concrete over the outside of the surface of the sheath or tendon support, or both.
C.2.8 Tensioning of tendons The following tensioning requirements are allowed for in the design: a) the minimum concrete strength required for initial tensioning; b) requirements for partial tensioning or tensioning at a specific stage; c) the overall sequence of tensioning; and d) the precamber at intervals not exceeding 0,25 times the span length.
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SABS 0100-2 Ed. 2
Annex D (informative)
Recommended specialist literature on massive concrete ADDIS, BJ (ed.). Fulton's concrete technology. 6th ed. Midrand: Portland Cement Institute, 1986. p. 710-735. American Concrete Institute. Cooling and insulating systems for mass concrete. Rev. ed. Detroit: ACI, 1986. ACI Committee Report 207.4R-80. BAMFORTH, PB. Mass concrete. Concrete Society Digest, 1984, No. 2.
Annex E (informative)
Bibliography BS 4447:1973 (1990), Specification for the performance of prestressing anchorages for post-tensioned construction. BS 4486:1980, Specification for hot rolled and hot rolled and processed high tensile alloy steel bars for the prestressing of concrete. BS 5896:1980, Specification for high tensile steel wire and strand for the prestressing of concrete. Basson, JJ. Deterioration of concrete in aggressive waters - measuring aggressiveness and taking counter-measures. Midrand: Portland Cement Institute, 1989. Fédération Internationale de la Précontrainte. Recommendation for acceptance and application of posttensioning systems. Slough: FIP, 1981.
sabs pta (pdf)
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