Concrete Specs

STANDARD SPECIFICATIONS

SECTION V- 2 502.01

CONCRETE CLASSES AND MIXES

Description

The concrete classes and mixes to be incorporated in the Works shall be as specified herein.

502.02

Concrete Classes

a.

General. Concrete shall have the mix designations and strength requirements indicated in Table 502.02 except for those specifically mentioned elsewhere in these Standard Specifications.

b.

Class Requirements. The approximate weights or volumes of the components for each class of concrete and any other data given in any table of these specifications or the Particular Specifications are as an aid to the Engineer for suggested trial mix and also will be of value to Tenderers and Contractors in determining the approximate quantities of components required. However, the minimum crushing strength of Work Test Cubes at 7 days and 28 days must be strictly adhered to. Acceptance of the work by the Engineer will be based on 28-day cube strength as determined under Clause 502.06, Testing, of these Standard Specifications. Concrete to be used shall include the mix designations and strength requirements indicated in Table 502.02. Method for Testing Concrete, BS 1881, shall govern for the manufacture of compressive strength test cubes for all classes of concrete, except as specified for piles in Section XI, Concrete Pile Foundations. Table 502.02 Requirements of Different Classes of Concrete Class of Concrete

Requirement

K140

K250

K335

K455

K500

K550

140

250

335

455

500

550

100

185

250

345

375

415

185

335

445

605

665

735

140

250

335

455

500

550

Water cement ratio (max.)

0.50

0.45

0.42

0.40

0.40

0.40

Minimum cement content kg/m³

220

300

400

435

445

450

Minimum crushing strength kg/cm² Preliminary Design Test Cubes at 7 days Minimum crushing strength kg/cm² Work Test Cubes at 7 days Minimum crushing strength kg/cm² Preliminary Design Test Cubes at 28 days Minimum crushing strength kg/cm² Work Test Cubes at 28 days

The minimum crushing strength at 28 days is assumed to be 1.18 times the compressive strength of 15cm by 30cm cylinders in kg/cm². Slump range to be agreed with the Version 2.0

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Engineer based on the different Concrete Classes, the particular application for the concrete, and the review and acceptance of trial mixes. Slump test results shall confirm that the slump of the tested concrete is approximately equivalent to the slump of the approved mix design for the specific class of concrete. c.

Uses of Different Classes of Concrete. Unless otherwise specifically specified herein or in the Particular Specifications: Concrete Class K140 shall be used for all blinding concrete and non-reinforced sections or as otherwise specified. Concrete Class K250 and K335 shall be used for non-reinforced and reinforced concrete, or as otherwise specified. Concrete Class K455 shall be used for cast-in-place reinforced concrete in pier shafts, abutments, walls, bored piles, pile caps and approach slabs, in bridge superstructure, barriers and precast panels, and where noted on the Drawings or in the Particular Specifications. Unless otherwise indicated on the Drawings or specified under the respective Sections, concrete Class K500 shall be used for all post-tensioned concrete including that specified in Section XIII, Post-Tensioned Concrete Works, and as indicated on the Drawings or in the Particular Specifications. Similarly, Class K550 shall be used for all prestressed concrete including that specified in Section VIII, Prestressed Concrete Works. Concrete classes above K550 shall be used on structures and at locations where specified in the Particular Specifications, indicated on the Drawings or included in the Bills of Quantities.

502.03

Mix Design

a.

Samples. Samples of all materials to be used in the mix shall be submitted to the Engineer for testing and such samples shall be tested in the Site Laboratories as directed by the Engineer. No materials forming any part of this mix shall be delivered to the Site before the Contractor receives the prior written approval by the Engineer of such material.

b.

Mix Design. After receiving written approval by the Engineer of the samples, the Contractor shall submit in writing to the Engineer a proposed mix design proportioned by weight and based on trial mixes conducted with the approved materials to be used for each specified class of concrete for the project. Each mix design submitted shall be accompanied by all relevant data. The Engineer will then examine the details and make the necessary tests for each mix design, and if he approves, will inform the Contractor in writing. If the Engineer does not approve the

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Contractor's mix design, he shall instruct the Contractor of the exact component composition for each class of concrete to be used by the Contractor for the working mix. No concrete works will be allowed to commence before the Contractor receives in writing from the Engineer either approval of the Contractor's proposed mix design or the Engineer's instructions in reference to the component composition of the working mix as aforesaid, including details of the proposed placement method. The Contractor must make arrangements for all the foregoing as early as possible and no claims for delay or compensation will be considered on account of waiting for the Engineer's written approval or instructions. In the event of any changes in characteristics or source of supply of any of the component parts, a new mix design must be approved by the Engineer as described. Any delay due to such changes will be entirely the responsibility of the Contractor and no claims for delay or compensation will be considered. During the progress of the work, the Engineer will take samples of the work mix at any time in order to check their compliance with the approved mix design. c.

Adjustments during Progress of Work. After the original proportions have been approved, as prescribed above, these proportions shall not be changed during the progress of the work except as follows:

502.04

1.

Adjustments for variations in workability. If it is found impossible to obtain concrete of the desired placeability and workability with the proportions originally determined, the Engineer will make such changes in aggregate weights as he may deem necessary.

2.

Adjustment for variation in yield. If the cement content of the concrete, determined by means of the yield test ASTM Designation C138, varies more than two (2) percent from the designated value, the proportions shall be adjusted so as to maintain a cement content which does not vary more than two (2) percent from the designated value.

3.

Adjustment for minimum strength. If it is found impossible to produce concrete having the minimum allowable strength specified, the cement content shall be increased as directed by the Engineer.

4.

Adjustment for new materials. No change in the source or character of the materials shall be made without due notice to the Engineer, and no new materials shall be used until the Engineer has accepted such materials and new proportions based on tests on trial mixes have been determined.

Contents of Chlorides and Sulphates

The amount of chlorides in the concrete mass shall not exceed 1,000 ppm when calculated on the Version 2.0

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total concrete mass, or 6,000 ppm when calculated on the amount of cement in the actual mix. The amount of sulphate in the concrete shall not exceed 800 ppm when calculated on the total concrete mass, or 5,000 ppm when calculated on the amount of the cement in the actual mix. For the above-mentioned calculations, the amounts of chlorides and sulphates shall be determined by laboratory analyses of the cement, aggregates, water and admixtures. The analyses shall be carried out by recognized methods.

502.05

Water-Cement Ratio

The quantity of water used in mixing shall be approved by the Engineer on the basis of preliminary tests and trial mixes and shall be the least amount that will produce a workable homogeneous plastic mixture which can be worked into the forms and around the reinforcement. In no circumstances shall the consistency of the concrete be such as to permit a separation of the aggregate from the mortar during handling. Excess water shall not be permitted and any batch containing such excess will be rejected. In measuring water for each batch of concrete, allowance shall be made for the water contained in the aggregates. The total water in the batch shall be deemed to consist of the water carried by the aggregates plus the water added. Frequent tests including the slump test shall be carried out to ensure that consistent water content is maintained.

502.06

Testing

In addition to all previously mentioned tests, the following tests shall be carried out. All tests must be carried out in a manner as directed by the Engineer. The Contractor shall bear all expenses involved in obtaining, cutting-out or sampling all specimens and/or component parts for testing. Nine test cubes (15cm) shall be made in accordance with BS 12390 from a sample taken from each randomly selected batch of concrete. Samples shall be taken at the point of discharge from the delivery vehicle. Unless otherwise instructed by the Engineer the rate of sampling shall be as given in the Table below but not less than one sample shall be taken on each day that concrete of that grade is used. Use of Concrete

Sample from One Batch Selected Randomly to Represent an Average Volume of Not More than the Lesser of:

Prestressed Concrete

10 m³ or 10 batches

Reinforced Concrete

20 m³ or 20 batches

Mass Concrete

50 m³ or 50 batches

Each test cube shall be numbered consecutively and marked with the date, the section of work from which it was taken and any other information required and dispatched to the approved laboratory for testing for compressive strength. Cubes Nos. 1, 5 and 9 shall be tested after 7 days. Version 2.0

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If the average of the three 7-day test cubes is below the minimum requirement, the Contractor must immediately stop all concreting until checks are made on the material and equipment and immediately rectify any defect which has become apparent as the result of such checking. If the Contractor elects to remove and replace the defective concrete without waiting for the results of the 28-day test, concreting can then continue entirely at the responsibility of the Contractor. Cubes Nos. 2 and 8, 3 and 7, and 4 and 6 will be considered three individual samples or sets and after 28 days of curing shall be tested as specified above. If either of the cubes in any set shows definite evidence, other than low strength, of improper sampling, molding, handling, curing or testing, it shall be discarded and the strength of the remaining cube shall then be considered the test result for that set. Final acceptance of the concrete works is based on 28 days' testing on the three sets of two cubes each. The work is considered in compliance if the average of the three sets of cubes equals or exceeds the minimum specified for the class of concrete being placed, and if the average of the two cubes in any one set does not fall below the specified minimum strength by more than 35 kg/cm². If the results of the 28-day testing are unsatisfactory, the Contractor, in accordance with the instructions of the Engineer, shall conduct tests in the suspect parts of the structure. The concrete may be test loaded in-situ or cylindrical test cores may be drilled out and tested in accordance with BS 1881. Should the tests prove that the concrete is unsatisfactory or below the standards specified, the Engineer may order the concrete to be removed and replaced with concrete of the specified quality or accept it at a reduced payment. All the above shall be at the expense and responsibility of the Contractor.

502.07

Slumps

Slump range for different Concrete Classes to be agreed with the Engineer. The method of making the slump test shall conform to AASHTO T119 or ASTM C143. Mixes of the stiffest consistency that can be placed efficiently shall be used. Mixes with excessive water cement ratios will be rejected.

502.08

Measurement and Payment

No separate measurement or payment will be made by the Department for the work or details as described in Section V-2, Concrete Classes and Mixes, of these Standard Specifications. All materials, labour, tools, equipment and appurtenances as required or as directed by the Engineer to complete the Concrete Works shall be considered as a subsidiary obligation to the Items included in the Bills of Quantities unless otherwise specified in the Particular Specifications.

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