Control of Thermal Cracking in Concrete Water Retaining Structures

Control of The Thermal rmal Cracking in Concrete Water Retaining Structures

Eng. Anura Mataraarac Mataraarachchi hchi

DESIGN REQUIREME NTS OF CONCRETE WATER RETAINING STRUCTURES

STRENGTH

DURABILITY

Water tightness

Post Graduate Student, Department of Civil Engineering University of Moratuwa

Prof. SMA Nanayakkara Professor, Department of Civil Engineering University of Moratuwa

Prevention / control of cracking

Dr. Shingo Asamoto Assistant Professor, Graduate School of Science & Engineering Saitama University, Japan

Significance of crack width on water tightness

Crack width limitation

Types of cracks in reinforced concrete structures

BS 8007 limitations on crack width Structural

0.2mm - severe or very severe exposure exposure condition condition

Plastic shrinkage and settlement

0.1mm - for surfaces surfaces where appearance is important

Ca(OH)2 + CO2

Intrinsic If c.w < 0.2mm, this action is effective at sealing cracks

CaCO3

Long term drying shrinkage

Can be controlled by providing r/f 

Thermal contraction

Autogenous healing Control of cracking

Calculation of Crack width as a result of heat of hydration and drying shrinkage in immature concrete

w max

 S max

Smax

 

Wmax

Concrete tensile strain

ult 

      cs  

   te  1  

 200  10  6 w max

 S max

2

 

   ult   

BS8007

 

te  

ult

w max

w max

 S max   2



   T   

1

S max  R      T    1

 T 2    

 T 

  

2  

 Annual Temp. variations

Fall in temperature between the hydration peak and ambient (T1)

 100  10  6

cs

      

Heat of Hydration

T1 depends on many factors

Typical values of T1- BS 8007/Table A.2 1

2

3

4

Needs to find the relevant T1

Walls Ground slab: OPC content, Kg/m3

Steel formwork: OPC content, Kg/m3

18 mm plywood  formwork: OPC content, 3 Kg/m

325

350

400

325

350

400

325

350

400

mm

C

C

C

C

C

C

C

C

C

300 500 700 1000

11 20 28 38

13 22 32 42

15 27 39 49

23 32 38 42

25 35 42 47

31 43 49 56

15 25 -

17 28 -

21 34 -

Section thickness

T 1

•Thickness of the section

40

•Cement & water content •Chemical composition of cement

   )    C    (35   e   r   u    t   a30   r   e   p   m   e25    T

T1

•Type of formwork •Concrete mixing temperature •Ambient temperature •Thermal properties of concrete &

20 0

1

?

 Note 1. For suspended slabs cast on flat steel formwork, use data in column 2  Note2. For suspended slabs cast on plywood formwork, use the data in column 4 The table assumes the following: (a) that the formwork is left in position until the peak temperature has passed. (b) That the concrete placing temperature is 20 C (c) That the mean daily temperature is 15 C (d) That an allowance has not been made for solar heat gain in slabs.

2

3

formworks

4

Time (days)

Local condition 32 C 28 C.

Modeling of Heat of Hydration

Hydration Model + Thermal  Analysis by FEM

Extensive experimental investigations

Minerals Components in Cement Clinker 

 Alit e [C3S – 3CaO.SiO2]

Microstructure Formation Model

+

Multi component hydration model

CEMHYD3D

45

Chemical composition of cement

Belite [C2S – 2CaO.SiO2]

+

CEMENT CLINKER

 Alumi nate [C3 A – 3CaO.Al2O3]

+

Experimental investigation + Non Linear Regression analysis

Ferrite [C4 AF – 4CaO. Al 2O3.FeO3]

C660 model

Heat of Hydration Model

Heat of Hydration of Cement C3S C2S C3A C4AF

Exothermic Chemical Reaction

+

H2O

C-S-H

+

Ca(OH)2

+ Heat

Heat Generation model

Hi = γ β i λ μ si Hi,T0 (Qi)EXP{-E/R[1/T-1/T 0]} Reference Heat

Hc=ΣpiHi

Generation [Hi,T0]

Interaction between mineral composition [μ]

Heat Generation Rate Curve

Pi – Weight composition ratio  Hi – Heat generation rate of mineral i 

Powder fineness [Si]

Heat of hyd.

Model should generate this curve

Qi=∫Hidt Temperature dependence [Ei/R]

Free water [βi] Ettringite, Hydrates, and Monosulfate formation

Qi – Accumulated heat of mineral i 

Reference Heat Generation Rates for Mineral Components

C3A

  i

Effect of Powder Fineness

At 293k temperature 

C3S

  H   ]   h   /   g   k   /   l   a   c   k   [

C4AF C2S

  e   t   a   r   t   a   e   H

H1

Heat generation rates, H2 > H1

Coarse particles

Blaine value, si si = Si/Sio

H2

Where, Si - Blaine value of component i Sio-Reference Blaine value of component i

Fine particles Accumulated heat [kcal/kg] Q i

Effect of free water, cluster thickness of hydrates, and powder fineness Cluster thickness, ηi

Free water, Wfree

Wfree

Modeling concept of Heat of hydration C3A   c

Heat rate

+ C4AF

ηi

Heat rate

+

Effect is given by;

C3S

s βi = 1 – EXP{ -r[(wfree/(100.ηi)) si1/2] }

Where; r = 5.0 , s = 2.4 wfree = {wtotal –  Σ wi}/C and, ηi = 1 –(1-Qi/Qi,∞)1/3

  H  ,   e   t   a   r   t   a   e   h   n   o   i   t   a   r   d   y   H

+

C - Cement content Qi – Accumulated heat Qi,∞ - Final heat

Time C2S

Thermal analysis by FEM

Transient thermal conduction analysis by ANSYS

Input Data [Material, Mix, Initial temp., and Geometry]

T  Multi-component Heat of Hydration Model

HC Input Data [Thermalproperties, Initial temp.]

Transient Heat Conduction Analysis [ANSYS]

Output Data [Temp. history, and distribution]

300mm

thick wall thick plywood formwork Meshed with Solid Elements 12mm

Temperature

Distribution with time

Calibration & Initial Verification of Hydration model

Main Features of the Hydration Model Prediction of Temperature rise in concrete based on

 Adiabatic Boundary Condition



Mineral Composition of cement



Cement fineness



Cement & Water Contents



Type of formwork

 Ambient

1.0x1.0x1.0m Concrete Cube

Case 1: Calibration

100mm thk. expanded polystyrene

Data Logger

18mm thick plywood formwork

Temperature & Placing Temperature Thermocouples

Hydration Model + Thermal Analysis by FEM

Prediction of Temperature rise in concrete structures



Two differe nt chemical compositions



Specific Heat Capacity, C = 0.26kCal/kg/K Case 2: Verification

Verification of Kconc & Hpw

Effect of mineral composition of cement on temperature rise Temperature Rise

300mm

Adiabatic Temperature Rise

Wall 

Thermal Conductivity of Concrete, K conc = 60 kCal/m/day/K



Thermal Conductance of Plywood,

Mineral Composition

  A   3   C

  F   A   4   C

OPC-M1

6.87

10. 04

62. 37 11.72

5.18

OPC-M2

6.56

11.56

64.56 8.64

4.52

3479

OPC-M3

7.18

11.87

53.09 21. 02

4.10

3364

OPC-M4

7.01

12. 17

56.68 17. 16

3.89

3093

OPC-M5

6.97

10. 35

61.83

5.62

3704

  S   3   C

Hpw = 108 kCal/m2/day/K

About 7 ~ 12% Difference

Prediction of T1    )   m   m    (   s   s   e   n    k   c    i    h    T    l    l   a    W

 Annual temperature variation, T2

4mm thick steel formwork

12mm thick plywood formwork

18mm thick plywood formwork

Cement content

Cement content

Cement content

T max Mean ambient temp. T a

380 kg/m3

400 kg/m3

380 kg/m3

400 kg/m3

380 kg/m3 400 kg/m3

300

17

18 (15)

31

34

32

34 (31)

500

27

29 (27)

38

40

38

40 (43)

700

34

36 (39)

41

44

42

44 (49)

1000

40

42 (49)

44

47

44

47 (56)

C3A – 6.92%, C4AF – 11.2%, C3S – 59.71%, CSH2 –4.66%, & Si – 3422cm2/g Concrete placing temperature = 32 0C Mean ambient temperature = 28 0C ( ) BS 8007 values

 ,   s  ]   s  g   /   e  2   n   e  m   n  [   c   i   F

  t  t   e  c   k  u   r  d   a  o   r   M   p

T 2

T min

T2 = Ta - Tmin

  S   2   C

10. 12

  2

  H           Ṡ   C

3468

Recommended Values for T 2

Conclusions T 1 can be predicted by using the proposed model incorporating the chemical and physical properties of cement. 

City Anuradhapura Badulla Bandarawela Batticaloa Colombo Galle Hambantota Katugastota Kurunagala Mahailluppalama Nuwaraeliya Puttalam Vavuniya

Mean ambient Temperature ( C)

Mean monthly minimum Temperature ( C)

T 2 ( C)

28.5 23.9 20.7 28.2 27.5 27.2 27.7 24.6 27.5 27.5 16.5 27.9 27.9 Average

17.9 12.3 10.1 20.4 19.9 20.6 20.0 13.0 17.0 16.3 4.3 17.9 16.1

11 12 11 8 8 7 8 12 11 11 12 10 12 10

°

°

°

The chemical composition of cements available in the market varies widely and corresponding change in T 1 values can be in the range 7% -12% depending on the thickness of the section. 

T 1 values given by BS8007 can be reduced significantly for thick sections under local conditions 

Based on the annual temperature records it was found that the mean ambient temperature is nearly 28 °C for most of the cities in Sri Lanka. 

T 2 value shall be based on difference between mean ambient and minimum ambient temperature and found that it varies in the range 7 – 12 °C depending on the city 

Thank You