Early-Age Heat and Temperature Profiles in Concretes Made With High g

Proportions of GGBS and Fly Ash in the Cement BindersCement Binders

Yunus BallimYunus BallimSchool of Civil and Environmental Engineering

University of the WitwatersrandJohannesburg, South Africa

Overview

• Measuring the rate of heat evolution from cement• Form of expression of the heat rate functionp• Effect of cement extenders on measured heat rate• Brief description of the Wits University p y

temperature prediction model• Effect of cement extenders on temperature p

development in a large concrete element

WITS Adiabatic CalorimeterUPS

A/D Convertor

SignalConditioning

MotorInterface circuits

and relaysPolystyrene cover

Tank

Motor

Stirer Tank heater

Tank temperatureprobe

Personal Computer

Water

Personal Computer

SampleChamber

Sample Sample Temperatureprobe

40

)

25

30

35 pe

ratu

re (d

eg. C

)

15

20

Tem

p

0 10 20 30 40 50 Time (hours)

2 5

3

3.5

bind

er)

150

200

f bin

der)

Total Heat

0 5

1

1.5

2

2.5

at R

ate

(W/k

g of

50

100

al H

eat (

kJ/k

g of

Heat Rateq C T Tm

t p t os .( )

0

0.5 H

ea0 To

ta

0 10 20 30 40 50 Time (hours)

Heat Rateq Cmt p t o

c.( )

Normalise the heat rate curve toheat rate curve to

q

as a function of MaturityM

as a function of Maturityand convert to clock time by

dtdM

Mq

tq

dtMt

Arhenius MaturityNormalisation

6

W/k

g)

Start Temp (oC)

0

2

4

Hea

t Rat

e (W 13

2129

Start Temp (oC)Mix ACEM I

00 20 40 60 80 100

Time (hrs)

2

3

heat

rate

1321

Start Temp (oC)

Mix A

0

1

0 50 100 150 200 250 300

Mat

urity

h 2129(CEM I)

0 50 100 150 200 250 300

Arrhenius Maturity (t20 hours)

2 0

2.5

3.0e

(W/k

g) 100% CEM 120% GGBS

1.0

1.5

2.0

rity

Hea

t Rat

e

40% GGBS60% GGBS80% GGBS Material Mass (g)

Binder St

420 1020

0.0

0.5

0 20 40 60 80 100

A h i M i ( h )

Mat

u StoneSand Water

10201060 280

Arrhenius Maturity (t20 hours)

2 5

3.0

kg) 100% CEM 1

1.5

2.0

2.5

eat R

ate

(W/k

20% FA40% FA60% FA80% FA

Effect of cement

0.5

1.0

Mat

urity

He 80% FAcement

extenders0.0

0 20 40 60 80 100

Arrhenius Maturity (t20 hours)

Effect on peak heat rate

4.0

W/k

g) A2640 A3206 A3880

A4400 A4980

2.0

3.0

rity

Heat

Rat

e (W A4400 A4980

Clinker A cements

0.0

1.0

0 10 20 30 40 50 60

Mat

ur

Maturity (t20 hours)

4 0

3.0

4.0

at R

ate

(W/k

g)

B2660 B3190 B3860

B4384 B4943

Clinker B cementsEffect of cement

1.0

2.0

Mat

urity

Hea

B4384 B4943

fineness

0.00 10 20 30 40 50 60

Maturity (t20 hours)

Modeling temperature development in mass concrete:development in mass concrete:

The WITS University temperature prediction model

TEMPERATURE PREDICTION MODEL

Element Modeled

T A

Element Modeled

Air

Tem

p. T

Concrete Block

Rock: k = kR; Temp = TR = f(τ)Time, τ

Finite Difference Analysis NodesN N

Finite Difference Analysis Nodes

PW E

S

PW E

R = node in rock

Δ; kR

S

(a) P is an internal node (b) P is a bottom node on rock

h TAPW

NP

ETA

h

PW

S

S

(d) P is an exposedsurface node(c) P is a corner node

Ambient Temperature ModelAmbient Temperature ModelT

T T T TA

d m

sin

( ) max min max min2 TA sin .

24 2 2

25

15

20

e (d

eg. C

)

5

10

Tem

pera

ture

0

5

Air

0 50 100 150 200 250

Measured Model

Time after casting (hrs)

Concrete profile modeledConcrete profile modeled• k=2,7 W/m.K (Granite aggregate)• Cp=1150 J/kg.K• h=25 W/m2.K for exposed surfacesp• h=5 W/m2.K for surfaces with formwork

(timber for the first 18 hours)(timber for the first 18 hours)• Concrete cast at 10h00 at To=15 oC;

A bi t t b t 12 oC d 25 oC• Ambient temp between 12 oC and 25 oC.• Finite difference x = y = 250 mm

Concrete element

• Concrete = 5m wide x 2m high• Concrete mixture details:Concrete mixture details:

Cem D 40% FA 60% FA 40% GGBS 60% GGBS Cem D 40% FA 60% FA 40% GGBS 60% GGBSBinder Water Sand

200 160 600

215 160 500

230 160 500

215 160 585

230 160 570

Stone 1600 1680 1660 1600 1600

GGBS Concretes

40

GGBS Concretes

303540

e (o

C)

100% CEM I

40% GGBS

202530

erat

ure

101520

Tem

pe 60% GGBS

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Distance from side face (m)Distance from side face (m)

Fly ash concretes

Fly ash concretes

303540

e (o

C)

100% CEM I

202530

erat

ure

40% FA

101520

Tem

pe 60% FA

10

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Di t f id f ( )

T

Distance from side face (m)

General Characteristics ofGeneral Characteristics of Temperature Development

Cem D 40% FA 60% FA 40% GGBS 60% GGBS Cem D 40% FA 60% FA 40% GGBS 60% GGBSTMax (oC)

tMax (t20 hrs) ΔTMax (oC)

35 80 20

25 72 11

22 64 8

28 94 13

27 116 13Max ( )

tΔT(t20 hrs) 90 66 64 90 114

Caution: Late temperatureCaution: Late temperature development

Future Work

• Develop a physico-chemical model for the maturity-based heat rate functiony

• Incorporate extenders at a fundamental level• Improved understanding and definition of• Improved understanding and definition of

boundary conditions in the modelAll f diff l fi i• Allow for different structural configurations

• Develop a cracking model

THANK YOU

With much acknowledgement to:• My research assistant Dr Peter GrahamMy research assistant, Dr Peter Graham• The Cement & Concrete Institute, Eskom

and the National Research Foundation (SA)and the National Research Foundation (SA) for generous funding support