Concrete Drying Shrinkage 17 November 2004 Roads Pavement Forum Sebasti Badenhorst, Pr. Eng Holcim...

Concrete Drying Shrinkage

17 November 2004

Roads Pavement Forum

Sebasti Badenhorst, Pr. Eng

Holcim (South Africa) (Pty) Ltd

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Roads Pavement Forum 17 November 2004

“ To look is one thing.

To see what you look at is another

To understand what you see is another.

To learn from what you understand is something else

But to act on what you learn is all that really matters”

Sir Winston Churchill

Concrete drying shrinkage research ...

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Performance-based specifications for shrinkage

“ To look is one thing.

To see what you look at is another…” WC

COLTO - Standard Specification for Road and Bridge

Works for State Road Authorities 1998

Shrinkage shall not exceed 0,04% , tested in accordance with SABS 1085

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Shrinkage tests...

SABS Method 1085:2001 - Initial drying and wetting

expansion of concrete

Controversial… severe drying... 50 to 55 C,15 to 25% RH

Cycles of heating and cooling

Small concrete samples

Poorly defined end point

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An investigation to review SABS 1085

“...To understand what you see is another….” WC

Establish how the SABS 1085 shrinkage test result relate to other international shrinkage tests methods?

International shrinkage test methods are based on natural (moderate) drying conditions Temperature between 22 to 25ºC Relative humidity between 50 to 70%

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Laboratory investigation...

28 Concretes...different combinations… aggregates cements

Same size specimens SABS 1085 natural drying test

•

...compared results...

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Results of investigation…aggregate type

0 50 100 150 200

Olifantsfontein Dolomite

Ferro Quartzite

Klipheuwel sand

Eikenhof Andesite

Verulam Tillite

Scoop Quartzite

Jukskei Granite

Coedmore Quartzite

% of Scoop quartzite shrinkage

SABS 1085

natural drying

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Results of investigation…cements

0 50 100 150 200

CEM I 42,5

79/21 GGBS

50/50 GGBS

70/30 FA

% of CEM I 42,5 shrinkage

SABS 1085

Natural drying

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Hilton Concrete Pavement trials…

“...To learn from what you understand is something else…” WC

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Dolerite concrete

Quartzite concrete

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Shrinkage investigation at Hilton

Seven pairs of crack measuring gauges installed

Perpendicular and centred to crack inducing plate

Non doweled joints

Determine movement at joints with time

Crack inducing plate

Crack measuring gauges

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Environmental conditions …day of casting

21,5°C

37% RH

Dolerite concrete

Quartzite concrete

13,3°C

72% RH

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Laboratory shrinkage testing

University of Witwatersrand…

6 samples …creep and shrinkage…quartzite and dolerite

Cement and Concrete Institute …shrinkage tests... SABS Method 1085

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Results…natural drying ...laboratory shrinkage

Shrinkage vs time

0

100

200

300

400

500

600

700

1 10 100 1000 days drying

shri

nka

ge,

mic

rost

rain

Dolerite, truck 2

Quartzite, truck 2

Dolerite, truck 3

Quartzite, truck 4

Quartzite higher shrinkage potential

Dolerite lower shrinkage potential

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Results … SABS 1085 shrinkage

Natural drying@ 168 days,microstrain

SABS 1085,microstrain

Truck 2, dolerite 443 370

Truck 3, dolerite 334 390

Truck 2, quartzite 488 510

Truck 4, quartzite 612 520

Dolerite concrete, meets COLTO specification

Quartzite concrete fails COLTO specification

SABS 1085 does not account for variability

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Field results

Quartzite cracked less, in spite of higher shrinkage potential

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Crack width…dolerite concrete

Crack widthJoint 18

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0 24 48 72 96 120 144 168 192 216 240 264 288

time (hours)

mov

emen

t (m

illim

eter

s)

0

5

10

15

20

25

30

35

gauge 3

gauge 4

Temperature

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Early concrete temperature changes

Concrete temperature after casting

0

5

10

15

20

25

30

35

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36

Time (hours)

Te

mp

era

ture

(d

eg

res

s c

elc

ius

)

Quartzite

Dolerite

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Conclusions...

Environmental condition at time of construction of greater significance in the formation of cracks than the shrinkage potential determined in the laboratory

Changes in early temperature...significant effect on crack propagation

Difference between... crack potential…shrinkage potential

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Further work...

“...But to act on what you learn is all that really matters” WC

Draft of SANRAL specification, clause referring to SABS 1085 scraped

CnCPave updated with revised shrinkage prediction model, no longer refer to SABS 1085

Draft ISO test method…based on natural drying tests... extrapolate the results from 28-days…under investigation

Concrete Drying Shrinkage 17 November 2004 Roads Pavement Forum Sebasti Badenhorst, Pr. Eng Holcim...

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