Concrete Drying Shrinkage
17 November 2004
Roads Pavement Forum
Sebasti Badenhorst, Pr. Eng
Holcim (South Africa) (Pty) Ltd
Concrete drying shrinkage research ...
“ 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
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17 November 2004
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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17 November 2004
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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17 November 2004
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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17 November 2004
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
Coedmore Quartzite
Jukskei Granite
Scoop Quartzite
Verulam Tillite
Eikenhof Andesite
Klipheuwel sand
Ferro Quartzite
SABS 1085
Olifantsfontein Dolomite
natural drying
0
50
100
150
200
% of Scoop quartzite shrinkage
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17 November 2004
Results of investigation…cements
70/30 FA
50/50 GGBS
79/21 GGBS
SABS 1085
Natural drying
CEM I 42,5
0
50
100
150
200
% of CEM I 42,5 shrinkage
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17 November 2004
Hilton Concrete Pavement trials…
“...To learn from what you understand is something else…” WC
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17 November 2004
Quartzite concrete
Dolerite concrete
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17 November 2004
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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17 November 2004
Environmental conditions …day of casting
Dolerite concrete
21,5°C
37% RH
13,3°C
72% RH
Quartzite concrete
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17 November 2004
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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17 November 2004
Results…natural drying ...laboratory shrinkage
Shrinkage vs time
700
shrinkage, microstrain
600
500
400
300
Dolerite, truck 2
Quartzite, truck 2
200
Dolerite, truck 3
Quartzite, truck 4
100
0
1
10
100
1000
days drying
 Quartzite higher shrinkage potential
 Dolerite lower shrinkage potential
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17 November 2004
Results … SABS 1085 shrinkage
SABS 1085,
microstrain
Truck 2, dolerite
Natural drying
@ 168 days,
microstrain
443
Truck 3, dolerite
334
390
Truck 2, quartzite
488
510
Truck 4, quartzite
612
520
370
 Dolerite concrete, meets COLTO specification
 Quartzite concrete fails COLTO specification
 SABS 1085 does not account for variability
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17 November 2004
Field results
 Quartzite cracked less, in spite of higher shrinkage
potential
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17 November 2004
Crack width…dolerite concrete
Crack width
Joint 18
35
0
30
movement (millimeters)
0.2
0
24
48
72
96
120
144
168
192
216
240
264
288
-0.2
25
-0.4
20
-0.6
15
-0.8
10
gauge 3
gauge 4
Temperature
-1
-1.2
5
0
time (hours)
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17 November 2004
Early concrete temperature changes
Temperature (degress celcius)
Concrete temperature after casting
35
30
25
20
15
10
Quartzite
5
Dolerite
0
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30 32 34 36
Time (hours)
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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
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