Post on 23-Dec-2015
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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Roads Pavement Forum 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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Roads Pavement Forum 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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Roads Pavement Forum 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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Roads Pavement Forum 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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Roads Pavement Forum 17 November 2004
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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Roads Pavement Forum 17 November 2004
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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Roads Pavement Forum 17 November 2004
Hilton Concrete Pavement trials…
“...To learn from what you understand is something else…” WC
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Roads Pavement Forum 17 November 2004
Dolerite concrete
Quartzite concrete
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Roads Pavement Forum 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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Roads Pavement Forum 17 November 2004
Environmental conditions …day of casting
21,5°C
37% RH
Dolerite concrete
Quartzite concrete
13,3°C
72% RH
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Roads Pavement Forum 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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Roads Pavement Forum 17 November 2004
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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Roads Pavement Forum 17 November 2004
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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Roads Pavement Forum 17 November 2004
Field results
Quartzite cracked less, in spite of higher shrinkage potential
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Roads Pavement Forum 17 November 2004
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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Roads Pavement Forum 17 November 2004
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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Roads Pavement Forum 17 November 2004
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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Roads Pavement Forum 17 November 2004
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