Transcript No Slide Title

Mechanical Performance of Self Consolidating Concrete
M. D. D'Ambrosia, D. A. Lange , A. J. Brinks
University of Illinois at Urbana-Champaign
OBJECTIVE
EXPERIMENTS
Determine how SCC strategies…
high paste content
VMA (thickeners)
smaller aggregate & controlled gradation
HRWR, SP (CAE)
Mineral fillers & additives
Strain ()
Restrained
0
6
-50
5
Cumulative
Shrinkage + Creep
-100
4
3
-200
2
Free Shrinkage
Load
-250
1
-300
0
0
 Slump flow of SCC mixtures was
specimens was measured from time
of casting
 Internal relative humidity in sealed
prism was also measured to asses
the driving force for autogenous
shrinkage
AUTOGENOUS SHRINKAGE AND TOTAL
SHRINKAGE DURING DRYING
0
6000
OPC1, w/c = 0.40
SCC1, w/c = 0.39
4000
-100
SCC1, w/c = 0.39
SCC3, w/c = 0.41
SCC4, w/c = 0.34
800
600
400
SCC2, w/c = 0.33
-50
-6
1000
-200
-100
OPC1, w/c = 0.40
-150
20
30
40
50
-600
OPC1, w/c = 0.40
SCC1, w/c = 0.39
-700
SCC3, w/c = 0.41
SCC4, w/c = 0.34
-900
-1000
-200
0
60
-500
-800
SCC3, w/c = 0.41
0
10
-400
SCC2, w/c = 0.33
200
0
-300
SCC2, w/c = 0.33
SCC1, w/c = 0.39
SCC4, w/c = 0.34
0
Free Shrinkage (x10 )
8000
SCC3, w/c = 0.41
2
4
6
8
0
10
5
10
Age (days)
Concrete Age (Days)
SCC Database
strain virtually constant over time (to
within 0.005mm )
 Summation of restrained deformation
allows for creep calculation
-6
10000
7
system applies a restraining force
with servo hydraulic actuator
 Instron Controller operated by a
Restraint Simulation Program (RSP)
(LabView)
SCC2, w/c = 0.33
2000
2.0
6
0
1200
12000
2.5
5
 Autogenous shrinkage of sealed
OPC1, w/c = 0.40
 SCC proportions differ from ordinary concrete
3
4
Time (days)
 Restraint Simulation Program keeps
Autogenous Shrinkage (10 m/m)
Graded
Aggregate
2
1400
14000
Tensile Strength (psi)
High Paste
Average w/cm = 0.41, w/p = 0.35
33% contain limestone powder (LSP)
52% contain fly ash, 37% contain slag
30% contain slag and fly ash
0% contain both LSP and pozzolans
45% contain VMA
1% contain both VMA and LSP
Only 3% contain 3 different size
aggregates
measure deformation
 Sealed barrier of aluminum foil applied
to impose symmetric drying
1
 Feedback controlled closed loop
EARLY AGE COMPRESSIVE AND TENSILE
STRENGTH DEVELOPMENT
Compressive Strength (psi)








 Drying began at concrete age of 1 day
 Environment was 50% RH and 23°C
 An LVDT extensometer was used to
measured for quality control
 A separate rheological study
was conducted (L. Shen, L.
Struble, J. Hidalgo)
UIUC SCC DATABASE
15
20
25
0
30
5
10
Age (d)
15
Age (days)
20
25
 SCC mixtures tend to have low w/c ratio and high paste%, and thus higher strength than most
 Low w/c drives autogenous shrinkage, which can then be a major contributor to total shrinkage
ordinary concrete. When compared to OPC with same w/c and paste%, strength is similar,
indicating that SCC admixtures had little effect of strength
at early age. High early age shrinkage leads to tensile stress and cracking when concrete is
restrained
Mixtures studied
1.5
30
SCC1
SCC3
RESTRAINED STRESS DEVELOPMENT, STRESS STRENGTH RATIO
AND RELAXATION BY TENSILE CREEP
1.0
Typical non-SCC
materials, according to
ACI mixture
proportioning method
SCC4
0.5
OPC1
0.0
50%
55%
60%
65%
70%
75%
80%
85%
90%
95%
100%
 Selected control mixtures from literature explore
various strategies of SCC mixture proportioning
SG
Cement (Type I)
Fly Ash (Class C)
Coarse Aggregate, 3/4" (20mm)
3.15
2.65
2.70
Unit
lb/yd
OPC1
726
SCC1
661
SCC2
601
SCC3
685
SCC4
679
kg/m3
431
392
357
407
403
lb/yd3
0
157
325
0
151
kg/m3
0
93
193
0
90
3
lb/yd
Coarse Aggregate, 3/8" (10mm)
Fine Aggregate (FM = 2.57)
Water
2.64
1.00
VMA
1.06
1.00
810
965
343
lb/yd
0
1075
0
0
1018
kg/m3
0
638
0
0
604
lb/yd3
1192
1403
1336
1389
1389
kg/m3
707
832
792
824
824
lb/yd3
290
311
301
278
267
3
172
185
179
165
158
fl oz/yd3
22
63
29
49
36
l/m3
0.84
2.44
1.12
1.89
1.38
fl oz/yd
Air Content
w/cm
22
3
0.84
3
32%
37%
40%
33%
34%
0.64
0.97
0.98
0.85
0.87
in
5
30
28
26
27
mm
100
750
700
650
700
%
2.5%
1.0%
2.5%
3.5%
3.0%
0.40
0.38
0.33
0.41
0.32
%
1.0
400
0.9
350
0.8
300
250
200
OPC1, w/c = 0.40
150
SCC1, w/c = 0.39
100
50
0.7
0.6
0.5
0.4
OPC1, w/c = 0.40
0.3
SCC3, w/c = 0.41
0.2
SCC3, w/c = 0.41
2
4
6
SCC4, w/c = 0.34
0.1
SCC4, w/c = 0.34
Age (days)
8
10

0.4
0.3

0.2
OPC1, w/c = 0.40
SCC1, w/c = 0.39
0.1

SCC3, w/c = 0.41
SCC4, w/c = 0.34
0.0
0.0
0
 An investigation of the EA mechanical
0.5
SCC1, w/c = 0.39
0
SUMMARY
0.6
579
218
FA/CA ratio
Slump flow (standard slump for OPC1)
1627
1099
l/m
Paste content by Volume
1365
3
kg/m
Superplasticizer (CAE)
367
3
kg/m
2.70
1853
3
Shrinkage Stress (psi)
Aggregate Content (%)
450
Specific Creep (x10-6 m/m/psi)
SCC2
Stress-Strength Ratio
FA/CA Ratio
7
-150
early age cracking
long term durability
surface scaling
freeze-thaw resistance
abrasion resistance
Mineral
Fillers
8
Load (kN)
50
segregation
shrinkage and creep
entrained air system
permeability
strength
VMA
9
Creep
Free Specimen
100
…and affect performance.





Restrained Specimen
150
…change hardened properties…





10
Applied Load (kN)





200
0
2
4
6
Age (d)
8
10
0
2
4
6
8
10
Age (days)
 Stress measurements indicate that to reduce the risk of early age cracking in SCC, using a w/cm ratio of 0.40 to 0.42 can prevent autogenous
shrinkage from causing significant stress, while at the same time minimizing drying shrinkage.
 Stress-strength ratios demonstrate that microcracking and damage may be occurring as early as one or two days after drying at early age.
 Creep capacity is directly proportional to paste content and is inversely proportional to w/cm ratio. The high stress-strength ratio of SCC1 induced
microcracking damage  High cracking risk
 In SCC4 the stress develops rapidly due to the lack of relaxation by creep and damage occurs rapidly right before failure Also high cracking risk

behavior of SCC has revealed a potentially
high risk for cracking in some mixtures
Mechanical properties can be influenced
by higher paste content and low w/c, BUT it
is best not to treat SCC as a group of
materials with similar mechanical behavior.
Autogenous shrinkage may cause
significant stress at early age
SCC Mix Design should minimize cement
paste content and use a w/cm that avoids
significant autogenous shrinkage while
achieving necessary flow characteristics
Providing external water during curing in
field applications will delay shrinkage
stress development at early age and
reduce the overall magnitude of shrinkage
and cracking risk.