EARLY AGE COMPRESSIVE AND TENSILE STRENGTH DEVELOPMENT OBJECTIVE Determine how SCC strategies… ...
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Transcript of EARLY AGE COMPRESSIVE AND TENSILE STRENGTH DEVELOPMENT OBJECTIVE Determine how SCC strategies… ...
EARLY AGE COMPRESSIVE AND TENSILE STRENGTH DEVELOPMENT
OBJECTIVEDetermine how SCC strategies…
high paste content VMA (thickeners) smaller aggregate & controlled gradation HRWR, SP (CAE) Mineral fillers & additives
…change hardened properties… segregation shrinkage and creep entrained air system permeability strength
…and affect performance. early age cracking long term durability surface scaling freeze-thaw resistance abrasion resistance
EXPERIMENTS
Mechanical Performance of Self Consolidating ConcreteM. D. D'Ambrosia, D. A. Lange , A. J. Brinks
University of Illinois at Urbana-Champaign
UIUC SCC DATABASE
SCC proportions differ from ordinary concrete
Selected control mixtures from literature explore various strategies of SCC mixture proportioning
VMA
Mineral Fillers
GradedAggregate
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
Slump flow of SCC mixtures was measured for quality control
A separate rheological study was conducted (L. Shen, L. Struble, J. Hidalgo)
SCC mixtures tend to have low w/c ratio and high paste%, and thus higher strength than most ordinary concrete. When compared to OPC with same w/c and paste%, strength is similar, indicating that SCC admixtures had little effect of strength
SG Unit OPC1 SCC1 SCC2 SCC3 SCC4
Cement (Type I) 3.15 lb/yd3 726 661 601 685 679
kg/m3 431 392 357 407 403
Fly Ash (Class C) 2.65 lb/yd3 0 157 325 0 151
kg/m3 0 93 193 0 90
Coarse Aggregate, 3/4" (20mm) 2.70 lb/yd3 1853 367 1365 1627 579
kg/m3 1099 218 810 965 343
Coarse Aggregate, 3/8" (10mm) 2.70 lb/yd3 0 1075 0 0 1018
kg/m3 0 638 0 0 604
Fine Aggregate (FM = 2.57) 2.64 lb/yd3 1192 1403 1336 1389 1389
kg/m3 707 832 792 824 824
Water 1.00 lb/yd3 290 311 301 278 267
kg/m3 172 185 179 165 158
Superplasticizer (CAE) 1.06 fl oz/yd3 22 63 29 49 36
l/m3 0.84 2.44 1.12 1.89 1.38
VMA 1.00 fl oz/yd3 22
l/m3 0.84
Paste content by Volume % 32% 37% 40% 33% 34%
FA/CA ratio 0.64 0.97 0.98 0.85 0.87
Slump flow (standard slump for OPC1) in 5 30 28 26 27
mm 100 750 700 650 700
Air Content % 2.5% 1.0% 2.5% 3.5% 3.0%
w/cm 0.40 0.38 0.33 0.41 0.32
0.0
0.5
1.0
1.5
2.0
2.5
50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100%
Aggregate Content (%)
FA
/CA
Rat
io
SCC Database
Mixtures studied
SCC4
OPC1
SCC3 SCC2
SCC1
Typical non-SCC materials, according to ACI mixture proportioning method
0
2000
4000
6000
8000
10000
12000
14000
0 10 20 30 40 50 60
Concrete Age (Days)
Com
pres
sive
Str
engt
h (p
si)
OPC1, w/c = 0.40
SCC1, w/c = 0.39
SCC2, w/c = 0.33
SCC3, w/c = 0.41
SCC4, w/c = 0.34
0
200
400
600
800
1000
1200
1400
0 2 4 6 8 10
Age (days)
Ten
sile
Str
engt
h (p
si)
OPC1, w/c = 0.40
SCC1, w/c = 0.39
SCC2, w/c = 0.33
SCC3, w/c = 0.41
SCC4, w/c = 0.34
AUTOGENOUS SHRINKAGE AND TOTAL SHRINKAGE DURING DRYING
-200
-150
-100
-50
0
0 5 10 15 20 25 30
Age (d)
Aut
ogen
ous
Shr
inka
ge (
10-6
m/m
)
OPC1, w/c = 0.40
SCC1, w/c = 0.39
SCC2, w/c = 0.33
SCC3, w/c = 0.41
-1000
-900
-800
-700
-600
-500
-400
-300
-200
-100
0
0 5 10 15 20 25 30
Age (days)
Fre
e S
hrin
kage
(x1
0-6
)
OPC1, w/c = 0.40
SCC1, w/c = 0.39
SCC2, w/c = 0.33
SCC3, w/c = 0.41
SCC4, w/c = 0.34
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 2 4 6 8 10
Age (d)
Str
ess-
Str
engt
h R
atio
OPC1, w/c = 0.40
SCC1, w/c = 0.39
SCC3, w/c = 0.41
SCC4, w/c = 0.34
RESTRAINED STRESS DEVELOPMENT, STRESS STRENGTH RATIO AND RELAXATION BY TENSILE CREEP
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8 10
Age (days)
Spe
cific
Cre
ep
(x1
0-6 m
/m/p
si)
OPC1, w/c = 0.40
SCC1, w/c = 0.39
SCC3, w/c = 0.41
SCC4, w/c = 0.34
-300
-250
-200
-150
-100
-50
0
50
100
150
200
0 1 2 3 4 5 6 7Time (days)
Str
ain
(
)
0
1
2
3
4
5
6
7
8
9
10
Applied L
oad (kN
)
Restrained Specimen
Free Specimen
Load (kN)
Creep
Cumulative Shrinkage + Creep
-300
-250
-200
-150
-100
-50
0
50
100
150
200
0 1 2 3 4 5 6 7Time (days)
Str
ain
(
)
0
1
2
3
4
5
6
7
8
9
10
Applied L
oad (kN
)
Restrained Specimen
Free Specimen
Load (kN)
CreepCreep
Cumulative Shrinkage + Creep
Cumulative Shrinkage + Creep
Free Shrinkage Load
Restrained
Drying began at concrete age of 1 day Environment was 50% RH and 23°C An LVDT extensometer was used to
measure deformation Sealed barrier of aluminum foil applied
to impose symmetric drying
Feedback controlled closed loop system applies a restraining force with servo hydraulic actuator
Instron Controller operated by a Restraint Simulation Program (RSP) (LabView)
Restraint Simulation Program keeps strain virtually constant over time (to within 0.005mm )
Summation of restrained deformation allows for creep calculation
Autogenous shrinkage of sealed specimens was measured from time of casting
Internal relative humidity in sealed prism was also measured to asses the driving force for autogenous shrinkage
0
50
100
150
200
250
300
350
400
450
0 2 4 6 8 10
Age (days)
Sh
rin
kag
e S
tre
ss (
psi
)
OPC1, w/c = 0.40
SCC1, w/c = 0.39
SCC3, w/c = 0.41
SCC4, w/c = 0.34
SUMMARY An investigation of the EA mechanical
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.
Low w/c drives autogenous shrinkage, which can then be a major contributor to total shrinkage at early age. High early age shrinkage leads to tensile stress and cracking when concrete is restrained
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