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Chemical Admixtures for Concrete
Bruno D’SouzaASCP Forum 10 November 2014www.basf-cc.com.au
Overview
Shrinkage Reducing Agent (SRA)
ASTM C 1581
Investigation of early age tensile stresses….
US DOT studies & recommendations
Thin White Topping (TWT) project (India)
4 x 4 for Rapid Pavement Repairs (USA)
Microspheres
Types of Shrinkage
PLASTIC SHRINKAGE
Thermal Contraction
DRYING SHRINKAGE
AUTOGENOUS SHRINKAGE
Carbonation Shrinkage
Shrinkage in Concrete
A Reduction in Length / Volume
Factors Affecting Drying Shrinkage
Concrete Mix Ingredients especially, Water & CoarseAggregate including shrinkage of the paste, the volumefraction of paste, the stiffness of the aggregate and thestrength of the bond between the paste and aggregate
Design & Construction Practices
Environmental Influences
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0.04
0.06
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0.4 0.5 0.6 0.7
WATER-CEMENT RATIO
DR
YIN
G S
HR
INK
AG
E (%
)
a/c = 3a/c = 4a/c = 5a/c = 6a/c = 7
Effect of Coarse Aggregate Content onDrying Shrinkage
Figure illustrates the Effect of Aggregate-Cement (a/c) ratio andWater-Cement ratio on Drying Shrinkage
EXPECTED WATER REDUCTION& DRYING SHRINKAGE
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Drying Shrinkage Data with Various Types of Admixtures
Effect of Water Content onDrying Shrinkage
SRA – Mechanism of Action
CementParticle
CementParticle
Cementparticle
Cementparticle
Loss of moisture
A meniscus forms at air-water interface due to surfacetension
SRA – Mechanism of Action
Surface tension forces exertinward pulling force on thewalls of the pores
Surface tension is mostsignificant in pore sizesranging from 2.5-50 nm
SRA – Mechanism of Action
CapillaryTension
Loss of moisture
A meniscus forms at air-water interface due tosurface tension
SRAs reduce the capillarytension by reducingsurface tension of water
SRA – Mechanism of Action
MasterLife® SRA 200Fresh and hardened properties of concrete
Mix WaterReducer
DosageSRA
Dosage Slump Air Freshdensity w/b
Water GPCement Fly Ash Coarse
SandFineSand
20/7Gravel
(ml/100kg) (L/m3) (mm) (%) (kg/m3) (l/m3) (kg/m3) (kg/m3) (kg/m3) (kg/m3) (kg/m3)
AMaster
Pozzolith80
300
- 0 115 1.6 2400 0.593 212
300 60 575 290 980B
MasterLife®
SRA 200
2 120 2.6 2370 0.588 208
C 4 130 2.8 2360 0.584 206
D 6 125 3.0 2360 0.583 205
Ambient temperature: 230C
Hardened property: Drying shrinkage strain up to 90 days
Ambient temperature: 230C
Hardened property: Drying shrinkage strain up to 90 days
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Summary of trials at Seven HillsSummary of trials at Seven Hills
MasterLife® SRA 200Drying shrinkage reduction versus dosage
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MasterLife® SRA 200Drying shrinkage reduction versus dosage
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4 L/m3 of MasterLife® SRA 200 reduces drying shrinkage by 100 microstrain at 90 days
6 L/m3 MasterLife® SRA 200 reduces drying shrinkage by 160 microstrain at 90 days
MasterLife® SRA 200 can reduce drying shrinkage by 30% to 50% at 6 L/m3
Shrinkage is lower as we progress to 90 days for all dosage levels
4 L/m3 of MasterLife® SRA 200 reduces drying shrinkage by 100 microstrain at 90 days
6 L/m3 MasterLife® SRA 200 reduces drying shrinkage by 160 microstrain at 90 days
MasterLife® SRA 200 can reduce drying shrinkage by 30% to 50% at 6 L/m3
Shrinkage is lower as we progress to 90 days for all dosage levels
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Long-term drying shrinkage
The magnitude of drying shrinkage is time dependent
On average, nearly 50 percent of the drying shrinkageobtained at 20 years occurred within the first 2 months ofdrying
And nearly 80 percent within the first year
These values are consistent with drying shrinkage valuesusing SRAs in concrete due to its absorption/adsorptionwithin the pore wall structure
Test Method ASTM C 1581
Standard Test Method for Determining Age at Cracking and Induced Tensile StressCharacteristics of Mortar and Concrete Under Restrained Shrinkage (a.k.a. “Ring Test”)
SummaryTest method measures concrete’sresistance to cracking underrestrained shrinkage
1. Concrete placed ininstrumented mould
2. Concrete shrinks3. Steel ring restrains shrinkage4. Concrete cracks5. Gauges measure time to
cracking and crack width
Test Method ASTM C 1581
Test Method ASTM C 1581St
rain
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adin
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Test Method ASTM C 1581
Cracking potential classification(Based on stress rate at time-to-cracking)
Time-to-Cracking,tcr, Days
Stress Rate at Cracking,S, MPa/Day
Potential for Cracking
0 < tcr ≤ 7 S ≥ 0.34 High
7 < tcr ≤ 14 0.17< S < 0.34 Moderate-High
14 < tcr ≤ 28 0.10 < S < 0.17 Moderate-Low
tcr > 28 S < 0.10 Low
Reduction in slab curling & plasticcracking potential
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Decrease in capillary stress Increase in viscosity of pore solution Decrease in rate of evaporation Decrease in settlement Decrease in plastic cracking potential
Investigation of Early Age Tensile Stresses, ShrinkageStrains in Pavements and Standard Drying ShrinkageTests [Liza O’Moore, Daksh Baweja & Peter Dux]
Crack prevention is often a critical parameter in the design and construction ofground and suspended concrete slabs. Often when the degree of restraint is high,uncontrolled cracking can influence the serviceability of a structure.
Designers often use the specification of maximum values for standard 56 daydrying shrinkage tests as determined by AS1012.13 in an attempt to controlcracking of concrete pavements.
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Investigation of Early Age Tensile Stresses, ShrinkageStrains in Pavements and Standard Drying ShrinkageTests [Liza O’Moore, Daksh Baweja & Peter Dux]
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32 MPa mix with SRA,Aliphatic alcohol(Evaporation retardant)& Curing compound0 – 60 microstrain
32 MPa mix without SRA,without Aliphatic alcohol(Evaporation retardant) butwith Plastic sheeting0 – 250 microstrain
Early-age crack mitigationstrategies
SRA reduces evaporation, settlement and stresses that develop on thesurface. Each of these benefits reduces the potential for the development ofplastic shrinkage cracks. Moreover, the crack width of plastic cracks arereduced.
Other studies indicate delayed or no cracking at early & latter ages
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Source: EVAPORATION, SETTLEMENT, TEMPERATURE EVOLUTION & DEVELOPMENT OF PLASTIC SHRINKAGE CRACKS INMORTARS WITH SHRINKAGE-REDUCING ADMIXTURES. Pietro Lura , Guy B. Mazzotta , Farshad Rajabipour and Jason Weiss
Early-age crack mitigation strategies(DOTs)
SRA is recommended to be used in concrete to mitigate early-age shrinkage crackingin concrete bridge decks (Washington State DOT report)
By incorporating a SRA the cracking resistance of concrete is increased (OkhlahomaDOT Final Report SPR 728)
California DOT (Caltrans) has selected SRAs as a method of crack control in cast-inplace decks on precast girders & steel girders with headed studs for composite action.Deck-on-deck rehabilitation is especially prone to cracking due to drying shrinkagestresses
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Thin White Topping (TWT) ,Bangalore, India
Thin White Topping (TWT),Bangalore, India
OPC = 430 kg/m3
FA = 30 kg/m3
W/C = 0.28SuperplasticizerPP FibresSlump @ 30’ = 40mm
TWT,Bangalore, India
Flexural strength of Concrete(Total no. of samples 60)
No. Sample size28 – day strength
(MPa)
60 per testMax: 7.35Min: 6.2Avg: 6.3
Compressive Strength of Concrete Cubes (Total no. of samples 936)
No. Sample size1-day
strength(MPa)
3-day strength(MPa)
7-daystrength(MPa)
28 – day strength(MPa)
60 cubes pertest
Max: 24.1Min: 21.1Avg: 22
Max: 48.2Min: 38.4Avg: 43
Max: 55.2Min: 48.4Avg: 51
Max: 67.2Min: 57.4Avg: 61
Concrete pavement & water curing,Rural India
Challenge: An alternative solution to expensive, rapid settingcement-based concrete
In response to this challenge, the 4x4 Concrete Systemwas developed by BASF.
U.S. Patent – No. 6,858,074
Faster-setting, user-friendly and costeffective
Develops 400 psi (2.8 MPa) flexural strengthwithin 4 hours after placement
Full depth highway, intersections and airporttaxiway repairs
4x4™ ConcreteStrength-on-Demand
Owner benefits– Economical - saves tax payers dollars
– Strength performance met consistently
– Open to traffic/airplanes sooner -reduced lane closure time
Contractor benefits– Alternative to expensive, existing
systems
– Slump/workability control
– Easy to place and finish
– No post-grinding for ride quality
4x4™ ConcreteOwner and Contractor Benefits
4x4™ Concrete Project ReferenceI-75 Pavement Replacement
I-75 Rehabilitation Project
(Kentucky / Ohio border)
Full-depth mainline paving concretereplacement
26,000 yd3 (19,880 m3) of very high-early strength concrete
Took 16 weekends to complete
1,600 yd3 (1,220 m3) of very high-early strength concrete placed everySaturday
Air Entrained Concrete
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Microspheres:Comparison to Air-Entrainment
Air Entrainment Microspheres
Mixing andTransport
Pumping, vibration,and finishing
Advantage
Right size andspacing
Robustness
Resilient
ConcreteProduction
Conclusions
SRAReduces plastic crackingReduces the frequency and width of cracksReduces short as well as long-term drying shrinkage values
Test MethodASTM C 1581 well gaining acceptance
TW ToppingAdopted for fast tracking projects in developing countries
4 x 4Rapid pavement repair option
MicrosphereAlternate technology for Air Entrained Concrete
DD.MM.YYYY LORUM IPSUM DOLORES 37
www.basf-cc.com.au
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