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GT CEE 8813 - Theory and Testing Methods of Self-Consolidating Concrete

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1Theory and Testing Methods of Self-Consolidating Concrete (SCC)CEE 881303/14/07Felix KimWhat is Self-Consolidating Concrete? “A highly flowable, yet stable concrete that can spread readily into place and fill the formwork without any consolidation and without undergoing significant separation”(Khayat, Hu and Monty, 1999)2Benefits No vibration needed Less labor needed Low noise-level in the plants and construction sites. Easier to pump Faster construction Improved quality and durability Higher strengthComparisonNormal Concrete Slump flow: 8 ~ 11 in Vibration required Somewhat self-leveling No segregationSCC Slump flow: 24 ~ 30 in No vibration needed Self-leveling No segregation3Tight Spacing(Kalkan, 2007)Concrete pour on 02/26/07Video(Kalkan, 2007)Concrete pour on 02/26/0743 Characteristics Filling abilityAbility to flow under its own weight both horizontally and vertically upwards without honeycombing around any shape Passing abilityAbility to flow freely through dense reinforcement without blocking Segregation ResistanceAbility to maintain homogenous mix during and after placement, without separation of aggregate from the past, or water from solids(Petersson et al., 2002)Flow ability vs. Segregation Resistance Difficult to achieve both flow ability and segregation resistanceFlow abilitySegregation Resistance5Mix Design Coarse Aggregate content: 28 – 32 %  Mortar fraction: 61%-68% Sand / Aggregate Ratio: 48%-57% Cementitious: 700-840 lb/cu yd Water: 290-310 lb/cu yd Admixtures: Viscosity Modifying Admixture (VMA), Superplasticizer (PolyCarboxylate)(Knight and Grace, 2002)Aggregate Fraction Coarse Aggregate content: 28 – 32 %  Mortar fraction: 61%-68% Sand / Aggregate Ratio: 48%-57%GravelGravelSandSandPastePWWAirSCCConventional Concrete(Okamura and Ouchi, 2003)6High Paste Volume Increases flow ability by reducing inter particle friction Increases heat generation Larger drying shrinkage Substitution of SCM can partially solve this problem – Fly Ash for heat reduction, Silica Fume for strength(Ng et al., 2006)Aggregate Gradation CA/Tot. Vol. governs the flow ability Gradation needs to be considered when spacing is close to Max. Size Aggr. (MSA) ¾” CA < 3/8” CA < FA (Ng et al., 2006)7Aggregate Gradation 25%-32% CA (reduce blocking) Aggr. gradation is very crucial½”1” ¾” 3/8” Sand Pan(Knight and Grace, 2002)Top Secrete% Viscosity and Flowability Viscosity - Measure of resistance of fluid to deform under shear Yield shear stress –required shear stress to initiate the flowoγμττ+=0oγτRate of shear, Shear stress,0τ1μ(Grace Construction Products, 2002)0τμ- Yield value (Pa)- Plastic viscosity (Pa-s)0τSuperplasticizer8Superplasticizer Steric Repulsion PolyCarboxylicFlow abilityViscositySuperplasticizerWater(Okamura, 1997)Shear Friction  Shear stresses increases when the mix goes through a close spacing because of higher probability of inter praticle collision (Sonebi and Bartos, 2002)στστ(Okamura, 2003)CAMortar9Effect of Fine Aggregate on Deformability(Okamura, 2003)τστσCrushed sandRiver sandLand sandSmall Large Sand contentστστCAMortarBlocking (Knight and Grace, 2002)Normal ConcreteSCCLow CA contentHigh paste volume“Passing ability”10Segregation Resistance Powder Method (Fly Ash) Viscosity Modifier Method- Hydrolyzed starches, Bipolymers (welumgum)- New generation Superplasticizer - Highly flowable mix with cohesion- Molecular structure of VMA facilitates the removal of large amount of water by physical adsorption (Mehta and Monteiro, 1993)Stoke’s Law and Segregation Resistance Yield stress – low enough to flow Viscosity – low enough to flow but high enough to prevent segregationμρρ18)(212−=gDV(Grace Construction Products, 2002)density=ρityviscos=μdiameterD=velocityV=11Bleeding Reduce strength Stiffness Bond to reinforcing bars DurabilitySCC Hardened Properties As good as or better than normal concrete Compressive and Tensile Strength- 28 day strength higher than normal concrete Durability- similar to conventional superplasticizedconcrete Shrinkage- similar to other high cementitious material12Slump Flow Test (ASTM C-1611)  The most commonly used test Filling ability, Segregation resistance Slump flow = (d1+d2)/2 20 ~ 26 in recommended VSISlump flow test performed on 02/26/2007 at GaTech Lab (picture taken by Felix Kim)Slump flow  The test judges the capability of concrete to deform under its own weight against the friction for the surface with no other external restraint present (Sonebi and Bartos, 2002)13Visual Stability Index (VSI)Very Subjective!(Horta, 2005)J-Ring (ASTM C-1621)(Horta, 2005)2)(21ddflowRingJ+=−Blocking = slump flow – J-ring flowPassing Ability14Column Segregation Test (ASTM C-1610) Lab test rather than field testTBTBTBCACAifCACACACAS >×⎥⎦⎤⎢⎣⎡+−= ,1002TopBottomTBCACAifS ≤= ,0Static Segregation onlyColumn Segregation Test(ASTM, 2006)15Proposed Method Direct relationship between SI and Pd (Bui et al., 2002) Dynamic and Static Segregation El-Chabib and Nehdi Dr. Struble has proposed a similar test method that ASTM is consideringSegregation Index (SI)Penetration depth (Pd)PdsegregationNo segregationProposed Method (El-Chabib and Nehdi, 2006)SI-StaticSI-dynamic16Future Research Development of Prediction Model (ANN) Optimum mix designQuestion


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