High Performance Concrete and Drilled Shaft Construction Dr. Dan Brown, P.E. Dr. Anton Schindler Auburn University A Proposal for High Performance Concrete • Similar concept as used for current high performance concrete, but • Performance characteristics for fresh concrete properties (rather than hardened) 1 Why? Workability and Passing Ability tremie rebar concrete Concrete with inadequate Concrete with good workability workability and filling ability 2 Congested Rebar Cage Exposure of Trapped Laittance Attributed to Inadequate Workability 3 Congested Rebar Cage SCC Mix 4 Conventional Concrete Workability Retention Fresh, fluid concrete Trapped Laittance Old, stiff concrete 5 600 Tremie Placement Loading Traveling Hopper # 1 500 Waiting Period 12:05 AM: tremie stuck, rigging failure resulted 12:30 AM: tremie re-rigged, pulled free. 400 12:35 AM: tremie over-flowed , pour stopped, cable up and down. 12:40 AM: flow resumed, but last 10CY in hopper would not come out, sprayed and wasted. 300 1:00 AM: new hopper, flow resumed. 5 hrs 34 min. 200 Concrete Volume (CY) Volume Concrete 100 0 PM PM AM 10:00 11:00 12:00 6:00 PM 6:00 PM 7:00 PM 8:00 PM 9:00 AM 1:00 AM 2:00 AM 3:00 AM 4:00 AM 5:00 AM 6:00 AM 7:00 Unit Weight (kN / cu. m) Anomaly – Probable Defect of Unknown Size Mean Minus 3 Standard Depth (m) Deviations Possible Contaminated Mean Concrete at Base of Shaft Near One Tube 6 Bleeding Bleeding Crack 7 Bleeding Cracks Bleeding 8 Temperature 14 T0 = Initial Temperature T0 = 90° F τ = 28.0 hrs 12 β = 1.50 αu = 0.850 ) 3 10 T0 = 80° F 8 6 T0 = 70° F 4 T0 = 50° F Generated Heat (W/cm Generated 2 0 0 10203040506070 Concrete Age (hours) High Performance Drilled Shaft Concrete • We need to define a “high performance concrete” based on fresh properties: o Workability o Passing ability (tight rebar cages) o Retarded set time o Avoid segregation & bleeding (need cohesive paste); will need fines & proper aggregate gradation o Control of hydration temperature 9 Strategies for Drilled Shaft Concrete Mix Design • Aggregates: o Use rounded gravel aggregates rather than crushed stone o Use No. 67 or 78 aggregate gradation rather than No. 57 o Use sand to total aggregate ratio in the range of 0.44 to 0.50 Strategies for Drilled Shaft Concrete Mix Design • Admixtures: o water reducing & hydration control admixtures o viscosity modifying admixtures (VMA) as needed to help control bleeding o fly ash and/or slag to increase cementitious content & reduce the portland cement content o Use 56 day or 90 day strength specifications with high dosage of fly ash or GGBF slag 10 Strategies for Drilled Shaft Concrete Mix Design • Temperature: o temperature affects admixture dosages! o use adiabatic or semi-adiabatic curing of specimens o Control the fresh concrete placement temperature to less than 80°F (75°F) o Utilize Type II cement + fly ash or slag to control heat of hydration & reduce DEF potential Strategies for Drilled Shaft Concrete Mix Design • Most Important: o Develop project-specific mix design o Fresh concrete performance requirements should be specific to application 11 Thanks for Listening! 12.