EARLY AGE COMPRESSIVE AND TENSILE STRENGTH DEVELOPMENT OBJECTIVE Determine 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 Concrete M. 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 Graded Aggregate 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 AUTOGENOUS SHRINKAGE AND TOTAL SHRINKAGE DURING DRYING RESTRAINED STRESS DEVELOPMENT, STRESS STRENGTH RATIO AND RELAXATION BY TENSILE CREEP  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 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