Stress distribution and crack formation in full-scaled ultra-high strength concrete columns

Abstract

Full-scaled model columns were placed both in summer and winter with an ultra-high strength concrete with a compressive strength more than 150 MPa, and stress distribution and cracking were experimentally evaluated. Specimens placed in summer exhibited cracks around the steel reinforcements which sometimes joined together. Specimens placed in winter showed, in addition to the cracks around the reinforcement, an internal crack perpendicular to the column axis as well as at the specimen surface. These cracks were found to be dependent on the temperature history due to hydration heat liberation and associated autogenous shrinkage strains. It was shown that the autogenous shrinkage of concrete increased when temperature after mixing was low and the maximum temperature during temperature history was high. This accounts for the numerous cracks found in the specimen placed in winter. Strain perpendicular to the axial direction was smaller than that of the axial direction implying the tensile stress due to autogenous shrinkage acting perpendicular to the axial direction as far as the autogenous shrinkage is isotropic. Finite element analysis confirmed the lateral stress due to autogenous shrinkage. Possible influences of autogenous shrinkage of ultra-high strength concrete on the structural performance include (1) early spalling of cover concrete and degradation of flexural strength, (2) degradation of bond and shear strength, and (3) prospect of longitudinal crack in center of the column and degradation of flexural strength.