Assessment of Static Stability of Concrete Using Shear Wave Velocity Approach

Flowable concrete is prone to segregation that can adversely affect its performance. The risk of segregation should be reduced through adequate mixture proportioning and proper placement technique. The objective of this paper is to evaluate the potential segregation of concrete by monitoring changes in shear wave (S-wave) velocity using the piezoelectric ring actuator technique (P-RAT) after the initial setting time. The S-wave that can only propagate into solid phase is sensitive to differences in properties of cement paste and aggregate and can therefore reflect changes in static stability associated with changes in aggregate concentration and porosity of the cement paste. The proposed technique consists of a column measuring 450 mm (17.72 in.) in height that is equipped with three pairs of P-RAT sensors fixed at different heights to evaluate the homogeneity of S-wave velocity. Eight self-consolidating concrete (SCC) mixtures designed to have different levels of segregation resistance were used to evaluate the ability of the proposed S-wave velocity approach to evaluate segregation resistance. Static stability was also evaluated using the column segregation test determined for fresh concrete as well as coarse aggregate distribution along P-RAT column samples in the hardened state. Homogeneity of primary wave (P-wave) velocities was measured along the same concrete prismatic samples. The proposed P-RAT column approach is shown to enable the assessment of static stability of SCC. Test results indicated that a higher degree of correlation can be obtained between the segregation index deduced from the P-RAT column test at 10 and 24 hours after casting and the physical tests determined on fresh and hardened concrete. The interpretation of the distribution of S-waves is shown to be more reliable than that of the P-waves for in-place assessment of static stability of concrete.