Ultrasonic assessment of early-age changes in the material properties of cementitious materials

Abstract

After casting, cementitious materials exhibit a continuous change in the mechanical properties with time due to a chemical reaction known as hydration. In addition, these materials also exhibit a change in state, from a fluid to a solid, in the first few hours. Conventionally, changes in the material properties are obtained by monitoring the visco-elastic moduli with time before setting and the increase in the elastic material properties of the solid cementitious material, after setting. An ultrasonic test setup and the data analysis procedures, which provide for continuous monitoring of the hydrating cementitious materials from a very early age through setting are presented in this paper. The test procedures for obtaining the ultrasonic test data and the inversion subroutines for assessing the material properties of the cementitious material at different stages of hydration are discussed. The experimental test results obtained from mortar mixtures of varying compositions are presented. The observed experimental trends are explained considering wave propagation in visco-elastic materials. There is a two-stage increase in the value of shear modulus of mortar with time. Experimental evidence suggests that initially there is a larger relative increase in the viscous component of the shear modulus while later there is a larger relative increase in the elastic component.