Properties of Early-Age Portland Cement Mortar Monitored with Shear Wave Reflection Method

Abstract

The setting and hardening process of concrete is considered the most critical time period during the life of a concrete structure. Thus, the nondestructive, in-place testing of early-age concrete properties is an important tool for the progress of many construction projects. This article reports on a study that examined the ability of a shear wave reflection method to monitor the hydration kinetics of Portland cement mortar. The wave reflection method measures the reflection loss of shear waves at an interface between a steel plate and the mortar. The study included mortars with water-cement ratios (w/c) of 0.35, 0.5, and 0.6, which were tested at isothermal curing conditions of 25 degrees C. The authors characterized the hydration behavior of the mortars by setting time, heat of hydration, compressive strength, dynamic shear modulus, and degree of hydration. The results show that compressive strength has a bilinear relationship to the reflection loss. Additional results suggest that the wave reflection measurements are qualitatively governed by the dynamic shear modulus of the mortar. Finally, the reflection loss data of all three tested mortars were found to be uniquely related to the gel-space ratio of the cement paste phase of the mortars.