Nondestructive Monitoring of Setting and Hardening of Portland Cement Mortar with Sonic Methods

The setting and hardening process of concrete is considered to be the most critical time period during the life of a concrete structure. Previous research has been conducted on an ultrasonic wave reflection method that utilizes a steel plate embedded in the concrete to measure the reflection loss of shear waves at the steel-concrete interface. The reflection loss has been shown to have a linear relationship to compressive strength at early ages. A procedure for strength prediction based on measured loss has been developed. The presented investigations continue this research by examining the fundamental relationship between the reflection loss, measured with shear waves, and the hydration kinetics of Portland cement mortar, represented by setting time, dynamic elastic moduli, compressive strength and degree of hydration. Dynamic elastic moduli are measured by fundamental resonant frequency and ultrasonic pulse velocity using compression and shear waves. Degree of hydration is determined by thermogravimetric analysis and adiabatic heat release. The water/cement ratio was varied for the tested mixture composition. The results presented herein show that compressive strength, dynamic shear modulus and degree of hydration have a linear relationship to the reflection loss for the tested mortars at early ages. This trend indicates that test methods based on measuring dynamic shear moduli have the ability to measure mechanical properties microstructural changes that determine early age properties of hydrating cementitious materials. The presented results validate and verify the previously developed strength prediction procedure based on the shear wave reflection method.