Hydration of cementitious materials by pulse echo USWR - Method, apparatus and application examples

In this paper, a novel nondestructive method based on a pulse echo ultrasonic shear waves reflection (USWR) technique is described. The method is implemented in a home-built field testing apparatus of which construction and operating principles are briefly explained. With the instrument, the time dependence of the reflection coefficient r due to the hydration of cementitious materials is measured automatically with the result continuously displayed and recorded. The changes of the reflection coefficient Deltar with time are related to the changes of the viscoelastic properties, in particular to the dynamic shear modulus G of the material investigated. From the application examples on selected cementitious materials shown, the sensitivity of the method and of the apparatus to different parameters (composition, water/solid ratio, fineness, addition of additives, aging) is evident. Possible practical applications are nondestructive measurements of the shear rigidity of the fragile Ct-IS structures with no external shearing applied and cement setting time determinations. (C) 2000 Elsevier Science Ltd. All rights reserved.