Review of Ultrasonic Wave Reflection Applied to Early-Age Concrete and Cementitious Materials

The ultrasonic wave reflection method, as applied to characterize early age cement-based materials, is reviewed. The topic is first introduced with a historical review of method development. The theoretical basis of the reflection technique within the context of wave mechanics is then considered, followed by a description of experimental techniques and associated requirements of testing setups. Then fundamental background information about the method is described, including effects of ultrasonic wave mode (compression and shear waves) and buffer material (metal, ceramic and polymer) on the results and required experimental apparatus. Several test application tasks, across a range of cementitious material ages (hydration states), are summarized, including determination of global constitutive properties, estimation of setting time (initial and final sets), evolution of strength, and assessment of microstructure (e.g. flocculation state in setting material and porosity in solid material). The analyses of various techniques are presented in a unified manner for elastic, viscoelastic and poroelastic idealizations of the cementitious material.