Experimental study of wave propagation through grouted concrete

The injection of cementitious grout into deteriorated civil structures is a common application for strengthening or repair purposes. The nondestructive estimation of the repair effect, which is always desirable, is not an easy task because geometry, constituent materials' property mismatch, and temperature-dependent hydration rate often impose difficulties to the characterization. In many cases, after the grout injection and the elimination of voids, the pulse velocity decreases unexpectedly, complicating the task of repair evaluation. In this work, an experimental study of stress wave propagation in concrete impregnated with injection cement is presented. It is revealed that, despite the common impression, wave velocity should not be expected to rise after repair in any case because the properties of grout are initially lower than the surrounding concrete. This effect can be emphasized by the low hardening rate that is imposed to the grout material in the case of low environmental temperature. The transmitted frequencies are also decreased shortly after injection and, therefore, the decrease of wave parameters such as velocity or amplitude should not necessarily be taken as a sign of unsuccessful repair or even deterioration.