NDT Determination of Cement Mortar Compressive Strength Using SASW Technique

Abstract

The spectral analysis of surface wave(SASW) method, which is an in-situ seismic technique, has mainly been developed and used for many years to determine the stiffness profile of layered media(such as asphalt concrete and layered soils) in an infinite half-space. This paper presents a modified experimental technique for nondestructive evaluation of in-place cement mortar compressive strength in single-layer concrete slabs of rather a finite thickness through a correlation to surface wave velocity. This correlation can be used in the quality control of early age cement mortar structures and in evaluating the integrity of structural members where the infinite half space conditions is not met. In the proposed SASW field test, the surface of the structural members is subjected to an impact, using a 12 mm steel ball, to generate surface wave energy at various frequencies. Two accelerometer receivers detect the energy transmitted through the medium. By digitizing the analog receiver outputs, and recording the signals for spectral analysis , surface wave velocities can be identified. Modifications to the SASW method includes the reduction of boundary reflections as adopted in the surface waves before the point where the reflected compression waves reach the receivers. In this study, the correlation between the surface wave velocity and the compressive strength of cement mortar is developed using on 36" x 36" x 4"(91.44x91.44x10.16 cm) cement mortar slab of 2,000 psi(140 kgf/sq.centimeter) and two 36" x36" x36"(91.44 x 91.44 x 10.16 cm) cement mortar slabs of 3,000 psi(210 kgf/sq.centimeter).