A laser interferometer robot for the study of surface wave sensitivity to various concrete mixes

The French national research project SENSO aims at providing a methodology combining several non destructive testing methods to evaluate indicators required for assessing the durability of concrete cover. A large set of 0.5m x 0.25m x 0.12m slabs has been built for various water/cement ratios, aggregate sizes and type. Those slabs have been subsequently studied under controlled water saturation level, chloride content and carbonation depth. To perform the numerous surface wave phase velocity dispersion curve measurements required for the data base, LCPC has designed a small size portable robot that records seismograms with a laser interferometer as a receiver. In this paper we describe the robot, the experimental protocol together with the signal processing technique used. Surface wave phase velocity is sensitive to shear and Young moduli (controlled by destructive tests) and to water content that are not necessarily uniform with depth and dispersion of surface wave is observed. Preliminary results of dispersion curves inversion illustrate these variations.