Assessing the spatial variability of concrete structures using NDT techniques – Laboratory tests and case study

•The spatial variability of concrete is assessed at various scales using NDT techniques.•The spatial correlation of NDT measurements is identified by geostatistical tools.•Estimation of the minimum number of NDT measurements. Spatial variability of concrete is an important characteristic, which qualifies the non-homogeneity of mechanical and physical properties on structural components. Assessing it can be of great interest for either locating potential damaged areas in an existing structure, or reliability analysis. A two-stage experimental program was carried out using non-destructive testing (NDT) on laboratory concrete slabs in outdoor environment and on an existing bridge. The spatial variability was assessed at three scales: point (repeatability), local and global, for several NDT techniques (ultrasonic, electrical resistivity, radar and rebound hammer). The experimental results were analyzed using statistical and geostatistical tools (descriptive and spatial statistics). In this study, the methodology consists of performing statistical analysis for assessing the spatial variability and estimating the required minimal number of NDT measurements. The spatial correlation of NDT measurements is studied with variographic analysis. Some correlation lengths were identified ranging 40–60cm for the laboratory slab and the investigated bridge pier. Kriging method was used as a robust geostatistical tool, which allows the representation of the spatial variability of concrete structures.