Experimental Study on the Spatial Variability of Concrete by the Core Test and Rebound Hammer Test

For the nonlinear analyses of concrete structures, the complete compressive stress-strain curve of concrete is the key basis. Spatial variability is one of the significant characteristics of the mechanical properties of concrete. It may affect the possibly partially damaged area and failure mode of concrete components. However, there are few investigations on the spatial variability of the complete compressive stress-strain curve of concrete. To this end, a plain concrete slab of $2.8\times 4.8\times 0.2\mathrm{m}$ was cast. In order to study the spatial variability of the rebound number, an intensive rebound hammer test was performed on this slab with spacing of 40 mm. Then a core test was carried out with partitioned uniform sampling. In order to obtain more information about the spatial variability of random field, the positions of cores were determined by three two-dimensional circular number theoretical nets. The test of the complete compressive stress-strain curve was performed on the obtained cores and a four-variate random field of the compressive constitutive parameters of concrete was obtained. Then the geostatistical method was adopted to study the spatial variability of the obtained random fields. The test results show that there is strong spatial correlation in the four compressive constitutive parameters of concrete. In addition, the size, shape, and failure mode of the concrete block have great influence on its complete compressive stress-strain curves. For the random field of the rebound number, there is obvious spatial correlation, but the spatial variability is dominated by randomness.