Assessing the Spatial Variability of Compressive Strength of In-Situ Concrete: From Laboratory to Construction Site

The non-homogeneity of in-situ concrete is owing to the intrinsic variability of the material mixture, the workmanship, the construction technology, and the environmental conditions. There is the reason for varying compressive strength of existing reinforced concrete (RC) structures that lead to spatial variabilities of a measurement. In this study, an experimental program on a new existing 25-story RC building has been conducted in order to assess the spatial variability of compressive strength of the laboratory-tested specimens and the on-site cores, coincidentally to find the distribution of these results based on statistical analysis. The spatial variability of compressive strength is identified from 315 cast specimens on-site and 312 specimens collected from the existing structures by the core drilling method. More specifically, the concrete strength variability obtained in RC structural components on-site was investigated through small-scale variability within a single member, large-scale, and global-scale variability between different members made of the same concrete. The casting-in-place cube is the most convenient specimen to ensure that the used concrete complies with the requirements of the design project through the variation of compressive strength in a set of three specimens per batch. According to the analyses presented in this study, there has been a correlation between the spatial variability obtained from cubic specimens and the small-scale spatial variability as found in the core specimens. However, there is a considerable difference between the global and local spatial variability of on-site concrete compressive strength.