An assessment of the reliability of rebound hammer for moist-cured specimens

This rebound hammer is a non-destructive concrete testing instrument. The instrument which measures the surface hardness of concrete is estimating the concrete compression strength by measuring the rebound number through a spring-loaded mass impacting against the concrete testing surface. The compression strength can be estimated from the calibration curves of rebound number, which is a mathematical model that is relates the rebound number of concrete cubes and the measured compression strength. Normally, the higher the rebound number, the higher the surface hardness and, consequent, the higher the concrete compression strength. Many studies investigated the rebound hammer as an none-destructive testing instrument (NDT). However, after numerous investigations, no conclusive findings have been made to suggest a mathematical relationship between the rebound number and the concrete compression strength. This is could be mainly due to the rebound hammer performance variations due to instrument specifications diversity, testing directions, and concrete materials compositions and diversity. In this investigation, nine different rebound hammers with different specifications (e.g. impact energy, spring constant..etc), properties, and manufacturers. Initially the calibration curves are developed and then used to compare with hammers performance and accuracy in estimating concrete strength. Other data analysis and statistical modeling parameters, such as the arithmetic mean, and coefficient of variation were developed for further referencing and achieving.