Hammer rebound index as an overall-mechanical-quality indicator of self-compacting concrete containing recycled concrete aggregate

The hammer rebound index has traditionally been solely and exclusively used to estimate the compressive strength of vibrated concrete. Its use has recently been extended to the prediction of the compressive strength of Self-Compacting Concrete (SCC) and concrete produced with Recycled Concrete Aggregate (RCA). The con- ventional use of the hammer-rebound test is further developed in this paper, by demonstrating how it can be used to estimate the overall mechanical behavior of SCC containing RCA. To do so, nine SCC mixes with different contents and fractions (coarse, fine, and powder) of RCA are analyzed. Following a simple-linear-regression validation and property standardization procedure, the hammer rebound index is then expressed as a linear combination of four mechanical properties, adjusted through a multiple regression. The hammer rebound index is therefore expressed as a weighting of both the mean value of compressive behavior (arithmetic mean of compressive strength and modulus of elasticity) amounting to a weight of 72.8%, and the mean value of bending- tensile behavior (arithmetic mean of splitting tensile strength and flexural strength) amounting to a weight of 27.2%. The hammer rebound index can therefore be construed as an overall-mechanical-quality performance indicator of the SCC containing RCA, which can also yield predictions of every mechanical property. In this way, the application of the hammer rebound index could likewise be of use in rehabilitation, pathology, and health- monitoring works where a full characterization of the mechanical performance of SCC with RCA is required, facilitating the use of SCC with RCA in real structures.