Experimental Investigations on Effect of Compaction, Curing, Water to Cement Ratio, Cement Type and Temperature Variation on the Rebound Hardness of Concrete

Abstract

It is a known fact that the concrete strength is not only affected by the ingredients present in it, but also by the other factors like types of cement used, compaction deficiency, curing condition, elevated temperature, and different w/c ratios. The influence on the rebound hammer has been illustrated in this paper concerning the hardness of the concrete specimens. The effect of cement types, compacting deficiency, w/c ratio, curing condition, and elevated temperature on concrete compressive strength and rebound hardness has been considered for the analysis. From an experimental study, it is found that the reduction of the compressive strength of concrete is between 6 to 41 percent due to insufficient compaction alone when tested using a destructive method. However, the rebound hammer results revealed that there is no reduction in the rebound index. The rebound hardness test cannot predict the compressive strength due to inadequate curing. It is also reported that the rebound index is significantly reduced, with the destructive strength of the concrete specimens. The study revealed that in the case of M30 and M40 grades of concrete, the percentage reduction of the average rebound index is almost higher in all the cases than the average compressive strength at a temperature ranging from 200°C to 800°C. The strength (rebound hardness) measured is either under or overestimated if no attention has been given to different influencing factors. Thus, a reliable and accurate evaluation of strength cannot be guarantee.