Experimental investigation on relationships between rebound index and compressive strength of cement concrete specimen influenced by physical factors

The hardness provides the concrete specimen's compression strength, which is affected by multiple variables such as concrete grade, cure period (days) and different brand cement types (PPC). Experimental study is performed to show the effects of concrete grades, curing periods and cement types (type-I and type-II) on the rebound index. It is found that the rebound index increases with the specimen age and concrete grade, but concrete prepared with type-II cement gives less rebound index compared to type- I cement. This is due to the concrete hydration phase that was very slow with type-II cement in the early days. The regression coefficient of both cement types may vary from 5% to 70% with regard to the B-Proceq curve. The trend line of concrete grade M 15 to M 25 lies above and crosses the curve of B-Proceq for type-I and type-II cement respectively but lies below in case of concrete of M1 0 grade. This paper, with the assist of ANOVA, presents a comparative analysis of the unconventional and expected compression strength values at a signifying level of 5%. Comparative analysis of the B- Proceq curve and rebound index curve also proves the limitation of the rebound hammer. Without taking into account the above variables, the use of rebound hammer can lead in imprecise mechanical characteristics of hardened concrete.