Statistical and Experimental Evaluation of Fresh State Behavior in Recycled Aggregate Concrete: A Comparative Study of M20 and M30 Grades

The rapid increase in construction and demolition (C and D) waste necessitates the scientific validation of Recycled Concrete Aggregate (RCA) as a sustainable alternative to natural coarse aggregate in structural concrete. In this study, the workability characteristics of M20 and M30 grade concrete, designed in accordance with IS 10262:2019, were systematically investigated by replacing natural coarse aggregate with RCA at intervals ranging from 0% to 100%, as per IS 383:2016.
Fresh concrete properties were evaluated using the slump test and compaction factor test, conducted in accordance with IS 1199, to quantify the rheological behavior of RCA-incorporated concrete. The experimentally obtained data were analysed using linear regression models to assess the extent and predictability of workability degradation due to RCA inclusion.
The results indicate a progressive reduction in workability with increasing RCA content. At 100% replacement, the maximum reduction in slump was observed to be 15.13% for M20 and 17.24% for M30 concrete. Higher-grade concrete (M30), characterised by a lower water–cement ratio, exhibited statistically significant higher sensitivity (p < 0.05) to the angularity and surface texture of RCA. The developed regression models demonstrated strong predictive capability, with coefficients of determination (R² > 0.97) for both slump and compaction factor, confirming that the loss of workability follows a linear and predictable trend.
Based on the experimental and statistical evaluation, the study establishes that RCA replacement levels up to 40% can be safely adopted for structural concrete applications without the use of chemical admixtures, while maintaining acceptable workability limits as per Indian Standards. The findings provide a validated experimental dataset and regression-based predictive framework that supports sustainable concrete mix design and promotes the effective utilisation of C and D waste in structural engineering practice.