Microstructural analysis and compressive strength evaluation of interlocking concrete paving blocks incorporating crumb rubber

Imaging Analysis Techniques (IATs) have become instrumental in civil engineering materials research, providing critical insights into the microstructural characteristics of mixtures and enabling associations between these features, numerical parameters, and laboratory-derived mechanical performance data. However, using IATs specifically for Concrete Paving Blocks (CPBs), particularly when modified with crumb rubber (CR), remains underexplored. In this study, two numerical parameters derived from IATs – interlocking parameter (PINT) and interlocking rate (IR) – were investigated for their correlations with the estimated compressive strength (fpk,est) of CPBs after a 28-day curing period. CPBs were prepared with CR at 5%, 10%, 15%, and 20% by mass, with a reference concrete mixture designed per American standards for no-slump concrete and a target fpk,est of 50 MPa. PINT and IR were calculated using custom Python-based software developed by the authors. Consistent with prior findings, increasing CR content resulted in a decrease in fpk,est, a trend that was well-represented by linear and power regression models. Both IR and PINT showed potential for explaining the reductions in fpk,est, with IR demonstrating stronger predictive capabilities. Consequently, IR proves to be a promising parameter for describing the microstructural characteristics of CPBs, whether containing CR or not, due to its consistently good correlations with both fpk,est, and CR content.