Crumb rubber concrete (CRC) is increasingly recognized as a sustainable construction material due to its environmental benefits and potential mechanical performance. However, achieving consistent CRC strength remains challenging, partly due to limited attention to crumb rubber aggregate (CRA) gradation, particle characteristics, and replacement techniques. This study introduces a novel Total Gradation Deviation (TGD) metric to optimize the aggregate packing and enhance mix-design consistencyโan aspect that is largely overlooked in most existing CRC research. Additionally, by using 10%โ30% finely graded CRA (0.6โ4.75 mm), this study offers a more integrated analysis than typically reported in the literature. The findings reveal that compressive strength (๐โฒ๐) and density reductions are influenced by not just CRA size but also the effective rubber dosage, specific gravity variation, and gradation alignment. These factors, which are often neglected, partially explain the inconsistent ๐โฒ๐ results reported in the literature across different studies. As a result, conventional replacement methods become problematic, frequently leading to misleading reductions in strength. Whereas the finer CRA particles (<1.2 mm) enhanced the ๐โฒ๐ by 5โ6 MPa (i.e., 16%โ30% increment) due to improved packing and reduced porosity, the broader CRA size distributions (0โ5 mm) yielded moderate but structurally acceptable strength (>20 MPa) that aligns with international standards. Optimized mix-designs with a sand-to-aggregate ratio (SAR) of 0.48โ0.51, CRA-to-cement ratio <0.12, and TGD less than 14% achieved 30โ35 MPa, yielding up to 36% ๐โฒ๐ gain compared to untreated CRA mixes reported in the literature. Overall, these findings offer an invaluable practical, low-cost alternative to other chemical pretreatment methods and support a shift toward more standardized, gradation-based CRC mix-designs that lays a foundation for future work on unified performance indices, environmental modeling, and microscale validation.
https://doi.org/10.1061/JMCEE7.MTENG-23466