The replacement of natural river sand with crumb rubber (CR) in crumb rubber concrete (CRC) has attracted attention for its remarkable toughness and environmentally friendly properties. Sand to aggregate ratio (SAR) needs special attention as an important parameter in the mix proportions design of CRC as the CR volume fraction will vary with the SAR, affecting the particle packing within the CRC and therefore having a significant impact on the CRC properties, such as workability, mechanical properties and micro-structures. Thus, present study discusses the impact of SAR on both fresh and hardened properties of CRC. Relationship between SAR and workability, strength (including compressive and flexural-tensile), dynamic elastic modulus and damping ratio are analyzed. Cumulative pore size distribution and micro-morphology for each mixture were assessed using mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) technology. Results show that the workability increases slightly and then decreases significantly with increasing SAR, and the best workability is demonstrated at a SAR of 40%. Wet packing density, compressive strength, and dynamic elastic modulus showed a monotonically decreasing trend with SAR from 30% to 70% due to the weaker bonding properties of the CR particles. Flexural-tensile strength and damping ratio exhibited an initial increase followed by a decrease with SAR, reaching peak values at 50%, measured at 9.75 MPa and 1.91%, respectively. Cumulative pore volume increased from 0.3244 to 0.4315 as SAR rose from 30% to 70%, potentially contributing to the decline in compressive strength and elastic modulus. Additionally, the micro morphology appeared to be more loose with the increase in SAR. Relationship between SAR and the above indicators is modelled. Radar charts were created to analyze the influence of SAR on the overall performance of CRC. The relative area shows a significant decrease when SAR exceeds 50%.

中文翻译：

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砂骨比对废旧胶粉混凝土力学性能及微观结构的影响

橡胶粉混凝土（CRC）中用橡胶粉（CR）替代天然河砂，因其卓越的韧性和环保性能而受到关注。砂骨料比 (SAR) 作为 CRC 配合比设计中的一个重要参数，需要特别注意，因为 CR 体积分数会随 SAR 变化，影响 CRC 内的颗粒堆积，从而对 CRC 性能产生重大影响，例如可加工性、机械性能和微观结构。因此，本研究讨论了 SAR 对 CRC 新鲜和硬化特性的影响。分析了SAR与工作性、强度（包括压缩和弯曲拉伸）、动弹性模量和阻尼比之间的关系。使用压汞孔隙率测定法 (MIP) 和扫描电子显微镜 (SEM) 技术评估每种混合物的累积孔径分布和微观形态。结果表明，随着SAR的增加，和易性略有增加，然后显着下降，并且在SAR为40%时表现出最佳的和易性。由于CR颗粒的粘结性能较弱，湿堆积密度、压缩强度和动弹性模量随着SAR从30%到70%呈单调递减趋势。弯曲拉伸强度和阻尼比随着SAR的变化呈现先增加后下降的趋势，在50%时达到峰值，分别在9.75 MPa和1.91%下测量。随着 SAR 从 30% 上升到 70%，累积孔隙体积从 0.3244 增加到 0.4315，可能导致抗压强度和弹性模量下降。此外，随着比吸收率的增加，微观形貌显得更加松散。对 SAR 和上述指标之间的关系进行了建模。创建雷达图是为了分析 SAR 对 CRC 整体性能的影响。当SAR超过50%时，相对面积显着下降。