Carbonation is unavoidable during the service of concrete, especially for recycled sand concrete (RSC). This paper presents a systematic experimental study of the various factors affecting the carbonation resistance of RSC. The carbonation test was conducted to investigate the effects of recycled sand (RS) replacement ratio (0 %, 30 %, 50 %, 70 %, 100 %), recycled fine powder (RP) content (3 %, 7 %, 10 %) in RS, degree of pre-wetting (0 %, 50 %, 100 %) of RS, water/binder (W/B) ratio (0.37, 0.45, 0.58), and various mineral admixtures on the carbonation resistance of RSC. Moreover, the variation of splitting tensile strength of RSC after carbonation was determined, and the microstructural change of RSC after carbonation was also analyzed using mercury intrusion porosimeter (MIP) and scanning electron microscope (SEM). Results indicate that the carbonation resistance of RSC can be improved by reducing the water/binder ratio, increasing the pre-wetting degree of RS, and adding composite mineral admixtures. The carbonation depth of RSC decreased by 59.8 % when the W/B was reduced from 0.58 to 0.37, and by 16.2 % when the pre-wetting degree of RS was increased from 0 % to 100 %. Ternary composite mineral admixture (15 % fly ash + 15 % ground granulated blast furnace slag powder + 8 % silica fume) reduces carbonation depth by 49 %. The increase in splitting tensile strength of RSC after carbonation is positively correlated with the depth of carbonation. This is due to the carbonation products filling some of the pores and improving the pore structure of RSC.

中文翻译：

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再生砂混凝土的抗碳化性能及其碳化后的劈裂抗拉强度


在混凝土使用过程中，尤其是对于再生砂混凝土 （RSC），碳化是不可避免的。本文对影响 RSC 抗碳化性的各种因素进行了系统的实验研究。进行碳化试验，研究再生砂 （RS） 替代率 （0 %， 30 %、50 %、70 %、100 %）、再生细粉 （RP） 含量 （3 %、7 %、10 %）、RS 的预润湿度 （0 %、50 %、100 %）、水/粘合剂 （W/B） 比 （0.37、0.45、0.58） 和各种矿物外加剂对 RSC 抗碳化性的影响。此外，还测定了碳化后 RSC 的劈裂拉伸强度变化，并使用压汞侵入孔隙度计 （MIP） 和扫描电子显微镜 （SEM） 分析了碳化后 RSC 的微观结构变化。结果表明，通过降低水/粘合剂比、提高RS的预润湿度和添加复合矿物外加剂可以提高RSC的抗碳化性能。当 W/B 从 0.58 降低到 0.37 时，RSC 的碳化深度降低了 59.8 %，当 RS 的预润湿度从 0 % 增加到 100 % 时，RSC 的碳化深度降低了 16.2 %。三元复合矿物外加剂（15% 粉煤灰 + 15% 磨碎的粒化高炉矿渣粉 + 8% 硅灰）可将碳化深度减少 49%。碳化后 RSC 劈裂拉伸强度的增加与碳化深度呈正相关。这是由于碳酸化产物填充了一些孔并改善了 RSC 的孔结构。