碳化和纳米SiO2改性再生粗骨料混凝土抗硫酸盐侵蚀性能

分别使用加速碳化和纳米SiO₂溶液浸泡的方式，对由两种强度等级混凝土(C30和C60)获得的再生粗骨料(RCA)进行改性；制备得到不同方式改性的再生粗骨料混凝土(RAC),并进行硫酸盐侵蚀实验.运用抗压强度实验和分光光度计法，分析RAC的宏观力学性能和硫酸根侵蚀深度的变化.利用扫描电子显微镜(SEM)、 X射线衍射(XRD)、显微硬度和热重分析(TGA)手段，研究硫酸盐侵蚀后两种改性RAC的界面过渡区(ITZ)微观结构、化学组成和微观力学性能的变化特征.结果表明，RAC的力学性能随着硫酸盐侵蚀龄期的延长先增加后急剧降低.相比而言，纳米SiO₂的火山灰效应和填充效应使制备的RAC水泥水化更加充分，老骨料-老砂浆ITZ更加平整致密，表现出更好的抗硫酸盐侵蚀性能.

Sulfate resistance of recycled concrete prepared with carbonation and nano SiO2 modified recycled coarse aggregates

Recycled aggregate concretes (RAC) were prepared by using carbonation and nano-SiO2 modified recycled coarse aggregates (RCA, obtained from different strength grades of concrete: C30 and C60), and sulfate erosion test on the prepared RAC were carried out. The macro-mechanical properties and sulfate penetration depth of RAC were analyzed by compressive strength and spectrophotometry methods. The change characteristics of microstructure, chemical composition and micromechanical properties of interface transition zone (ITZ) in RAC under sulfate attack were detailly investigated by using scanning electron microscope (SEM), X-ray diffraction (XRD), microhardness and thermal analysis (TGA). The results show that the mechanical properties of RAC are increased first and then decreased sharply with the erosion time extending. In comparison, the pozzolanic effect and filling effect of nano-SiO2 make the concrete hydrating better and old aggregate - old mortar ITZ more compact and smoother, and thus exhibiting superior sulfate resistance. In addition, the RAC prepared with high strength of RCA shows better sulfate resistance compared with the one with low strength.