碳酸性侵蚀与AAR作用下纳米混凝土的耐久性

地铁混凝土处于地下空间,容易受到地下水的碳酸性侵蚀；碱集料反应 (AAR)是一种严重的混凝土耐久性问题,既难以发现又难以修补,由两者共同作用引起的混凝土耐久性降低严重影响地铁隧道的正常使用.为研究纳米材料对地铁混凝土在碳酸性侵蚀和AAR共同作用下耐久性的影响,在普通混凝土中掺入适量纳米SiO₂和纳米Fe₂O₃,利用自行研制的碳酸性侵蚀试验箱进行试验,采用碳酸性侵蚀深度、膨胀率和声速作为测试指标来评价纳米混凝土在碳酸性侵蚀和AAR共同作用下的耐久性.试验结果表明:掺入纳米颗粒后,混凝土的膨胀率和侵蚀深度有了明显降低,而声速有了明显提升,说明纳米混凝土的耐久性优于普通混凝土；在182 d龄期时,掺量为2%的纳米SiO₂混凝土耐久性改善最明显,侵蚀深度和膨胀率最小,声速最大且声速下降幅度最小；其次是掺量为1%的纳米Fe₂O₃混凝土.由于纳米颗粒特殊的物理化学性质,改善了混凝土内部的微观结构和孔溶液的化学组成,使碳酸性侵蚀和碱集料反应共同作用下混凝土的耐久性得到了提高.

Durability of concrete with nano-particles under combined action of aggressive CO2 and alkali aggregate reaction

Subway concrete is easy to be attacked by aggressive CO₂ in underground space, and alkali aggregate reaction (AAR) is a severe durability problem which is difficult to find and repair. Durability decrease of subway concrete caused by these two problems seriously affects the normal use of the subway tunnel. To investigate the impact of nano-particles on the durability of subway concrete under the combined action of aggressive CO₂ and AAR, two kinds of nano-particles (nano-SiO₂ and nano-Fe₂O₃) were respectively mixed into plain concrete to prepare concrete with nano-particles. Durability test was carried out by using a self-developed equipment, and erosion depth, expansion, and sonic velocity were selected as indices to evaluate the durability of the concrete with nano-particles under the combined action of aggressive CO₂ and AAR. Test results show that after mixed with nano-particles, the erosion depth and expansion of the concrete were decreased obviously, while the sonic velocity was increased significantly, which demonstrates that the durability of the concrete with nano-particles was better than that of plain concrete. At the age of 182 d, the concrete with 2% of nano-SiO₂ showed the best durability performance that the erosion depth and expansion were the smallest and the sonic velocity was the largest with least decrease, followed by the concrete with 1% of nano-Fe₂O₃. The enhancement of durability was due to the special physical and chemical properties of the nano-particles which improved the microstructure of the concrete and the chemical composition in pore solution.