碳化对混凝土微孔特征和吸水性能的影响

Effects of Carbonation on Microscopic Pore Characteristics and Water Absorption Performance of Concrete

为研究碳化对混凝土毛细吸水性能的影响,对比开展了不同水灰比非碳化与碳化混凝土的毛细吸水试验,并通过压汞试验,定量获取了碳化前后混凝土的孔隙结构参数,通过电镜背散射图像扫描和热重分析定性观察分析了孔隙结构变化特征。结果表明,碳化后混凝土的毛细吸水能力下降20.0%~26.5%,毛细吸水系数下降30.8%~37.8%。相较未碳化混凝土,碳化混凝土的最可几孔径减小13.9~15.1 nm,最高减小幅度达41.8%,且水灰比越高降低越显著。测试观察到碳化导致氢氧化钙转化为碳酸钙,孔径减小。计算表明,碳化混凝土毛细吸水性能使用Lucas-Washburn等人提出的模型依然有效,且选取最可几孔径作为等效孔径时模型效果最佳。

Capillary water absorption tests on noncarbonated and carbonated concrete specimens with different water-cement ratios were conducted to investigate the effects of carbonation on capillary water absorption performance of concrete.Mercury intrusion porosimetry(MIP),backscattered electron microscopy(BSE)and thermogravimetric analysis(TGA)were used to identify the pore structure of concrete before and after carbonation.The results show that the water absorption performance of carbonated concrete greatly decreases,and absorption capacity declines by 20.0%to 26.5%,and the water absorption coefficient falls by 30.8%to 37.8%.Compared with non-carbonated concrete,the most probable pore diameter of the carbonated concrete decreases by 13.9 nm to 15.1 nm,with the highest reduction rate reaching 41.8%.The reduction is more significant for concrete with higher water-cement ratios.The carbonation process is found to result in the transformation of calcium hydroxide into calcium carbonate and a decrease in pore diameter.The calculation results indicate that the model proposed by Lucas-Washburn et al.is still effective for carbonated concrete water absorption,and the selection of the most probable pore diameter as the equivalent pore diameter has the best model performance.