Zhang Dongsheng, Wang Yafan, Ma Mingxiao, Guo Xiangjun, Zhao Shuangquan, Zhang Shuxiang, Yang Qiuning
School of Civil and Hydraulic Engineering, Ningxia University, Yinchuan 750021, China.
Research Group RecyCon, Department of Civil Engineering, KU Leuven, Campus Bruges, 8200 Bruges, Belgium.
Materials (Basel). 2022 Feb 18;15(4):1550. doi: 10.3390/ma15041550.
Concrete is prepared by substituting an equal volume of fly ash for fine aggregate, and the effect of substitution rate on its carbonation resistance is studied. Using a rapid carbonation test, the distribution law of the internal pH value of concrete with fly ash as fine aggregate (CFA) along the carbonation depth under different substitution rates (10%, 20%, 30%, and 40%) after carbonation is studied and compared with the test results of phenolphthalein solution. Then, to further clarify the damage mechanism of fly ash replacing fine aggregate on concrete carbonation, the changes in the pore structure and micromorphology of CFA after carbonation are studied by means of mercury intrusion pressure and electron microscope scanning tests. The results indicate that the carbonation depth of CFA increases gradually with increasing carbonation time. In particular, in the later stage of carbonation, the carbonation rate of concrete decreases significantly with an increase in the substitution rate. The carbonation depth X of CFA measured by phenolphthalein solution is approximately 0.24-0.39 times of the complete noncarbonation depth measured by the pH method. The pH value test is a reliable test method that can reveal the carbonation mechanism of CFA. Carbonation can significantly reduce the proportion of more harmful holes in concrete with a large amount of fly ash, but it can also increase the proportion of less harmful and harmful holes. In general, the pore size distribution and micromorphology of concrete can be improved by replacing fine aggregates with fly ash.
通过等量体积的粉煤灰替代细集料来制备混凝土，并研究替代率对其抗碳化性能的影响。采用快速碳化试验，研究了以粉煤灰为细集料的混凝土（CFA）在不同替代率（10%、20%、30%和40%）碳化后内部pH值沿碳化深度的分布规律，并与酚酞溶液的试验结果进行了比较。然后，为进一步阐明粉煤灰替代细集料对混凝土碳化的损伤机理，通过压汞试验和电子显微镜扫描试验研究了CFA碳化后的孔结构和微观形貌变化。结果表明，CFA的碳化深度随碳化时间的增加而逐渐增大。特别是在碳化后期，混凝土的碳化速率随替代率的增加而显著降低。用酚酞溶液测得的CFA碳化深度X约为用pH值法测得的完全未碳化深度的0.24 - 0.39倍。pH值测试是一种可靠的测试方法，能够揭示CFA的碳化机理。碳化可显著降低大量粉煤灰混凝土中较多有害孔的比例，但也会增加较少有害孔和有害孔的比例。总体而言，用粉煤灰替代细集料可改善混凝土的孔径分布和微观形貌。
