Zhou Yong, Zhang Weiping, Tong Fei, Gu Xianglin
Key Laboratory of Performance Evolution and Control for Engineering Structures of Ministry of Education, Tongji University, 1239 Siping Road, Shanghai 200092, China.
Department of Structural Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China.
Materials (Basel). 2022 Aug 10;15(16):5498. doi: 10.3390/ma15165498.
The moisture transport of axial-compression-damaged mortar and concrete was experimentally and analytically studied in this paper. Five stress levels, i.e., 25%, 40%, 55%, 70%, and 85%, of the corresponding ultimate compressive strengths were selected for mortar and concrete specimens with the water cement ratio (w/c) of 0.5. Porosities and sorptivities of mortar or concrete before and after axial compression were measured and compared. Based on the Lucas-Washburn equation on absorption, the relationship between sorptivity and pore size distribution as well as porosity was established. A damage-representative radius was proposed to simply quantify the variation of pore characteristics of damaged mortar and concrete, and the moisture transport of axial-compression-damaged mortar and concrete could be predicted by summing the contributions to water absorption from the original pore system and the pore-equivalent microcrack system. It is shown that the porosities of mortar and concrete only slightly increase with the damage level, but the sorptivities are sensitive to axial compression damage, i.e., increasing nearly monotonically with the stress level from 0.3326 to 0.3533 mm/min5 for damaged mortar specimens (w/c = 0.5) and from 0.1970 to 0.2226 mm/min for damaged concrete specimens (w/c = 0.5). The increase trend became more apparent for both materials after a threshold of 40-55% of the corresponding ultimate compressive strengths, which is within the service load of structures, indicating that damage should be considered for chloride ions and water transport in concrete in the tidal zone. The predicted moisture diffusivities of damaged mortar and concrete show marginal difference from those of sound materials because the damage-representative radius could be underestimated due to elastic recovery of materials after unloading.
本文通过实验和分析研究了轴向压缩损伤的砂浆和混凝土的水分传输。对于水灰比（w/c）为0.5的砂浆和混凝土试件，选取了相应极限抗压强度的五个应力水平，即25%、40%、55%、70%和85%。测量并比较了轴向压缩前后砂浆或混凝土的孔隙率和吸水率。基于吸收的卢卡斯-沃什伯恩方程，建立了吸水率与孔径分布以及孔隙率之间的关系。提出了损伤代表半径以简单量化损伤砂浆和混凝土孔隙特征的变化，并且通过将原始孔隙系统和孔隙等效微裂纹系统对吸水的贡献相加，可以预测轴向压缩损伤的砂浆和混凝土的水分传输。结果表明，砂浆和混凝土的孔隙率仅随损伤程度略有增加，但吸水率对轴向压缩损伤敏感，即对于损伤的砂浆试件（w/c = 0.5），吸水率从0.3326几乎单调增加到0.3533 mm/min5，对于损伤的混凝土试件（w/c = 0.5），吸水率从0.1970增加到0.2226 mm/min。对于两种材料，在相应极限抗压强度的40 - 55%的阈值之后，增加趋势变得更加明显，该阈值处于结构的使用荷载范围内，这表明在潮汐区的混凝土中，对于氯离子和水分传输应考虑损伤。损伤砂浆和混凝土的预测水分扩散系数与完好材料的预测值略有差异，因为卸载后材料的弹性恢复可能会低估损伤代表半径。
