干湿交替下开裂混凝土中水分传输的细观数值分析

对于海洋浪溅区或潮汐区的混凝土结构,水分主要以气相和液相两种形式存在于混凝土内部孔隙结构中。基于混凝土毛细吸水的非饱和流体理论,建立了干湿交替下开裂混凝土中水分传输的一维非线性方程。考虑水分在干燥与湿润阶段传输的滞后性,分别建立了干燥和湿润两阶段单条裂缝处水分的传输速度模型。在细观层次上,将混凝土看作由粗骨料、砂浆、界面过渡区(ITZ)以及裂缝所构成的四相复合材料,利用含单条裂缝的二维格构网络模型,开展了干湿交替下开裂混凝土中水分传输的细观数值仿真分析。通过与已有文献中的试验数据对比,验证了所建立的干湿交替下开裂混凝土中水分传输模型的正确性。利用以上数值模型,进而分析了干湿循环机制(干湿循环时间比、循环次数)以及裂缝宽度对水分分布的影响规律。结果表明:对于给定裂缝宽度,干湿循环时间比和循环次数决定着裂缝处和垂直裂缝方向的水分含量分布;当裂缝宽度介于0.05~0.3 mm时,裂缝处和垂直裂缝方向的水分含量随着裂缝宽度的增大而减少。

Mesoscale numerical analysis on moisture transport in cracked concrete subjected to drying-wetting cycles

For the splash and tidal zone of marine concrete structures, there are two main existing forms of the moisture involving both gas and liquid phases, which exist within the pores of concrete. Based on the unsaturated flow theory of capillary absorption by concrete, the one-dimensional nonlinear differential equation for moisture transport in cracked concrete subjected to drying-wetting cycles is developed. With consideration of the transport hysteresis during drying and wetting period,the models accounting for moisture transport coefficients during this process in an individual crack are respectively proposed. In terms of the mesoscale methodology that the cracked concrete is treated as a four-phase composite material consisting of coarse aggregate, mortar, interfacial transition zone (ITZ) and crack, the two-dimensional lattice network model with a single crack is adopted to conduct the numerical simulation of moisture transport in cracked concrete subjected to drying-wetting cycles. Compared with the existing experimental results, the proposed models are utilized to verify the transport theory of drying-wetting cycle in cracked concrete. Furthermore, by means of the above numerical models, the effect of drying-wetting cyclic mechanism (i.e., the ratio of drying-wetting time and cyclic times) and crack width on water distribution of cracked concrete are numerically carried out and reasonably analyzed. The numerical results suggest that water content distribution profiles within the crack and in the location perpendicular to crack direction depend on the ratio of drying-wetting time and cycles for the constant crack width. For the crack width ranging between 0.05-0.3mm, water content within the crack and perpendicular to crack direction decreases with the increase of crack width.