损伤混凝土毛细吸水性能试验研究和水分分布预测分析

混凝土内部微裂缝的产生或贯通,加快了水及侵蚀性介质侵入混凝土内部的速度,是引起混凝土性能劣化和结构耐久性不足的重要原因.开展了混凝土试件的轴心受拉、受压试验,采用持载、反复加载方式,对混凝土试块分别加载至极限荷载的70%、80%、90%后卸载.为了实现吸水过程的连续性,利用改进后的吸水装置开展损伤混凝土的累积吸水量测试试验.与未加载试件的吸水结果对比分析表明,荷载水平是影响混凝土毛细吸水速率的重要因素.对不同荷载水平的累积吸水曲线i-t1/2,采用线性拟合方法可得到混凝土的初始吸水率(S1)和后期吸水率(S2).根据吸水率试验结果,结合非饱和毛细吸水理论模型,引入Bolzmann变量,建立了损伤混凝土内相对含水量分布的预测分析方法,为开展混凝土内有害介质(如氯离子或者硫酸根离子等)的传输分析提供了工具.

Experimental study of capillary water absorption in damage concrete and prediction of water content distribution

It is generally recognized that the formation or interconnection of microcracks within concrete is the important cause for deterioration of the concrete performance and poor durability of structure, which speeds up water and aggressive agents to transport into concrete. The experiments of concrete specimens are firstly carried out under axial tensile and compressive loading and subjected to either sustained or repeated loads with three load levels of 70%, 80% and 90% of the ultimate strength. After unloading, in order to realize the continuity of the suction process, the samples are then moved to an improved gravimetrical device for cumulative water measurement. Compared with the results of unloading specimen, it is indicated that the loading-induced damage (microcracks) is the key factor to influence the capillary water absorption of concrete. By linearly fitting the two portions of the cumulative water absorption curve i - t 1/2 with different load levels, the initial and the second sorptivities S 1 and S 2 of concrete after subjected to different load levels are obtained. In terms of the test results of sorptivity, and combined with the theoretical model of capillary absorption of unsaturated water, the prediction method for relative water content distribution in concrete is proposed by means of introducing the Bolzmann variables, which is foreseen to facilitate the transport analysis of aggressive agents (such as chloride or sulfate ions) through concrete.