混凝土收缩裂缝几何特征及其对氯离子渗透的影响

Geometrical characteristic of concrete shrinkage crack and its effect on chloride ion permeability

摘要:

为准确表达收缩裂缝的几何特征并分析其对混凝土中氯离子渗透规律的影响，通过对干缩开裂混凝土板进行取样，观测和统计分析了收缩裂缝的几何特征，并采用ASTM法研究了裂缝对混凝土中氯离子渗透的影响规律.结果表明：混凝土收缩裂缝存在显著的深宽比特征，其均值约为44.31，开裂角度均值约为2.6度；对比不同的裂缝宽度表征参量如最大宽度、最小宽度、平均宽度以及比表面积等与ASTM法6 h电通量关系后发现，最大宽度是表征裂缝对开裂混凝土渗透性影响的适宜参量；开裂混凝土中氯离子的渗透系数与裂缝最大宽度成正线性关系，并且当收缩裂缝宽度小于0.18 mm时，裂缝对渗透系数影响可以忽略.收缩裂缝的宽度变化会显著影响混凝土的抗渗性能，实际工程中应该根据混凝土保护层厚度来确定其容许的最大裂缝宽度.

Abstract:

To accurately describe the geometrical characteristic of shrinkage crack and determine the influence on chloride ion permeability in concrete, by taking samples of shrinkage cracking concrete slab and observing the morphology, the characteristics of shrinkage cracks was statistically analyzed, and the effect law of cracks on chloride ion permeability, tested with ASTM method, was studied. The experimental result shows that the depth and width of shrinkage cracks in concrete are obviously related, which the depth-to-width ratio is 44.31, and the crack tip angle is 2.6 by average. Based on the comparative analysis of the relationship between width parameters e.g. maximum width, minimum width, average width, specific surface area etc. and 6 h electric flux, the maximum width is a suitable parameter for describing the effect of shrinkage crack on permeability of concrete. The permeability coefficient of cracked concrete has a positive linear relation with cracks' maximum width, and the impact of cracks on the permeability coefficient can be neglected when the width is less than 0.18 mm. The width changes of shrinkage cracks significantly affect the impermeability of the concrete, in practical project the allowed maximum width should be determined in accordance with the thickness of concrete cover.