体积分数对梯度结构混凝土扩散系数影响研究

通过室内氯离子侵蚀加速试验及氯离子分布测试，结合Fick第2定理拟合出梯度结构混凝土（GSC）的氯离子浓度扩散系数，以研究面层体积分数、加速试验龄期对扩散系数的影响；采用压汞技术测试面层材料与结构层材料的孔结构参数，分析氯离子扩散系数与孔结构之间的关系。结果表明：GSC体系的氯离子扩散系数随面层体积分数的增加而下降，并逐渐趋于平缓；GSC体系氯离子扩散系数则随加速试验龄期的延长而减小，最后也趋于稳定；与面层体积分数V=0试件相比，其它GSC试件具有更大的时间衰减系数值，说明其抵抗氯离子侵蚀的能力更好。最后根据相似性理论，建立了考虑面层体积分数变化的GSC氯离子扩散系数时变模型，分析显示，与结构层材料相比，面层材料具有较低的孔隙率及最可几孔径，使得孔的曲折性越大、连通性越低，因而面层材料具有更低的扩散系数。

Effect of volume fraction on chloride ion diffusion coefficient of grade structure concrete

Combined with the Fick’s Second Law the chloride ion diffusion coefficients of gradient structure concrete (GSC) were calculated for studying the effect of surface-layer volume fractions and accelerating period, by conducting the Chloride ion migration rapid test and determining the distribution of chloride ions. At the same time, the pore structure parameters were obtained by mercury intrusion porosimetry to study the relationship between chloride ion diffusion coefficient and pore structure parameters. The results show that chloride ion diffusion coefficient of the GSC is reduced with the increase of volume fractions of the surface-layer, and reaches a steady state finally; the chloride ion diffusion coefficient in GSC gradually decreases along with the increase of accelerating period, and also reaches a steady state finally. Compared with the specimens with 0 % volume fractions of surface-layer, the others with a higher volume fraction have a greater time decay coefficient of diffusion coefficient. At last, the relationship of chloride ion diffusion coefficient, surface-layer volume fraction and accelerated period were put forward based on the similitude theory. Furthermore, compared with the structural layer material, the surface-layer material has small pore spaces and low pore connectivity caused by a low porosity and small pore size, and then, it has a low choloride diffusirity.