基于电阻率法研究混凝土渗透性能演变规律

Permeability evolution of concrete by electrical resistivity measurement

将非接触式电阻率测定仪设计成新型渗透试验装置,研究混凝土渗透性能随龄期的变化规律.导电溶液贯通混凝土试件后电阻率将发生突变,利用试验装置可以直观地得到混凝土渗透完结时间.对水灰质量比为0.60、0.53、0.45,龄期为12h、18h、1d、2d、3d、7d、14d、28d的混凝土分别进行新型渗透试验,分析溶液渗透速率指标的时变规律,结合压汞法孔结构测试结果进行分析讨论.试验结果发现,在3d之前,混凝土的渗透性急剧下降,对混凝土抗渗性不利的孔隙率显著减小;3d之后,混凝土的渗透性先小幅回升,而后缓慢下降,最后趋于稳定.0～3d是混凝土渗透性能较大、氯离子侵蚀的危险期.混凝土的凝胶特性使其在毛细孔连通路径封堵之后仍然保持较稳定的可渗透性.

A new permeability experimental device based on the NC-ERM was designed and applied to study the permeability evolution of concrete. The device showed high sensibility in detecting the percolation threshold of the penetrating solution. Thus, the critical percolating time can be easily obtained. The permeation rate of concretes with various water cement ratios was tested at the ages of 12 h, 18 h, 1 d, 2 d, 3 d, 7 d, 14 d, and 28 d, with their porosity and pore size distribution measured by MIP simultaneously. Results showed that the permeation rate of concrete slumped in the first three days, corresponding well with the notably decreasing of harmful porosity during this period~ the permeability of concrete would recover slightly after 3 d, then declined in a slow rate, and leveled off finally. According to the experimental results, 0-3 d can be marked and defined as the vulnerable period for chloride ion ingression in view of the significantly greater permeability during this stage. The fact that concrete remained steadily permeable after depercolation of capillary porosity revealed the intriguing connected property of gel pores inside concrete.