In order to study the durability behavior of marine reinforced concrete structure suffering from chloride attack,the structural service life is assumed to be divided into three critical stages,which can be characterized by steel corrosion and cover cracking.For each stage,a calculated model used to predict the lifetime is developed.Based on the definition of durability limit state,a probabilistic lifetime model and its time-dependent reliability analytical method are proposed considering the random natures of influencing factors.Then,the probabilistic lifetime prediction models are applied to a bridge pier located in the Hangzhou Bay with Monte Carlo simulation.It is found that the time to corrosion initiation t0 follows a lognormal distribution,while that the time from corrosion initiation to cover cracking t1 and the time for crack to develop from hairline crack to a limit crack width t2 can be described by Weibull distributions.With the permitted failure probability of 5.0%,it is also observed that the structural durability lifetime mainly depends on the durability life t0 and that the percentage of participation of the life t0 to the total service life grows from 61.5% to 83.6% when the cover thickness increases from 40 mm to 80 mm.Therefore,for any part of the marine RC bridge,the lifetime predictions and maintenance efforts should also be directed toward controlling the stage of corrosion initiation induced by chloride ion.
In order to examine the effect of load-induced transverse cracks on the chloride penetration in flexural concrete beams, two different concretes, Portland cement concrete(PCC) and fly ash concrete(FAC), were tested with various crack widths. Total 14 reinforced concrete(RC) beams, ten of which were self-anchored in a three-point bending mode, were immersed into a 5% NaCl solution with the condition of dry-wet cycles. Then, the free chloride ion contents were determined by rapid chloride testing(RCT) method. Based on the proposed analytical models of chloride penetration in sound and cracked concrete subjected to dry-wet cycles, the apparent chloride diffusion coefficient and chloride diffusivity of concrete were discussed. It can be found that the performance of chloride diffusivity in both concretes will be improved with the increase of crack width, and that the influence of convection action will also be augmented. Based on the two samples obtained in sound concrete after 15 and 30 cycles, the time-exponent, m, for chloride diffusion coefficient was determined to be 0.58, 0.42, 0.62 and 0.77 for PCC1, PCC2, FAC1 and FAC2 specimens, respectively. Finally, two influencing factors of fly ash content and crack width on chloride diffusivity were obtained by regression analysis of test data, and it can be seen that factors kf and kw can be expressed with quadratic polynomial functions of fly ash content, f, and crack width, w, respectively.
