The Durability Of Reactive Powder Cincrete Under Coupling Effect Of Seawater And Freeze-thaw

ABSTRACT:Marine concrete structures in coastal areas is suffering the long-term coupling effects of marine corrosion and freeze-thaw cycles, which may result in damage inside, carrying capacity falling and using function degradation. In harsh environment, reactive powder concrete structures with remarkable mechanical properties and excellent durability will have practical significance. In this paper, reactive powder concrete with2%steel fibers was studied. Silica fume was replaced by fly ash and mineral powder.Mass loss, strength loss and chloride ion content in different depthswere measured, separately. Meanwhile, microstructure morphology before and after freeze-thaw cycle was studied by SEM. Based on these results, durability of reactive powder concrete underthe coupling impact of sea water corrosion and freeze-thawcycles was analyzed. The main work and conclusion are as follows:Durability of reactive powder concrete in the coupling impact of marine corrosion and freeze-thaw cycles is far superior to C50concrete. As the mass of reactive powder concrete increased with the coupling impact of sea water corrosion and freeze-thaw cycles, strength loss rather than mass loss is recommended as the evaluation index under Sea water wet/dry cycles.Initial strength of reactive powder concrete will deceased with the incorporation of fly ash or mineral powder, but durability of reactive powder concrete will be improved under the coupling impact of sea water corrosion and freeze-thaw cycles.The coupling impact of sea water corrosion and freeze-thaw cycleshave a great influence on microstructure morphology of concrete SEM results showed that:after the coupling impact of sea water corrosion and freeze-thaw cycles, CH in C50decreased and AFt increased, meanwhile, corrosion products of magnesium with low cohesiveness generate. AFt crystals and F salt exist in the microstructure of reactive powder concrete, but no corrosion product of magnesium was observed.Fly ash and mineral power has a great influence on the freedom chloride ion penetration of reactive powder concrete. Chloride ion diffusion coefficient D was fitted based on Fick’s second law, considering the time dependence of D, it is concluded that, chloride ion diffusion coefficient D has an exponential relationship with time. Prediction model of structural life under the coupling impact of sea water corrosion and freeze-thaw cycles was established. When freeze-thaw cycles damage is the main influencing factors, concrete life of C50is less than30years and reactive powder concrete is more than80years. Monte Carlo numerical simulation was carried on the service life prediction when chloride ion erosion damage is considered as the main influencing factors, the service life which got from the stochastic simulation has a better obedience to the two parameters Weibull distribution, the results indicate that fly ash and mineral power can improve the service life, but content changes of these two admixture have different influence on the life improvement, while increasing the thickness of the protective layer is an important measure to improve concrete service life.