The Effects Of GGBS On Chloride Condensation In Pore Solution Of Cement-based Materials

The deterioration of reinforced concrete structure caused by reinforcement corrosion is a worldwide concrete durability problem, in which chloride-related corrosion accounts for most of them. Chloride ions may derive from aggregates/mixing water (internal chloride), or penetrate into steel surface during exposure to chloride-bearing environments (intruded chloride). When a sufficient amount of free chloride ions reach the steel bar, a localized breakdown of the passive film occurs and corrosion is then initiated. The corrosion development can be very fast, especially for marine structure. Chloride ions may either be chemically bound in compounds like Friedel’s salt, be physically adsorbed onto, for instance, the amorphous calcium silicate hydrate (C-S-H) gel, or existed in free state in pore solution of cement pastes. However the free state chloride ions in pore solutions are mainly responsible for the corrosion of reinforcement steel. Many researchers found that the concentration of free chloride ions in pore solution of cement pastes measured by pore solution expression was higher than that in the exposed solution, which was called as "condensation".Granulated blast-furnace slag (GGBS) is a kind of siliceous materials and widely used in cement and concrete. The use of slag can decrease the cost and improve the mechanical properties and durability of concrete. This paper’s achievements mainly focused on the effects of slag on chloride condensation in pore solution and micro structure and electrochemical performance of cement-based materials:According to measuring the chloride concentration in pore solution of samples with different content of slag by pore solution expression, the effects of slag replacement on chloride condensation index in pore solution of cement-based materials were studied. It was found that the addition of slag (0%,20%,40%,60%) decreased the chloride condensation index in pore solution when soaking time was short. However, with the increase of soaking time, the growth rate of condensation index of samples with slag was higher than that of samples without slag obviously. After soaking in chloride solution365d, the condensation index of slag samples was higher than that of reference group.By comparing the development of chloride condensation index of cement-based materials after different curing and soaking time, the influences of curing and soaking time on chloride condensation, before and after the addition of slag, were studied. The experimental results showed that chloride condensation index increased with soaking time firstly, then became stable; in some groups, condensation indices even had a slight drop with soaking time after several days. When the curing time of samples increased, the variation tendency of condensation index with soaking time may be different and longer curing time was needed to for chloride condensation index of in pore solution to get the maximum value. Meanwhile, when replace part of cement by slag, the time chloride condensation index reaches the maximum point needed was postponed.It was investigated of the influences of chloride concentration of mixing water and slag content on zeta potential of freshly mixed cement paste. As chloride concentration of mixing water increasing, the zeta potential of freshly mixed cement paste gradually increased. With the increase of slag content, zeta potential of freshly mixed cement pastes gradually increased.After bath curing28d, the zeta potential of hardened cement paste soaking in different concentration of chloride solution56and91d gradually decreased with the increase of chloride concentration. When soaking in lower concentration of solution, slag had negative effects on zeta potential. However, when concentration of soaking solution increased, the influences of slag on zeta potential of samples were weakened. Zeta potential and chloride condensation index in pore solution showed linear relationship.