Renovate RC structures with newly developed mortar, considering chloride binding and inverse diffusion phenomenon

Abstract

In Japan, many RC bridges and infrastructure along the coast line have been deteriorated due to ingression of chloride ions. The objective of this study is to develop high durable repair mortar with ion-exchange resin as an admixture to enhance life span by eliminating chloride ion from existing RC structures. And as a part of the objective, this paper discusses the effectiveness of typical commercially available anion exchange resin in preventing chloride induced corrosion within concrete by using its excellent ion-exchange and binding ability, though its real effectiveness with concrete is not still clearly identified. A number of immersion tests were conducted using small mortar specimens mixed with ion-exchange resin and high-early strength Portland and blast furnace slag cements. The volume contents of ion-exchange resin were 1.0, 2.0 and 3.0%. The specimens were immersed into 10% sodium chloride (NaCl) solution for one day and then exposed in drying condition for 6 days. These exposure procedures were repeated for 28, 56 and 84 days. Then total and free chloride contents at various depths in all tested specimens were measured in each time period. The inverse diffusion test was conducted with mortar specimens casted with high-early strength Portland cement maintaining 10% chloride ion only up to 8 cm while top 2 cm casting with 3% ion exchange resin mixed mortar. Total chloride was measured in four consecutive depths after 28 and 140 days. Test results showed the significant enhancement of chloride binding in newly developed mortar with ion-exchange resin compared to normal mortar. The linear relationship between free and bound chloride was also noticed in all specimens, irrespective to the cement types. The absorption of chloride by ion-exchange resin was further increased with increment of chloride concentration in order to achieve its optimum capacity. At last, the effective adsorption of chloride from matured concrete by newly developed repair mortar, using outward movement (inverse diffusion), was clearly observed.