Effect of curing environments on strength, porosity and chloride ingress resistance of blast furnace slag cement concretes: A construction site study

► Seawater-cured concretes showed a higher early strength but a lower ultimate strength as compared with air-cured concretes. ► The chloride diffusion coefficient is time dependent, depending on concrete types and curing conditions. ► HBFC concretes showed better resistance to Cl− penetration than OPC concretes. Durability of concrete structures in marine environments has become a major concern to the scientific community over the past several decades. Many publications have reported the excellent performance of concrete containing mineral admixtures (MAs), such as ground granulated blast furnace slag (GGBS) and pulverized fuel ash (PFA), in coastal marine environments. However, the rate of hydration or pozzolanic activity of MAs in the concrete is slow. As a result, the resistance offered to the penetration of chloride ions also increases slowly with time. This paper reports the results of an experimental study conducted to evaluate the effect of curing conditions on the strength, porosity, and chloride ingress characteristics of concretes made with high slag blast furnace cement (HBFC) and ordinary Portland cement (OPC). A total of six different concrete mixtures were cast and tested. The experimental variables included water-to-binder ratio (W/B) ratios, curing environments, and curing durations. W/B ratios used were 0.33, 0.34, and 0.36. Two types of curing conditions are investigated: seawater immersion and marine atmospheric exposure during curing at 4, 7, 28, 90, 180, and 360day intervals. The results indicated that the curing condition had pronounced effects on the related properties. Seawater-cured specimens showed a slightly higher early strength but a lower ultimate strength as compared with air-cured specimens. The HBFC concretes had lower MIP porosity than the corresponding OPC concretes with the same design strength. The chloride diffusion coefficient of the HBFC concretes was much lower than that of the corresponding OPC concretes. Therefore, it may be concluded that the HBFC concretes showed considerably better resistance to chlorides ion penetration than the OPC concretes.