Effects of Various Ions in Seawater on Chloride Ion Behavior in Mortar Using Ground Granulated Blast-Furnace Slag

Abstract

Concrete using ground granulated blast-furnace slag (GGBS) is said to have a greater effect on suppressing chloride penetration than concrete using only ordinary Portland cement (OPC). However, the chloride behavior and change of the pore structures in concrete using GGBS in the presence of various ions such as magnesium ions or sulfate ions in seawater have not been well investigated. This study aims to clarify the effects of various ions in seawater on chloride behavior in the mortar using GGBS. Two types of mortar were prepared with a water to binder ratio of 0.50. Only OPC and a mix of OPC and GGBS with a replacement ratio of 50% were used as binders. Crushed sand and tap water were used as fine aggregate and mixing water, respectively. After water curing of specimens at 20 ℃ for 28 days, an immersion test was conducted with four types of solutions for 28 or 56 days. The parameters for investigations in the immersion test were the total chloride content, the amount of Friedel’s salt measured with powder X-ray diffraction analysis, the porosity, and the pore size distribution. The results showed that the effect of various ions in seawater on the penetration of chloride ions was smaller for the mortar blended with GGBS than for the mortar using only OPC. In the chloride binding ability tests, regardless of the presence of various ions, the mortar blended with GGBS produced more Friedel’s salt than the mortar using only OPC. In addition, it was confirmed that the amount of Friedel’s salt in mortars using only OPC was reduced due to the influence of sulfate ions. Also, for the mortar using only OPC, the filling of hydrates into pores was observed after immersion in the solution with various ions, but only slightly for the mortar blended with GGBS.