Performance of Carbonated Low-lime Calcium Silicate Composites Upon Exposure to Sea Water

This presentation compares the seawater resistance of carbonated mortar specimens made with a nonhydraulic calcium silicate cement and those made with Type I portland cement (OPC). Seawater resistance tests were conducted following procedures adapted from ASTM C1012, with all specimens exposed to artificial seawater prepared according to ASTM D1141-98 under three conditions: (a) room temperature (RT), (b) 60°C, and (c) deionized water (DI) as a reference. The study involved measuring length changes, visually assessing changes in specimen’s appearance, conducting microstructural characterization using scanning electron microscopy (SEM), performing thermogravimetric analysis (TGA), and analyzing the chemical composition of the soak solution using inductively coupled plasma optical emission spectroscopy (ICP-OES). The carbonated calcium silicate (CCS) mortar bars exposed to sea water solution at 60ºC showed only slightly greater expansion than those submerged at room temperature and their ultimate expansion remained below the critical limit (< 0.1% at 18 months [1]). In contrast, the OPC mortar bars surpassed this threshold after approximately 3 months of exposure to sea water at room temperature. The SEM examination did not reveal any significant deterioration of the CCS specimens’ matrix after sea water exposure. However, it indicated noticeable de-calcification of the near surface region of the bars and ingress of magnesium species into the bulk paste. TGA results quantifying calcium carbonate phases aligned with SEM observations, while chemical analysis of the soak solutions further confirmed calcium leaching and magnesium infiltration into the CCS matrix.