Chloride ingress and binding of coral waste filler-coral waste sand marine mortar incorporating metakaolin

Abstract

The present study investigates the chloride ingress and binding behaviors of coral waste filler-coral waste sand marine mortar and the influence imposed by metakaolin (MK) addition. The mortars were cured for 4 months and followed by exposing to 0.5 M sodium chloride solution for 45 days. Thereafter, the chloride profiles of mortars were determined by titration method and the phase assemblies of mortars at different depths were determined by X-ray diffraction and thermogravimetry. The results show that coral waste mortars demonstrate dramatically lower ability to resist chloride ingress than normal mortar due to the loose structure of coral waste mortar. Due to the combination of pozzolanic reaction, formation of additional carboaluminate and improved chloride binding capacity by MK addition, chloride penetration is significantly restrained. Carboaluminate can decompose to possible solid solution between hemicarboaluminate (C4Ac0.5H12) and Friedel’s salt (C4ACl2H10) in a low chloride concentration, while it directly converts to Friedel’s salt in a high chloride concentration. Since the large amount of coral waste in system restrains the formation of monosulfoaluminate (C4AsH12), the Kuzel’s salt (C4As0.5ClH12), as an intermediate phase from monosulfoaluminate to Friedel’s salt, is not formed even in low chloride concentration. Owing to the synergistic effects of carbonation and the leaching of calcium ions, the outmost layers of the mortars bind less chloride compared to their neighboring layers.