Effect of oyster shell powder addition on hydration of Portland cement-calcium sulfoaluminate cement-blast furnace slag or -metakaolin ternary cement

Supplementary cementitious materials (SCMs) are used to partially replace Portland cement (PC) to reduce the CO₂ footprint of concrete. Although many studies have been conducted regarding the uses of SCMs as well as oyster shell (OS) with PC, there has been limited investigation into the use of OS coupled with SCMs to replace PC. This study investigated the properties of different types of ternary cement containing OS powder. Ternary cement samples consisting of PC-calcium sulfoaluminate (CSA)-blast furnace slag (BFS) or PC-CSA-metakaolin (MK) were prepared and characterized after 28 and 90 days of curing. The addition of OS formed monocarbonate and hemicarbonate instead of monosulfate, stabilizing ettringite in the samples. As a result, the hydration degree was higher in the CSA-containing samples, whereas the extent of OS consumption was greater in the BFS-containing samples. The results provide new insights into the achievement of an optimal mixture when ternary cements are used with OS.