Study on the compressive strength of mortar and concrete using oyster shell aggregate as a river sand replacement

Abstract

This study evaluates the effect of using crushed oyster shell aggregate as a partial replacement for river sand on the compressive strength of mortar and concrete. Mortar specimens were prepared with river sand replacement rates of 0%, 5%, 10%, and 15%; the concrete mixture used the optimal 15% replacement level. The results indicate that, for mortar, the highest 28-day compressive strength was achieved at a 15% replacement level. For concrete, although the slump decreased by approximately 37.5%, the 28-day compressive strength remained comparable to that of the control mixture. The stability in compressive strength was attributed to the rough surface texture of the oyster shells and the contribution of CaCO₃ to secondary chemical reactions. This research highlights the potential of using oyster shell waste as a sustainable material in construction applications in Vietnam.