Evaluation of the eco-friendly crushed waste oyster shell mortars containing supplementary cementitious materials

Abstract

The ever-increasing demand for natural aggregates in the concrete industry has resulted in substantial consumption of a dwindling supply of natural resources, leading to irreversible environmental damage. One solution to solve this problem is through the use of waste materials as alternatives to natural aggregates. In this study, 30% of natural river sand was replaced by crushed waste oyster shells (WOS). Full cement (control), different proportions (20%, 30%, and 40%) of cement replaced by fly ash (FA), and ground granulated blast-furnace slag (GGBS) were used. The hardened densities, mechanical properties, durability-related properties, microstructures, and sustainability of the WOS–Control, WOS–FA, and WOS–GGBS mortars were investigated. The test results indicated that, because of the low pozzolanic reaction activity, the inclusion of FA and GGBS decreased the hardened densities and mechanical properties of early-age crushed WOS mortars. Scanning electron microscopy with energy dispersive X-ray spectroscopy analyses indicated low hydration degrees of FA and GGBS in the early stage. These reductions decreased with increasing curing time. The secondary hydration products generated by supplementary cementitious materials considerably filled and compacted the microstructures of the WOS mortars in the later stage. The crushed WOS mortars with FA and GGBS had approximately identical hardened densities and mechanical behaviors to the control mortar. The chloride ion penetration of these blended samples decreased rapidly. The use of these waste materials would offset the demand for natural fine aggregate and cement, decreasing both CO2 emissions and associated costs. A greener mortar with adequate engineering properties could be produced by incorporating FA and GGBS and crushed WOS in limited quantities.