Synergistic Effects of Fly Ash and Oyster Shell Powder in Ternary Low-Carbon Cementitious Materials: Macro–Micro Experimental Studies and Life Cycle Evaluation

As a result of global urbanization, the construction industry has mainly emitted CO2 from ordinary Portland cement (OPC). Partially replacing cement with supplementary cementitious materials is a widely studied approach for reducing emissions. While previous studies have explored binary systems such as fly ash (FA)–cement and oyster shell powder (OSP)–cement, limited research has been conducted on ternary systems that combine FA, OSP, and cement. The differences in macro- and microsustainability performance between binary and ternary mixes remain unclear and require further exploration. To address this gap, this study verified the feasibility of using FA and OSP for partially replacing OPC in concrete. The environmental and mechanical performances of these materials were evaluated through macro- and microlevel experiments, as well as through life cycle assessments (LCAs). The results show that there is a synergistic effect in the FA-OSP-OPC ternary mixed cement (28-day strength: 40.44 MPa), which promotes the hydration of the three-component cement. Compared with the FA-OPC (28-day strength: 39.38 MPa) and OSP-OPC (28-day strength: 26.85 MPa) two-component cements, the strength is increased by 2.7% and 50.61%, respectively. At the same time, the resistivity of the three-component cement is also increased. The resistivity is increased by 19.27% ((50.69 − 42.5)/42.5) compared with the pure cement group. On this basis, the three-component cement also reduces carbon emissions by about 15% ((13.09 − 11.19)/13.09). FA-OSP-OPC ternary mixed cement improves strength and durability, reduces carbon emissions, and is an excellent new ternary mixed gel material that can be sustainably utilized.