Development of low-carbon ultra-high performance concrete with low cement content: Workability, mechanical properties, and microstructure characterization

Abstract

To reduce the carbon footprint, a tailored low-carbon ultra-high performance concrete (LC-UHPC) with low cement content (30 %) was developed in this study at room temperature, in which the dual roles of cement acted as the binder and the alkaline activator to the slag were exploited. To evaluate its practical applicability, systematic investigations on the workability, mechanical properties, microstructure, hydration products, and environmental impact of the proposed LC-UHPC were conducted. The results showed that the substitution of cement with slag at a large proportion will induce notable modifications in the microstructures and phase compositions of LC-UHPC, leading to the alteration in the macroscopic mechanical responses. Compared with OPC-UHPC, LC-UHPC with only 30 % cement content possessed superior mechanical performance that exhibits comparable ultimate compressive strength and peak strain, while a significant improvement in toughness by 58 %. Moreover, in comparison with the fiber-free specimen, the ultimate compressive strength and toughness of LC-UHPC containing 2.0 % steel fiber content were further improved by 1.12 times and 31.17 times, respectively. At last, upon the analyses using SEM-EDS, XRD, TG, and thermodynamic modeling, it is revealed that 30 % cement content in the binder is sufficient to activate the hydration activity of slag and generate a significant amount of densely packed hydration products at the microstructural level. This capability enables LC-UHPC to achieve a substantial reduction in cement content and carbon emission without compromising the mechanical performance, providing a new routine for the development of LC-UHPC.