Dynamic mechanical properties and microstructure of ultrafine slag powder cement paste utilizing solid waste industrial tailings powder and fly ash

Abstract

Ultrafine slag powder cement paste (USP-CP) is a promising green cementitious material with excellent mechanical properties and environmental benefits. In this study, the effects of elemental molar ratios in raw materials (n(Si)/n(Al) ranged from 1.2 to 1.4 with a gradient of 0.1; n(Fe)/n(Al) ranged from 0.15 to 0.21 with a gradient of 0.03; and n(S)/n(Al) ranged from 0.20 to 0.28 with a gradient of 0.04.) on the workability, mechanical properties, and microstructure of USP-CP were investigated. The main products of USP-CP are α-SiO2, AFt, gypsum, and α-C2SH. The molar ratio of Si/Al has the greatest influence on workability, while the molar ratio of S/Al has the greatest influence on setting time. For mechanical property tests, higher USP content can improve the early compressive strength of USP-CP, while its long-term compressive strength is affected by the anhydrous calcium sulfate (CaSO4) content. Specifically, when the molar ratios of Si/Al, Fe/Al, and S/Al are 1.2, 0.21, and 0.24, respectively, the 28-day dynamic and static compressive strengths of USP-CP specimens reach the maximum values, which are 121.3 MPa (321/s) and 42.0 MPa (10-2/s), respectively. Furthermore, the static compressive strength is comparable to that of pure cement of the same grade.The molar ratio of S/Al has a more significant effect on dynamic compressive strength than static compressive strength. The excessive increase of Na and Si elements in the alkaline activator inhibits the dynamic mechanical enhancement performance of USP-CP. This study provides theoretical and practical reference value for the application of USP in impact-resistant structural materials and static load-bearing materials. It also fully utilizes waste materials to reduce the use of cement and achieves environmental benefits of carbon reduction.