Effect of water quenched silicomanganese slag as fine aggregate on mechanical properties and microstructure characteristics of solid waste-based mortar and concrete

Abstract

Research on water quenched silicomanganese slag (WQSMS) has primarily focused on grinding it into micro-powder to be used as auxiliary cementitious materials or to synthesize alkali-activated cementitious materials. However, there is a lack of research on utilizing WQSMS as fine aggregates instead of natural aggregates. Although its properties are similar to granulated blast furnace slag (GBFS), most studies investigating the use of GBFS as fine aggregates have mainly focused on mechanical properties rather than microstructure analyses. Meanwhile, to make full use of industrial solid waste, reduce CO2 emissions, and save energy consumption, solid waste cementitious material based on steel slag (SS), desulphurized gypsum (DG), and GBFS, as well as WQSMS as fine aggregate to replace ISO standard sand and washed-out sand (WOS) in various proportions(0%, 25%, 50%, 75%, and 100%) to prepare mortar and concrete, respectively. Analyses of workability, mechanical properties, and microstructure were carried out, and the improvement of mechanical properties of WQSMS was analyzed by SEM-EDS, SEM-BSE, and the microhardness test. The results show that with the increase of WQSMS, the workability of mortar and concrete decreased, while the mechanical strength increased first and then decreased. The mechanical strengths of them reached the peak when the WQSMS addition reached 50%. The flexural and compressive strengths of the mortar increased by 40% and 9.7%, respectively, while the tensile splitting strength and compressive strength of the concrete increased by 11.9% and 3.4%, respectively. The microstructure of the interfacial transition zone(ITZ) was greatly enhanced by WQSMS, which decreased the porosity by 10.49%, decreased the thickness by 27.27%, and increased the microhardness by 11.0%. However, when the content surpasses 50%, the mechanical strength of mortar and concrete declined due to the loose porosity and poor mechanical strength of WQSMS, and there was insufficient cementitious material to fill these holes. Nonetheless, with 100% content, the mortar maintained its high-performance status, with a flexural strength of 8.0 MPa and a compressive strength of 47.9 MPa, and the concrete still fulfilled the specifications of regular concrete C40. Both the fine aggregate and the cementitious material were composed of solid waste, showing potential environmental benefits and interesting green products for future studies.