Preparation and properties of alkali and sulfate coactivated ternary cementitious matrix and its application in high-strength cold bonded lightweight aggregates

Abstract

In this study, a novel alkali and sulfate coactivated ternary cementitious matrix (ASAM) was produced using sulfur-aluminum low-carbon cementitious material (LCM), red mud (RM), and blast furnace slag (SG). The mechanical properties, mineral components, hydration characteristics, microstructures and pore size distributions of ASAM were systematically investigated, and the results indicated that the compressive strength of ASAM was apparently higher than that of the LCM–RM binary matrix. Based on the alkali and sulfate coactivation effect, the ettringite formed by sulfate-activated SG and the C(N)–A–S–H generated by alkali-activated SG, as well as the U-phase products were the main mineral components of ASAM, which jointly contributed to the compressive strength of ASAM. The maximum compressive strength of ASAM was 34.5 MPa at a curing age of 56 d, when the mass ratio of SCM:RM:SG was 3:5:2. Furthermore, the leaching behaviors and solidification mechanism of Na+ in ASAM were analyzed. The results illustrated that the Na+ could be effectively solidified by C(N)–A–S–H and U-phase, through physical encapsulation and chemical adsorption. The maximum solidification ratio of Na+ was up to 44.3%, when the mass ratio of LCM:RM:SG was 3:5:2. Finally, the optimal ASAM was employed to prepare cold bonded lightweight aggregates (CBLA), and high-strength CBLA with a crushing strength of 11.6 MPa, loose bulk density of 1180 kg/m3 and water absorption of 5% were obtained. Hence, this work provides a new approach for the preparation of a novel ASAM using 100% solid waste, and also verified its potential application in CBLA production.