Effects of dosage and reactivity of modified dolomite dust waste on mechanical properties and shrink-resist of mortar

Abstract

Dolomite dust waste (DDW) has the potential to be used as an expansive agent for mortar due to its richness in magnesium and calcium. This paper reports the possibility of developing low-cost expansive agent for mortar using DDW through various activation methods. The changes in the physicochemical properties of the activated DDW and the shrinkage resistance, flexural strength, and compressive strength of the composite mortar prepared by partially replacing cement were systematically investigated. The hydration products and microstructure of DDW-composite mortar were investigated by XRD and SEM-EDS techniques. This study confirmed the feasibility of activated DDW as mortar expansion agents and the necessity of activation treatment for the resourceful use of DDW. The results showed that the activation treatment enhanced the activity of DDW, and the higher hydration reactivity significantly improved the shrinkage resistance and mechanical properties of composite mortar compared to raw DDW. The addition of 10% C800 DDW (thermal at 800 °C) showed a full-age compensatory effect on the volume shrinkage of the mortar. Substituting cement partially with 10% C900 DDW (thermal at 900 °C), the volume expansion rate of composite mortar after 28 d of standard curing exhibited 24.49% higher than normal, and its compressive strength (40.1 MPa) at 60 d exceeded 6.40% than normal mortar (37.7 MPa). The drying shrinkage of G30-10 (mechanically activated) and A0.1-10 (chemically activated) at 60 d resulted in 6.23% and 5.19% lower than normal mortar, respectively. Microanalysis revealed that the addition of DDW promoted the generation of C-M-S-H gels. The findings are instructive for the preparation of green and low-cost mortar expanders using DDW.