Experimental Study on MgO-Na2CO3 Combined Excitation Recycled Fine-Powder-Slag Cementitious System and Modification

Abstract

The hydration mechanism and strength development of alkaline salt-activated cementitious materials primarily rely on the alkaline activators and mineral admixtures employed. However, the impact of increased Mg2+, Al3+, and Si4+ resulting from the addition of MgO and steel slag (SS) on the hydration mechanism of these systems remains undetermined. This study delves into the hydration mechanism and mechanical properties of a Na2CO3-MgO-activated regenerated micropowder-slag-based cementitious material system. Mechanical properties were assessed by measuring dry shrinkage and compressive strength at various ages, up to 28 days. The reaction mechanism was scrutinized using X-ray diffraction and a thermogravimetric analysis. The main reaction products contributing to the strength development are C-S-H, C-(A)-S-H gel, and hydrotalcite. Other carbonate-containing phases make smaller contributions. The findings reveal that when SS usage is at 10%, it yields higher early strength compared to ordinary samples. Samples incorporating MgO and SS achieved strengths similar to or surpassing those of the control samples. A noteworthy observation is the synergistic excitation effect between sodium carbonate (NC) and MgO, leading to the generation of a significant amount of gelling substances. These substances fill the pores of the structure, resulting in the formation of a dense microstructure. Consequently, the enhanced interaction between NC and MgO contributes to the overall strength development of the cementitious material.