The influence and modification mechanism of magnesium oxide with varying activities on the performance of sodium sulfate activated slag

Abstract

Sodium sulfate activated slag (SSAS) is a low-carbon cementitious material. The low alkalinity of Na₂SO₄ results in an extremely low hydration rate, leading to reduced early strength. It is found that adding magnesium oxide (MgO) can effectively improve the mechanical properties of SSAS. The main preparation method of magnesium oxide is calcining magnesite. However, the calcination temperature in the preparation of MgO greatly affects its activity. Based on this, this article uses different active MgO as modifiers in the preparation of SSAS. The results indicate that the addition of MgO accelerates the hydration reaction of SSAS, effectively enhancing its early compressive strength. The MgO with high activity accelerates the hydration of SSAS, it leads to the formation of hydrotalcite phase, significantly affecting the later-stage strength. The lower active MgO mainly forms Mg-doped Calcium Alumino Silicate Hydrate (CASH) gel in SSAS, which improves the hydration degree of slag and the long-term strength of SSAS compared with higher active MgO modified SSAS. Incorporating 3 % of active MgO calcined at 700 °C into SSAS, the compressive strengths at 28 and 90 days reached 52.5 and 75 MPa.