Effect of nano-MgO on working, mechanical properties and microstructure of PC clinker-CSA-C$ ternary system cement

A lot of research focuses on the effect of magnesium oxide (MgO) on the shrinkage of cement-based materials, but there is a lack of systematic research on the mechanism of nano-MgO on the working performance, mechanical properties and microstructure of cement-based materials. In this study, an economical and efficient surface modification method was used to modify nano-MgO, and the effects of different dosage of modified nano-MgO (NMgO) on the setting time and strength of portland cement clinker (PC clinker)- sulphoaluminate cement (CSA)- anhydrite (C$) ternary system were explored. At the same time, isothermal calorimetry (TAM), X-ray diffraction (XRD), thermogravimetry (TG), low-field nuclear magnetic resonance (LF NMR) and scanning electron microscopy (SEM) were used to analyze the mechanism. The results show that the addition of NMgO delays the early hydration heat release rate of cement and prolongs the setting time. When adding 2 % NMgO, the flexural strength and compressive strength of mortar are the highest in 28 days, which are increased by about 8.44 % and 10.55 % respectively compared with the control group. At the same time, NMgO participates in hydration and generates Mg-Al layered double hydroxides (Mg-Al LDHs) inside the cement, which effectively fills the internal pores of the cement paste and increases the compactness. However, it is found that too much NMgO will cause cracks in cement, increase porosity and decrease flexural and compressive strength . • The average particle size of nano-MgO modified by stearic acid decreases to 115.05 nm. • NMgO improves the early working performance of the system. • When adding 2 % NMgO, the compressive strength increased by 10.55 % at 28 days. • When adding 2 % NMgO, the porosity of the system is only 10.46 % at 28 days. • NMgO reacts with cement components to generate Mg-Al LDHs in situ.