Effect of Nano-Magnesium Oxide on the Expansion Performance and Hydration Process of Cement-Based Materials.

Yuxun Ye,Yaohui Chen,Tao Shi,Yanming Liu,Haobo Wang,Lei Zhong,Zhuojun Hu

doi:10.3390/ma14133766

Abstract

Many scholars are concerned about the effect of nano-MgO as an expansion agent on the performance of cement-based materials at an early age, but over a long period less attention is paid to expansion stability and mechanical properties. This article examines the influence of nano-MgO on the long-term consistency, fluidity, expansion stability, hydration, and mechanical properties of 30% fly ash cement-based materials and improves research into nano-MgO as an expansion agent. Expansion performance, flexural and compressive strength, and stability after boiling and autoclave treatment were tested for specimens mixed with a 2, 4, 6, 8 and 10% cementitious material mass of nano-MgO. X-ray diffraction (XRD) and scanning electronic microscopy (SEM) were employed to study their hydration process and microstructure. The results showed that nano-MgO had an obvious effect on the consistency, fluidity and expansion performance of cement paste. After curing in water for 365 days and autoclaving thereafter, the hydration of nano-MgO was relatively complete. The volumetric expansion pressure of the magnesium hydroxide (Mg(OH)2) crystals and the crystallization pressure generated after their continuous precipitation were the main reasons for the expansion of the slurry. Nano-MgO improved the microstructure of cement paste and significantly enhanced its long-term flexural strength and compressive strength. When the content of nano-MgO was less than 10%, the cement with 30% fly ash had good long-term stability with the potential to compensate for the shrinkage of large-volume concrete.

Highlights

Many scholars are concerned about the effect of nano-magnesium oxide (MgO) as an expansion agent on the performance of cement-based materials at an early age, but over a long period less attention is paid to expansion stability and mechanical properties
With the increase of nano-MgO dosage, it decreased almost linearly, which was consistent with the law of cement paste consistency
The effect of nano-MgO dosage on the fluidity of cement paste was relatively obvious, and the fluidity of cement paste decreased with the increase in nano-MgO dosage

Summary

Introduction

Many scholars are concerned about the effect of nano-MgO as an expansion agent on the performance of cement-based materials at an early age, but over a long period less attention is paid to expansion stability and mechanical properties. Flexural and compressive strength, and stability after boiling and autoclave treatment were tested for specimens mixed with a 2, 4, 6, 8 and 10% cementitious material mass of nano-MgO. 1. Introduction with regard to jurisdictional claims in Portland cement, a widely used building material, cracks because of chemical, drying and autogenous shrinkage caused by temperature stress. Burned magnesium oxide (MgO) has a micro-expansion effect with relatively stable hydration products, compensates for the shrinkage of cement-based materials over the long term, and can replace some cementitious materials.

Methods

Results

Conclusion