Long-term phase composition and microstructure characteristics of phosphoric acid modified magnesium oxychloride cement exposed to natural environment

Abstract

Magnesium oxychloride cement (MOC) is widely used as fireproof materials, decorative materials, and adsorption materials, etc. However, its poor water resistance limits the engineering application as a building material. The existing researches mainly focus on improving the short-term durability and water resistance, but few focus on long-term durability of MOC. In this paper, phosphoric acid-modified MOC samples with an age of 2–16 years from China and the Netherlands were collected. Their phase composition and microstructure characteristics were studied, which is of practical engineering significance for the modification of MOC. The results indicate that MOC modified by phosphoric acid would be decomposed and carbonated, and water in the ambient where MOC exposed to is the main factor. MOC exposed to humid environment presents a loose and porous morphology, but shows dense matrix with drying shrinkage cracks in dry air condition. MOC exposed to the air shows good carbon capture ability. The carbonated wood-MOC shows lower porosity than fresh wood-MOC paste. Carbonation phase on the surface of MOC products is beneficial to the internal structure and stability of MOC matrix. Besides, MOC is an environmentally friendly material. The manufacture of MOC requires less energy compared to ordinary Portland cement and shows good carbon neutralization potential under service life.