Long-term mechanical properties and micro mechanism of magnesium oxychloride cement concrete

Abstract

According to the C20 Portland cement concrete (PCC) batching standard, magnesium oxychloride cement concrete (MOCC) is made using bischofite from salt lakes and light-burned magnesium oxide as the main raw materials. In this work, the mechanical properties of MOCC (setting time and compressive and flexural strengths) were tested. The rules governing the phase composition and microstructure changes of the hydration products were analysed using X-ray diffraction and scanning electron microscopy. The results showed that MOCC solidifies rapidly, has high early compressive and flexural strengths and exhibits excellent long-term mechanical properties, far superior to those of the same grade of C20 PCC. The main phase at different curing times was found to be 5Mg(OH)2.MgCl2.8H2O (5.1.8). With hydration from 7 to 365 d, the amount of 5.1.8 fluctuated between 30% and 37% and the microscopic crystal morphology of the MOCC changed significantly. Importantly, fibre-like and rod-like crystals were observed to transform into their respective gel phases from 180 to 270 d. This phenomenon explains the fact that the content of 5.1.8 was the lowest but the mechanical strength of MOCC was the highest at 180 and 270 d. It was also confirmed that 5.1.8 gel is one of the main strength phases.

Research and Engineering Application of Salt Erosion Resistance of Magnesium Oxychloride Cement Concrete

“…Most researchers apply magnesium chloride to produce a series of magnesium products including magnesium metal, anhydrous magnesium chloride, magnesium hydroxide, and magnesia whiskers, but these magnesium chlorides have not been fully exploited, and they accumulate for a long time, causing 'magnesium damage' and seriously affecting the surrounding environment. Recently, the development and utilization of magnesium oxychloride cement (MOC) has become an ecological, economic, and effective means of solving the problem of the accumulation of magnesium chloride [6].…”

“…Magnesium Oxychloride Cement Concrete (MOCC) uses the gelling properties of magnesium oxychloride cement to prepare a unique and new type of concrete by adding aggregates such as sand and crushed stone. It has the advantages of high strength in the early stage and in stable strength in the later stage [6].…”

Effect of Calcination Temperature on Mechanical Properties of Magnesium Oxychloride Cement

“…In addition, they can cause 'magnesium damage', which seriously affects the surrounding environment. As well as using magnesium chloride to produce a series of magnesium products-such as magnesium metal, anhydrous magnesium chloride, magnesium hydroxide, and magnesia whiskers-the development and utilisation of magnesium oxychloride cement have become an ecological, economic, and effective means of solving the problem of magnesium chloride accumulation [1,2].…”

Mechanical Properties and Pore Structure Characteristics of Magnesium Oxychloride Cement Modified by Highland Barley Straw Ash

“…There is a wide application prospect in the engineering field due to the advantages as high early strength, good brine corrosion resistance, and good wear resistance, etc. [4,5]. However, the characteristics of poor water resistance and corroded steel bar limit its further application [6,7].…”