Potential application of highland barley straw ash as a new active admixture in magnesium oxychloride cement

Magnesium oxychloride cement (MOC) has excellent salt corrosion resistance; however, its poor water resistance limits its wide application in engineering structures in salt lakes and saline soil areas. The incineration of waste crop highland barley straw produces a large amount of ash powder. After appropriate treatment, highland barley straw ash (HBSA) can be used in MOC, which can effectively reduce the wastage of natural resources. This study investigates the suitability of incorporation of HBSA into MOC. Herein, HBSA was added into MOC using two different approaches: external and internal addition. The influence of the foregoing on the performance of MOC and the optimal amount and mixing method of HBSA were evaluated. Through a pore structure test and microstructure characterization, the mechanism of HBSA affecting the properties of MOC was revealed. Combined with the theoretical analysis of the hydration reaction, this paper expounds the dynamic law of HBSA affecting the performance of MOC from the aspects of the hydration reaction process and hydration product composition. The results reveal that HBSA is a new admixture suitable for MOC, which can significantly improve the water resistance of MOC. Different from the findings of previous studies, we discovered that the addition of HBSA into MOC can not only improve the water resistance but also improve the mechanical properties. When HBSA is added at a content of 10%, and the external mixing method is used, sufficient magnesium silicate hydrate is formed in the hydration product of MOC, which optimizes the pore structure and improves the water resistance of MOC. However, when HBSA is added into MOC using the internal mixing approach, the water resistance and mechanical properties degrade.