Effect of pressing pressure on the mechanical properties and water resistance of straw/sawdust-magnesium oxychloride cement composite

In this study, straw/sawdust-magnesium oxychloride cement composite (SMOCC) was made by a compression molding process with straw, sawdust, and magnesium oxychloride cement (MOC) as the primary raw materials. The effects of different pressing pressures on their compressive strength, flexural strength, and water resistance were investigated. The physical phase composition, pore structure characteristics, and microscopic morphology were also analyzed by XRD, MIP, and SEM. The results showed that the mechanical properties of SMOCC enhanced as the pressing pressure increased. When pressing pressure increased from 2.5 MPa to 3.3 MPa, the compressive and flexural strength increased by 38% and 81%, respectively. Increasing the pressing pressure can effectively reduce the porosity, redistribute the pore size and refine the pore structure. In addition, it can improve the bonding strength between straw/sawdust-cement matrix, forming a more stable microstructure and ultimately improving the strength of SMOCC. However, increasing the pressing pressure did not significantly promote the softening coefficient and thickness swelling rate of SMOCC after 28 d of water immersion, and its water resistance still requires further enhancement.