Experimental study on the preparation of magnesium oxysulfate cement-based composites using waste locust powders to replace non-renewable magnesium oxide

Magnesium oxysulfate cement is a new type of environment-friendly cement with low energy consumption and promising development potential. But the raw material MgO is not renewable. To improve the utilization of forestry wastes and save MgO, composites containing locust powders with 0 -25 % mass of MgO were prepared by mechanical mixing and curing for 3d -100d. The slurry's fluidity, mechanical property, water resistance and microstructure were studied. Strength data at 100d were found to be essential for property evaluation. The maximum locust dosage based on fluidity was 25 %, and composites with 10 %-25 % locust exhibited flexural strength of 13.37 -15.12 MPa and compressive strength of 56 -64.3 MPa at 100d. The corresponding flexural strength improvement and compressive strength reduction comparing to cement with no locust were by 13.5 %-28.35 %, and 21.86 %-31.95 %, respectively. Regarding relations of flexural force and displacement before fracture at 100d, locust with 10 %-25 % dosage improved the displacement and energy absorption capacity by 56.88 %-125.58 % and 52.48 %-108.49 %, showing lower brittleness. Composites containing 10 %-25 % locust improved the flexural strength by 14.23 %-48.82 % when soaking in water, and the softening coefficient was larger than 0.85 if cured for 35d and soaked for 7d, indicating good water resistance. Effects of locust dosage on primary functional groups, phase changes, thermal stability and microstructure were analyzed by various techniques. A new optimization method based on seven indicators is proposed, capturing the optimal locust dosage as 20 % mass of MgO. This paper proposed an environmental-friendly approach to improve the utilization of forestry wastes and develop new cement-based building materials.