Experiment on preparation of calcium silicate board based on a mixed gel system of carbide slag and coal-based solid waste

The purpose of this study was to reduce the loss of raw material calcium in the preparation of calcium silicate board and improve the synergistic utilization efficiency of solid waste. This test used a carbide slag-coal-based solid waste gelling system as the raw material to develop high-strength pure solid waste calcium silicate board. The main mineral components produced in the calcium silicate board and the variation in calcium silicate board strength with different proportioning were analyzed using thermogravimetry-differential scanning calorimetry (TG-DSC) and X-ray diffraction (XRD) test. The results show that the use of carbide slag completely substitutes cement. Fly ash and silica fume were mixed in mass ratio of 1:1 to prepare a mixed gelling system. Finally, the tobago mullite pure solid-waste calcium silicate template could be made with a water-cement ratio of 0.3. When silica fume was added in the mass percent of 0-10%, the bending strength of the template strengthened. Flexural strength of the calcium silicate board reached maximum when the amount of silica fume was 10%. Here, raw material particles composed of various dimensions were fully mixed. Also, crystals and hydrated gels closely interacted. Thus, the mechanical properties of the calcium silicate board significantly improved. The bending strength of the calcium silicate board tends to increase first, and then decrease with increasing NaOH dosage. The surface of the calcium silicate board was smooth when the mass percent of NaOH was 4% and mechanical strength reached a maximum of 11.8 MPa. This proved to be the optimum amount of added NaOH. The hydration reaction of the gelling system can achieve the best stimulating effect when 4% NaOH is added using scanning electron microscopy analysis. Moreover, the microstructure of material billets has an important impact on the final mechanical properties. However, the mechanical strength of the pre-cured calcium silicate board is not decisive of the final mechanical properties. The internal hydration gel number, shape, and connection are linked to each other inside the calcium silicate board; this is the key factor in determining the final mechanical properties of the calcium silicate board.