Research on the composition optimization and mechanical properties of sulfate activated full solid waste non-clinker cementitious materials based on simplex-centroid design method

Abstract

To explore the feasibility of converting industrial solid waste in Hebei Province into cementitious materials, three industrial solid wastes, iron tailings sand, coal gangue powder and blast furnace slag were as the raw materials and desulfurization gypsum as sulfate-based activators to establish sulfate activated-full solid waste non-clinker cementitious materials (FSC). The influences of component dosages on the mechanical properties of sulfate activated-FSC mortar and setting time of sulfate activated-FSC were explored through single-factor design method, and the component dosages ranges of sulfate activated-FSC were determined. On this basis, the optimal composition of sulfate activated-FSC was designed based on the simplex-centroid design method, and the variation laws of compressive strength and flexural strength of sulfate activated-FSC mortar were evaluated. The results displayed that the increase in the dosage of iron tailings sand and coal gangue powder would reduce the strength of sulfate activated-FSC mortar and prolong the setting time of sulfate activated-FSC. The dosage of desulfurization gypsum within the range of 10% to 20% would enhance the strength of sulfate activated-FSC mortar after short-term curing. The optimal proportions of sulfate activated-FSC were 18% iron tailings sand, 16% coal gangue powder, 50% blast furnace slag, and 16% desulfurization gypsum. And then, the mechanical properties of sulfate activated-FSC mortar under optimal proportions were analyzed based on the freeze-thaw resistance test, drying shrinkage test and salt erosion resistance test, respectively. The test results showed that sulfate activated-FSC mortar exhibited good freeze-thaw resistance and salt erosion resistance performance. The compressive strength loss rates and weight loss rates of sulfate activated-FSC mortar after 30 freeze-thaw cycles were 8.57 % and 0.34 %, respectively, and its erosion resistance coefficient was 85.76% soaked in a 10% NaCl and Na₂SO₄ mixed solution for 30 days. Finally, the results of X-ray diffraction test and scanning electron microscopy test showed that the hydration reactions between desulfurization gypsum and raw materials would generate the hydration products, including calcium silicate hydrate gel, calcium aluminate hydrate gel and ettringite, to form the dense network structure in sulfate activated-FSC mortar, and improve its mechanical properties.