Characterization of the mechanical properties and microcosmic mechanism of Portland cement prepared with soda residue

摘要

This work studies the feasibility of the application of soda residue (SR) to the preparation of cement. SR was added to the cement raw materials at 0, 5, 10, and 15 wt%, and four types of cements were synthesized. The free CaO and Cl- contents in the cement clinker, the flexural and compressive strengths, setting times, consistency, fineness, soundness, permeability coefficients, and freeze-thaw resistance of the produced cements were tested. Meanwhile, X-ray diffraction (XRD), thermogravimetric (TG) analysis, and scanning electron microscopy (SEM) were used to study the phases and hydration products of the clinkers and the cements, respectively. The results showed that SR addition could decrease the calcination temperature for clinker preparation. With increased SR content, the initial and final setting times of the produced cements clearly decreased, whereas their water demand and volume expansion continuously increased. When the SR addition was 5 wt%, the flexural and compressive strengths of the produced cement were 4.1 and 23.4 MPa at three days, and 7.5 and 53.1 MPa at 28 days, satisfying the requirements for a 52.5 grade cement. The XRD results demonstrated that the phases of clinkers prepared with SR were alinite, calcium chloroaluminate, and calcium chlorosilicate, as well as alite, belite, aluminate, and ferrite. The Cl- content analysis of clinkers revealed that although a mass of Cl- would be introduced into the cement raw mix due to the SR addition, its contents in all clinker samples was less than 0.06 wt%. Additionally, the XRD, TG, and SEM results showed that the petal-like Friedel's salt and layered calcium chloride silicate sulfate formed in the hydration products of cements prepared with SR, compared with that of ordinary Portland cement. Finally, the impermeability and freeze-thaw resistance of cement pastes were weakened due to the addition of SR. (C) 2020 Elsevier Ltd. All rights reserved.