Preparation of sustainable backfill cementitious materials: Mix proportion optimization, hydration mechanism, and sustainability assessment

Abstract

Using cement as a filling cementitious material is challenging because of high energy consumption, high cost, and considerable carbon emissions. Thus, a new type of filling cementitious material, which involved soda residue (SR), calcium carbide slag (CS), ground granulated blast-furnace slag (GGBS), and fly ash (FA) as raw materials, was proposed in this study to replace conventional Portland cement. Response surface tests were conducted on test specimens to determine the optimal mixture proportion. The hydration mechanism of the developed filling cementitious material was investigated using low-field nuclear magnetic resonance, scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The results indicated that the optimal mixture proportion of the developed cementitious material was as follows: SR : CS : FA : GGBS = 15:7.41:37.27:40.32. The 28-d unconfined compressive strength (UCS) of the composite filling material was 23.01 MPa. The test results indicated a 28-d UCS of 24.14 MPa and a fluidity of 164 mm. Response surface methodology was used to optimize the performance of the filling cementitious material. The CS concentration of the material exhibited the most significant influence on the UCS, followed by FA and SR. Microstructural analyses indicated that the main hydration products of the new material were Friedel’s salt (FS), ettringite, hydrotalcite, C–(A)–S–H gel, and hemicarbonate, among which the C–(A)–S–H gel and FS were the dominant sources of strength in the material. The developed cementitious material can effectively reduce carbon emissions by 92% relative to cement-based binders. It can be used as a substitute for cement in mine filling with excellent economic and environmental benefits.

Keywords

Cement paste backfilling / Filling cementitious material / Response surface methodology / All solid waste / Synergistic activation / Carbon emission

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