Effect of sodium-silicate activated slag at different silicate modulus on the strength and microstructural properties of full and coarse sulphidic tailings paste backfill

• Published in: Construction & building materials 2018-10, Vol.185, p.555-566
• Main Authors: Cihangir, Ferdi, Ercikdi, Bayram, Kesimal, Ayhan, Ocak, Sinan, Akyol, Yunus
• Format: Article
• Language: English
• Subjects: Acid attack; Alkali-activated slag; Analysis; Building materials durability; Ca/Si ratio; Cemented paste backfill; Cements (Building materials); Chemical properties; Durability; Mechanical properties; Polymerization; Silicate modulus; Sodium-silicate; Sulphate attack
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2018.07.105

•Cemented paste backfill (CPB) is among the best available waste management techniques.•Silicate modulus (Ms) of sodium-silicate significantly influences the strength gain rate of CPB.•Optimum Ms value is around 1.25 irrespective of tailings particle size distribution.•Decrease in Ms was observed to cause the formation of secondary gypsum minerals.•Increase in Ms and use of coarse tailings significantly refined the microstructure of CPB. In this study, strength and microstructural development of full (FT) and coarse sulphidic tailings (CT) cemented paste backfill (CPB) produced from sodium-silicate activated slag (SSAS) at different silicate modulus (Ms) were investigated in the short- and long-term. SSAS samples (SSASs) with varying Ms for both FT and CT produced 1.5–3.5 fold unconfined compressive strengths in the long-term compared to ordinary Portland cement samples (OPCs). Optimum Ms values were 1.0–1.25 for FT and 1.25–1.50 for CT considering the short- and long-term strength gain and microstructural properties of CPBs based on the polymerization degree and balance of C–S–H gel. Strength losses were observed in OPC-CT and in SSASs at Ms = 0.75 for FT and CT in the long-term. Formation of secondary expansive minerals such as ettringite, decalcification of C–S–H gel and the weakening of microstructure were found to be the main reasons for the strength losses due to the coupled effect of acid and sulphate attack. The use of CT and SSAS together significantly improved the microstructure of CPB. Increase in Ms decreased the porosity, refined the pore structure providing more compact microstructure and alleviated the decalcification of C–S–H gels in consequence of higher rate of polymerization.