Investigation of the effect of microstructure on the strength and durability properties of paste backfill

The purpose of this thesis study was to investigate the effect of liquid sodium silicate (LSS) and sodium hydroxide (NaOH:SH) activated slag binder use instead of ordinary Portland cement (OPC) on paste backfill (CPB) performance. Samples prepared from the DA produced higher strength and durability than the NA under the same binder content. In case of binder content less than 6.0wt.% is insufficient in terms of strength and durability properties of CPB when sulphide rich tailings is used. Approximately 3.0–4.0 and 1.5–2.0 fold strengths were obtainedwhen LSS–S and SH–C samples were used instead of OPC. Increasing binder dosages led to increase in strength development and durability besides resistance to acid and sulphate effects. OPC samples suffered from strength losses after 56 days. The use of alkali–activated slag (AAS) binder reduced the acid and formation of sulphate on CPB. MIP analysis showed that the increase of binder content and use of the DA improved the microstructure and reduced the total volume of porosity. The strength losses at long term were due to the weakening of C–S–H and formation of ettringite and gypsum for the samples prepared from the lower binder ratios for OPC. The reason for strength loss fo SH–C is the weakening of C–S–H and the drying shrinkage. AAC especially LSS–C samples were also seen to decrease the decalcification of C–S–H.