Utilization of high-sulfur iron ore tailings in cement mortar by considering the influence of curing temperature and tailing content

This work investigates the usage of graded iron ore tailing sands (GIOT) as aggregates in cemented mortar to reduce the pollution of iron ore tailings (IOT) and shortage of river sands. Fresh and hardened properties of graded tailings cemented mortar (GTCM) with partial replacement of standard sands (SS) by GIOT were investigated, by considering the effect of substitution ratios (0 %-50 %) and curing temperatures (20 degrees C, 40 degrees C and 60 degrees C). It is illustrated that an increase in the GIOT content leads to the reduction in fluidity and increment in apparent density of fresh GTCM. With increasing GIOT content, the dry density and UCS of hardened GTCM show a decreasing trend first (0 %-20 %) and then increase against the substitution ratios of GIOT (30 %-50 %). The variation of water absorption with increasing GIOT is opposite to that of dry density. In addition, the curing temperature is also proved to be a remarkable influencing factor, which can promote the hydration reaction and improve the properties of GTCM, even at 60 degrees C. The physico-mechanical properties of 28 d samples are better than that of 7 d samples because the increasing hydration products are produced with increasing the curing age. The XRD results show that the sulfur facilitates the formation of AFt. The SEM images and MIP results further confirmed that a low tailing content of 10 % may induce micro-cracks due to the unmatched particle size and shape, however, mortars with 50 % IOT content possess a denser microstructure, but more capillary and gel pores. For the curing age of 28 d, the optimum substitution ratio may exceed 50 %, and the best curing temperature is 60 degrees C. The influence of GIOT content and curing temperature on the long-term properties of high-sulfur GTCM beyond 28 d need further research.