The regeneration of cement from completely recyclable mortar: effect of raw materials’ compositions

In this study, cement was regenerated using completely recyclable mortar (CRM) as raw cement meals. The effects of silica modulus (SM) and alumina modulus (AM) on the properties of CRM, burnability of raw meal and the clinker’s properties were studied. The results showed that, with a higher SM and lower AM, less melt would be available to facilitate the diffusion of calcium oxide towards belite to form alite. The compressive strength of recycled cement increased with the increase of AM when SM = 2.7 and 2.2 and decreased with the increase of AM at a low SM (SM = 1.7). The suggested rate value of raw meals using CRM is a medium SM (SM = 2.2 or SM = 2.7) and AM = 1.5–1.8 with a calcination temperature of 1400°C. The strength of both the CRM and the recycled cement clinker obtained is relatively high. Moreover, the calcination temperature could be further reduced to 1300°C or 1350°C with a low SM (SM = 1.7) and AM (AM = 0.9–1.5). Although the CRM had a lower early strength, it had a relatively high strength in the later stage. However, its water absorption was significantly increased compared to the control group.