Effect of NaAlO2 and Superplasticizers on Properties of Dehydrated Cement Paste with Slag Recycled Composite Cementitious Materials

The disposal of cement-based construction waste is a big bottleneck in the cement and concrete industry. However, this issue can be tackled through preparation of dehydrated cement paste (DCP) by thermal reactivation of cement stone. Additionally, DCP has the problems of low compressive strength, poor flowability, and extremely short setting time compared with ordinary portland cement. Therefore, this study aims to investigate the effect of NaAlO2 and two different superplasticizers, naphthalene and polycarboxylate, on the properties of DCP with slag recycled composite cementitious materials (RCCM). The flowability, setting time, compressive strength, and synergetic mechanism of the RCCM were assessed. It has been found that the addition of NaAlO2 promoted the formation of C─ S─ H gel and C─ A─ H gel in RCCM, enhanced the compressive strength of RCCM and prolonged the setting time (the optimal dosage is 0.5% by weight). The addition of slag prolonged the setting time and improved the flowability of RCCM. The maximum compressive strength was 26.00 MPa (3 days) and 51.30 MPa (28 days) when the slag content was 50%. The effect of naphthalene on the compressive strength and flowability of RCCM was better than polycarboxylate, and both of them prolonged the setting time of RCCM. Additionally, DCP weakened the effect of superplasticizers in RCCM. Therefore, when DCP and superplasticizers are used together, this effect should be considered. The results of this study will contribute to the research related to the construction performance of DCP and promote its application.