Performance and Mechanism of Polycarboxylate Superplasticiser in Red Mud Blended Cementitious Materials

The utilisation of red mud by blending them into cement paste is still facing the poor workability issues due to the finer particle size and higher water absorption of the red mud, which can be solved by the addition of polycarboxylate superplasticiser (PCE) to effectively maintain the working performance. However, the specific mechanisms by which different topologies of PCEs, in terms of water-reducing (WR) and slump-retaining (SR) type PCEs, influence red mud blended cement paste require further clarification. This research investigates the effect of WR-PCE and SR-PCE on the rheological properties, mechanical properties, and microscopic morphology of red mud blended cement paste under different red mud contents. Results demonstrated that at saturated dosages of 0.5% WR-PCE and 0.75% SR-PCE, both type PCEs improved paste fluidity, reduced plastic viscosity and shear stress. Moreover, the time-dependent fluidity loss rate of the SR-PCE incorporated paste was lower to that of the WR-PCE incorporated paste at 30 and 60 minutes. With 0% and 25% red mud contents, compressive strengths at 1, 3, 7, and 28 days were higher by WR-PCE other than SR-PCE due to enhanced hydration of C ₂ S and C ₃ S, particularly with WR-PCE. Furthermore, hydration products in the WR-PCE incorporated paste were more uniformly distributed compared to the SR-PCE incorporated paste. However, a 50% red mud content negatively impacted paste strength, likely due to high alkalinity destabilizing the PCE. This study aims to elucidate the mechanistic relationship between PCE topology and the improved performance of red mud blended cement paste.