Effect of superabsorbent polymer characteristics on rheology of ultra-high performance concrete

Changes of rheological properties in ultra-high performance concrete (UHPC) suspending mortar incorporated superabsorbent polymer (SAP) were investigated. The effect of chemical composition of two SAP types (S1, acrylamide/acrylic sodium copolymer and S2, acrylamide polymer) and the S1 SAP with mean particle sizes of 95.1 and 471.3 μm on water absorption was evaluated. The effect of these parameter for dry SAP used at content of 0–0.6%, by mass of cementitious materials, on the rheology of the UHPC mortar was evaluated. The S1 SAP was also employed at 0.4% content in a pre-absorbed state to investigate the effect of the preconditioning method on the rheological properties. Test results show that the rheology of UHPC made with SAP depend on the water absorption/desorption properties. The water desorption after reaching the maximum water absorption limit for the S1 SAP can led to a decrease or stagnation of yield stress between 15 and 30 min of age. The increase in particle size of the SAP was shown to delay this stage of decrease or stagnation. The variation in yield stress of UHPC mortar made with the S2 SAP over time increased from 1 to 4 times compared to the reference mixture given the longer time for water absorption. The addition of the S1 SAP reduced the plastic viscosity and thixotropy, regardless of the size, content, and preconditioning method. The use of dry S2 SAP increased plastic viscosity by approximately 10 Pa.s and the thixotropy. The preconditioning method of SAP had no significant influence on thixotropy.