Shrinkage and strength development of UHSC incorporating a hybrid system of SAP and SRA

The individual use of super-absorbent polymer (SAP) or shrinkage reducing admixture (SRA) impairs some properties required for ultra-high strength concrete (UHSC). This study used SAP and SRA in hybrid systems in order to enhance their role on autogenous shrinkage, drying shrinkage and compressive strength of UHSC. Accordingly, the water absorption and the surface tension of pore solution containing the hybrid system of SAP and SRA were measured, and the effect on internal relative humidity (RH), porosity and hydration degree were examined. The results showed that the interaction of SAP and SRA reduced the water absorption capacity of SAP and limited the reducing effect of SRA on the surface tension. However, the hybrid system of SAP and SRA compensated the adverse effect of each on the properties of UHSC. It was also found that the surface tension of pore solution was more effective than the internal RH on the autogenous shrinkage of UHSC. Overall, the specimens with 0.3% SAP and 2% SRA had the minimum autogenous and drying shrinkage.