RETRACTED: Investigation of SAP content on the shrinkage and tensile properties of ultra-high performance concrete (Retracted Article)

Extensive studies have focused on superabsorbent polymer (SAP) as an internal curing admixture to reduce the autogenous shrinkage of ultra-high performance concrete (UHPC). However, studies on the effect of SAP content on the tensile properties of UHPC are still limited. As we all know, tensile performance of UHPC is an aspect that cannot be ignored. Therefore, this paper investigates the effect of SAP content on the shrinkage and tensile properties of UHPC. First, according to mercury intrusion porosimetry (MIP) analyses, the moderate addition of SAP can refine the pore structure of matrix due to its internal curing effect. However, excess SAP brought more space filled with capillary water, thus increasing the porosity of matrix. The results of shrinkage test showed that the autogenous shrinkage of UHPC decreased first and then increased with the increase in SAP content. While the drying shrinkage of UHPC increased when SAP content increased. When 0.15% SAP was added, the 7 days autogenous shrinkage and 28 days total shrinkage of UHPC were the lowest, 51.3% and 30.1% lower respectively than those of UHPC without SAP. In addition, the moderate incorporation of SAP improved the tensile properties. Since the internal curing effect of SAP promoted the hydration of expand agents (EA) and cement, the microstructure of matrix became denser, enhancing the bond between fibers and matrix. Thus, the tensile strength of UHPC was improved. However, excess SAP have negative effect on the tensile strength due to the negative effect on pore structure. Furthermore, the tensile strain capacity of UHPC increased first and then decreased with the increase in SAP content. Finally, the micromechanical principle was proven to be a feasible method to evaluate tensile strain-hardening behaviors of UHPC. The trend of pseudo-strain-hardening (PSH) index and tensile strain capacity of specimen remained consistent. Additionally, when the ratio of maximum fiber bridging stress and matrix tensile cracking strength of UHPC was more than 1.1 rathan than 1.3, which was required in the filed of engineering cementitious composites (ECC), UHPCs exhibited obvious strain-hardening response. This indicated that the adjustment of the strength criterion in the micromechanical principle will be the key to its effective and reasonable evaluation of the tensile strain-hardening response of UHPC.