Effects of superabsorbent polymers and magnesium oxide-based expansive agent on shrinkage and mechanical properties of UHPSSECC-LC3

Limestone Calcined Clay Cement (LC 3 ) is a recently developed ternary blended cement that has been applied in engineering cementitious composites (ECC). Although the incorporation of calcined metakaolin (MK) and limestone powder (LP) reduces the shrinkage rate compared to traditional ECC, the shrinkage rate of this material remains high. A large number of studies have focused on the use of superabsorbent polymers (SAP) and magnesium oxide (MgO) as internal curing agents and expansive agents to reduce the shrinkage of cement-based materials. However, research on the effects of SAP and MgO on the tensile properties of ECC remains limited. This paper introduces SAP and MgO to mitigate the shrinkage of Ultra-High Performance Seawater Sea-sand Engineering Cementitious Composite (UHPSSECC-LC 3 ) incorporating limestone powder and calcined clay. The effects of different dosages of SAP and MgO on the shrinkage and mechanical properties of UHPSSECC-LC 3 were investigated, and micromechanical tests were conducted to verify the mechanisms by which SAP and MgO influence tensile performance. The results indicate that although the addition of SAP and MgO reduces the workability of the material, it can effectively decrease both autogenous and drying shrinkages . SAP and MgO reduce shrinkage by lowering the internal moisture loss rate and generating expansive products, respectively. Compared to the reference group, the addition of SAP and MgO reduces the early mechanical properties of the material, but the later mechanical properties show improvement. At 90 and 180 days, the compressive strength of the group with 8 % MgO and the group with 0.2 % SAP and 8 % MgO slightly decreased compared to the 56-day results. This suggests that excessive MgO negatively affects the later mechanical properties of the material, and the addition of SAP enhances the expansive effect of MgO. The addition of 0.1 % SAP and 4 % MgO reduces the autogenous and drying shrinkage by 48.99 % and 45.43 %, respectively, while the microstructure of the matrix becomes denser, the bond strength between the fibers and matrix is improved, and both the tensile strength and tensile strain capacity of the material are enhanced.