Effects of SAP on the properties and pore structure of high performance cement-based materials

Abstract

Water-to-binder ratio (w/b) directly affects the pore structure and performance of concrete, and drying conditions enhance the influence of water-to-binder ratio. Superabsorbent polymer (SAP) is effective to adjust the water in the concrete. In this paper, the effect of SAP and extra water on drying shrinkage, pore structure and the permeability of high performance cement-based material with w/b from 0.18 to 0.24 were studied to reveal the adjusting role of SAP for the influence of water-binder ratio at a 60% of relative humidity (RH). The permeability was determined through the vacuum saturation method, the diffusion of steady-state Cl− ion and carbonation testing. The structure of harden mortar and SAP voids were evaluated by mercury intrusion porosimetry (MIP) and backscatter electronic microscopy (BSEM). At the same effective w/b, SAP reduces the strength, and raises the drying shrinkage and permeability. However, the effect of SAP on the above properties is exactly opposite when the same total w/b is used. The greater the SAP particle size is, the more obvious those favorable effects are. SAP can weaken the effect of total w/b. The addition of SAP also results in the formation of the hydration diffusion layer in SAP void and the refinement of pore structures.