Effect of gel-polymerized superabsorbent polymers-SAPs on concrete freeze-thaw resistance

Abstract

Synopsis: Superabsorbent polymers (SAPs) are attracting attention as a material that can improve the resistance to freezing and thawing. SAPs incorporated in concrete dry mixes absorb ambient water in few minutes when water is added to the dry mixtures. As the concrete hydrates, the relative humidity of the surrounding area is lowered and SAP releases water. When SAP absorbs water in concrete mix, it expands about thirty times its dry volume. This expansion creates air-voids which might improve the freeze-thaw resistance of concrete. Sodium polyacrylate cross-linked SAP made by gel polymerization is the most widely produced SAP type and is known to be relatively safe for the human body. This research elucidates the effects of the gel-polymerized SAP on air-voids and capillary pores. Experimental analysis using mercury intrusion porosimetry (MIP) were performed to investigate how gel-polymerized SAP affects the characteristics of air-voids and capillary pores. Pore properties, such as pore size and related pore distribution, are studied. Finally, the freeze-thaw cycles performed on a number of concrete specimens-according to CEN/TS 12390-9 (with 3% NaCl solution)-make it possible to observe and to quantify concrete deterioration, in both the surface and internal layers.