Superabsorbent polymer (SAP) is attracting attention as a water-entraining admixture\nthat reduces shrinkage or heals cracks in concrete. Cross-linked sodium polyacrylate SAPs, which\nare the most widely produced SAPs in the global market, are applicable as concrete admixtures.\nHowever, there have been contradictory results on the freezeâ??thaw resistance of concrete with SAPs.\nThis study aims to clarify these results considering the water absorption behavior of SAPs in hardened\nconcrete when effective water-to-cement ratios are different. Firstly, the absorbencies of one kind of\ncross-linked sodium polyacrylate SAP (SAP_SP) in pore solution and fresh mortar were measured\nby a tea bag test and flow test, respectively. Pore size distribution, capillary water absorption, and\ndeformation during freezeâ??thaw cycles were analyzed for mortar samples with varying SAP_SP\ndosages. In the main tests, concrete samples with three different SAP_SPs/cement ratios (0.1%, 0.2%,\nand 0.3%) and a reference sample were prepared, and internal damage and salt scaling were measured\nunder freezeâ??thaw cycles. Because SAP_SP absorbs water in fresh mixtures, additional water was\nadded to the mixture considering the water absorbency of the SAP_SP. It was found that the used\nSAP_SPs prematurely release their stored water so the effective water-to-cement ratio was increased\nwhen a larger amount of SAP_SP was used. The higher effective water-to-cement ratio caused more\ninternal damage and salt scaling due to the weaker cementitious matrix. In addition, mortar samples\nwith a high SAP_SP content show a larger absorption of capillary water than the reference sample.\nThe result can be interpreted by an observation that SAP_SP in air voids absorbs water and expands\nto relatively large capillary pores or neighbor air voids during the capillary water absorption process.
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