The mechanism of water release in superabsorbent polymer under different temperature and humidity environments

The water release behavior of superabsorbent polymers (SAPs) in cement paste under varying temperature and humidity was investigated using an ultra-depth-of-field microscope and a microhardness tester. SEM analysis characterized SAP morphology and elemental composition, while backscattered electron (BSE) stripe segmentation was applied to examine the SAP and matrix interface and quantify porosity and unhydrated cement (UHC) content around SAP-induced pores. The results indicated that higher temperatures and greater humidity differences increased both the water release rate and total released volume. Elevated temperature expanded the water release distance and progressively raised microhardness, whereas higher humidity reduced both. Distinct interfacial cracks were observed at 60 °C under large humidity differences, whereas only fine cracks appeared at 20 °C with small humidity variations. Furthermore, the content of UHC increased progressively with increasing distance from the pore wall. Porosity was high near the pore wall but decreased significantly beyond about 3 mm.