Research of Water Absorption and Release Mechanism of Superabsorbent Polymer in Cement Paste

Abstract

The water absorption and release properties of superabsorbent polymers’ (SAP) internal curing agent are affected by many factors, such as solution properties, the ambient temperature and humidity and the particle size of SAP, which determine the curing effect and the durability of cement concrete structures directly. In this paper, the variation rule of the water absorbing capacity of SAP in simulated cement paste under different solutions and environmental conditions was studied. Based on microscopic image technology, the dynamic swelling behavior of the SAP particles was explored. The water release performance of SAP in cement paste was analyzed by both the tracer method and the negative pressure method. The results show that the water absorption of SAP in cement paste varied from 27 to 33 times. The ionic valence had a significant effect on the water absorption capacity of SAP, which suggests that the larger the ionic radius, the lower the absorption of SAP. The higher the temperature of the solution, the greater the water absorption rate of SAP. While the SAP particle size was less than 40–80 mesh, a slight ‘agglomeration effect’ was prone to occur, but the absorption state of SAP was more stable. Based on the swelling kinetic equation of SAP and the time-dependent swelling morphology of SAP in cement paste, a swelling kinetic model was established. The water release performance of SAP was less affected by the capillary negative pressures, and it would not release the water prematurely during the plastic stage, which was conducive to the continuous internal curing process of hardened paste in the later stage.

Investigating the Impact of Superabsorbent Polymer Sizes on Absorption and Cement Paste Rheology

“…In contrast, SAP B exhibited signs of water release in all cases after 30-60 min. However, in pH 13, absorption capacity was significantly increased from 23.89 g/g at 3 h to 30.10 g/g at 24 h. The increase in pH from 11 to 13 resulted in a decrease in absorption capacity for both SAPs, consistent with studies conducted by [11,26]. Both SAPs showed higher absorptivity in the filtration method than the tea-bag method [25,31].…”

“…The absorption capacity and rate of SAPs can be modified based on chemical compositions, physical a ributes, and the properties of the surrounding fluid, including composition, ionic concentration, pH, temperature, and pressure [9,11]. Additionally, the particle size, quantity, and chemical composition of SAPs play a crucial role in their performance in concrete, impacting mechanical stability during mixing and rheological properties such as yield stress, plastic viscosity, and thixotropy over time [12][13][14][15].…”

Experimental Study of a Superabsorbent Polymer Hydrogel in an Alkali Environment and Its Effects on the Mechanical and Shrinkage Properties of Cement Mortars

“…The compressive strength of cement paste is negatively affected due to the addition of SAPs. Qin et al [ 18 ] reported that the ionic valence substantially affects SAPs’ water absorption capacity, implying that the bigger the ionic radius, the less the SAP absorbs. SAPs’ water absorption rate increases as the temperature of the solution rises.…”