The Characteristics of Swelling Pressure for Superabsorbent Polymer and Soil Mixtures

Abstract

Superabsorbent polymers (SAPs) are used in agriculture and environmental engineering to increase soil water retention. Under such conditions, the swelling pressure of the SAP in soil affects water absorption by SAP, and soil structure. The paper presents the results of swelling pressure of three cross-linked copolymers of acrylamide and potassium acrylate mixed at the ratios of 0.3%, 0.5% and 1.0% with coarse sand and loamy sand. The highest values of swelling pressure were obtained for the 1% proportion, for coarse sand (79.53 kPa) and loamy sand (78.23 kPa). The time required to reach 90% of swelling pressure for each type of SAP differs. Samples of coarse sand mixed with SAP K2 in all concentrations reached 90% of total swelling pressure in 100 min, while the loamy sand mixtures needed only about 60 min. The results were the basis for developing a model for swelling pressure of the superabsorbent and soil mixtures, which is a fully stochastic model. The conducted research demonstrated that the course of pressure increase depends on the available pore capacity and the grain size distribution of SAPs. The obtained results and the proposed model may be applied everywhere where mixtures of SAPs and soils are used to improve plant vegetation conditions.

The Assessment of Water Retention Efficiency of Different Soil Amendments in Comparison to Water Absorbing Geocomposite

“…Misiewicz et al [77] proposed a model that may be used to determine the theoretical swelling pressure generated in loamy sand soil and coarse sand. It is the first version of the model and has a fixed soil type and bulk density, although it allows modification of the concentration of superabsorbent polymer or the choice of a superabsorbent polymer with suitable granulation.…”

“…Differences in the quantity of water retained between freely swelling samples and samples swelling under a load reached up to 94% [75]. In relation to the swelling pressure generated [77], certain types of SAP have a significant impact on soil bulk density and porosity, the effects of which have been described by Han et al [78] and Bai et al [79]. In the case of SAP application in relatively large amounts, changes can be observed in the values of soil shear strength or hydraulic conductivity [80].…”

“…Because SAP is usually used by mixing it with soil, the depth of application and the density of the soil are vital parameters, reflected in the soil load that has to be overcome so that SAP can swell effectively and thus retain water in the soil in the form of a hydrogel. Research in this area was conducted by Lejcuś et al [75] and Misiewicz et al [76,77]. Differences in the quantity of water retained between freely swelling samples and samples swelling under a load reached up to 94% [75].…”

The Characteristics of Time-Dependent Changes of Coefficient of Permeability for Superabsorbent Polymer-Soil Mixtures

“…However, systematic laboratory experiments are beginning to unravel the origins of these conflicting results. One factor that is now appreciated to play a key role is the pressure experienced by the SAP inside soil: in real-world applications, SAP swelling upon contact with water is highly dependent on the local pressure [3,27,28]. Indeed, SAP absorption of water has been shown to be dramatically reduced upon simply loading a SAP-soil mixture with a top layer of soil, due to the increased pressure inside [29].…”

“…Given these gaps in knowledge, here, we built on our previous studies [3,27,28] to characterize how the addition of SAP to soil changes its coefficient of permeability over time, which is a novel approach, and how these dynamics depend on SAP grain size and soil grain size. We found that even small amounts of SAP can dramatically decrease the soil permeability, in some cases even causing complete blockage of water infiltration that can have important consequences in real-world settings.…”