The Characteristics of Absorbency Under Load (AUL) for Superabsorbent and Soil Mixtures

Abstract

Various applications of superabsorbent polymers (SAP) include the use of these materials in agriculture and environmental engineering to increase soil water retention. Under such conditions, there is water absorption of the SAP in soil under load. This paper presents the results of absorbency under load (AUL) of a cross-linked copolymer of acrylamide and potassium acrylate mixed at ratios of 0.3%, 0.5% and 1.0% with coarse sand and sandy loam. The mixtures were subjected to loads equivalent to 10, 20 and 40 cm of soil. The highest differences in AUL values for both soils, compared to the control sample, were obtained after 24 hours and at a maximum load of 5.9 kPa, which corresponds to a load of a 40 cm thick topsoil layer. The AUL was 71.4 g∙g−1 for coarse sand and 52.7 g∙g−1 for sandy loam with a 1.0% SAP addition, which corresponded to 24.0% and 18.0%, respectively, of the absorption in the control sample. All the conducted tests revealed a significantly low rate of water absorbency, which is especially important for capturing the water that infiltrates into the soil profile. The results demonstrate that water absorption by SAPs decreased with the increase in SAP addition.

Transformation of non-water sorbing fly ash to a water sorbing material for drought management

“…Hence, the WAC increases with the initial increase in initiator content. However, exceeding the initiator content beyond 1.5% lead to an increased number of radical active sites in the monomer, and chain propagation gets terminated 18 , 40 , 41 . This results in a decrease in the molecular weight of the polymer chain, and subsequently, the WAC is reduced.…”

“…The commercially available SAH for horticulture has a water-absorbing capacity (WAC) of 100–300 g/g 14 – 16 . Due to high WAC, these polymers are receiving much attention in the hygiene industry, drug delivery, food storage, wastewater treatment, biosensors, and tissue engineering 17 , 18 . The use of SAH as agricultural soil amendment was recommended by the United States Department of Agriculture (USDA) in the 1960s.…”

Influence of Environmental Factors on the Swelling Capacities of Superabsorbent Polymers Used in Concrete

“…The swelling experiments were performed under atmospheric pressure. Although the uptake and release of water under load differs from that at atmospheric pressure [ 27 , 28 ], shrinkage cracking in concrete—which should be prevented by the addition of SAP—occurs on the surface, where the SAP are not subject to particularly high hydrostatic pressures [ 36 , 37 ]. The time-dependent swelling experiments of the as-received samples ( Figure 2 ) indicated high degrees of swelling of approx.…”

The Characteristics of Swelling Pressure for Superabsorbent Polymer and Soil Mixtures

“…The SAP-soil mixture in the full saturation state is a 3-phase medium, where the share of SAP influences the mechanical properties of the mixture [ 12 ]. This is noticeable while testing absorbency under load (AUL), where the higher amount of SAP in the mixture results in higher swelling pressure, which results in pushing out the top layer of soil [ 35 , 45 ]. Due to that, the nature of swelling of SAP-soil mixtures requires special attention, especially from the point of view of practical applications, where the SAP is applied in superficial layers of soil.…”

“…The shape and orientation of soil pores and solid phase elements allow for diagnosis of soil structure change upon external factors [ 33 ]. The swelling SAP will exert pressure on surrounding soil changing its structural integrity, and on the topsoil layer causing one-dimensional deformation [ 34 , 35 ]. The pore volume available for SAP is an important factor that indicates how long SAP particle can swell freely from initial, dry state, to constrained swelling that leads to exerting stress on upper soil layer [ 36 ].…”