Effects of a novel hybrid polymer material on the hydro-mechanical behavior of subgrade silts considering freeze-thaw cycles

Freeze-thaw (FT) cycles are considered to be a potential threat to the hydro-mechanical behavior of subgrade soils in seasonal frozen regions. Enhancing the resistance of the soils to FT cycles therefore becomes a pressing problem that needs to be solved. This paper developed a durable polyacrylate intercalated bentonite superabsorbent polymer (BT-SAP) employing the solution polymerization method, which is a novel hybrid polymer material with the function of reducing the sensitivity of subgrade soils to FT cycles. To evaluate the effects of BT-SAPs on the hydro-mechanical behavior of subgrade silts experiencing FT cycles, the 3D pore structure, volumetric strain (εv), soil-water characteristic curve (SWCC), and resilient modulus (MR) of the soil modified with BT-SAPs were determined using a series of laboratory tests. Specimens with three BT-SAP contents (BC) compacted at their respective optimum moisture content and maximum dry density were first subjected to different numbers of FT cycles (NFT). Then, they were dried or wetted to specific moisture contents (w) before the determination of (i) SWCCs using the filter paper method and (ii) MR from cyclic triaxial tests. Finally, the 3D pore structure of specimens after FT cycles was measured by X-ray μ-CT. Experimental results show that the viscous and micro-swelling effects of the generated BT-SAP-water-gels can inhibit the emergence and development of larger pores and cracks inside the soil after FT cycles. The addition of BT-SAPs significantly reduces the sensitivity of the soil's volume and water retention capacity to FT cycles. The MR decreases with NFT but increases with BC. The important finding is that an optimal BT-SAP content of 0.25% was determined suitable for fine-grained subgrade soils. In addition, an artificial neural network (ANN) model was developed using 1200 sets of the MR measurements obtained in this study and well predicts the MR considering several factors such as BC, NFT, w, dry density, and stress levels. This study provides useful guidelines for the application of BT-SAP materials in subgrade engineering in seasonal frozen regions.