Feasibility of Using Modified Silty Clay and Extruded Polystyrene (XPS) Board as the Subgrade Thermal Insulation Layer in a Seasonally Frozen Region, Northeast China

Abstract

To achieve the purposes of storing industry solid wastes and enhancing subgrade stability in seasonally frozen regions, Structure III, which utilized the modified silty clay (SC) and extruded polystyrene (XPS) board as a novel subgrade thermal insulation layer (NSTIL), was presented. The above modified SC consisted of oil shale industry solid waste, fly ash and SC. In terms of environmental impact, the average single pollution index, the Nemerow integrated pollution index and national standards were carried out to estimate whether the modified SC could be used as a subgrade filler. These results show that, although the modified SC will produce pollution to the environmental background, the concentration of each hydrochemical constituent from the modified SC meets the corresponding national standards in China. In terms of the thermal insulation capability, the numerical simulation of coupling moisture and temperature was applied to analyze that of Structures I, II and III. The research results show that the numerical results of the Structure I are approximated to the official website information of Jilin province, indicating that the above numerical simulation is effective for coupling moisture and temperature of frozen soil. Both modified SC and NSTIL have the advantage of good thermal insulation property, but the thermal insulation property of the NSTIL is greater. Furthermore, the NSTIL at the top of the Structure III can protect the SC of the experimental road from the damage of frost heave. The research results are of great significance for reducing environmental pollution caused by oil shale industry solid waste and fly ash, increasing the utilization rate of industrial waste and enhancing the subgrade stability in seasonally frozen regions.

Experimental and Numerical Research on Utilizing Modified Silty Clay and Extruded Polystyrene (XPS) Board as the Subgrade Thermal Insulation Layer in a Seasonally Frozen Region, Northeast China

“…In order to highlight the difference between considering the above effect and without that, the numerical simulations of coupling moisture and temperature, considering the effects of freeze-thaw cycles by applying the improved calculation functions of thermal conductivity and specific heat capacity, were conducted for Structures I, II, and III ( Figure 1), and the simulation results were compared with the results of Li et al [15]. The research methods of the improved calculation functions of thermal conductivity and specific heat capacity are explained in Section 3.2.2; the details of the numerical simulations are explained in Section 3.2.3.…”

“…Turner [18] proved that the silty sand, which was processed with OSA, obtained significant improvement in strength, resilient modulus, and F-T durability. In previous literature, research on soil stabilization with both OSA and FA is inadequate, and it focuses on the author's previous research [11,15,23]. Wei et al [11,23] modified silty clay (SC) by OSA and FA (In the following interpretation, the silty clay, modified by OSA and FA, will be referred to as MC for short), and conducted a battery of laboratory tests to research the mechanical characteristics and environmental impacts of MC; research results showed that the modified SC was suitable for road construction in seasonally frozen areas.…”

“…Wei et al [11,23] modified silty clay (SC) by OSA and FA (In the following interpretation, the silty clay, modified by OSA and FA, will be referred to as MC for short), and conducted a battery of laboratory tests to research the mechanical characteristics and environmental impacts of MC; research results showed that the modified SC was suitable for road construction in seasonally frozen areas. Li et al [15] proved the feasibility of using MC and the XPS board as a road subgrade thermal insulation layer, by the numerical modeling and environmental evaluation on an experiment road located in the Jilin province; however, in their numerical modeling, they viewed the specific heat capacity and thermal conductivity of the MC, XPS board, and SC under F-T cycles as a constant value, so their results could not show the real changes of their thermal insulation performance under freeze-thaw cycles, and thus, their research results exaggerated or belittled the thermal insulation effect of the MC and XPS board. Therefore, research on the effect of F-T cycles on the specific heat capacity and thermal conductivity of the MC, XPS board, and SC is of great significance to accurately evaluate the thermal insulation performance of the MC and XPS board.…”

“…In the experimental road, there are two experimental structures named Structure I and II ( Figure 1); Structure I is composed of sand gravel and silty clay, and Structure II replaces 30 cm depth of sand gravel by MC, utilized as the subgrade thermal insulation layer. Based on Structures I and II, Structure III is inspired to present the thermal insulation performance of both MC and XPS board, which is called the novel subgrade thermal insulation layer (NSTIL) in a previous paper by the authors [15].…”

“…Sustainability 2019, 11, x FOR PEER REVIEW 4 of 15 dry density were 12.2% and 1.93 g/cm3, respectively. For Structures I, II, and III, both information about the source of OSA and FA and their chemical composition, and the source of the XPS board ( Figure 2) and its volumetric water absorption, unconfined compressive strength were introduced in Section 2 of reference [15].…”