Evaluating the efficacy of polyethylene glycol and magnesium chloride as anti-freeze agents on the mechanical properties of clays subjected to freeze-thaw cycles

Abstract

The construction industry frequently encounters significant challenges due to adverse weather conditions, leading to project delays and increased costs. Approximately 45% of global construction projects are interrupted by weather-related incidents, resulting in billions of dollars in additional expenditures annually. One critical issue in colder climates is the impact of freeze-thaw (F-T) cycles, which disrupt soil stability and permeability, causing cracks, expanding pore spaces, and affecting water retention and drainage. These cycles reduce soil strength and cohesion, increasing the risk of erosion and runoff and compromising the structural integrity of construction projects. Traditional soil stabilization methods, such as mixing soils with cement or lime, have limitations, particularly in mitigating the effects of F-T cycles. These methods often fail to prevent the loss of soil strength and volume changes after successive F-T cycles, necessitating the development of more robust solutions. This study investigates the potential of Polyethylene Glycol (PEG 400) and magnesium chloride (MgCl2) solutions as antifreeze and stabilizing agents for fine-grained soils. The research evaluates the effects of these solutions on soil properties, including plasticity, strength, and durability, under both unfrozen conditions and after F-T cycles. By understanding these effects, the study seeks to identify effective methods to mitigate the detrimental impact of F-T cycles on soil embankments in cold climates. Initial experiments with PEG 400 included Atterberg limits tests, compaction tests, unconfined compressive strength (UCS) tests, and a single F-T test at -20°C. The results indicated that higher concentrations of PEG increased the soil's Atterberg limits, decreased the maximum dry density, and increased the optimum water content. Although PEG acted as an antifreeze by preventing strength loss after one F-T cycle at higher concentrations, it significantly reduced soil strength initially due to its hydrophilic properties, rendering it ineffective as a stabilizing additive. Further tests on a clay-cement mixture with PEG showed that PEG significantly reduced the strength of the mix. Strength tests after one F-T cycle at -5°C revealed that higher concentrations of PEG could not prevent strength loss and further decreased the mixture's strength. This indicated that PEG negatively affected the cement hydration process, making it unsuitable for soil stabilization in cold climates. In contrast, MgCl2 showed more promising results. A comprehensive range of tests, including Atterberg limits tests, UCS tests, compaction tests, volume change measurements, F-T cycle tests, and microstructural analyses using FTIR, SEM, and XRD, demonstrated that higher concentrations of MgCl2 (14% solution) significantly lowered the soil's Atterberg limits, improved compaction by increasing the maximum dry density and reducing the optimum water content, and enhanced soil strength even without curing. Curing showed minor effects, with higher MgCl2 concentrations further improving UCS. MgCl2 also demonstrated durability under F-T cycles, maintaining soil strength and volume stability. Durability index (DI) values quantified the stability of MgCl2-treated soils after F-T cycles. At -10°C, soils treated with 9% and 14% MgCl2 solutions maintained their strength through seven F-T cycles, whereas untreated and 4% MgCl2-treated soils showed significant strength reductions. At -20°C, untreated and 4% MgCl2-treated soils lost considerable strength, while 9% MgCl2-treated samples exhibited smaller strength reductions, and 14% MgCl2-treated samples maintained consistent strength across seven cycles. DI values confirmed that precise MgCl2 concentration adjustments are crucial for soil stability in cold climates. Volume stability tests showed that untreated and 4% MgCl2-treated samples expanded with F-T cycles, while 9% and 14% MgCl2-treated samples showed no significant volume changes, indicating effective stabilization. Microstructural analyses revealed that MgCl2 promoted clay flocculation and particle size enlargement, aligning with observed improvements in soil properties. Comparative analysis of MgCl2 and PEG under F-T conditions highlighted MgCl2's superior performance in enhancing soil strength, durability, and volume stability. MgCl2's ability to improve soil properties and maintain structural integrity under challenging environmental conditions makes it a more effective antifreeze and stabilizing agent than PEG. The findings suggest that adopting MgCl2 as a stabilizing and antifreeze agent can significantly improve the performance of soil embankments in cold climates. By preventing the adverse effects of F-T cycles, MgCl2 ensures that construction projects can continue during colder periods, reducing delays and associated costs. This research provides a foundation for future studies to explore the full potential of MgCl2 in various geotechnical applications and contribute to the development of more resilient infrastructure in regions prone to harsh weather conditions. In summary, this thesis provides compelling evidence that MgCl2 is an effective antifreeze and stabilizing agent for fine-grained soils in cold climates. Its ability to improve soil properties, maintain structural integrity, and enhance durability under F-T cycles makes it a valuable additive for the construction industry. Future research should build on these findings to optimize MgCl2 concentrations for different soil types and climatic conditions, ultimately contributing to the development of more resilient and sustainable infrastructure.