Journal of Cold Regions Engineering

Abstract

In extremely cold regions with frequent extreme weather conditions, coupled factors make concrete corrosion by garbage landfill leachate become more complicated. Although previous studies have characterized the effects of individual factors, the mechanisms of coupled effects under specific conditions require further research. Therefore, this study analyzed the individual and coupled effects of landfill leachate, salt solution, and freeze–thaw cycles. The corrosion mechanism of landfill leachate was explained by analyzing the mechanical properties, surface morphology, and microstructure of the concrete. The individual factor tests showed that landfill leachate affected the performance of concrete more significantly than salt solution in the short term. In the immersion tests, the strength of concrete specimens corroded by landfill leachate was always minimized throughout the process, and the compressive and flexural strengths of concrete in landfill leachate decreased by 6.40% and 7.83%, respectively. In the coupled tests, freeze–thaw cycles amplified the effect of landfill leachate on concrete, exhibiting more severe damage than that with only landfill leachate. After four test cycles, the compressive strength of the concrete in the coupled test group decreased by 22.5%, 19.7%, and 31.3% and the flexural strength decreased by 40.2%, 26.7%, and 46.3%, respectively. Through surface morphology and microstructure analyses, we found that the inorganic salt ions in the landfill leachate reacted to form expansive ettringite and gypsum, which initially optimized the internal structure of the concrete but caused severe damage in the later stage. Concrete corrosion by landfill leachate was significantly enhanced under the influence of freeze–thaw cycles. The experimental results of this study provide basic data and theoretical support for designing and protecting concrete buildings in extremely cold environments.

Practical Applications

The deterioration of concrete buildings in landfills by landfill leachate corrosion has received widespread attention, and this problem is pronounced in cold regions. This study selected landfill leachate, salt solution, and freeze–thaw cycles as the corrosion conditions for the concrete corrosion test under one-factor conditions. At the same time, landfill leachate and salt solution were coupled with freeze–thaw cycles for the concrete corrosion test. The severity of concrete damage was compared by the changes in mechanical properties and microscopic morphology of the concrete during the test. The results of the one-factor corrosion test showed that the landfill leachate would cause more damage to the concrete in the short term. Meanwhile, the coupled-factor corrosion test results showed that freeze–thaw cycles amplify concrete corrosion by landfill leachate, resulting in a significant reduction in the mechanical properties of concrete and damage to the internal structure. In addition, the study characterized the mechanism of action of landfill leachate corrosion on concrete. This could also provide theoretical support for constructing and protecting concrete structures in landfills in cold regions.

To investigate the dynamic mechanical response and damage evolution behavior of ice-rich frozen clay, split Hopkinson pressure bar (SHPB) tests were performed on frozen clay specimens with initial moisture contents of 20%–1,000% under different temperatures, strain rates, and stress states. The stress–strain curves, dynamic strength, peak strain, absorbed energy density, failure mode, and failure progress were studied. The experimental results revealed the following: (1) in the radial-free state, the stress–strain curve of frozen clay with initial moisture contents ranging from 20% to 85% and 1,000% could be divided into three stages: elasticity, plasticity, and failure. In addition, a double peak phenomenon occurs in the stress–strain curves within the initial moisture content range of 120%–480%. (2) In the radial-free state, as the initial moisture content increased, the dynamic strength first increased to a maximum value, then decreased to a minimum value less than the dynamic strength of ice, and eventually increased marginally to the dynamic strength of ice. However, the variation in dynamic peak strain with initial moisture content followed a decrease–increase–decrease three-stage pattern. (3) In the passive confining pressure state, the initial moisture content of frozen soil determined its sensitivity to the confining pressure. (4) The high-speed camera test results indicated that the failure of the ice-rich frozen clay was mainly caused by tensile cracks. The degree of failure of the frozen clay specimens became more evident as the moisture content and strain rate increased. In the passive confining pressure state, the ice-rich frozen clay specimens remained intact except for a small amount of edge peeling.

Concrete can be cast and cured at freezing temperatures when additive-based freeze protection (ABFP) is included in the concrete mixture. However, the effects of extremely cold temperatures on the mechanical properties of concrete with ABFP have not been studied. In addition, the impact of cold temperatures on shear strength and modulus of rupture of concrete with or without ABFP have not been measured. The present study measures the effects of decreasing temperatures on the compressive strength, modulus of elasticity, shear strength, and modulus of rupture of concrete with and without ABFP. Different types of aggregates and ABFP systems were used to manufacture conventional concrete (without ABFP) and concrete with ABFP. Concrete with ABFP is mixed, cast, and cured at −5°C and conventional concrete, at 20°C. Specimens are conditioned at 20°C, −5°C, −20°C, −40°C, or −60°C for 24 h and then tested. Generally, it was found that the mechanical properties of both types of concretes increased as the test temperature decreased. However, ABFP lowers the pore solution’s freezing point and lowers the relative compressive strength increase rate compared with conventional concrete. Concrete with ABFP can have a higher rate of increase in relative elastic modulus than conventional concrete. This is due to the two-phase system of an ABFP pore solution at low temperatures, where ice fills voids, and the unfrozen concentrated pore solution continues to fill capillary voids and wet calcium silicate hydrate. The increase in shear strength from the aggregates and hydration products is greater than the contributions of the pore solution’s frozen properties. Finally, the rise in rupture strength is attributed to the increase in the strength of concrete materials because there is no significant change in the tensile strength of ice with decreasing temperature.

Ice-coring auger machines can cost thousands of dollars and are generally made for vertical extraction from sea ice or glaciers. This project required specimens from ice accreted onto vertical piles at the Port of Alaska (POA) in Anchorage, Alaska, which meant the extraction was horizontal and had to be completed during the short low-tide window. In this paper, we describe the development of a method for economically harvesting and processing the accreted ice from the POA into cylindrical cores and shear beams. The ice was harvested by cutting large cubes out of the in situ mass with a chainsaw and then lifting these onto the port deck using a crane. The cubes were then transported to a laboratory walk-in freezer to be processed. Ice cores were drilled from the cubes using a custom-fabricated core bit made from metal tubing and hole saws. This simple core bit quickly produced smooth ice surfaces, provided there was a mechanism for evacuating the cut ice chips during drilling. To facilitate this, an alignment template was used to locate and drill two adjoining evacuation holes prior to coring. These evacuation holes had to be precisely located to be adjacent, parallel, and connected with the outside diameter of the forthcoming core, but were not allowed to impinge on the core. With this new method, an ice block can be converted into up to a dozen test-ready compression ice cores within a few hours. The variability in the diameter of the ice cores was found to be small, with a coefficient of variation of < 0.4%.

The hydrothermal field status of soil–rock mixture–concrete interface changes significantly under freeze–thaw cycles, which causes pore structure changes, interface debonding, and cracking; therefore, the shear strength deteriorates and the safe operation of buildings in cold regions is affected. Indoor direct shear and nuclear magnetic resonance (NMR) tests and numerical simulations were conducted to explore the strength deterioration mechanism at the interface between the soil–rock mixture and concrete with different roughness degrees under freeze–thaw cycles in this study. The results suggest that freeze–thaw cycles have little effect on the rotation and displacement of particles, and roughness has a considerable effect. There are primarily three types of pores in the interface layer: (1) micropores; (2) mesopores; and (3) macropores. By increasing the number of freeze–thaw cycles, the T₂ spectral peaks of the pore structures shifted to the upright side and the total T₂ spectral area increases. The increase in the roughness degrees tends to increase the proportion of mesopores and enhances the interfacial strength. The results could benefit research on soil–rock and concrete interface systems and provide effective guidance for the construction, operation, and maintenance of pile foundation engineering in cold regions.

The numerical simulation of wind-induced snowdrift often employs a one-way coupled scheme that neglects the interaction between moving snow particles and turbulent wind. However, this approach can result in significant errors when the mass concentration of snowdrift near the snow surface is high. To address this issue, a modified two-way coupled scheme for simulating three-dimensional wind-induced snowdrift was developed. This scheme reasonably considers the interaction between snow particles and turbulent wind and introduces a double-loop nested framework. To illustrate the effectiveness of this method, a simulation was conducted for large-scale wind and snow fields on the roof of a terminal building in northwest China. The results were compared with field observation data of snow depth, demonstrating the applicability and superiority of the proposed method. The modified two-way coupled scheme was shown to provide a more accurate simulation of wind-induced snowdrift compared to the one-way coupled scheme. Based on this improved accuracy, predictions of wind-induced snow redistribution on the building roof were made, considering a 100-year return period for wind and snow loads. These predictions are crucial for the safety design of long-span roof structures in cold regions.

Performance measures that are commonly used in winter maintenance provide valuable information. However, some metrics are subjective (i.e., visual inspection), rely on historical records, depend on agencies’ practices, or only capture specific information. Winter maintenance performance measures are evaluated independently, and relationships among variables are not assessed. Therefore, the metric travel disruption (TD) is proposed in this study to perform a multispectral evaluation with input, output, and outcome-based performance measures to compare salt brine with solid salt applications. The metric TD integrates different sources of information to estimate a continuous performance measure that accounts for storm, vehicle operations, and roadway conditions over time instead of intermittent measurements or one-time observations, such as roadway friction or time to bare/wet. The input performance measures included storm conditions, type of chemical material, frequency of application, and application rate. The output performance measures were the amount of material used and the lane kilometer (miles) covered. The outcome performance measures consisted of time to bare/wet, speed reduction period, speed recovery period, storm impact period, maximum speed reduction, and TD. For salt brine, previous research has shown reduced salt usage, shorter times to bare/wet, and higher friction. However, there are some concerns regarding the operational and safety performance of roadways that are treated with salt brine. Winter treatment field data and vehicle probe data from the National Performance Management Research Data Set (NPMRDS) were collected from the study (salt brine) and control (solid salt) routes in Wisconsin. For the amount of salt used, the study routes used 32.6% less overall salt than the control routes per storm. The TD indicated that, on average, there was no statistically significant difference between the study and control routes. Despite the lower amount of salt that was used, roadways that were treated with salt brine had a similar operational performance as roadways that were conventionally treated with solid salt, which made salt brine application a cost-effective strategy. This evaluation demonstrated a multispectral performance evaluation of winter maintenance to appropriately quantify the effectiveness of treatments.

Abstract

A vast amount of waste disposable face masks (FM) has threatened the ecosystem since COVID-19 became a pandemic. Given the urgency of the situation, this study innovatively assessed the potential utilization of the waste FM fibers to reinforce the subgrade in the permafrost regions. The effect of FM contents (0.5%, 1%, and 1.5%) and length–width (LW) ratios (1, 2, and 3) of the frozen silty clay specimens (−10°C) with different initial moisture contents (w = 15%, 20%, and 25%) on the mechanical behavior, including the peak deviatoric stress (q), the increment of peak deviatoric stress (λ), and the initial elastic modulus (E₀), was analyzed. The pore structure change mechanism under the influence of FM and w was further revealed via nuclear magnetic resonance (NMR). The results indicated that the incorporation of FM improved the soil strength at a certain w, while the FM content and LW ratio were found to have different effects on the q values. The most effective reinforcement can be identified at w = 20%, according to the relatively large λ values (29.2%–79.1%). Moreover, the E₀ values of specimens with higher initial moisture content and FM content were smaller, which can be explained by the cracks generated due to the water-ice phase change and uneven distribution of FM. NMR results revealed that the FM had less effect on the pore-water relaxation characteristics, and the change in soil structure was more remarkable in the frozen specimens with higher w. This study pointed out that the tension of FM and its bonding soil particles played the leading role in soil stress–strain behavior.

Practical Applications

The results of this study recommend that waste face masks (FM) be added to the soil in the subgrade to improve its strength in permafrost regions. The mechanical properties (including the peak deviatoric stress and initial elastic modulus) of soils reinforced by various FM contents and different FM sizes were determined via experiments. The reinforcing mechanism is discussed by observing the surface of frozen soils and detecting the change in pore structure before and after freeze–thaw to explain the complex mechanical behavior of reinforced soils. The moisture content of soils is a significant factor influencing the reinforcement effect. According to the test results, different reinforcement parameters, for example, the content of additive FM and the FM size, should be selected in the specimens with different moisture contents for the best reinforcement effect. This paper provides novel and valuable guidance for waste FM utilization and subgrade strengthening in permafrost areas.

Substantial degradation can occur to warm permafrost due to changes in surface conditions resulting from infrastructure development and climate warming. The associated geohazards, including differential settlement, slope instability, and liquefaction of degraded, unconsolidated materials in seismically active warm permafrost regions, pose substantial threats to the built infrastructure. Among them, seismic hazards of degraded permafrost have received little attention. This paper aims to provide a case study of an airport built on warm permafrost about 80 years ago, focusing on climate changes, permafrost degradation, and observed seismic hazards during a strong earthquake. The study site, that is, the Northway Airport, is located in a discontinuous permafrost area in Interior Alaska. Geotechnical data from 1973, 1991, and 2005 were compiled and analyzed to reveal permafrost degradation at various surface conditions, and are compared with the well-known degradation data from a site in Fairbanks. Furthermore, the responses of the airport runway during the 2002 Denali earthquake (M_w = 7.9), including liquefaction and lateral spreading displacements, are described and analyzed. And the seismic hazards of civilian airports built on permafrost across Alaska are surveyed. Distinct trends are revealed in two periods, namely, from 1943 to 1975 and from 1976 to 2021, for air temperature, precipitation, and wind speed. Permafrost tables were observed to drop with time at various rates for different surface conditions. Liquefaction and lateral spreading were observed extensively during the earthquake. The locations of observed liquefaction at the airport are mapped, and the lateral spreading displacements are estimated based on available photos. The standard penetration test data collected during geotechnical investigations are analyzed, and a liquefiable layer is identified at the talik between the active layer and the permafrost table. Moreover, 55% of Alaska's civilian airports are in permafrost areas. Among them, two-thirds fall within seismic zones with a risk level of 3 or above. This study demonstrates the high seismic risks of degraded permafrost and its potential impact on the built infrastructure.