Journal of Cold Regions Engineering

Understanding the freezing and thawing processes in porous media such as soils is important, especially in regions experiencing seasonal frost or permafrost. These processes have a wide range of implications as diverse as how to maintain the structural integrity of roads, railways, pipelines, and buildings, to when to plant seeds during the growth season. Thawing of frozen ground is the opposite process of ground freezing but has not received nearly as much attention as the latter in research studies or field experiments. Accurately predicting thaw depth or thaw rate is a challenging task. Many mathematical models have been proposed to describe the thawing process, with different perspectives and complexity. This paper provides an overview of historical modeling efforts made for predicting heat and mass transfer during thawing. Assumptions and premises for each model are discussed, as well as limitations and some applications. In addition, this paper reviews historical and modern approaches to thawing of frozen ground in cold regions, lists pros and cons of each method, and gives examples of applications. The review shows the need for further research and more accurate models, specifically for predicting thaw depth and thaw rates in frozen ground subjected to artificial thawing.

Thermal cracking of asphalt pavements is primary distress in cold regions. The Bending Beam Rheometer (BBR) can be used as a thermal cracking prediction tool for asphalt mixtures based on AASHTO TP 125. This study investigates the change in the low-temperature performance after aging asphalt mixtures in both indoors (forced-draft oven in the laboratory) and outdoors (open environment on a roof). The BBR thin-beam specimens aged outdoors were tested for up to 5 years. As the BBR test is nondestructive, the same thin-beam mixture specimen can be tested frequently to obtain its aging information. Therefore, after 5 years of aging, a relationship between laboratory aging and natural aging can be obtained. An Aging Index was proposed in this study to differentiate among mixture characteristics and aging methods. It is a measurement of the mixture-specific sensitivity to the aging of the material. It was found that the laboratory aging methods used in this study would simulate approximately 5 years of aging in the field, which is similar to the AASHTO R30 protocols. Successful application of this idea can connect AASHTO TP125 with the AASHTO R30 aging protocols and make BBR testing applicable as a performance test in the field.

Icing of wind turbine blades poses a great challenge for wind farms in cold climates, this challenge is addressed by implementing various deicing practices that require significant cost to operate. Thus, alternative and potential solutions are needed to improve wind power production in cold climate. The present study is investigates the effectiveness of a new deicing system consisting of infrared heaters. Two types of heaters were selected based on wavelength, input power, and investment cost. The heaters were tested on blades covered with soft rime ice. A thermal camera was used to image the deicing procedure together with a load cell to measure the weight of the ice melted. It was found that a combination of two different types of heaters provides effective deicing at a distance of 1.5 m compared with multiple units of the same type of heaters. It was observed that the infrared deicing system has a larger area of heat distribution, which is one of the major advantages compared with traditional systems.

In recent decades, road weather information systems (RWISs) have gained in popularity with road maintenance authorities. However, RWIS stations only provide point measurements that are often unrepresentative of distant surrounding areas. To address such limitations, this study employs a hybrid geostatistical interpolation method, regression kriging (RK), to fill in the large spatial gaps at unmonitored locations. Road surface temperature (RST) data collected by an automated vehicle system along selected interstate highways were used to model the RST spatial variation patterns via semivariograms, which were then used to interpolate the conditions in between RWIS stations. Cross-validation results indicated that RK successfully captured the spatial variation of RST along the highway segment. The nugget-to-sill ratio obtained from semivariograms was further utilized to characterize the weather events, and the results implied that stronger winds and heavier rainfalls were likely to form a stronger spatial dependence within RST. The findings of this research contribute to better understanding of the influences of meteorological factors in RST as well as improved models for inferring the road surface conditions between RWIS stations.

Chilled gas pipelines generally traverse a long distance through various soils and may operate for decades with varying temperatures of gas, surrounding soil, and ground surface. The present study investigates the effects of key factors on frost heave using two-dimensional finite-element modeling of the coupled thermomechanical process by implementing the Konrad–Morgenstern segregation potential model. A simplified approach is proposed to estimate the thaw-back effects on long-term frost heave. The seasonal variation of ground surface temperature significantly affects the heave, especially for pipelines at shallow burial depths and for long-term heaving. An increase in cohesion of the frozen soil and a reduction in the initial ground temperature reduce the heave. Modeling of frozen fringe and stress effects on segregation potential are discussed. Subzero gas temperature has a smaller effect on heave for lower initial ground temperatures; however, it significantly affects long-term heave for higher ground temperatures.

Abstract

Many engineering problems are caused by the destruction of cement-based materials through the combination of salt mixtures and freezing/thawing. To improve the performance of cement-based materials under harsh environmental conditions, mortar was selected as a research object, and its mechanical and phase transformation characteristics were investigated by adding nano-CaCO₃, silica fume, epoxy resin, and mixtures of these components. Laboratory tests were conducted on salt mixtures and freeze/thaw cycles, and the compressive strength and mass loss rate of the mortar recorded before and after freezing/thawing were compared. Subsequently, the effects of the type and amount of additive on the compressive strength and mass loss rate of the mortar were analyzed. The microstructural characteristics of the modified mortar were investigated using scanning electron microscopy, and the mechanisms of the physical and mechanical properties of the mortar modified by additives were revealed. Furthermore, the phase transition properties of water and salt in the modified mortar were studied using differential scanning calorimetry, and the crystallization amount, unfrozen water content, supersaturation ratio, and crystallization pressure in the mortar were calculated on the basis of heat balance and mass balance. The results indicate that during the cooling process, the solution in the internal pores of the mortar undergoes a crystallization phase transition, and the maximum crystallization pressure can reach a value of 30.1 MPa. The additive forms a compact structure inside the mortar to prevent harmful ions from infiltrating the mortar, thereby mitigating the damage caused to the mortar. The apparent deterioration reduced and the compressive strength of the modified mortar improved after several salt and freeze/thaw cycles, and an improvement rate of 15% for the epoxy resin was the most prominent result.

Practical Applications

The variation in temperature in this study was defined to model cold regions in northwest China and there are similar saline soils in cold regions in other parts of the world, such as the Mediterranean Basin, California, Southeast Asia, Arctic coast, and Central Siberia (Hivon and Sego 1993; Serrano and Gaxiola 1994; Bohren and Albrecht 1998; Shaterian et al. 2005). Therefore, cement-based materials worldwide suffer damage from salt erosion and freeze/thaw cycles. Although there are differences in temperature and salt concentration in different regions of the world, this research has practical reference value for improving the quality of mortar. For the additives considered in this study, all mass loss ratios of the improved mortar significantly reduced. In soil containing sodium chloride, a mixture of silica fume and epoxy resin is suggested to improve the durability of mortar based on reduced crystallization inside pores. In soil containing sodium sulfate, adding a mixture of na-CaCO₃ and epoxy resin can improve the physical and mechanical properties of mortar by reducing salt and ice crystallization in pores. Although the improvement of mortar under the action of salt and freeze/thaw cycles was investigated in this study and the internal mechanisms of mass loss rate and compressive strength enhancement were discussed, the relationship between freeze/thaw cycles and actual environmental temperature changes has not yet been established, and phase changes in porous materials are closely related to the speed of temperature variation. The manner in which freeze/thaw cycles correspond to an actual environmental cycle and the improvement and phase transformation of mortar under ultralow temperatures (below −20°C) are worth studying in the future. Furthermore, the volume of a specimen has a significant influence on the transition temperature, in which supersaturation and supercooling decrease as the volume of soil increases (Wan et al., 2021). Furthermore, the effects of volume on the law of phase transition in mortar remain to be addressed in future studies.

To reduce the environmental damage caused by traditional deicing methods, the feasibility of conductive rubber composites in road deicing was studied. In this study, a method for preparing conductive ethylene propylene diene monomer rubber composites was introduced. The effects of different voltages and ambient temperatures on the use of the conductive rubber composite for heating pavement were investigated. The ice melting process was determined by melting ice of different thicknesses. The resistance stability was studied by simulating the engineering service time. The results showed that the higher the voltage, the faster the conductive rubber composite heated. The temperature of the asphalt samples revealed that the conductive rubber composite generated heat uniformly. The ambient temperature had little effect on the heating rate. Thicker ice took a longer time to melt. However, the ice melting rate increased with increasing ice thickness. Furthermore, the heat generation performance of the conductive rubber composite changed little during the first 5 years of operation. This result indicated that the electrical resistance was stable. The deicing method proposed in this study can melt ice uniformly and quickly and is more environmentally friendly and sustainable than traditional deicing methods.

This paper is concerned with electrically heated asphalt pavements; it numerically explores the possibility of such technology to actively suppress frost penetration under seasonal cold-weather conditions. A thermal model is outlined for the investigation based on the one-dimensional heat equation including latent heat effects. This model is applied to a multilayer medium containing a buried heat source representing the heating system. Utilizing cold-climate weather data from northern Finland, calculations were performed to track the evolution of the frost front depth in an idealized pavement structure with no heating. Then the model calculations were repeated with the heating activated. A parametric study was performed with different heat production intensities and several embedment depths for the heating system. It is numerically demonstrated that embedded electrical heating can suppress frost penetration depth and duration in asphalt pavements, rendering the explored application practically feasible.

Structural snow fences have been increasingly used in northern regions of the United States. They are known as a cost-effective and efficient technology to prevent snow accumulation on highways and, therefore, improve road safety. Structural snow fences, however, are used only during winter, and to add more value to the structure, an idea to install solar photovoltaics (PV) panels on structure snow fences was first proposed by the Minnesota Department of Transportation (MnDOT), who was interested in looking at the feasibility of integrating structural snow fences with PV panels, called PV snow fences (PVSF). The PVSF would be constructed by replacing the rails between the poles of the structural fences with customized PV panels that have the same dimension as the rail. This arrangement is to ensure that the original function of the snow fences, that is, eliminating blowing and drifting snow on highways, would not be affected. Considering different factors or parameters, such as project size, panel size, installation angle or orientation of the panels, discount rate, energy selling price to a utility company, availability of incentives, ownership of the PV system, etc., a comprehensive cost–benefit model has been established to analyze the pros and cons of different implementation plans. The analysis results show that the longer the length of the PVSF is, the more cost-effective the project is, due to a lower capital cost and increased power generation. A Power Purchase Agreement (PPA) would significantly shorten the payback period in consideration of the key benefits brought through a PPA, including minimal up-front capital costs, lower energy costs, no risk, no upkeep, leveraging available tax credits, and enhancing the value of the property, which is, therefore, more realistic and would be a higher priority for an agency like MnDOT or other state DOTs.