State of the art and practice of pavement anti-icing and de-icing techniques

WenBing Yu , Xin Yi, Ming Guo, Lin Chen

State Key Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental Engineering Research Institute,Chinese Academy of Sciences, Lanzhou, Gansu 730000, China

1 Introduction

Snow and ice problem of roads causes heavy losses in many countries each year. In northern cold regions and southern freezing rain areas of China, snow and icing problems are serious and dangerous to traffic.There were eight major traffic accidents caused by icing of bridge pavement in Guizhou, Sichuan, and Hunan Provinces during the winter of 2010–2011, and data from the Ministry of Transport of the PRC indicate that there are many more traffic accidents in snow and icing seasons (Li, 2006). Snow and icing of pavements cause enormous economic losses as well. In January,1996, traffic in the northeastern United States was paralyzed by a snowstorm for four days, with a direct economic loss of US$10 billion. In November, 2005,continuous snowfall in northwestern Germany resulted in more than 2,000 traffic accidents and direct economic losses of 100 million Euros. In December, 2005,Weihai and Yantai in Shandong Province suffered a continuous, 15-day heavy snowstorm and incurred direct economic losses of 370 million Yuan (Wang HJ,2007), and in 2008, freezing rain in southern China caused direct economic losses of 6.2 billion Yuan.

Given these high economic losses and risks to public safety, considerable research has been done on snow and ice melting techniques and applications all over the world. There are two general methods for dealing with pavement snow and ice: clearance and melting. The clearance method is simply the manual removal of snow and ice using snow removal machines, coupled with the mechanical application of salt and sand. The melting method includes chemical melting (snow melt agents and pavement materials that have lower freezing points) and thermal melting(e.g., geothermy, solar energy, electricity, conductive concrete, and infrared heating systems). For the past 60 years these techniques have produced good results,but environmental pollution, high cost, and limited application conditions still exist. Environmentfriendly and high-efficiency melting techniques are still being developed.

Currently in China, only snow melt agents and snow removal machines are used; ice removal machines are inadequate. Scattering melt agents requires labor, and the shortage of systematic planning and forecasting of pavement icing is disadvantageous to traffic in winter. Heat melting is still in the early stages of development in China, and no practical application has ever been reported. Therefore,this paper is intended to provide valuable references for pavement snow/ice removal in China.

2 New developments in snow melt agents and applications

Snow melt agents are most commonly used worldwide, and they include various types of chlorine salt, non-chlorine salt, and mixed salts. The fundamental principle is that the snow melt agent can decrease the vapor pressure of the solvent (snow), and thus the freezing point (ice point) of the entire solution is decreased. Foreign countries started to use snow melt agents in the 1930s, and mainly used sodium chloride. Now there are five kinds of snow melt agents used in the United States, including three types of chlorine salts (sodium chloride, calcium chloride,and potassium chloride) and two types of non-chlorine salts (calcium magnesium acetate and carbamide). The latter are not used widely because of their low efficiency, high application rates, and cost.Japan started to use sodium chloride in the 1960s and calcium chloride in 1995 (Chenget al., 2004; Wang HJ, 2007). China started to use sodium chloride in the 1980s and other chlorine salts in 2000.

The application rates have increased significantly.In Beijing since 2002, the average annual usage amount was 8,000–10,000 tons, and even reached 35,000 tons in 2010. But in 2011 the use of melt agents was cut greatly and the government invested 390 million Yuan in new snow and ice removal machines; the mechanization rate reached 90% (Gu and Liu, 2011). Shenyang also started to reduce the use of snow melt agents, believing that cities with strong economies should improve the level of mechanization to protect the environment.

Snow melt agents have both advantages and disadvantages. They have adverse effects on the environment, buildings, and plants while melting the snow.Chlorine salt can cause a strong corrosive action on pavement structure (rebar, concrete, asphalt,etc.) and usually damages bridge structures in 10–15 years,which is one of the most important potential safety hazards on roads and bridges. David (1992) estimated that every 1 ton of snow melt agent causes US$615 in bridge corrosion, US$113 in vehicle corrosion, and US$75 in plant damage. Considering the negative effects of chlorine salts, technical specifications and restrictions have been put in place in many counties.

A new direction in research is on environment-friendly, salt-based snow melt agents. These new salt-based snow melt agents have a non-chlorine corrosion inhibitor to remove snow and ice. Guo and Wang (2010) proposed zinc dihydrogen phosphate-sodium tungstate-thiourea-SDBS as a corrosion inhibitor. Calcium chloride with this added corrosion inhibitor reduces corrosion and plant damage but has the same melting speed, which makes it a high-efficiency melt product. Another new development in snow melt agents is changing from single-component to multi-component composites, exchanging traditional inorganic components for organic ones, and using wastewater from the ester,sugar, and pulp industries and municipal refuse (Xu,2008). Xuet al. (2007) chose biodegradable,low-cost acetic acid liquid (wood vinegar) to study the use of low-cost calcium magnesium acetate(CMA) snow melt agent and then created mixed carboxylic acid, calcium, and magnesium salts. Their series of tests indicated that CMA had good performance with low melting temperature, high melting efficiency, and low corrosion of metal, plants, and structures. Linet al. (2010) developed a chromogenic, environment-friendly snow melt agent with added corrosion inhibitor and plant calcium, which is benign on plants. The quantity of this agent can be controlled through the color of the agent in order to reduce corrosion to metal, pavement, and plants.Almost all of these kinds of alternative snow melt agents perform much better than sodium chloride.

3 New developments in mechanical methods

Mechanical snow and ice removal is a traditional and widely used method which simply uses machines to remove snow and ice. In heavy snow country, research into superior functioning machines is extremely important. Snow removal machines can be classified according to the working principle, the usable range, the chassis form, and the moving type(Hu, 2010). The five types of working principles are push type, helical rotor type (stroke type), rolling type, shovel type, and hammer crusher type. The push type includes shovel type, front side shovel type, V-shaped snow plough, and snow removal truck. The helical rotor type can be either a milling cutter rotor type or an impeller rotor type. There are two types of chassis: exclusive-use chassis and dual-use chassis, and they are further classified into tire type and crawler type. In practical work, snow removal machines are classified as either plough type or cutter head type, and these are further differentiated by how they are applied: general snow removal machine, pavement snow removal machine,railway snow removal machine, or expressway snow removal machine.

At present, mechanical snow removal equipment and methods are becoming more mature, but there are still many limitations such as varying pavement conditions, snow layer thickness, and temperature. For example, one type of machine described above might not be able to clear ice and snow from a certain kind of pavement, which limits its use as a snow removal machine.

There are now more types of snow removal machines in developed countries and, given the higher demand placed on snow removal machines, they are becoming more automated and multi-functional.Some massive, exclusive snow removal machines are in use now. For example, the Schmidt TS4 stroke-type snow removal machine (Aebi Schmidt Deutschland GmbH, St. Blasien, Germany) can deal with 6,000 tons of snow per hour.

Other developments in mechanized snow and ice removal (Zhang, 2008) include: (1) high-performance,dedicated chassis commonly using fluid-torque power shift devices and automatic electro-hydraulic control systems. These lessen the burden on the driver while still achieving high-speed snow removal;(2) multi-function snow removal vehicles; (3) highefficiency, mounted gas-type snow removal and melting devices, which eliminate the high expense of transporting snow out of cities to suburbs; (4) further research into the physical properties of snow, which could provide new theoretical bases for machine design work; and (5) improvement of the mechanical efficiency, safety, operability, and comfort. This is a prominent direction in Japan.

Research on snow removal machines and methods in China started late, after the 1980s, with the reinforcement of the reform and the explosive growth of roads and motor vehicles. More than ten new prototypes were produced and put to use in snow removal operations. Guanet al. (2003) designed a microwave de-icing schematic diagram based on the study of microwave heating. Based on frequent freezing rains in southern China, Liu (2010) did a detailed theory analysis and design calculation on a vibration de-icing roller, a de-icing sheepfoot roller, a hydraulic vibration system, and a vibration shaft and eccentric block-type vibration mechanism. Hu (2010) developed a multi-purpose snow shovel, which is suited to pavements in cold areas. It is mounted on the front end of a vehicle and can swing all around to clear snow and ice; it can adapt to a variety of conditions and can clear road snow and ice quickly and radically.

With the continuing development of snow removal science and technology, mechanical-electrical-liquid integration has been applied on snow removal machines. Computerized, highly sensitive sensors are in widespread use on controls, measurements, alarms,obstacle removal, and intelligent operation (Guo and Zhou, 2010). These techniques have made snow removal machines more infallible, multi-functional,supermatic, safe, and comfortable for the operators.

4 New developments in thermal snow melting techniques

Thermal snow melting techniques can prevent and clear roads of snow and ice. The principle is to use external thermal energy to heat the road to keep the temperature higher than 0 °C, thus preventing the accumulation of snow and ice on the road. Depending on the nature of the thermal energy, these methods use geothermy, electricity, infrared, and solar.

4.1 Geothermal heat systems

Geothermal heat energy includes the heat in shallow soil, geothermal hot water, and steam. The energy in shallow soil can be transported to the pavement through heat pipes, and the energy in geothermal hot water and steam can be transported to the pavement through circulating pipelines. Geothermal heat systems are relatively common in Europe, America, Japan, Argentina, and Canada, but have not yet been used in China.

4.1.1 Heat pipes

Geothermal energy in shallow soil can be transmitted to the pavement by fluid antifreeze in pipes, by which the pavement is heated to above 0 °C (Figure 1).This type of configuration was first used in Trenton,New Jersey in 1969 (Lund, 2000). The pipes were embedded 5 cm below the pavement with 60-cm spacing between the vertical pipes. In winter, the temperature at the 2-m depth varied between 8.8 °C and 13.8 °C, and the moving antifreeze temperature in the pipes ranged between 4.4 °C and 11.1 °C during snow storms. Typical measured snow melting rates were 0.60–1.25 cm/h when the corresponding air temperature ranged between -6.7 °C and 1.7 °C.

A second project, using the results of the Trenton experience, was to test the efficiency of a vertical or gravitational thermal probe. Ammonia and freon were utilized as the working fluid instead of an eth-ylene-glycol mixture. With a 1:1 ratio, the experiment was conducted on a highway ramp in Oak Hill, West Virginia and on two ramps near Cheyenne, Wyoming with a gradient of 7% (Nydahlet al., 1997). The experiment utilized 177 heat pipes in 984 m2of pavement. Each heat pipe had 30-m evaporation sections and empty condensation sections (36 m in total). The geothermal temperature of the trial road section was 12.2 °C, and the results were good.

Two more elaborate heat pipe design experiments were carried out at the Sybille Valley and at the Chunxi Bridge in 1976 and 1980 respectively in Greece. Similar heat pipe systems were tested in Japan and in Glenwood Springs, Colorado. The Glenwood Springs heat pipe system adopted well water instead of geothermal source.

Figure 1 Schematic of a pavement heated by geothermal heat pipes

4.1.2 Geothermal fluid

The geothermal fluid heating technique transmits underground hot water and steam to the pavement or the surface of pavement to melt snow and ice. Fukui City in Japan used to sprinkle roadway surfaces with underground warm water. The 15 °C groundwater flowed through heat exchanger ducts buried in the sidewalk, where the temperature was reduced to 7.2 °C. After melting the snow on the pavement, the water was then sprinkled on the adjacent roadway.This method could possibly cause subgrade settlement,so the water needed to be collected and re-channeled.Also, the temperature should not be too low or the frozen water could cause more serious problems.Therefore, Fukui City began to use other thermal heating systems after 1990.

At Sapporo, Japan, underground hot water has been used for snow melting on roads since 1966. Initial construction used steel pipes, but they were replaced with polybutene pipes in 1973. The inlet temperature of the hot water ranged from 76 °C to 81 °C.A current pavement snow melting system on Gaia Road in Ninohe, Japan consists of three 89-mm-diameters, 150.2-m-long concentric tube heat exchangers and a heat pump system with one 15-kW motor and two 0.75-kW circulating pumps. The 16-mm-diameter polybutylene heat pipes are placed 10 cm below the surface of the asphalt concrete pavement, with 20-cm spacing between the pipes. The total thermal power is 50 kW. After many years of operation, the system has been proved to use 20% less power than an electric heat system. As of 2005, more than 25 other geothermal pavement snow melting systems have been installed in parking lots, highway ramps, and sidewalks in Japan.

The United States was the first country to use hot water to heat pavement. The oldest geothermal pavement snow melting system was installed in Klamath Falls, Oregon in 1948. This was a 137-m-long cement street section. The grid consisted of 1.8-cm-diameter iron pipes placed 7.5 cm below the surface of the concrete pavement, with 45-cm spacing between the pipes. A glycol-water solution was adopted as the antifreeze, and the circular flow was about 300 t/s. The heat source came from nearby geothermal wells. The temperature dropped from the original temperature of 37.7–54.4 °C to -1.1 to -1.7 °C. By 1997, after almost 50 years of operation, the system had failed due leaks in the grid caused by external corrosion. In 1998 a contract was issued to reconstruct the bridge deck and highway pavement along with replacing the grid heating system. The concrete pavement and bridge deck were removed and a new crushed rock base added, and 1.8-cm cross-linked polyethylene tubing(PEX) was then used for the grid section. According to Lund (2000), the entire cost of the reconstruction project was approximately US$430,000, the estimated annual maintenance cost will be US$500, and the annual operating cost (for the circulating pump) will be US$3,000.

In 2003, the Oregon Department of Transportation invested US$1,300,000 to reconstruct the Eberlien Street Bridge and Wall Street Bridge in Klamath Falls.Due to the 13.25%-grade ramp on the Wall Street Bridge, the geothermal heat systems, the pipeline construction, and the machinery cost of the entire systems were US$170,000 and US$36,000 respectively. The systems cover 960 m2, including the deck and sidewalk area of 346 m2. The design snowmelt heat load is 189 W/m2. The heat source of the system is provided by a heat transfer station consisting of a type 316 stainless steel plate heat exchanger at a heat power of 174 kW, at a work pressure of 1.3 MPa. The Oregon Technology College has installed a snowmelt system on the ladder road in front of the comprehensive building.

In the Copahue-Caviahue Thermal Area of Argentina, geothermal steam is used for heating streets and a road to Villa Copahue, a ski resort (Pesce, 1998).The steam is produced from a 1,400-m-deep geothermal well. The steam is transported through a 2.6-km-long pipeline to the pavement in the city.Winter temperatures in the area are as low as -12 °C,wind speed can reach 160 km/h, and the average snowfall thickness is 32.5 cm. Using geothermal heat,the pavement temperature can be kept between 12.2 and 16.1 °C.

In 1998, an airport runway snow melting system was installed in Poland. The average temperature is 68 °C and underground water flow reaches 50–150 m3/h. Considering the influence of the temperate marine climate, the system design parameters are as follows: relative humidity of 80%, an average snowfall of 2 mm/h, and an average wind speed of 3.4 m/s.When the system bears the maximum heat load of 200 W/m2, the inlet and outlet water temperatures are 55 °C and 25 °C, respectively. When the system stays in a dissolved state that bears a heat load of 100 W/m2,the inlet and outlet water temperatures are 30 °C and 5 °C, respectively. The system flow rate is constant at 5.7 L/(m2·h). The pipe grid consists of DN20HDPE pipes placed 80–100 mm below the surface of the pavement with 250-mm spacing. Ethylene glycol is used as the antifreeze.

Geothermal resources are abundant in Iceland. By 2000, road melting systems had been installed over an area of more than 3.5×106m2, and the ratio of geothermal water application was about 33%.

4.2 Non-geothermal heating systems

The heat resource of non-geothermal heating systems is non-geothermal energy, such as waste heat from urban water supplies, domestic wastewater, and gas heating. The Virginia Department of Transportation has built a heat bridge in Amherst County on which burning propane heats a circulating antifreeze mixture of propylene glycol and water. The circulatory system transmits the heat to the bottom of pipes, and then the working medium in the pipes transmits the heat to the surface of the bridge (Figure 2). The pipes were originally filled with freon but the resulting heat output was inadequate. In 1999, the system was converted to ammonia. The bridge is about 35 m long and 13 m wide.The project contains approximately 3.2 km of steel piping, including 241 heat piles. The heating system was built at a cost of US$181,500, and about 27.3% of the project takes advantage of urban wastewater in heating the pavement.

A solar energy snow melting project reported by Rauder (1995) was been installed on a bridge on Road 8 in the Swiss highway network. The aim of the project was to collect the solar heat of the asphalt bridge surface during the summer period, store the heat in an underground heat sink, and utilize the heat to heat the bridge surface in winter, thus preventing the formation of ice. The essential components of the system are the heat exchange tube system embedded in the asphalt layer of the bridge, covering a surface of 1,300 m2, the underground heat sink, and the hydraulic system. Including preliminary studies, the total cost of the project amounted to the equivalent of US$3 million.

Figure 2 Schematic of a bridge heated by a non-geothermal system

Wang QY (2007) obtained the moving regularity of the temperature field and phase boundary during the snow melting process through analysis of the snow melting mechanism in a solar-soil thermal storage snow melting system. Liu and Zhu (2005) analyzed the economic and environmental benefits of solar-soil thermal storage snow melting techniques and recommended this approach. Wanget al. (2007)did a numerical analysis of the heat transfer characteristics of a solar-geothermal heat road snow melting system, built up a model of pavement heat transfer of a road snow melting system, and did numerical simulations of unsteady heat transfer based on the hourly weather data of a typical year and composite boundary conditions. The different effects on the performance of road snow melting at different depths of pipes and heating temperatures were analyzed and the relationships among the maximum heat load, snowfall,air temperature, relative humidity, and wind speed were derived.

The main problems anticipated with this system were to make sure all joints were sealed and that the pipes were protected against corrosion. Construction costs were increased because of the excavation and drilling needed for pipe burial.

4.3 Electric heat systems

Electric heat systems use electricity in cables or conductive pavement materials to heat the pavement.This method is relatively mature in northern Europe and there are even some companies engaged in professional design, installation, and after-sale service of these systems. The United States was the first country to use electric cables to heat pavement. The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) design handbook specifies the design, cable distribution, line connection, and installation tests (ASHRAE, 1985). This technique is still in early adoption in China. Tanget al. (2002a,b;2006) did a finite element analysis on conductive concrete de-icing and snow melting. Liet al. (2004)researched the snow melting performance of steel fiber graphite conductive concrete, and obtained the temperature and power consumption data. Houet al.(2002, 2005) and Hou (2003) and Hou and Li(2004a,b; 2005) did considerable research on carbon fiber conductive concrete. Wu (2005) studied pavement snow melting by heating cables and concluded that the design power of the pavement snow melting system depends on the material properties of the structure layer, meteorological conditions, and the paving scheme.

In another approach to snow melting, Chen (2003)did a numerical simulation on infrared snow and ice melting systems, and Guanet al.(2003) designed a microwave de-icing schematic diagram based on a study of microwave heating.

Still another way to melt snow is by changing the freezing point of the pavement material. Adding anti-freezing material to asphalt concrete can, to some extent, protect the pavement itself from freezing and can enhance the friction coefficient of pavements in cold regions. Zhang and Sun (2010) described two different approaches: (1) the chemical method,wherein an anti-freezing chemical material is added to the pavement material to decrease the freezing point of pavement. The chemical can be dissolved out through capillarity; because the anti-freezing material is within the pavement, it can release out continuously,even though the pavement is abraded continuously.Thus, good-quality material has a life of more than six years; and (2) the physical method, wherein an elastic material is added to the pavement material to change the contact status between the pavement and vehicle tires, and to change the deformation behavior of the pavement. Because of the higher deformation capacity,the adaptive stress of the pavement under external force can break the freezing ice and melt it. This method takes advantage of pavement deformation to achieve the final goal, but it is not ideal in heavy snowfalls.

5 New developments in research on the temperature fields of pavement structures

The temperature fields of pavement structures and thermal loads are currently the major fields in thermal melting system research. Two general approaches are being taken: (1) the statistical analysis method (Kingham, 1969; Jing and Yan, 1980; Christison, 1992;Choubance, 1995), which determines the relationship between the pavement temperature and the local temperature and solar radiation using large samples of measurement data. However, this method relies on taking measurements, which cost significant manpower and money, and the resulting empirical formulae are generally only relevant to the measurement location; and (2) the theoretical analysis method,which is based on climate data and derives the temperature field of the pavement through heat transfer theory. This method was first introduced by the American engineer F. S. Barber (Barber, 1957). He considered the pavement as a semi-infinite body, and the atmospheric temperature and the amount of solar radiation as sine functions, and thus derived pavement temperature field calculation formulae. However,those calculation results are not applicable to low-temperature processes.

Pretorius (1970) analyzed the temperature field of a layered pavement structure by the finite element method. Yan (1984) regarded pavement as a layered structure; he studied the one-dimensional temperature field of concrete pavement, and based on theories of climatology and heat transfer, analyzed the different responses of pavements made of different base materials. He concluded that the emulation functions of temperature and solar radiation are only applicable to normal weather. Wu and Zhang (1993,1995) also treated the pavement as a layered structure but they studied the two-dimensional temperature field of concrete pavement. Unfortunately, their calculation process is too difficult to apply to practical use. Song (2005) pointed out a solution method mainly focused on cyclical climate conditions.However, road surface cracks occur under non-cyclical climate conditions (such as persistent low temperature and a significant cooling climate) as well as under cyclical climate conditions. Considering the composite heat transfer coefficient of the road surface with the external environment changes as a constant, discounting the solar radiation or correcting the temperature amplitude to estimate the effective reflectivity of the road surface will bring greater errors in calculation results.

Christison (1972) and Thompson and Hill (1987)solved the temperature field distribution under the low-temperature condition based on the basic principles of heat transfer. But these models used empirical formulae and it was lack of experiment data to test the models. Hermansson (2000) proposed a new computational model to estimate the temperature distribution of asphalt pavement under high temperatures in summer, but it is not applicable in low-temperature conditions. Qin and Sun (2005,2006) applied a prediction model to asphalt pavement in China based on statistical analysis. Zhou(2005) did field tests on asphalt pavement temperature in Hunan Province and found the relationship between the temperatures at different depths and local meteorological data (temperature and solar radiation). He provided a prediction method of asphalt pavement temperature. Using the basic theory of heat transfer and the heat conduction differential equation, Jiaet al. (2007) provided the discrete equation of the internal nodes of asphalt pavement temperature fields under the different boundary conditions, and achieved the numerical prediction of the two-dimension non-steady state temperature of asphalt pavement affected by the natural environment.

The above researches were based on the solar radiation energy conservation principle, they used numerical weather prediction as weather element field resources, and they derived one-dimensional and two-dimensional heat transfer equations without considering the pavement phase transition at low temperature or seepage during rain or snow melt, both of which can significantly affect pavement temperature.

6 Conclusions and recommendations

Pavement snow and icing are worldwide problems, but effective countermeasures are just beginning to be developed in China. Traditional snow melt agents are harmful to the environment and are expensive, so mechanized snow removal and de-icing machines must be the future trend. The following measures are therefore recommended: (1) snow melting and/or removal plans should be made well in advance, especially for key roads, streets, and bridges; (2) widely-broadcast snow and ice weather alarm systems are important for public safety; and (3) continued research on environment-friendly and intelligent snow removal/melting techniques are encouraged, particularly those that will have practical application in China. Traffic congestion and accidents can be reduced in northern cold regions and southern freezing rain areas by application of sound science.

This study was supported by the National Natural Science Fund of China (No. 41121061), the National Key Basic Research and Development Program (No. 2012CB026102), and the Fund of the"Hundred People Plan" of CAS (to WenBing Yu).We would like to thank the editors and the anonymous reviewers for their work.

American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), 1985. ASHRAE Handbook: Fundamentals. ASHRAE, Atlanta, GA, pp. 20–25.

Barber FS, 1957. Calculation of Maximum Pavement Temperature from Weather Report in Washington D.C. Highway Research Board Bulletin, Washington D. C. National Research Council.

Chen G, 2003. Numerical Modeling of an Infrared-heating System for Snow Removal Machine. Technology University of Dalian,China.

Cheng G, Han P, Du SJ, 2004. Discussion on the conditions and main problem of the de-icer. Shanxi Science & Technology of Communications, 5: 45–46.

Choubance BTM, 1995. Analysis and verification of thermal gradient effects on concrete pavement. Journal of Transportation Engineering, 121(1): 75–81.

Christison JT, 1972. The response of asphalt pavement to low temperature climatic environment. Proceedings, 3rd International Conference on the Structure Design of Asphalt Pavement.Grosvenor House, Park Lane, London, England.

Christison TJ, 1992. The Response of Asphalt Concrete Pavements to Low Temperature Climatic Environments. Ann Arbor, MI,The University of Michigan.

David V, 1992. Economic assessment of the social costs of highway salting and the efficiency of substituting a new deicing material. Journal of Policy Analysis and Management, 11(3):397–418.

Gu Y, Liu YR, 2011. Snow melt agents faded out from snow melting in Beijing. Economic Daily, 2011-9.

Guan MH, Xu YG, Lu TJ,et al., 2003. Application of microwave heating on removing ice on streets. Journal of Northern Jiaotong University, 4: 79–83.

Guo JY, Wang SX, 2010. Development of anti-corrosive snow-melting agent of calcium chloride. Journal of the Salt and Chemical Industry, 6: 12–14.

Guo RC, Zhou J, 2010. Research on the present situation of snow plowing and its developing trends. Shandong Jiaotong, 6: 61–63.

Hermansson A, 2000. Simulation model for calculating pavement temperature including maximum temperature. Transportation Research Record, 1699(134): 134–141.

Hou ZF, 2003. Research on Making and Application of Carbon Fiber Electrically Conductive Concrete for De-icing and Snow-melting. Wuhan Technology University, Wuhan, China.

Hou ZF, Li ZQ, 2004a. Experiment study on fiber graphite conductive concrete. China Concrete and Cement Products, 5: 42–44.

Hou ZF, Li ZQ, 2004b. Experiment study on the resistance changes of fiber graphite conductive concrete. Concrete, 3: 3–4.

Hou ZF, Li ZQ, 2005. Experiment study on the resistance of fiber graphite conductive concrete. Journal of Changjiang University,7: 23–25.

Hou ZF, Li ZQ, Hu SL, 2002. Influence of external circumstances on effect of deicing or snow-melting system by electrically conductive concrete. Journal of Wuhan University of Technology, 5: 581–584.

Hou ZF, Li ZQ, Wang JJ, 2005. Influence of aggregates on properties of carbon fiber electrically conductive concrete for deicing or snow melting. Journal of Wuhan University of Technology,5: 704–706.

Hu YL, 2010. Innovation of snow melting equipment. China New Technologies and Products, 18: 64.

Jia L, Sun LJ, Huang LK, 2007. A numerical temperature prediction model for asphalt concrete pavement. Journal of Tongji University, 8: 1039–1043.

Jing TR, Yan ZR, 1980. Investigations on the temperature conditions of cement concrete pavements. Journal of Tongji University, 3: 34–38.

Kingham RL, 1969. A new temperature correction procedure for Benkelmen-Beam rebound deflection. The Asphalt Institute Research Report, 1: 35–37.

Li D, Dong FQ, Shen G, 2004. Application of steel fiber graphite conductive concrete. New Building Materials, 11: 61–64.

Li H, 2006. Overview of the national road traffic accidents. Road Traffic Management, 1: 4–5.

Lin YB, Li C, Wei GL,et al., 2010. Studies on snow-melting agent with colouration and environmental protection. Environmental Science and Management, 3: 146–149.

Liu CS, 2010. Design of vibration drum of highway deicing machine used in south China. Journal of Central South University of Forestry & Technology, 9: 85–90.

Liu YQ, Zhu Q, 2005. Analysis of economics and environment of snow melting by using solar-soil energy. Construction Science and Technology, 17: 98–99.

Lund WJ, 2000. Pavement Snow Melting. GHC Bulletin, pp. 12–19.

Nydahl J, Pell K, Lee R, 1997. Evaluation of an earth heated bridge deck. U.S. DOT Contact No. DTFH61-80-C-00053.University of Wyoming, Laramie, WY, U.S..

Pesce AH, 1998. Direct uses of geothermal energy in Argentina.Geothermal Resources Council Transactions, 22: 269–273.

Pretorius PC, 1970. Design Consideration for Pavements Containing Soil Cement Base. Ph.D. Thesis, Berkeley, CA: Department of Civil Engineering, University of California.

Qin J, Sun LJ, 2005. Overview on the forecast ways to pavement temperature. Journal of China and Foreign Highways, 6: 19–23.

Qin J, Sun LJ, 2006. Study on asphalt pavement temperature field distribution pattern. Journal of Highway and Transportation Research and Development, 8: 18–21.

Rauder M, 1995. Energy from road surfaces. Caddet Renewable Energy Newsletter, 1: 25–27.

Song CN, 2005. General situation of studies on non-linear temperature field in layered pavement structural system. Highway, 1:49–53.

Tang ZQ, Li ZQ, Hou ZF,et al., 2002a. Power analysis on deicing and snow melting by electrically conductive concrete. Journal of Chongqing Jianzhu University, 3: 101–116.

Tang ZQ, Li ZQ, Hou ZF,et al., 2002b. Properties analysis on electrically conductive concrete road material and conductive additive selection. Concrete, 4: 28–31.

Tang ZQ, Qian JS, Yang ZF, 2006. Research progress of electrically conductive concrete. Journal of Chongqing Jianzhu University, 6: 135–139.

Thompson MR, Hill H, 1987. Characterizing temperature effects for pavement analysis and design. Transportation Research Record, 549: 14–22.

Wang HJ, 2007. Study of Heat and Mass Transfer of Hydronic Snow Melting Process for Pavement. Tianjin University, Tianjin.

Wang HJ, Zhao J, Chen ZH,et al., 2007. Numerical study on heat-transfer behavior of the pavement in road snow-melting system with solar and geothermal energy. Acta Energiae Solaris Sinica, 6: 608–611.

Wang QY, 2007. Research on Roadbed Heat Storage and Snow-Melting Mechanism in Solar-Heat Storage in Soil Snow-Melting System. Technology University of Dalian, Dalian.

Wu GC, Zhang GS, 1993. The calculation theory of the nonlinear pavement temperature field. Journal of Foshan University, 6:10–18.

Wu GC, Zhang GS, 1995. Calculation of effective radiation and its influence on the bituminous pavement temperature field. Journal of Foshan University, 2: 45–50.

Wu HQ, 2005. A Study of Applied Technology in Deicing and Melting Snow on Road Surface by Electric Heating Cable.Beijing Industry University, Beijing, China.

Xu PY, 2008. Study and development directions of snow melt agents. Forestry Science and Technology Information, 4:68–72.

Xu YM, Zhang QM, Zhang W,et al., 2007. Study on the preparation and performance of low-cost environmental CMA deicers.Liaoning Chemical Industry, 1: 10–15.

Yan ZR, 1984. Analysis of the temperature field in Layered Pavement System. Journal of Tongji University, 3: 78–82.

Zhang HG, Sun W, 2010. Way to limit the freezing point of pavement in snow ice area. Communications Science and Technology Heilongjiang, 12: 94–96.

Zhang QJ, 2008. Summary of snow removal machinery development. Construction Machinery Technology & Management, 3:63–66.

Zhou JH, 2005. Test study on temperature fluctuations in asphalt pavements. Central South Highway Engineering, 2: 185–187.