Intersection-pavement de-icing:comprehensive review and the state of the practice

ZhaoHui Joey Yang

University of Alaska Anchorage,Anchorage,Alaska,USA

ABSTRACT Winter maintenance operations are crucial for pedestrian and motorist safety and public mobility on urban streets and highways in cold regions,especially during winter storms.This study provides a comprehensive literature review of existing deicing technologies,with emphasis on electrical resistance-heating deicing technologies for possible applications in areas with concentrated traffic,such as street intersections and crosswalks.A thorough review of existing and emerging deicing technology for snow/ice melting was conducted.The performance of various deicing methods was evaluated and the installation and operation cost of the electrical resistance-heating methods compared.Finally,current state of the practice of intersection/crosswalk winter maintenance was surveyed among state departments of transportation in North America.The intersection/crosswalk winter maintenance procedure adopted by the State of Alaska Department of Transportation and Public Facilities was described,and the annual winter maintenance and operation cost per intersection was estimated.It was found that the annual energy cost of an electrical resistance-heating method such as the carbon-fiber-tape deicing technology is about the same as the average annual maintenance and operation cost of current practice.In addition,an automatic electrical resistance-heating deicing system will bring benefits such as minimized delay time and improved safety for pedestrian and vehicular traffic in an urban application.

Keywords:deicing technology;intersection;crosswalk;electric resistance heating;state of the practice

1 Introduction

Winter maintenance operations are crucial for pedestrian and motorist safety and public mobility on urban streets and highways in cold regions,especially during winter storms.Hansen et al.(2014)predicted global warming will cause warmer and wetter winters and more icing events in the arctic,which would likely result in an increased burden of winter maintenance and operation for the broad cold regions,including Alaska.Shi et al.(2014)conducted a review of highway winter maintenance operations at extremely low temperatures.Study on urban crosswalk and street-intersection maintenance in winter is very limited.For example,Anastasio(2016)reported issues with crosswalks and sidewalks in New York City as being a persistent problem;as one comment reads,"This is a truly disgusting problem—one that makes New York City look like a third-world country whenever it snows".

2 Review of existing and emerging deicing methods

Traditional deicing has been accomplished by mechanical,chemical,and thermal methods.This section provide a comprehensive review of these methods,with the emphasis on emerging new technologies.

2.1 Mechanical and chemical deicing methods

In mechanical ice removal,large equipment and vehicles are used to plow and scrape snow and ice from the pavement.The expense of employing equipment operators is a major factor contributing to the high cost of mechanical deicing.Removing compacted snow and ice with shovels or snow blowers is not always an easy task due to the strong bond between ice and pavement.Chemical treatment helps break the bond by melting the ice(Henderson,1963).Deicing of roads has traditionally been done by a combination of mechanical and chemical methods.Salt,often mixed with sand and gravel,is spread on slick roads by snowplows or dump trucks;and the ice loosened by salting is plowed from roadways.Chloride-based salts including sodium chloride,magnesium chloride,and calcium chloride are the most common chemicals used for ice and snow control because they are inexpensive and effective(Menzies,1992).These salts,however,can corrode vehicles and reinforcing steel in the concrete and pollute the environment(Jones et al.,1992;Williams et al.,2000;Shi et al.,2009b).

To reduce damage to concrete structures,some complex chemical solutions have been applied(Zenewitz,1977;Kuemmel,1994).In recent years,acetatebased deicers such as potassium acetate,calcium-magnesium acetate,or calcium-magnesium-potassium acetate have been given preference as deicers,as they tend to decompose faster and do not contain chloride.However,acetates pose a risk to the durability of concrete and asphalt pavements and are costly(Hassan et al.,2002;Fay et al.,2008;Pan et al.,2008;Shi et al.,2009a,2011).Calcium-magnesium acetate(CMA)is noncorrosive to steel reinforcement;but it requires large trucks for transport,and is less effective than salts,that is,it performs more slowly than salts;and its application temperature range is smaller(Slick,1988;Fay et al.,2008).

More recently,organic compounds generated as by-products of agricultural operations,such as the refining of sugar beets or the distilling process that produces ethanol,have been applied for ice and snow control.When mixed with other chlorides,such as magnesium chloride,these organic compounds have longer residual effects when spread on roadways.Additionally,mixing common rock salt with some of the organic compounds and magnesium chloride results in spreadable materials that are effective at colder temperatures(-34°C)and require lower overall rates of spreading per unit area(http://www.magicsalt.info/Magic%20Salt.htm).Nevertheless,organic compounds mixed with chloride can harm the environment and are costly.It is worth mentioning that urea,a soluble nitrogen compound,is commonly used for airport-pavement deicing because of its low corrosiveness.

2.2 Thermal methods

A number of alternative thermal methods have been developed to control snow and ice formation on ramps and bridge decks.Yehia and Tuan(1999)have provided a comprehensive literature survey of road deicing/anti-icing methods used over the past 30 years.The thermal methods are categorized into two groups,i.e.,internal and external,depending on how the heating elements are installed.

2.2.1 Pavement deicing with internal heating elements

2.2.1.1 Ground-source heat pipe

Initial experimental testing of ground heat pipes was conducted in 1970 by the Dynatherm Corporation at the Federal Highway Administration(FHWA)Fairbanks Highway Research Station(Bienert et al.,1974).In 1975,Long and Baldwin(1980)conducted experiments using a heating system that had 1,213 heat pipes extending 18 m into the ground on a highway ramp in Oak Hill,West Virginia.This system was successfully used to prevent snow and ice accumulation,except when drifting snow occurred.The far-field ground temperature in this case averaged around 13°C.A gravity-operated heating pipe system that used a manifold ground-heat exchanger was implemented for a bridge deck in 1981 in Laramie,Wyoming(Lee et al.,1984).This system used field-assembled heat pipes to transfer energy from 30-m vertical evaporators in the ground.The results show that the heated surface was approximately 2-14°C warmer than the unheated portion of the bridge during operation,which was sufficient to prevent preferential freezing of the bridge-deck surface and provided some snow-melting function.The main disadvantage was that the assembly of the heat pipes was complicated,and 40%of the total cost was for drilling and grouting the pipes.Zenewitz(1977)described another example of using a geothermal source in snow and ice control in Oregon.In this case,a hot-water heating system with copper pipes containing antifreeze heated by a geothermal source was installed in reinforcedconcrete pavement approximately 122 m long on the deck of a canal bridge to keep the deck free of ice.

2.2.1.2 Hot-fluid heat pipe

In 1993,rubber hoses containing antifreeze fluid heated by a gas boiler were embedded in a concrete pedestrian overpass in Lincoln,Nebraska(Cress,1995).The installation cost of the system was$161/m2(hereafter all such figures refer to U.S.dollars if not otherwise specified),and the operating cost per storm was about$250 to melt snow 76-mm thick.A heating system that consisted of steel pipes and carried Freon heated to 149°C by a propane-fired boiler was installed in the Buffalo River Bridge at Amherst,Virginia,in 1996(ASCE,1998).This system used the latent heat released during condensation of the evaporated Freon for deicing,and the estimated annual operating cost was approximately$1,000.Similar hydronic systems have been installed in Ohio,Oregon,Pennsylvania,South Dakota,and Texas.Nowadays,a hydronic system consisting of plastic pipes embedded in Portland cement concrete(PCC)pavement and glycol heated by gas-or oil-burning boilers is commonly used in Anchorage,Alaska(e.g.,Downtown Anchorage intersections and sidewalks)and other cold regions for deicing and anti-icing purposes(Wheeler et al.,2012).Heating fluid leakage in the supply and return lines is a common issue observed in a hydronic system.In addition,such system requires a fairly large space to install a boiler.

2.2.1.3 Solar-source heat pipe

Zhao et al.(2010)reported a deicing system in Japan that uses solar energy.The solar energy is collected from the road surface by a water pump when the temperature is high in summer and stored underground by horizontal and vertical pipes embedded in the pavement.In winter,the water pump brings warm water through the pipes to the pavement for deicing.Only the water pump consumes electric energy in this system.The energy used for deicing comes from solar radiation and a geothermal heat source.

Wu et al.(2009)and Chen et al.(2011a,b)described a similar system,called an asphalt solar collector,based on thermally conductive asphalt concrete(AC).The idea was to add thermally conductive fillers such as graphite powders(Wu et al.,2005)to an asphalt-concrete mixture to improve its thermal conductivity,which facilitates harvesting during summer of the solar-radiation energy through water circulating in copper tubes embedded in the asphalt.The heated water is stored underground for ice/snow melting in winter.The circulating fluid can also help cool the asphalt concrete,hence reducing its risk of permanent deformation due to high temperature in summer months.

A system such as this is essentially a hydronic system that is used to harvest solar energy in summer and melt snow/ice in winter.This type of system utilizes renewable energy and is environmentally friendly.However,the melting process is quite slow if not coupled with another energy source such as geothermal heat,as the temperature of the stored water is not very high.It also inherits all the disadvantages of a hydronic system,such as high maintenance cost,vulnerability to cracks/deformation in the pavement,the requirement of a large underground water storage,etc..

2.2.1.4 Electric heating cable

Electric heating cables were installed on the approach and the deck of a highway drawbridge to remove snow/ice in Newark,New Jersey,in 1961(Henderson,1963).Power density was 378 W/m2for the bridge deck and 430 W/m2for the road pavement.The heat generated by electric current was sufficient to melt a layer of 25-mm-thick snow per hour.However,the installation was later abandoned because the electric cables pulled out of the asphalt-concrete(AC)overlay due to the traffic load on the pavement.A similar system was installed in two ramps and a bridge deck in Teterboro,New Jersey,in 1964(Zenewitz,1977).This system was reported to work well for deicing.The power density was about 375 W/m2,and the annual operating cost was approximately$5/m2.Installation of similar systems can be found in Nebraska,Ohio,Oregon,Pennsylvania,South Dakota,Texas,and West Virginia.

2.2.1.5 Carbon-fiber heating wire

Carbon-fiber wires have been used as a heating element for deicing.Zhao et al.(2010,2011)reported a field experiment in which carbon-fiber heating wires were embedded in a PCC slab for a pavement-deicing study.The slab of 1m×2m×0.25m(L×W×H)was cast using C40 PCC concrete.Carbon-fiber heating wires were wound around the reinforcing mesh longitudinally,and the interval between the reinforcing bars was 100 mm.The power density was in the range of 500-800 W/m2,and the annual operating cost was in the range of$0.375-2.8/m2per storm.Xiang(2014)was granted a patent on using carbon heating wires for deicing of AC sidewalks.The carbon-fiber heating wires are embedded in the AC layer to generate heat for snow/ice melting.No field studies were found for AC pavement.Lai et al.(2015)and Liu et al.(2015)reported a larger-scale field experiment to study the snow-melting performance of carbon-fiber heating wires.In this experiment,PCC slabs of 4.6m×4.6m×0.4m were built with a carbon-fiber grille(or mesh)assembled with reinforcing steel mesh and 48k carbon-fiber heating wires and buried 5 cm below the pavement surface.The heating wires were spaced at 10 cm,and the power density was 350 W/m2.

This method has the advantage of easy installation,as it can be combined with the reinforcing mesh.The key issue is that the heat power is not uniformly distributed within the pavement,creating a temperature gradient and thermal stress,which could lead to thermal cracking.In addition,the effects of the insu-lated-carbon heating wire wound around reinforcing steel bars on the steel-PCC pavement bondage and structural function of the pavement are not clear.If installed by itself in the AC pavement,the heating wires could be pulled out of the AC overlay due to the traffic load on the pavement,as happened with metal heating wires(Henderson,1963).

2.2.1.6 Magnetic snowmelt device

Zhang et al.(2011)described a quite interesting snowmelt method that utilizes a magnetic heating device embedded in pavement for highway-pavement deicing.The magnetic heating device takes advantage of the so-called magneto-caloric effect,which causes temperature change of certain ferromagnetic or ferrimagnetic material when it is exposed to a changing magnetic field.This method was represented as being fast,easy to operate,and energy efficient.The field experiment indicated the segment with the heating device melted the snow much sooner than the segments without a snow-melting device.However,the snow that fell the first day did not completely melt until the third day.

2.2.1.7 Carbon-nanofiber polymer sheet(CNFP)and graphite-PET sheet

Li et al.(2013)reported a novel deicing system consisting of a carbon-nanofiber polymer thermal source and multiwall-carbon-nanotube(MWCNT)cement-based thermal conductive composite.This system utilized a thermally insulated substrate made of an Aluminum Nitride(AIN)-ceramic wafer to improve the energy efficiency.The power density used in the limited-scale field experiment was 600 W/m2to 1,800 W/m2,and the snow melting performance was very impressive.However the heating source,i.e.,carbon-nanofiber polymer,is very expensive and has poor mechanical properties.This system is quite complex and still far from large-scale field application.Recently,Zhang et al.(2016)developed a thin,flexible,sandwiched-graphite-laminate with Polyester Insert(PET)heating element for deicing.A waterproof membrane was used to protect the heating element.A heating element of this type has improved mechanical properties.However,its long-term durability remains to be verified by field application.

2.2.1.8 Electrically conductive Portland cement concrete

Conventional PCC is not electrically conductive.In electrically conductive concrete,a certain amount of electronically conductive components replaces a certain portion of the fine and coarse aggregates to attain stable and relatively high electrical conductivity.Electrically conductive(EC)concrete is a patented technology developed at the National Research Council of Canada(Xie et al.,1995,U.S.Patent No.5447564;Pye et al.,2003,U.S.Patent No.6503318 B2).

EC concrete can be classified into two types:fiberreinforced EC concrete with highermechanical strength and lower conductivity(100 Ω⋅cm),and aggregate-containing EC concrete with lower compressive strength and higher conductivity(10 to 30 Ω⋅cm)(Xie and Beaudoin,1995;Xie et al.,1996).EC-concrete cement-based composites with both high conductivity and mechanical strength were applied to melt snow/ice in the laboratory and in the field(Xie and Beaudoin,1995;Xie et al.,1996).A compositeconcrete slab consisting of a base ECC layer and a PCC overlay was used to melt snow.The overlay had a w/c ratio of 0.325 and a mix design of cement/fine aggregate/coarse aggregate of 1:2:2.The dimensions of the experiment slab were 0.24m×0.31m×0.05m(L×W×H).For typical applications,voltages were always less than 15 V;and the primary current through the ECC layer was less than 30 A(Pye et al.,2003).The current through the overlay was extremely small(0.012 mA).Alternately,the thickness of the overlay can be increased to reduce the current through the overlay.However,the energy efficiency for snow melting would be compromised with a very thick overlay(Tumidajski et al.,2003).

Yehia and Tuan(1998)developed an EC-concrete mix with steel fibers and steel shavings specifically for bridge-deck deicing.Over 50 trial mixes of EC concrete were prepared using steel fibers and steel shavings.The heat generated by the EC concrete was stable and uniform,using 15%-20%conductive material(i.e.,steel fibers and shavings)by volume.Experiments using small-scale slabs showed that an average power density of approximately 520 W/m2was generated by the EC concrete;and it took 30 min to raise the slab temperature from-1.1 °C to 15.6 °C(Yehia and Tuan,1998,1999).In 1998,Yehia and Tuan conducted several groups of laboratory deicing and antiicing experiments.They found that steel shavings of 20%per volume and steel fibers of 1.5%per volume were the upper bound;a higher amount of shavings or steel fibers results in poor workability and surface finishability(Yehia and Tuan,2000;Yehia et al.,2000).

Two 9-cm-thick EC-concrete overlays,2m×2m and 1.2m×3.6m,were cast on top of 15-cm-thick conventional concrete slabs for conducting deicing experiments in the natural environment.Deicing and anti-icing experiments were conducted in five snowstorms in 1998.An average power density of about 590 W/m2was generated by the EC-concrete overlays to prevent snow and ice accumulation(Yehia and Tuan,2000).The average unitenergy cost was about$0.8/m2for each storm,with an assumed electricity cost of$0.08/(kW⋅h)(Yehia and Tuan,2000;Tuan,2004).

In spring 2001,carbon products were used to replace the steel shavings in the EC concrete.Based on the findings from laboratory tests,the EC concrete with carbon products was applied on a bridge deck at Roca,Nebraska(referred to as the Roca Spur Bridge)for deicing(Tuan and Yehia,2004).A 36-m-long and 8.5-m-wide EC-concrete inlay was built and instrumented with temperature and current sensors for heating-performance monitoring during winter storms.The inlay was divided into 52 isolated slabs of 1.2m×4.1m(Tuan,2008).Three-phase 208-V,600-A AC power was supplied to the EC-concrete slabs for deicing.All mixes contained 1.5%steel fibers and 25%carbon products per volume of EC concrete.Operation of this deicing system in four winter seasons has shown that power density was in the range of 203-431 W/m2;and the unit-energy cost was about$250 per snowstorm,or about$0.8/m2(Tuan,2008).

Heymsfield et al.(2014)reported a Federal Aviation Administration(FAA)-sponsored pilot study using an EC-concrete-overlay panel and renewable energy to develop an anti-icing airfield runway.Ten overlay panels of 1.22m×3.05m were constructed with EC concrete in Arkansas to conduct anti-icing tests with photovoltaic panels and a battery storage system.It was concluded that the energy warranted to sustain the thermal mass of ten large overlay panels at an above-freezing temperature is difficult to attain by a solar-based renewable-energy system.The authors further proposed to attach heat wires,such as copper wires,to concrete pavement surface and power it by solar energy to develop an anti-icing system.However,practical issues of installing and protecting wires under vehicular loads exist.

In summary,the EC-concrete-overlay approach shows promise for deicing and anti-icing application.However,it has not been widely used for deicing/snow melting to date due to issues such as high resistivity,low electrothermal efficiency,and steel-fiber corrosion.In addition,practical issues such as thermal(transverse)and longitudinal cracking,deterioration of electrical properties,and rutting of the overlay will significantly impact the reliability and life-span cost of the EC-concrete-overlay method.

2.2.1.9 Electrically conductive asphalt concrete

EC-asphalt concrete(AC)can be used to generate heat and hence provide another method for snow melting and deicing.Pan et al.(2015)provided a review on the structure design,performance,and engineering applications of EC AC.Conventional AC contains coarse and fine aggregates,asphalt binder,and mineral filler.It behaves as an electrical insulator with a resistivity value between 108and 1012Ω⋅m.EC materials have to be added to an AC mixture to make it conductive;and these materials include:(1)powders,including graphite,carbon black,and aluminum chips(Wen and Chung,2004;Huang et al.,2009);(2)fibers,including carbon fiber,steel fiber,steel wool,and carbon nanofiber(García et al.,2009);and(3)solid particles,such as steel slag,substituting for the coarse and fine aggregates(Ahmedzade and Sengoz,2009).

Derwin et al.(2003)reported a field application of an EC-AC pavement system(with the commercial name Snowfree®)for snow melting at O'Hare International Airport.The Snowfree®EC-AC pavement consists a blend of graphite and asphalt;copper buses,alternating between live and ground,were placed at intervals of 4.9 m and cast within a 5-cm layer of the graphite-infused AC.In collaboration with the Federal Aviation Administration(FAA),this type of system was installed on 697 m2of a taxiway in November 1994.The installation costs were$161.5/m2(no inflation adjustment).During the three and a half years of operation,the EC-AC system consistently produced a power density of 484 W/m2while in operation and satisfactorily cleared snow and ice.Throughout the evaluation period,200,000 aircrafts travelled on the graphite-infused AC;and no significant cracking was observed.However,the FAA deemed that the operating cost was high,and no other airport has utilized this technology(Lopez,2012).

However,the addition of EC materials would require a substantial change of the mixing procedure and would also impact the mechanical performance of the pavement.Furthermore,asphalt as a typical viscoelastic material is extremely sensitive to temperature;thermal cracking will deteriorate the conductive network,hence resulting in increased resistivity over time.In addition,cold regions'pavement are subjected to intense loading by climatic and environmental factors,which intensify the damaging effect of heavy loads acting on the pavement structure,leading to accelerated deterioration,and hence more frequent maintenance and even replacement of the pavement(Doré and Zubeck,2009).These factors could render the EC-AC approach unreliable and expensive.

2.2.1.10 Carbon-fiber-tape deicing method

The carbon-fiber-tape(CFT)-based deicing method is a recently patented technology(Yang,2012;Yang et al.,2012;Zhou et al.,2012;Singla et al.,2014).This method takes advantage of CFT's unique properties,including low resistivity,high strength,and light weight,to assemble commercially available CFT into heating panels with CFT strips connected by two bus bars in parallel.The heating panels can be of rectangular or other shapes to suit deicing needs of ar-eas with different geometry.The CFT-panel bus bars are then connected to a low-voltage(less than 36 V)AC-power source to heat the pavement for anti-icing or deicing purposes.The heating panels are embedded about two inches below the pavement surface so they are protected against pavement-surface damages,and they can be reused even if the surface pavement has to be milled and replaced.

The advantage of CFT-based deicing can be summarized as being safe,durable,easy to maintain,and efficient;and the approach has received favorable reviews from recent studies(e.g.,Ceylan et al.,2014;Shi et al.,2014).As a low voltage(less than 36 V)is supplied to power the system and the heating panels are embedded in the pavement,it poses minimum risk for pedestrians.The carbon-fiber material is lightweight,strong and durable,and free of corrosion.As the carbon-fiber tape can distribute the heat more uniformly than the wires in a carbon-fiber or metal-wire mesh,or the pipes in a hydronic system,CFT heating panels induce minimal thermal stress in the pavement.All these features lead to a very durable system.As there is no fluid or moving parts,the CFT deicing system requires a minimal amount of maintenance.The heat can be uniformly distributed on the pavement surface to melt the snow/ice.Coupled with a snow/icedetection sensor and automatic controller,this system is quite efficient in operation,as will be evidenced in the operation-cost comparison with hydronic systems presented hereafter.

2.2.2 Pavement deicing with external heating elements

2.2.2.1 Microwave

Hopstock(2003)conceived the idea of testing magnetite-bearing taconite aggregate and microwave technology for two potential road-use applications:(1)all-season,hot-mix pothole patching and curing;and(2)chemical-free deicing of surfaces paved with AC,including highways,bridge decks,pedestrian walkways,and airport runways.Results from a preliminary bench-scale assessment of this idea using a conventional microwave oven show that magnetitebearing taconite aggregate is indeed an excellent microwave absorber(Hopstock,2003;Hopstock and Zanko,2005).When a truck-mounted microwave generator is driven over an ice-covered roadway constructed with crushed taconite as the aggregate,the microwaves should pass through the ice and be absorbed as heat at the road/ice interface,allowing the ice to be easily detached and scraped away.However,these findings have not been validated in a full-scale,practical testing program(Hopstock and Zanko,2005).

2.2.2.2 Infrared-heat lamp

An infrared heat-lamp was used as an external heating element in an ice-prevention system installed on the Mississippi Avenue Bridge in Denver,Colorado(Zenewitz,1977).The infrared lamps were used to heat the underside of the bridge deck with a power density of 75 W/m2.It was found that the heat-lamp system was insufficient to prevent ice formation on the road surface,due to excessive lag time and inadequate power density.

3 Performance evaluation and cost comparison

3.1 Evaluation ofmechanical,chemical,and thermal methods

Deicing has traditionally been accomplished by mechanical,chemical,and thermal methods.These methods have drawbacks in that some of them damage the pavement,pollute the environment,and corrode vehicles and reinforcing steel in concrete;and some require complicated installation or are too expensive to install and operate.Table 1 presents an evaluation of the advantages of combined chemical/mechanical,hydronic,and various electrical resistance-heating(ERH)deicing methods.Although the mechanical/chemical method remains the most cost-effective for winter-road maintenance,heated pavement,particularly the ERH methods,offers many promising benefits such as being environmentally friendly,as well as the potential for innovation.In addition,heated pavement can reach areas outside the plow track/brine application area,such as curb to curb.It could also expose crosswalk striping more consistently throughout winter than the plow/brine applications,to further define the crosswalk for all users.Although the operation cost may prohibit application of the ERH method in very large areas such as highways,it offers a great alternative snow/ice-melting technology for small areas with concentrated traffic,such as urban crosswalks,sidewalks,bus stops,and bridge decks prone to icing.

3.2 Evaluation of existing ERH deicing systems

Various ERH deicing systems have been reviewed.To help understand the advantages and disadvantages of these systems,Table 2 presents an evaluation of different electrical heating deicing methods that have been field-tested,including the heating-wire method using metal or carbon-fiber wires,EC-PCC or-AC pavement methods,magnetic snowmelt devices,and CFT heating-panel method.Different aspects including constructability,durability,safety,field performance,and application examples are addressed.Compared with other field-tested ERH methods,CFT has certain advantages in terms of being easy to install,no need to change the AC mix,durable,safe,and satisfactory performance.However,its performance in AC pavement is yet to be verified.

Table 1 Evaluation of advantages between mechanical/chemical and various heated-pavement snowmelt methods in PCC

Table 2 Evaluation of different ERH deicing methods

3.3 Cost comparison

Cost-effectiveness is always an important factor affecting the applicability of a deicing system.The installation and operation costs are compared among the electrical resistance systems whenever such data is available.As discussed in the previous section,the deicing cost is very sensitive to air temperature.The experiments conducted in the CFT deicing system had air temperatures that varied from-17.7 to 2.2°C,while the data of other deicing systems reported in the literature were for narrower air-temperature ranges.To make a reasonable cost comparison,it is necessary to select an air-temperature range,say from-6 to 3°C,for comparing average unit-energy cost with other systems.

Table 3 compares the various reported ERH deicing systems in terms of installation cost,annual operating costs,power density,and unit-energy cost.The operating cost per storm is defined as the average cost for operating a deicing system to melt snow on a unitsurface area(m2)during each deicing/anti-icing experiment.The annual operating cost indicates the average operating cost of all deicing and anti-icing experiments conducted during one year.Note that the electricity cost was assumed to be$0.08/(kW∙h)in order to compare all systems reported in the literature on the same basis.

The installation cost for the CFT deicing system was calculated based on the sum of the costs of the heating panels,electrical and control equipment,and insulation boards used in the three test-sidewalk blocks of 1.83m×1.22m.It did not include the labor cost and the cost of the sidewalk materials.For the electric heating-cable system(Henderson,1963),the cost of the installation was calculated so as to integrate the cost of laying the cable,installing electrical and control equipment including transformers,and electric service facilities.For the EC-concrete heating system(Tuan,2008),the installation cost includes the cost of building and installing control facilities,and the cost of integrating and programming the deicing operation controller.For the hot-water deicing system reported by Cress(1995)and the EC-concrete deicing system reported by Yehia and Tuan(1999),the installation costs were quoted directly from the literature.The installation cost of the carbon-fiber heating-wire system reported by Zhao et al.(2010)was not available and was not considered in this comparison.

It can be seen in Table 3 that the CFT deicing sys-tem has the lowest power density and unit-energy cost,and a relatively lower installation cost among the systems compared.The high efficiency of the CFT deicing system is likely due to the use of an insulation layer,and the system's rather uniform heating,coupled with its low power density.For applications in Alaska,the average air temperature will be lower than-6°C;and the unit-energy cost will be higher.The data show that the CFT deicing system has the potential to become quite a cost-effective deicing technology in the future.

Table 3 Cost comparison of different ERH deicing systems

4 Intersection/crosswalk maintenance:the state of the practice

4.1 DOT survey and results

Intersections and crosswalks are prone to being the site of traffic accidents during winter storms.It is therefore important to understand the current practice of their maintenance.This section presents a survey designed to find out the state of the practice on crosswalk maintenance at the state departments of transportation(DOT)level.Note that municipalities were not surveyed because their practices and road inventory vary too greatly from traditional DOT roads and responsibilities.This survey including a total of seven questions was designed to gather information regarding the state of the practice on how state DOTs are dealing with crosswalk winter maintenance(Yang,2016)and was sent to all state DOTs for survey in January 2016 via the American Association of State Highway and Transportation Officials(AASHTO)Research Survey Advisory Committee List Serv.

Seventeen states or provinces responded to the survey(Yang,2016).Among these states,six states indicated they do not need to clear crosswalks,as these are left to municipalities or towns;nine indicated that they do not treat crosswalks,if any,differently from the highway itself in their states.Only two states/provinces,i.e.,Alaska and British Columbia,Canada,indicated they treat crosswalks differently and maintain a certain standard for crosswalks during winter season.A typical snow/ice-treatment procedure for crosswalks would include plowing and applying salt and sand,depending on weather conditions and temperatures.In some states,anti-icing is used pre-storm in the form of MgChl and salt brine.Some states(for example,Montana)indicated that it has been used in sidewalks to melt snow and ice.A hydronic system has been used on some occasion.In at least some locations,the heat generated from computer servers has been used to heat the sidewalks around the building.It is interesting to note that no ERH methods have been applied by any state DOT in maintaining crosswalks/intersections.

4.2 Current state of the practice in Alaska and cost estimation

The survey result from the Central Region Maintenance and Operations(M&O)of the State of Alaska Department of Transportation and Public Facilities(AK DOT&PF)collected in this survey provided a good example of the state of the practice for cost analysis(WWH,2003;Yang,2016).For Alaska,the Central Region M&O maintains quite a large number of crosswalks on the Seward and Minnesota freeways and major arterials throughout Anchorage.Priority is given to freeways(same day),then major arterials(1 day),and then other streets(2+days)maintained by AK DOT&PF.There is a specific procedure for intersection/crosswalk maintenance.For fresh snow,a nose plow with a belly blade is used to plow a 30-m approach and the intersection,and to dispense the sand/brine mixture.This operation requires one employee and one truck.If ice is packed on the intersection,it would require another employee and a grader to treat the surface first.Brine solution is applied at crosswalks and intersection approaches pre-storm or during freeze/thaw events.No other method is used currently for snow/ice management.The personnel-time estimation for intersection winter maintenance can be found in Yang(2016).The time estimation ranges from about 10-min travel time for a two-lane intersection to 25 min for a five-lane intersection.For comparison,a two-lane intersection was assumed.Table 4 summarizes the personnel,equipment,and amount of materials used for each two-lane intersection for the central region.Depending on the nature of the snow/ice event,the cost of intersection maintenance is estimated to be in the range of$46.77 to$88.41 per storm.Assuming three events per month and five winter months per year,the cost of winter maintenance is in the range of$701.55-$1,326 per year.

If a CFT deicing system is used,for a two-lane intersection,the area of the intersection itself plus pedestrian walkway is about 107 m2(area=7.31m×3.65m×4,assume no approach is covered);the annual operation cost due to electricity consumption would be around$1,080,which is about the average annual M&O cost of the current practice.The manageable operation cost and the benefits of an automatic deicing system,such as the minimized delay time and improved safety for pedestrian and vehicular traffic,show that an ERH deicing system,such as the CFT system,might be well worth consideration and the initial investment in future intersection/crosswalk design.

Table 4 Per-storm cost for personnel,equipment,and amount of materials for winter maintenance of a two-lane intersection with crosswalk

5 Conclusions

The purpose of this study was to provide a comprehensive literature review of existing deicing technologies with an emphasis on the electrical resistance-heating methods for possible application in asphalt approaches and crosswalks.A comprehensive review of existing and emerging deicing technology for snow/ice melting was conducted.The performance of various deicing methods was evaluated,and the cost of various ERH systems were compared.Finally,current state of the practice of intersection/crosswalk maintenance was surveyed among state DOTs;and the results were summarized.The intersection/crosswalk winter maintenance procedure adopted by the Central Region Maintenance&Operation of AK DOT&PF was described,and the cost of annual winter maintenance was estimated and compared with that of a CFT deicing system.The following conclusions can be drawn:

1.Deicing has traditionally been accomplished by mechanical,chemical,and thermal methods.The mechanical/chemical method is the most cost-effective,but heated pavement methods—particularly the electrical resistance-heated-pavement—offer many promising benefits such as being environmentally friendly and stimulating the potential for innovation.

2.Although the operation cost may prohibit application of an ERH method in very large areas,it offers a great alternative snow/ice-melting technology for small areas with concentrated traffic,such as urban crosswalks,sidewalks,bus stops,and bridge decks.

3.Compared with other field-tested ERH methods,the CFT method has certain advantages in terms of being easy to install,no need to modify AC-mix ra-tio,durability,safety,and observed satisfactory performance.However,its performance in AC pavement is yet to be verified.

4.The survey results show that most DOTs do not have responsibility for intersection/crosswalk winter maintenance or do not treat intersections/crosswalks differently than a highway.Only Alaska and British Columbia treat crosswalks differently and maintain a certain standard for winter maintenance of intersections/crosswalks.

5.A typical snow/ice-treatment procedure for intersections/crosswalks would include plow and application of a sand/brine mixture,depending on weather conditions and temperatures.Anti-icing treatment is used pre-storm or during freeze/thaw events.

6.The energy cost of the CFT deicing system is about the same as the average annual M&O cost of current practice in Anchorage.In addition,an automatic ERH deicing system would bring the benefits such as minimized delay time and improved safety for pedestrian and vehicular traffic.

As AK DOT&PF maintains quite a large inventory of intersections/crosswalks—and global warming might bring warmer and wetter winters to and increase the burden of winter maintenance in the arctic,including Alaska—an ERH deicing system such as the CFT system is well worth consideration and the investment in future design of intersections/crosswalks and is recommended to be tested in asphalt pavement to verify its suitability for applications in intersection/crosswalk winter maintenance.

Acknowledgments:

The research reported herein was supported by AK DOT&PF and FHWA(Project#64006).The author would like to express his appreciation to Ms.Anna Bosin,P.E.,Research Engineer,Research Development and Technology Transfer of AK DOT&PF,for her continuous support during the entire course of the study.