Annotated Literature Review for NCHRP Report 640 (2009)

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35 1.9 Ketcham, S.A., L.D. Minsk, R.B. Blackburn, and E.J. Fleege. “Manual of Practice for an Effective Anti-icing Program. A Guide for Highway Winter Maintenance Personnel.” FHWA-RD-95-202. U.S. Department of Transportation. Federal Highway Administration. June 1996. 1.9.1 General This manual of practice provides information for the successful implementation of an effective highway anti-icing program. As this infers, the manual of practice is for all highway surfaces and does not specifically deal with anti-icing operations for permeable friction courses. Prior to discussing the specifics of the manual, a number of terms related to winter maintenance are provided. Black Ice Term for a very thin coating of clear bubble-free, homogeneous ice which forms on a pavement surface having a temperature at or slightly above 0˚C (32˚F) and when the temperature of the air in contact with the ground is below the freezing point of water. This causes small slightly supercooled water droplets to deposit on the pavement surface and flow together before freezing. Dry Chemical Spread Rate This term refers to the anti-icing chemical application rate for solid chemical applications with the spread rate being the mass of the chemical applied per lane kilometer (or mile). For liquid chemical applications, the spread rate is the mass of dry chemical in solution applied per lane kilometer (or mile). Freezing Rain Supercooled droplets of liquid precipitation that falls onto a pavement surface whose temperature is below or slightly above 0˚C (32˚F). These droplets result in a hard, slick, generally thick coating of ice. This formation of ice is generally called glaze or clear ice. Frost Dew or water vapor cause the formation of ice crystals in the form of scales, needles, feathers or fans on surfaces when the temperature of the pavement surface is at or below freezing. This is also called hoarfrost. Light Snow Snow falling at a rate less than 12.5mm (1/2 in.) per hour. Visibility is generally not reduced. Liquid Chemical A chemical solution in the form of a liquid. Moderate or Heavy Snow Snow falling at a rate greater than 12.5mm (1/2 in.) per hour. Visibility may be adversely affected. Sleet A mixture of rain and/or snow that has been partially melted due to falling through an atmosphere that is slightly above freezing. Slush Accumulation of snow that lies on an impervious surface and is saturated with water in excess of its drainage capacity. Slush will not support any weight but will “squish” until the base support is reached.

36 Anti-icing defined is the preventing of formation or development of bonded snow and ice to a pavement surface. This is accomplished by applying chemical freeze-point depressant chemical to the pavement surface at the proper concentration and at the proper time. Anti-icing is different than deicing in that anti-icing is designed to prevent the buildup of snow and ice, while deicing is the process of weakening or destroying the bond between snow/ice and the pavement. 1.9.2 Benefits of Permeable Asphalt Mixes No specific benefits were given. 1.9.3 Materials and Mix Design No specifics on materials and mix design were given. 1.9.4 Construction Practices No specific construction practices were given. 1.9.5 Maintenance Practices There are two distinct winter maintenance strategies that make use of freezing-point depressants: anti-icing and deicing. Even though both of these strategies use chemicals to maintain roadways during winter events, the fundamental objective of each is different. Anti-icing operations are conducted to prevent the formation of development of bonded snow and ice to the pavement surface. Deicing operations are performed to break the bond of already bonded snow and ice. Therefore, anti-icing operations are preventative and deicing operations are reactive. A winter maintenance program is a very complex endeavor. One primary element of a successful program is to select the level of service (LOS), or road conditions, for the pavement during the winter event. The LOS will likely depend upon many factors, but primarily the importance of the road and the amount of traffic. Figure 5 illustrates the components of an anti-icing program based upon the LOS. As illustrated in Figure 5, an effective anti-icing program includes two components to support the anti-icing program and operations. Tools to support an effective anti-icing program include three tool boxes: operations, decision making and personnel. The operations toolbox includes the materials and techniques that are available for an anti-icing program. The materials include solid chemicals, chemical solutions, pre-wetted chemicals and plowing. Dry solid chemicals can be an effective anti-icing treatment in many instances; however, some form of moisture must be available for two reasons: prevent the loss of the dry chemicals from a dry pavement surface and to trigger the solution of the chemical. For this reason, dry solid chemicals are generally applied after sufficient precipitation has fallen, but before bonding between the pavement and snow occurs. The most common form of dry solid chemical is sodium chloride.

37 Level of Service Bare Pavement Policy; and strategies of support Other Other StrategiesDeicing Anti-icing Tools to Support Anti-icing Operations to Support Anti-icing Decision Making Toolbox Operations Toolbox Personnel Toolbox Initial Operation Solid Application Capability Long/Mid Term Weather Forecasts Trained Personnel Liquid Application Capability Road and Road Weather Forecasts Standby and Call-Out Procedures Prewetted Solid Application Capability Nowcasting Plowing capability Traffic information Patrols Evaluations of treatment effectiveness Subsequent Operations Figure 5: Outline of the Components of an Anti-icing Program in the Context of a Winter Maintenance Program

38 Liquid (solids in solution) anti-icing measures can be advantageous in small amounts for some conditions at pavement temperatures of about -5˚C (23˚F) and above. Liquid applications can be uniformly and quickly applied to a dry pavement as a pre-storm treatment. Liquid applications can be used at temperatures below -5˚C (23˚F) by increasing the application rate. There are five chemicals that are generally used for liquid anti-icing treatments: sodium chloride, magnesium chloride, calcium chloride, calcium magnesium acetate and potassium acetate. Presetting solid chemical treatments can improve the effectiveness of the treatment. Prewetting also accelerates the process of the solid chemical going into solution. Other benefits of prewetting include a more uniform application rate because particles stick to the pavement surface, spreading speed can be increased, and in some instances, the road surface dries more quickly. Sodium chloride has been the most common solid chemical when applying prewetted chemicals. Finer graded (smaller particle sizes) solid chemicals are more appropriate for the prewetting process. Because of the smaller particle sizes and, therefore, larger surface area, the time for solution to form and cover the pavement surface will decrease. The final tool in the Operations tool box is plowing. The primary purpose of plowing within an anti-icing program is to remove as much snow or loose ice prior to applying the chemical treatment. As shown in Figure 5, the next tool box within the tools to support an anti-icing program is decision making. The decision making toolbox includes weather forecast information, road and road weather information, nowcasting, traffic information, patrols and evaluations of treatment effectiveness. Accurate weather forecast information is essential to deciding whether or not to initiate a treatment, when to start and what treatment to apply. Weather forecasts would include when precipitation is expected to start, what form the precipitation will be, the probable air temperatures and the temperature trend during and after the storm, and the wind direction and speed. Road and road weather information includes real-time knowledge of the state of the pavement surface in order to make informed decisions on the appropriate anti-icing treatment. Information required would include pavement temperature, whether the pavement is wet or dry and some indication of the concentration of a treatment. The most important of these is pavement temperature. The solubility of all chemicals varies with temperature, the lower the temperature the less solubility. An effective method of monitoring pavement temperature is to place pavement sensors. Pavement temperature sensors can be used to generate a forecast of pavement temperature. Some pavement sensors can also provide a relative indication of how much chemical concentration is left on the pavement from the previous anti-icing treatment. A road weather information system (RWIS) is also an effective method of providing real-time information on weather conditions. A RWIS is a network of roadside weather data-gathering and road condition monitoring systems that can be remotely accessed and analyzed.

39 The third component of the decision making toolbox is nowcasting. Nowcasting refers to the use of real-time data for short-term forecasting. Nowcasting can use RWIS stations, radar, patrols and/or any other data sources to make an educated judgment on the probable condition of a roadway over the short-term. Another component of the decision making toolbox is traffic information. Vehicles can affect the condition of the pavement surface through tires compacting, abrading, displacing or dispersing snow and heat created by tire, engines and exhaust systems. Vehicles can also disperse dry solid chemicals in the absence of any moisture on the pavement. Patrols are also an important component in the decision making toolbox. Patrols provide visual observations of weather conditions and pavement conditions. Trained personnel prepared to judge the severity of conditions and to make recommendations or corrective actions are invaluable. The final component of the decision making toolbox is the evaluation of treatment effectiveness during an event. Observations from patrols will provide real-time estimates of the effectiveness of treatments. Pavement sensors that provide an indication of chemical concentration can also provide an indication of treatment effectiveness. Specialized vehicles can also measure pavement friction during storm events to provide an evaluation of treatment effectiveness. The final toolbox needed for an effective anti-icing program is personnel. The personnel toolbox includes trained personnel as well as effective standby and call out procedures. Operations to support an anti-icing program include initial operations and subsequent operations. The initial anti-icing operations includes assembling the necessary data to make an educated decision on the type treatment required, making the decision and then acting on the decision. Subsequent operations will require monitoring weather and pavement conditions, determining if or when additional treatments are required and acting on the required subsequent action. Ketcham et al also provide guidance for anti-icing operations for various storm events. Tables 16 through 21 provide these recommendations. 1.9.6 Rehabilitation Practices No specifics on rehabilitation practices were given. 1.9.7 Performance No specific performance measures were given. 1.9.8 Structural Design No specifics on inclusion within structural design were given.

40 1.9.9 Limitation No specific limitations were given.

41 Table 16: Weather Event: Light Snow Storm PAVEMENT INITIAL OPERATION SUBSEQUENT OPERATIONS COMMENTS TEMPERATURE RANGE, AND TREND pavement surface at time of maintenance action dry chemical spread rate, kg/lane-km (lb/lane-mi) maintenance action dry chemical spread rate, kg/lane-km (lb/lane-mi) initial operation liquid solid or prewetted solid liquid solid or prewetted solid Above 0oC (32oF), steady or rising Dry, wet, slush, or light snow cover None, see comments None, see comments 1) Monitor pavement temperature closely for drops toward 0oC (32oF) and below 2) Treat icy patches if needed with chemical at 28 kg/lane-km (100 lb/lane-mi); plow if needed Above 0oC (32oF), 0oC (32oF) or below is imminent; Dry Apply liquid or prewetted solid chemical 28 (100) 28 (100) Plow as needed; reapply liquid or solid chemical when needed 28 (100) 28 (100) 1) Applications will need to be more frequent at lower temperatures and higher snowfall rates 2) It is not advisable to apply a liquid chemical at the indicated spread rate when the pavement ALSO -7 to 0oC (20 to 32oF), remaining in range Wet, slush, or light snow cover Apply liquid or solid chemical 28 (100) 28 (100) temperature drops below -5oC (23oF) 3) Do not apply liquid chemical onto heavy snow accumulation or packed snow -10 to -7oC (15 to 20oF), remaining in range Dry, wet, slush, or light snow cover Apply prewetted solid chemical 55 (200) Plow as needed; reapply prewetted solid chemical when needed 55 (200) If sufficient moisture is present, solid chemical without prewetting can be applied Below -10oC (15oF), steady or falling Dry or light snow cover Plow as needed Plow as needed 1) It is not recommended that chemicals be applied in this temperature range 2) Abrasives can be applied to enhance traction Notes CHEMICAL APPLICATIONS. (1) Time initial and subsequent chemical applications to prevent deteriorating conditions or development of packed and bonded snow. (2) Apply chemical ahead of traffic rush periods occurring during storm. PLOWING. If needed, plow before chemical applications so that excess snow, slush, or ice is removed and pavement is wet, slushy, or lightly snow covered when treated.

42 Table 17: Weather Event: Light Snow with Period(s) of Moderate or Heavy Snow PAVEMENT INITIAL OPERATION SUBSEQUENT OPERATIONS COMMENTS TEMPERATURE RANGE, AND TREND pavement surface at time of maintenance action dry chemical spread rate, kg/lane-km (lb/lane-mi) maintenance action dry chemical spread rate, kg/lane-km (lb/lane-mi) initial operation liquid solid or prewetted liquid solid or prewetted solid solid light snow heavier snow light snow heavier snow Above 0oC (32oF), steady or rising Dry, wet, slush, or light snow cover None, see comments None, see comments 1) Monitor pavement temperature closely for drops toward 0oC (32oF) and below 2) Treat icy patches if needed with chemical at 28 kg/lane-km (100 lb/lane-mi); plow if needed Above 0oC (32oF), 0oC (32oF) or below is imminent; Dry Apply liquid or prewetted solid chemical 28 (100) 28 (100) Plow as needed; reapply liquid or solid 28 (100) 55 (200) 28 (100) 55 (200) 1) Applications will need to be more frequent at lower temperatures and higher snowfall rates 2) Do not apply liquid chemical onto ALSO -4 to 0oC (25 to 32oF), remaining in range Wet, slush, or light snow cover Apply liquid or solid chemical 28 (100) 28 (100) chemical when needed heavy snow accumulation or packed snow 3) After heavier snow periods and during light snow fall, reduce chemical rate to 28 kg/lane-km (100 lb/lane-mi); continue to plow and apply chemicals as needed -10 to -4oC (15 to 25oF), remaining in range Dry, wet, slush, or light snow cover Apply prewetted solid chemical 55 (200) Plow as needed; reapply prewetted solid chemical when needed 55 (200) 70 (250) 1) If sufficient moisture is present, solid chemical without prewetting can be applied 2) Reduce chemical rate to 55 kg/lane-km (200 lb/lane-mi) after heavier snow periods and during light snow fall; continue to plow and apply chemicals as needed Below -10oC (15oF), steady or falling Dry or light snow cover Plow as needed Plow as needed 1) It is not recommended that chemicals be applied in this temperature range 2) Abrasives can be applied to enhance traction Notes CHEMICAL APPLICATIONS. (1) Time initial and subsequent chemical applications to prevent deteriorating conditions or development of packed and bonded snow. (2) Anticipate increases in snowfall intensity. Apply higher rate treatments prior to or at the beginning of heavier snowfall periods to prevent development of packed and bonded snow. (3) Apply chemical ahead of traffic rush periods occurring during storm. PLOWING. If needed, plow before chemical applications so that excess snow, slush, or ice is removed and pavement is wet, slushy, or lightly snow covered when treated.

43 Table 18: Weather Event: Moderate or Heavy Snow Storm PAVEMENT INITIAL OPERATION SUBSEQUENT OPERATIONS COMMENTS TEMPERATURE RANGE, AND TREND pavement surface at time of maintenance action dry chemical spread rate, kg/lane-km (lb/lane-mi) maintenance action dry chemical spread rate, kg/lane-km (lb/lane-mi) initial operation liquid solid or pre- wetted solid liquid solid or pre- wetted solid Above 0oC (32oF), steady or rising Dry, wet, slush, or light snow cover None, see comments None, see comments 1) Monitor pavement temperature closely for drops toward 0oC (32oF) and below 2) Treat icy patches if needed with chemical at 28 kg/lane-km (100 lb/lane-mi); plow if needed Above 0oC (32oF), 0oC (32oF) or below is imminent; Dry Apply liquid or pre-wetted solid chem.. 28 (100) 28 (100) Plow accumulation and reapply liquid or solid 28 (100) 28 (100) 1) If the desired plowing/treatment frequency cannot be maintained, the spread rate can be increased to 55 kg/lane-km (200 lb/lane-mi) to accommodate longer operational cycles ALSO -1 to 0oC (30 to 32oF), remaining in range Wet, slush, or light snow Apply liquid or solid chemical 28 (100) 28 (100) chemical as needed 2) Do not apply liquid chemical onto heavy snow accumulation or packed snow -4 to -1oC (25 to 30oF), remaining in range Dry Apply liquid or pre-wetted solid chemical 55 (200) 42-55 (150-200) Plow accumulation and reapply 55 (200) 55 (200) Wet, slush, or light snow Apply liquid or solid chemical 55 (200) 42-55 (150-200) liquid or solid chemical as needed 1) If the desired plowing/treatment frequency cannot be maintained, the spread rate can be increased to 110 kg/lane-km (400 lb/lane-mi) to accommodate longer operational cycles 2) Do not apply liquid chemical onto heavy snow accumulation or packed snow -10 to -4oC (15 to 25oF), remaining in range Dry, wet, slush, or light snow cover Apply prewetted solid chemical 55 (200) Plow accumulation and reapply prewetted solid chem.. as needed 70 (250) 1) If the desired plowing/treatment frequency cannot be maintained, the spread rate can be increased to 140 kg/lane-km (500 lb/lane-mi) to accommodate longer operational cycles 2) If sufficient moisture is present, solid chemical without prewetting can be applied Below -10oC (15oF), steady or falling Dry or light snow cover Plow as needed Plow accumulation as needed 1) It is not recommended that chemicals be applied in this temperature range 2) Abrasives can be applied to enhance traction Notes CHEMICAL APPLICATIONS. (1) Time initial and subsequent chemical applications to prevent deteriorating conditions or development of packed and bonded snow -- timing and frequency of subsequent applications will be determined primarily by plowing requirements. (2) Apply chemical ahead of traffic rush periods occurring during storm. PLOWING. Plow before chemical applications so that excess snow, slush, or ice is removed and pavement is wet, slushy, or lightly snow covered when treated.

44 Table 19: Weather Event: Frost or Black Ice PAVEMENT TRAFFIC INITIAL OPERATION SUBSEQUENT OPERATIONS COMMENTS TEMPERATURE RANGE, TREND, AND CONDITION maintenance action dry chemical spread rate, kg/lane-km (lb/lane-mi) maintenance action dry chemical spread rate, kg/lane-km (lb/lane- mi) RELATION TO DEW POINT liquid solid or prewetted solid liquid solid or prewetted solid Above 0oC (32oF), steady or rising Any level None, see comments None, see comments Monitor pavement temperature closely; begin treatment if temperature starts to fall to 0oC (32oF) or below and is at or below dew point -2 to 2oC (28 to 35oF), remaining in range or falling to 0oC Traffic rate less than 100 vehicles per h Apply prewetted solid chemical 7-18 (25-65) Reapply prewetted solid chemical as needed 7-18 (25-65) 1) Monitor pavement closely; if pavement becomes wet or if thin ice forms, reapply chemical at higher indicated rate 2) Do not apply liquid chemical on ice so thick (32oF) or below, and equal to or below dew point Traffic rate greater than 100 vehicles per h Apply liquid or prewetted solid chemical 7-18 (25-65) 7-18 (25-65) Reapply liquid or prewetted solid chemical as needed 11-32 (40-115) 7-18 (25-65) that the pavement cannot be seen -7 to -2oC (20 to 28oF), remaining in range, and equal to or below dew point Any level Apply liquid or prewetted solid chemical 18-36 (65-130) 18-36 (65-130) Reapply liquid or prewetted solid chemical when needed 18-36 (65-130) 18-36 (65-130) 1) Monitor pavement closely; if thin ice forms, reapply chemical at higher indicated rate 2) Applications will need to be more frequent at higher levels of condensation; if traffic volumes are not enough to disperse condensation, it may be necessary to increase frequency 3) It is not advisable to apply a liquid chemical at the indicated spread rate when the pavement temperature drops below -5oC (23oF) -10 to -7oC (15 to 20oF), remaining in range, and equal to or below dew point Any level Apply prewetted solid chemical 36-55 (130-200) Reapply prewetted solid chemical when needed 36-55 (130-200) 1) Monitor pavement closely; if thin ice forms, reapply chemical at higher indicated rate 2) Applications will need to be more frequent at higher levels of condensation; if traffic volumes are not enough to disperse condensation, it may be necessary to increase frequency Below -10oC (15oF), steady or falling Any level Apply abrasives Apply abrasives as needed It is not recommended that chemicals be applied in this temperature range Notes TIMING. (1) Conduct initial operation in advance of freezing. Apply liquid chemical up to 3 h in advance. Use longer advance times in this range to effect drying when traffic volume is low. Apply prewetted solid 1 to 2 h in advance. (2) In the absence of precipitation, liquid chemical at 21 kg/lane-km (75 lb/lane-mi) has been successful in preventing bridge deck icing when placed up to 4 days before freezing on higher volume roads and 7 days before on lower volume roads.

45 Table 20: Weather Event: Freezing Rain Storm PAVEMENT INITIAL OPERATION SUBSEQUENT OPERATIONS COMMENTS TEMPERATURE RANGE, AND TREND maintenance action chemical spread rate, kg/lane-km (lb/lane-mi) maintenance action chemical spread rate, kg/lane-km (lb/lane-mi) Above 0oC (32oF), steady or rising None, see comments None, see comments 1) Monitor pavement temperature closely for drops toward 0oC (32oF) and below 2) Treat icy patches if needed with prewetted solid chemical at 21-28 kg/lane-km (75-100 lb/lane-mi) Above 0oC (32oF), 0oC (32oF) or below is imminent Apply prewetted solid chemical 21-28 (75-100) Reapply prewetted solid chemical as needed 21-28 (75-100) Monitor pavement temperature and precipitation closely -7 to 0oC (20 to 32oF), remaining in range Apply prewetted solid chemical 21-70 (75-250) Reapply prewetted solid chemical as needed 21-70 (75-250) 1) Monitor pavement temperature and precipitation closely 2) Increase spread rate toward higher indicated rate with decrease in pavement temperature or increase in intensity of freezing rainfall 3) Decrease spread rate toward lower indicated rate with increase in pavement temperature or decrease in intensity of freezing rainfall -10 to -7oC (15 to 20oF), remaining in range Apply prewetted solid chemical 70-110 (250-400) Reapply prewetted solid chemical as needed 70-110 (250-400) 1) Monitor precipitation closely 2) Increase spread rate toward higher indicated rate with increase in intensity of freezing rainfall 3) Decrease spread rate toward lower indicated rate with decrease in intensity of freezing rainfall Below -10oC (15oF), steady or falling Apply abrasives Apply abrasives as needed It is not recommended that chemicals be applied in this temperature range Notes CHEMICAL APPLICATIONS. (1) Time initial and subsequent chemical applications to prevent glaze ice conditions. (2) Apply chemical ahead of traffic rush periods occurring during storm.

46 Table 21: Weather Event: Sleet Storm PAVEMENT INITIAL OPERATION SUBSEQUENT OPERATIONS COMMENTS TEMPERATURE RANGE, AND TREND maintenance action chemical spread rate, kg/lane-km (lb/lane-mi) maintenance action chemical spread rate, kg/lane-km (lb/lane-mi) Above 0oC (32oF), steady or rising None, see comments None, see comments 1) Monitor pavement temperature closely for drops toward 0oC (32oF) and below 2) Treat icy patches if needed with prewetted solid chemical at 35 kg/lane-km (125 lb/lane-mi) Above 0oC (32oF), 0oC (32oF) or below is imminent Apply prewetted solid chemical 35 (125) Plow as needed, reapply prewetted solid chemical when needed 35 (125) Monitor pavement temperature and precipitation closely -2 to 0oC (28 to 32oF), remaining in range Apply prewetted solid chemical 35-90 (125-325) Plow as needed, reapply prewetted solid chemical when needed 35-90 (125-325) 1) Monitor pavement temperature and precipitation closely 2) Increase spread rate toward higher indicated rate with increase in sleet intensity 3) Decrease spread rate toward lower indicated rate with decrease in sleet intensity -10 to -2oC (15 to 28oF), remaining in range Apply prewetted solid chemical 70-110 (250-400) Plow as needed, reapply prewetted solid chemical when needed 70-110 (250-400) 1) Monitor precipitation closely 2) Increase spread rate toward higher indicated rate with decrease in pavement temperature or increase in sleet intensity 3) Decrease spread rate toward lower indicated rate with increase in pavement temperature or decrease in sleet intensity Below -10oC (15oF), steady or falling Plow as needed Plow as needed 1) It is not recommended that chemicals be applied in this temperature range 2) Abrasives can be applied to enhance traction Notes CHEMICAL APPLICATIONS. (1) Time initial and subsequent chemical applications to prevent the sleet from bonding to the pavement. (2) Apply chemical ahead of traffic rush periods occurring during storm.