Wintertime Pavement Maintenance Practices (2024)

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9   This chapter summarizes existing studies and guidance on reactive pavement maintenance performed during the winter months. Cold temperatures, precipitation, and freeze-thaw cycles are well known as primary causes of pavement failures. Less certain is how to effectively repair pavement distresses that occur in winter months and threaten driver safety and vehicle damage when waiting until warmer weather is not an option. The sources reviewed below include state DOT maintenance manuals and sponsored research, other published research, and federal guidance. The literature includes resources that address pavement repair in general—fewer resources address reactive pavement maintenance performed over the winter months specifically. This chapter consists of the following sections: basics of reactive pavement maintenance, including state DOT guidance; winter considerations for reactive pavement repair, including materials and techniques; and innovations in winter pavement maintenance. Basics of Reactive Pavement Maintenance Transportation agencies carefully plan flexible and rigid pavement maintenance throughout their roadway networks. Pavement condition and age, traffic levels, and other factors determine when resurfacing or other pavement maintenance is needed. Agencies typically schedule road maintenance in spring, summer, or fall to avoid weather-related barriers to maintaining road surfaces effectively. Potholes and other pavement distresses such as cracking, rutting, concrete spalling, and other pavement damage can appear at any time of year. Colder regions with significant freeze-thaw cycles are particularly prone to these distresses. Regardless of scheduled maintenance, agencies must react as soon as feasible to repair potholes and other road damage year-round due to safety concerns and the risk of vehicle damage. Vehicle repairs from pothole damage cost an estimated $26.5 billion in 2021 alone (Edmonds 2022). Transportation agencies also expend significant resources to repair potholes. Illinois DOT (IDOT), for example, spent more than $25 million repairing potholes in 2019 (Hajj and Lu 2021). Most transportation professionals and researchers support the concept of “doing [the repair] right the first time” (Hajj and Lu 2021). Because reactive or emergency maintenance generally must be done quickly with a minimum of traffic disruption, reactive repairs are often temporary, requiring additional repair when the weather improves (WSDOT 2020, Nebraska Department of Roads 2002). Unless a road is scheduled for repaving or other substantial rehabilitation soon, temporary patches requiring repeated fixes become costly and inconvenient. C H A P T E R 2 Literature Review

10 Wintertime Pavement Maintenance Practices In 1993, the Strategic Highway Research Program (SHRP) produced a comprehensive review of pavement repair and treatment options (Smith et al. 1993) in the form of a manual. The manual, updated in 2001 after the FHWA’s Long-Term Pavement Performance (LTPP) program conducted another 5 years of research, remains a seminal compilation of ideas and recommenda- tions on planning, implementing, and monitoring asphalt pothole repairs, standardizing termi- nology, and providing a basis for developing improved materials, techniques, and innovations (Smith and Romine 2001). State DOT maintenance manuals, federal guidance, and research reports describe how to manage and maintain pavement and present options for repairing potholes, cracks, and other damage. Despite the availability of guidance, engineering judgment is often relied on in determin- ing where and when to repair pavement and what materials and methods to use (McDaniel et al. 2014). Practices can vary substantially among different districts within a state (Hajj and Lu 2021). A 2021 IDOT study exploring best practices for general pothole repair reviewed research, national reports, and information from all 50 states, finding that most states do not have centralized guid- ance for pothole repair. Researchers concluded that “few states provide meaningful guidance in terms of the more temporary repairs, especially for localized potholes. In fact, there is little, if any, guidance in terms of choosing cold mixes, when to use specific mix types, and preparation for temporary patching” (Hajj and Lu 2021). The IDOT study includes a Summary of Pothole Patch- ing Guidelines in Each US State Based on Publicly Available Online Resources, which “summarizes the overall specifications and other documents provided by 22 states and Washington, D.C., that describe pothole patching procedures and are available online.” Other state guidance for reactive winter pavement maintenance is examined in the case examples in Chapter 4 of this synthesis. Winter Considerations for Reactive Pavement Repair Pavement repair in winter’s cold temperatures and inclement weather presents several chal- lenges. Road base material may be frozen and additional freeze-thaw cycles are likely (Smith and Romine 2001). Emergency or reactive road repairs in winter months require different materials, procedures, and other considerations such as deicing, snow and ice removal, worker safety, and extreme temperatures. The costs and effectiveness of winter pavement repairs can vary depend- ing on the materials and equipment, required labor, and other factors. Because winter pave- ment repairs frequently fail due to limitations in materials, barriers to using certain methods, and other challenges, agencies generally consider the repairs temporary and schedule follow-up repair in the spring or summer when temperatures warm (NMDOT 2023). Reactive Winter Pavement Maintenance Materials and Techniques Common materials and techniques used for reactive maintenance in the winter months are summarized in the following paragraphs. Transportation agencies manage and repair both flex- ible (asphalt surface course) and rigid (concrete surface course) pavements. Concrete pavement does not develop potholes in the same manner as asphalt pavements; concrete distresses also include spalling, popouts, and blowups (FHWA 2019). Because asphalt can be used to patch both asphalt and concrete pavements (McDaniel et al. 2014), this literature review rarely distinguishes between asphalt and concrete. Many of the difficulties presented by cold temperatures and inclement weather when repairing asphalt also apply to concrete. However, temperature plays a more significant role when repairing concrete. An Iowa DOT study notes that fresh concrete needs to be protected from frost and freezing until it sufficiently cures, and the subgrade and existing concrete cannot be frozen. The manual

Literature Review 11   produced to aid local agency maintenance workers also cites the American Concrete Pavement Association (ACPA) recommendation that, if the air temperature is expected to fall below 40°F in the first 72 hours, the new pavement should be covered with insulating blankets, mats, or foam sheets (Smith 2006). Ideally, before patching a pothole, it must be cleaned and dried. The material must be ade- quately compacted in the hole and be allowed to cure sufficiently. Winter weather hinders all these steps. Pavement patches placed under winter conditions generally do not last as long as repairs made during milder weather, and the goal is often for them to simply last several months (Smith and Romine 2001). Materials Hot and cold mixes are the most common materials for pavement patching. Although hot mix provides a more durable and permanent repair, it is generally not available in winter because asphalt plants operate seasonally (Hajj and Lu 2021). Also, hot mix does not bond well with very cold pavement (Zanko et al. 2016). Hot mixes with modified binders (e.g., polymers, which may be expensive, or less-costly recycled polymers that include rubber and wax) can result in a stronger, more durable asphalt patch (Hawesah 2022). Although some researchers may recom- mend a hot mix for larger potholes, even in winter (Dailey et al. 2017), cold mixes are primarily used for reactive winter pavement maintenance. Cold mix may have additives (e.g., fiber reinforcement) to enhance performance (WSDOT 2020, Hajj and Lu 2021), and some observe that proprietary cold mixes perform better than non-proprietary mixes (Hajj and Lu 2021). Winter cold mixes, however, may not perform opti- mally when ambient temperatures are below 20°F (MnDOT 2018a). One laboratory study found that winter cold mixes do not get sufficiently strong because low temperatures do not allow for appropriate curing unless an external heat source is used. Given the poor mechanical properties of the material, the repairs are temporary, and these sites need to be repaired multiple times in the same winter season (Ghosh et al. 2018, MnDOT 2018). Mixtures need to be workable at low temperatures so crews can easily mix and compact the material in a pothole (Smith and Romine 2001). A propane torch can aid in drying the holes and heating the mix for good compaction (WSDOT 2020). A hot box (also referred to as a “heater box”) attached to a maintenance truck can warm cold mix to a working temperature, and rollers or plate compactors can tamp the material into the hole tightly (Rhode Island DOT 2023). Using a tack coat to line the pothole may also help with bonding (Transportation Association of Canada 2019). Cold mixes, however, can soften as temperatures warm, resulting in the compaction loosen- ing and material spilling out of the hole (City of St. Paul, Minnesota 2023). Methods Spray injection is a successful method of winter pavement patching in some states (McDaniel et al. 2014). Truck-mounted blow-patchers use air pressure to apply a mix of aggregate and asphalt emulsion (Nebraska Department of Roads 2002). The air pressure also works to blow water and debris from the hole (Nazzal et al. 2014). Spray injection patching can be quickly applied on asphalt or concrete (Hajj and Lu 2021, McDaniel et al. 2014) (Figure 1). Although the equipment may be more costly, the material— generally crushed aggregate and emulsified asphalt—and labor costs may be lower (Hajj and Lu 2021), although the material must be skillfully applied to be effective (McDaniel et al. 2014). Reclaimed asphalt pavement (RAP) may also be an option to use in spray injection patching (Kwon et al. 2018).

12 Wintertime Pavement Maintenance Practices Throw-and-go refers to using a shovel to manually fill a pothole with hot or cold mix and letting traffic compact the material. Throw-and-roll uses truck tires to compact the patch immediately after placement of the material and is generally more effective than throw-and-go (McDaniel et al. 2014, MnDOT 2018a, Hajj and Lu 2021). Both are quick application methods and may involve removing debris or water from the hole before repair (Nazzal et al. 2014). The throw-and-roll procedure, if used with a high-quality material compacted by truck tires, can be a cost-effective pavement patch in winter conditions (Smith and Romine 2001), however the difference in temperature between the patch and existing pavement can impair the bonding, leading to water continuing to enter the hole (Nazzal et al. 2014). University of Tennessee researchers compared the cost-effectiveness of various throw-and-roll patches (hot mix and cold mix) with more semipermanent repairs performed with combinations of hot mix, heat, and other materials. Performance indices were calculated for each mix based on the amount of dishing, edge disintegration, and missing patches in the context of factors that included the size of the patch, road speed limits, and freeze times. Researchers found that approximately 70% of the throw-and-roll patches lasted less than 14 months, and when patches survived one winter it was due to sufficient compaction and curing. Comparing performance to the costs of labor, equipment, and materials for different patch types, throw-and-go patches were more cost-effective in the short term (patches lasting between 8 and 14 months) but semi- permanent patches had higher cost-effectiveness in the long term because they lasted 20 months or more (Dong et al. 2014). The edge-seal method is like the throw-and-roll method, but the interface between the patch- ing material and existing pavement is sealed after the patched area has dried for a day, after which a layer of sand is applied (Hajj and Lu 2021). Semipermanent patching involves cleaning the pothole, saw-cutting around the hole to square up the patch area, filling the hole, and using vibratory compaction (Hajj and Lu 2021). Although cold mix can be used in this method, it is generally not used in winter months, given the increased labor and equipment needed. Slurry seal uses a mixture of aggregate, emulsion, asphalt cement, and water and is applied using a special machine. The International Slurry Surfacing Association notes that the method should not be used if the air temperature is below 50°F, rain is imminent, or there is a potential for freezing temperatures (Dailey et al. 2017). Figure 1. A blow-patcher in use. (Minnesota DOT 2018)

Literature Review 13   In a 2022 study, Ohio DOT researchers field-tested combinations of seven materials and four methods and concluded that the performance of a repair patch was dependent on many factors, including patching materials and methods, pothole size and depth, number of freezing days, and time to first snowfall after the patch. Combining test results with cost-effectiveness analyses, researchers developed a decision tree to provide guidance in different circumstances and focusing on cost-effective solutions for local governments (Nazzal et al. 2022). Crack Repair In general, pavement cracks should be cleaned, dried, and potentially routed out before being treated (FHWA 2019). Hot- or cold-applied sealants are commonly used on working cracks— those that expand in winter and contract in summer—to keep water and debris from entering the cracks (Marti and Miller 2023). Researchers conducting a 2019 Minnesota DOT (MnDOT) study, however, did not recom- mend crack-sealing in winter because proper cleaning and drying of the pavement area could not be achieved and the seal would likely fail quickly (Barman et al. 2019). Additionally, if a sealant is applied to a crack in the winter when it is at its widest, it will be squeezed out in warmer temperatures when the crack contracts (Decker 2014). Other researchers note that non-working cracks—those that do not change between the seasons—can be filled with various patch mixes after they are routed out (Marti and Miller 2023). A North Dakota DOT (NDDOT) study on crack repair surveyed more than 20 states with climates like that of North Dakota and found that most require dry conditions and ambient temperatures of at least 40°F and up to 50°F in one case. Exceptions included if the engineer determined a hot air lance could sufficiently warm the crack for proper bonding or treating the crack was in the public interest (Ragab et al. 2013). Innovations in Winter Pavement Maintenance Understanding the substantial needs of transportation agencies repairing pavement in winter, researchers continue to develop new ideas and methods for more durable pavement patching during these months. The proposed solutions reviewed below primarily focus on new materials, methods of generating heat, or both. Although some promising options are on the horizon for winter pavement repair, further research is likely needed to continue to identify new materials and methods and refine existing ones. Transportation agencies will also benefit from robust cost-effectiveness analyses that can justify new reactive winter pavement maintenance practices. Materials Asphalt materials reinforced with graphite nanoplatelets (GNP) can have superior compaction, mechanical, and strength properties over traditional cold mix (Ghosh et al. 2020). GNP asphalt materials modified with taconite have also been shown to have significant electrical conductivity capacity (Le et al. 2021) and can be heated by microwave energy (Ghosh et al. 2018, MnDOT 2018). Although relatively expensive, a proprietary hot-applied, polymer-modified asphalt mastic product has been found to be extremely flexible and performs well in cold weather for filling cracks and ruts. The product must be heated before applying and may require specialized equip- ment and training (Ghosh et al. 2018, MnDOT 2018). One researcher found this mastic material to be as strong as regular hot mix (Ghosh et al. 2020). Another mastic material was described in a recent state DOT innovations report as a notable, but more expensive innovation for durable pothole repair (Utah DOT 2019).

14 Wintertime Pavement Maintenance Practices Methods Ohio DOT researchers explored a tow-behind combination infrared asphalt pavement heater and infrared reclaimer (see Figure 2) as a winter pothole patching method and compared it to the throw-and-roll and spray injection methods. The reclaimer is a hopper heated by two infrared heaters that can recycle asphalt material by reheating it to a workable temperature. The seamless patches that result can improve the performance and longevity of the repair. Researchers found that infrared patching took more than four times the average time of the throw-and-roll method and over twice as much as the spray injection method. However, infrared patches lasted at least 14 times the expected life of the throw-and-roll and spray injection methods (Nazzal et al. 2014). Minnesota DOT (MnDOT) researchers explored the use of taconite mining byproducts and co-products in mixes and techniques for pavement repair. Magnetite-containing aggregate (taconite rock) or magnetite alone was mixed with RAP, placed in a pothole, and microwaved until the binder in the RAP softened enough to compact (Figure 3). Magnetite enhances microwave absorption and heats quickly. The microwave also heated the existing pavement, contributing to a good bond between it and the patch. Incorporating recycled asphalt shingles provided additional binder to Figure 2. Tow-behind combination infrared asphalt pavement heater and infrared reclaimer. (Nazzal et al. 2014) Figure 3. Microwave equipment heating a pavement patch.

Literature Review 15   the mix. This method did not require hot or cold asphalt mixtures or binders. Instead, recycled asphalt materials were used to create a stronger patch (Zanko et al. 2016). Research conducted by the U.S. Army Engineer Research and Development Center (initially in support of maintaining U.S. Air Force runways) resulted in the development of pre-packaged inductive hot mix that will heat in a matter of minutes using a field induction heater (Cox et al. 2019). The heater works like a microwave with high-energy electromagnetic radiation (USACE Engineer Research Development Center 2021a). Inductive steel aggregate particles incorpo- rated into an asphalt mixture provide the convenience of a cold mix and the durability of a hot mix. Material costs were estimated to be greater than standard proprietary cold mixes but less than premium proprietary cold mixes, and costs associated with the field induction heater were expected to be less than a spray injection patcher (Cox et al. 2019). Successfully tested in sub- zero winter temperatures in northern Canada (USACE Engineer Research Development Center 2021a) the research won a Federal Lab Consortium award. Although efforts were underway to commercialize this technique, it was not clear at the time of the writing of this synthesis that this has been accomplished (USACE Engineer Research Development Center 2021b).