Pavement Patching Practices (2014)

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3 This chapter introduces the synthesis topic and need for infor- mation on current pavement patching practices. It defines the scope of the project and the approach used to gather pertinent information. It also defines terms used in the synthesis to describe pavement distresses, patching types, such as reactive versus planned repairs, and patching techniques. Lastly, the results of the Strategic Highway Research Program (SHRP) studies on pavement patching are reviewed for comparison with current practices. BACKGROUND Despite advances in material selection and pavement design, pavement distresses and failures still occur. When they do so on a small scale or in fairly isolated locations patching is the most common maintenance technique used to restore pave- ment functionality. While actual figures are difficult to obtain, it is safe to assume that well over $1 billion is spent each year to main- tain roadways in the United States. In 1999, it was esti- mated that more than $1 billion was spent annually in the United States on pothole and spall repair (1) and costs have increased since then. With such a large expenditure of tax dol- lars, it is important to ensure that the funds are spent in a cost- effective manner and that the investments in patching result in improved pavement performance and longer service lives. SYNTHESIS SCOPE This synthesis documents the current state of the practice regarding pavement patching practices and updates the infor- mation available on patching practices to enable agencies to make informed decisions about their own patching policies and procedures. It is intended to document the state of the prac- tice for patching relatively small-scale defects or distresses in both asphalt and concrete pavements. Large-scale patches, wedge and level (or level-up patching), and pre-overlay patch- ing are not the focus. In particular, the synthesis examines the following: • Current programs for repair and patching; • Pavement distress factors that identify a good candidate for repair and patching; • Performance information under different conditions such as season, time available, and traffic; • Repair and patching materials and associated perfor- mance for both asphalt and concrete pavements; • Review of public and private repair and patching speci- fications, including quality measurement practices such as smoothness and density control for asphalt patching and opening strength for concrete patches; • Repair and patching design and construction practices for manual and automated repairs; • Traffic control requirements and practices for pavement repair and patching; • Repair and patching equipment, including types of auto- mated equipment; • Methodology to track and report on patches, such as Global Positioning System (GPS) and geographic infor- mation system (GIS) mapping tools and maintenance management condition assessment systems or processes; • Unit cost information; and • Ongoing research and future needs. The main focus of this synthesis is on reactive, manually installed patches over relatively small areas; however, some information was also gathered on planned and machine- fabricated patches. The focus is also on patching that is intended to serve traffic for some time, whether temporarily or permanently, and does not include patches placed imme- diately before placement of an overlay. SYNTHESIS APPROACH AND REPORT ORGANIZATION The information presented in this synthesis was collected in several ways. First, a comprehensive literature search was performed using the TRID database, Google, Elsevier, and Compendex. Pertinent citations were also suggested by sur- vey respondents and others. The citations were reviewed and categorized as to their primary topics (e.g., patching asphalt or concrete pavements, equipment, management, specifications, and health and safety). The literature review primarily, but not exclusively, focused on publications released since the SHRP research, because the SHRP researchers had conducted exten- sive reviews of literature published prior to the SHRP program. More than 100 references were reviewed in preparing this syn- thesis, and the information from this literature review is pro- vided in chapter two. A second approach was a survey of U.S. state agencies, which was used to collect electronic responses to a screening chapter one INTRODUCTION

4 survey to identify states with the most information on particu- lar aspects of patching practices. A total of 48 states plus the District of Columbia responded to the survey; a response rate of 96.1%. A copy of the survey, list of agencies responding to the survey, and tabulations of survey responses are provided in Appendices A–C. Following the screening survey, to elicit additional informa- tion, selected states were interviewed by phone or questioned by e-mail. A core set of follow-up questions was developed and used during the phone interviews to guide the discussion; however, the interviews were loosely structured to allow lati- tude to gather as much information as possible. Summaries of the findings of the U.S. survey and follow-up interviews are provided in chapter three. A similar survey was distributed to a number of local U.S. transportation agencies. A request for information was sent to the Local Technical Assistance Program (LTAP) offices in 16 states representing different climatic regions. The LTAP centers were asked to forward the request to the appropriate agencies within their states. In one case, the LTAP center felt informed enough to provide answers for the local agencies in the state as a whole. A total of 20 responses representing local agencies in eight states were received. These responses are summarized and compared with the responses from state agencies in chapter four. A third electronic survey was developed and sent to agen- cies in the United Kingdom and Ireland, including national agencies, local (city or county council) agencies, and some pri- vate contractors. A total of 36 responses were received. Lastly, responses were received from five Canadian agencies; three provincial and two from large cities. Information from this sur- vey is presented and comparisons with U.S. practices are made in chapter four. Chapter five includes four case examples of selected agen- cies and their innovative or informative practices. Chapter six summarizes the collective findings of the synthesis effort and identifies gaps in the knowledge and future research needs as identified by the survey respondents. BASIC CONCEPTS AND DEFINITIONS This synthesis is focused on patching practices for both asphalt and concrete pavements. Many of the terms used frequently throughout this report are defined here for clarity. As a general note, the District of Columbia is, for purposes of this summary, grouped with the state agencies. When the term “state” is used, it is intended to include the District of Columbia. Distresses Suitable for Repair by Patching For the most part, the definitions of the distress terms used herein correspond to those in the Distress Identification Manual for the Long-Term Performance Program, commonly referred to as the DIM (2). Many states use this manual and therefore are familiar with the terminology. In asphalt pavements, the most common distresses that can be repaired by patching include potholes, deterioration around cracks, delaminations, rutting, or raveling. The DIM does not include deterioration around a crack as a distress, but does include high severity cracking, which could describe this type of deterioration. In this document, the term “delamination” refers to the separation of one layer of an asphalt pavement from the underlying layer; some refer to this as “peeling.” In the DIM, this would be categorized as a pothole. One distin- guishing feature of a delamination versus a pothole is that a delamination has a flat bottom at the top of the underlying layer, whereas a pothole is bowl-shaped. Figures 1 and 2 illus- trate potholes and delaminations, respectively. Technically speaking, concrete pavements do not experi- ence potholes. The term pothole, however, is sometimes used in the literature as a generic term for a hole requiring patching. In this document, the area to be patched is sometimes referred to as a “hole” for brevity, although the area to be patched may exhibit some distress other than a pothole. FIGURE 1 Potholes caused by poor drainage (Source: Cornell Local Roads Program, CLRP).

5 In concrete pavements, some of the distresses that can be addressed through patching include deterioration around cracks (such as durability “D” cracks, map cracking, and longitudinal or transverse cracks), scaling, popouts, and blow- ups. In addition, jointed concrete pavements may experience joint spalling (Figure 3), corner breaks (Figure 4), faulting, and damage caused by water pumping that can be repaired by patching. Continuously reinforced concrete may be sub- ject to punch-outs as well. As with asphalt pavements, the DIM does not consider deterioration around cracks as a distress type on concrete pavement; however, deterioration around a crack could be considered analogous to spalling at a joint. Patching is also used to repair deteriorated patches or around previous patches on both pavement surfaces (Figures 5 and 6). If the area around a patch continues to deteriorate, the first patch did not solve the problem. Types of Patches Some of these distresses can happen suddenly, requiring reac- tive or emergency repairs, while others progress more gradu- ally, allowing an agency time to plan, and perhaps contract out, the repair. In this document, these are referred to as reactive and planned patches, respectively. Reactive patching is some- times called demand patching in the literature. Depending on factors such as the time of year, availability of repair materials, or traffic conditions, temporary patches are often placed to hold the pavement over until more permanent patches can be placed. Temporary patches are often placed in the winter or during other adverse conditions to address an imme- diate safety or ride quality problem. The term semi-permanent is sometimes used in the literature to refer to longer lasting repairs on asphalt pavements, while long-lasting patches on concrete pavements are often considered permanent. FIGURE 2 Delamination of surface layer (Source: CLRP). FIGURE 3 Patched concrete joint spalls (Source: R. McDaniel). FIGURE 4 Patched corner break in concrete pavement (Source: R. McDaniel). FIGURE 5 Multiple asphalt patches on concrete pavement (Source: R. McDaniel).

6 Patch Materials A wide variety of materials is used for patching, especially for concrete pavements. Some form of asphalt mixture is com- monly used to patch both asphalt and concrete pavements. Asphalt patches on concrete pavements are frequently con- sidered temporary patches. Concrete pavements may also be patched using cementitious materials of various types, which are generally considered to be more permanent repairs. Poly- meric materials have been used on both types of pavement as well. Injection patching, by blowing asphalt emulsion and aggregate into the area to be patched, is sometimes used, espe- cially in winter when hot mix materials are not available. As used herein, hot mix asphalt is a typical asphalt mixture produced through a hot mix plant. Few states reported using warm mix asphalt, but if they do that mix would be similar to a hot mix. Cold mix, cold emulsion mix, or generic stockpile mix are terms used to refer to asphalt mixtures that can be stock- piled and worked when cold; they are often produced through a hot mix plant, then allowed to cool in a stockpile for later use. Proprietary cold mix is similar but utilizes some proprietary formulation, often of the asphalt binder; these are designated by their trade names. Proprietary patching materials are some- times sold in bags rather than being stockpiled. Materials used for patching concrete pavements, aside from asphalt patching materials, include mixtures with cementi- tious materials such as normal hydraulic cement, rapid strength hydraulic cement, calcium aluminate, calcium sulfoaluminate, magnesium phosphate, and other cementing agents. At times latex or polymer-modified concretes are also used. Epoxy materials are less common, but also available. Patch Preparation and Placement Methods There are a number of different methods of preparing the area to be patched and placing the patching materials. These were standardized to some extent during the SHRP research that is discussed in the following section. As defined by SHRP and used in this document the methods are described as follows. For placing asphalt patching material, either on an asphalt or a concrete surface, the descriptive term throw-and-go refers to simply filling the hole with patching material and moving on to the next hole. Somewhat more effort is expended in the throw-and-roll technique, where truck tires are used to com- pact the patching material after placement (Figure 7). Both the throw-and-go and throw-and-roll methods can be used for temporary patching under adverse conditions, such as in winter or for a sudden problem under heavy traffic, although the throw-and-go technique is generally not recommended. A semi-permanent patch involves considerably more pre- paration and compaction and therefore is usually not feasible under adverse conditions (Figure 8). In this method, used for asphalt surfaces, water and debris are removed from the area by an air compressor or broom (mechanical or manual). The sides of the area to be patched are cut back to sound material and made vertical by hand or power equipment (such as saws, FIGURE 6 Multiple patches on asphalt pavement (Source: R. McDaniel). FIGURE 7 Rolling a patch with truck tires (Source: CLRP).

7 picks and shovels, or milling machines). The patching mix is placed in the prepared hole and is compacted using a vibrat- ing plate, vibratory roller, or other equipment (3). The edge seal method is similar to the throw-and-roll or semi-permanent technique except that a crew returns after the patch has set and seals the edges of the patch. This is usually used on asphalt surfaces only (see Figures 9 and 10). During the SHRP research, one similar agency-requested technique evaluated was used in Illinois and involved sealing the entire surface of the patch, rather than just the edge, and dusting it with sand (4). In all of these cases, the SHRP Manual of Practice calls for checking that the patch has a slight crown to help drain away water and to allow for some densification under traffic (4). The spray injection method uses specialized trailer- or truck-mounted equipment to blow water and debris from the pothole, spray a tack coat into the hole, blow asphalt and aggregate together into the hole, then cover the patch with a layer of aggregate (see Figure 11). Because the aggregate and emulsion are propelled into the patch area with high pressure air no further compaction is necessary. Spray patching can be used on asphalt or concrete pavements and is sometimes done under adverse conditions because of the speed with which it can be accomplished (5). Many types of distress on concrete pavements can be repaired using partial or shallow depth patching if the distress is confined to the top third to half of the slab; the unsound material is removed and a patch installed. (Deeper distresses require full-depth repairs.) Techniques for permanent patching FIGURE 8 A semi-permanent patch on asphalt pavement (Source: R. McDaniel). FIGURE 9 Excellent edge seal on semi-permanent asphalt patch (Source: R. McDaniel). FIGURE 10 Edge seal misapplied on throw-and-roll patch (Source: R. McDaniel). FIGURE 11 Patching with trailer-mounted spray injection patcher (Source: Ohio DOT).

8 of concrete pavements as used in the SHRP research on partial depth spall repair include the following (6): • Saw and patch—where straight vertical faces are pro- duced by sawing. • Chip and patch—where loose or unsound material is removed by pneumatic hammer or other tools and con- crete faces at least 1 in. deep are formed around the patch. • Mill and patch—where a milling machine is used to remove unsound material to a depth of at least 1.5 in. and vertical edges are formed in corners with chip- ping hammers. • Waterblast and patch—where unsound concrete is removed to a depth of at least 1.5 in. and vertical faces are formed by waterblasting. • Clean and patch—where unsound concrete is removed with hand tools; during the SHRP research, this was used only with the spray injection method. Figure 12 shows an example of a sawed and patched repair where the concrete tining has been reinstated over the patched area. These techniques are still used today. Milling and water- blasting to prepare the areas to patch are generally less com- mon than the other techniques because of the equipment required. STRATEGIC HIGHWAY RESEARCH PROGRAM RESEARCH ON PATCHING As mentioned in the Introduction (chapter one), one goal of this synthesis is to compare today’s practices with the recom- mendations made in the SHRP research on pothole and spall repair. To do that, the SHRP findings must be recognized and discussed. This section briefly outlines some of the main find- ings of the SHRP research on patching. Beginning in the late 1980s and ending in 1993, SHRP was directed to develop high-payoff products in six focused areas of national need. One of these areas was highway maintenance. As a part of that effort, three SHRP contracts, H-105, H-106, and H-107, addressed materials, procedures, and equipment for some routine maintenance activities. Under H-105, Inno- vative Materials and Equipment for Pavement Surface Repair, an extensive literature review was undertaken and highway agencies across the country were surveyed to identify prom- ising options for the repair or treatment of potholes, cracks, joints, and spalls. (This review will focus on the findings regarding pothole repair in asphalt-surfaced roadways and spall repair on concrete surfaces; joint and crack repair are beyond the scope of this synthesis.) Based on the results of H-105, H-106 evaluated the construction and performance of field test sections with various materials, patching proce- dures, climates, traffic levels, and other factors. These test sections were monitored for approximately 18 months after installation, until the end of the SHRP program. At the close of the SHRP program, the Long-Term Pavement Perfor- mance (LTPP) team at FHWA agreed to let a contract to con- tinue monitoring the test sites for an additional 48 months. The final reports and manuals were published by FHWA in 1999. The third contract, H-107, resulted in the development of automated equipment for pothole patching, as well as joint and crack sealing. SHRP Research on Pothole Repair Research conducted under contracts H-105 and H-106 led to several reports including Evans et al. (3) and Smith et al. (7), and a Manual of Practice for Materials and Procedures for the Repair of Potholes in Asphalt-Surfaced Pavements (4). As mentioned previously, the manual was updated by FHWA in 1999 (5). The field studies under contract H-106 involved the place- ment and performance monitoring of 1,250 pothole patches at 22 sites in four climatic regions on two pavement types (flexible and composite). The patches evaluated used cold mix stockpile materials and spray injection; hot mix was not included because the focus was on materials that could be placed in any weather. A proprietary product named UPM, placed with the throw-and-roll technique defined earlier in this chapter, was considered the control and was used at all the test sites. The materials and repair procedures used are shown in Table 1. UPM, Perma-Patch, and QPR 2000 are proprietary patch- ing materials. As noted previously, UPM was considered the control material for these field evaluations. The HFMS mix- ture used a high float medium setting emulsion to produce a non-proprietary cold mix suitable for stockpiling until needed. The Pennsylvania DOT (PennDOT) mixes were also suitable for stockpiling. They used a gradation similar to the UPM with clean, angular aggregates, but had different binders and were not proprietary; PennDOT 486 included fibers to aid in FIGURE 12 A sawed patch on concrete pavement with reinstated tining (Source: R. McDaniel).

9 stability and prevent draindown of the binder. Spray injection patching was defined in “Patch Preparation and Placement Methods.” The “Local Materials” were generic, “every day” cold mixes (8) common to each state, and “Agency Request” signified a technique or material the agency wanted to evalu- ate. One example was Illinois’ previously mentioned use of sealing over the entire patch area and spreading with sand. Among the repair procedures the throw-and-roll placement technique is widely used, especially under adverse weather conditions, because it has a high productivity rate and repairs can be effected quickly. The technique is considered superior to the throw-and-go technique because the effort to com- pact the material into the pothole generally leads to a longer lasting patch that is less likely to be affected by traffic than loose material (4). The spray injection method involves higher costs for the equipment, but the higher productivity rate and reportedly lower material costs make it attractive. Because of the speed at which patching can be performed, there is less worker exposure to traffic as well, making the operation safer. The findings from the field evaluations generally showed that (3, 8, 9): • The performance of patches placed with the throw-and- roll technique was comparable to the semi-permanent patches in head-to-head comparisons with three dif- ferent materials. In addition, the throw-and-roll tech- nique was more cost-effective (higher productivity and lower costs). Since the performance was comparable, the lower costs made throw-and-roll more cost-effective on a life-cycle basis. • The success of the throw-and-roll technique depended on the use of high-quality materials, such as proprietary cold mixes. • Spray injection was a “viable” option and performed as well as the control patches at all locations (8). However, the method was found to be more heavily dependent on the skills of the operator than the other methods and to require use of angular aggregates and a compatible asphalt emulsion. It was noted that the absorption of the aggregate needed to be taken into account to ensure there is enough binder added. • The methods best suited to use in winter conditions were the throw-and-roll or spray injection methods because of the speed with which patches could be installed. • Patches placed in the wet-freeze climatic area did not perform as well as those placed in the dry-freeze region. Similarly, patches placed under adverse weather con- ditions did not perform as well as those placed during warmer, drier periods. • The first few weeks after the patch was placed were deemed the most critical as the material was still setting during this time. • With good materials and proper techniques patches could perform for several years. The Manual of Practice (4, 5) covers the use of cold mix stockpile materials using the throw-and-roll or semi-permanent techniques and the use of the spray injection method. The steps are as outlined in “Patch Preparation and Placement Methods.” The manual also addresses safety issues, including traffic control, following manufacturers’ guidelines, referring to the Material Safety Data Sheets (MSDSs) for proprietary materi- als, and wearing eye protection when using the spray injection method. The manual recommends use of the throw-and-roll technique in winter conditions with patching mix made with high-quality aggregate, few fines, and an emulsion with an anti-strip additive. In spring conditions either the throw-and- roll, spray injection, or semi-permanent installation methods are recommended. The materials used in the spring may be the same as in the winter, although they reportedly may be sticky and harder to work with at warmer temperatures. The manual also suggests testing the compatibility of the asphalt binder and aggregate, at least if the combination has not been used before. This testing would require checking: 1. Coating—at least 90% retention; 2. Stripping—at least 90% coating retention; and 3. Drainage—loss of no more than 4% of the weight of residual binder. (This is now more typically called drain down from experience with open-graded asphalt and stone mastic asphalt mix design.) The specific test methods are described in the manuals (4, 5). For acceptance of patching material, the manual also rec- ommends testing the workability with a workability box and TABLE 1 MATERIALS AND PROCEDURES USED IN H-106 FIELD EVALUATIONS Material Repair Procedure UPM High Performance Cold Mix (control) Throw-and-roll Edge seal Semi-permanent PennDOT 485 Throw-and-roll Edge seal Semi-permanent PennDOT 486 (polyester fibers) Throw-and-roll Local Materials Throw-and-roll Surface seal Heated with propane torch HFMS-2 with Styrelf Throw-and-roll Perma-Patch Throw-and-roll QPR 2000 Throw-and-roll Semi-permanent Spray Injection Spray injection Agency Request Agency request Source: Mojab et al. (6).

10 modified pocket penetrometer. Another acceptance test eval- uates the cohesion of the patching material. Again, the test methods are described in the manuals (4, 5). A method to determine the patch survival rate based on the number of patches remaining in place over time is also pre- sented. A worksheet to estimate patching costs is provided in the manuals (4, 5). The productivity of the various pothole patching opera- tions was evaluated at each test site. Table 2 summarizes the times to place different types of patches (9). Again, throw- and-roll and spray injection were comparable in terms of tons per hour placed and time per patch. It is important to note, however, that the productivity reported here includes the time for patching only and does not include such fac- tors as mobilization. Evaluation of the test sections placed under H-106 was continued under the LTPP Program. A 1999 Tech Brief on the subject (10) concluded that: • The throw-and-roll technique was more cost-effective in most cases than the semi-permanent procedure, if qual- ity patching mixtures were used. • After roughly three to four plus years, 56% of the patches placed had survived, 31% had failed, and 13% had been overlaid. • The spray injection technique continued to demonstrate good performance with a skilled operator. • Three of the eight agencies that placed test sections had converted from using their local patching mixtures to one of the tested materials and one agency had purchased a spray patcher based on the good performance and cost- effectiveness observed during the study. In addition, this longer review under LTPP confirmed the recommendations offered in the SHRP reports regarding using throw-and-roll or spray patching practices in adverse weather conditions, using high-quality materials, considering safety and user delay when selecting the patching technique, and test- ing compatibility of the asphalt and aggregate (10). SHRP Research on Spall Repair Spalls on a concrete surface are typically repaired with shal- low depth patching. Research under SHRP contracts H-105 and H-106 evaluated the performance of various materials and repair procedures used in different climates and under differing atmospheric conditions at the time of placement. In the course of the SHRP research, 1,600 spalls were repaired and monitored for approximately 18 months. Partial-depth patches might be expected to last for five to ten years; therefore, the findings in the SHRP report were considered preliminary (6). These spall repairs were monitored by FHWA/LTPP for an additional four years and a final report, manual, and Tech Brief were published in 1999 (11–13). The products evaluated in the field included Type III Port- land Cement, Duracal®, Set-45®, Five Star® HP, MC-64, SikaPronto® II, Percol FL, UPM High Performance Cold Mix, Pyrament® 505, Penetron® R/M-3003, and spray injection cold mix (using two different devices, AMZ and Rosco) (6). Six different preparation techniques were used, including the saw and patch, chip and patch, mill and patch, waterblast and patch, and clean and patch methods defined in “Patch Prepara- tion and Placement Methods.” In addition, minimal prepara- tion under adverse conditions was also done as a worst-case scenario. In this case, only hand tools were used to remove unsound concrete and water was sprayed into the hole, if not already present. If dowel bars were exposed or the depth of removed material was greater than half the nominal pavement thickness, a full-depth patch was recommended instead of a partial-depth patch. The findings included the following (6): • Partial-depth patches performed well over the course of the study. • There were significant performance differences between some of the cementitious and polymer materials in terms of many performance measures in some or all climates. • There were also some differences in various aspects of the performance of asphalt materials in the wet-freeze and wet-nonfreeze regions. TABLE 2 PRODUCTIVITY OF PATCHING USING DIFFERENT METHODS Method Range (min/patch) Average (min/patch) Ave. Productivity (tons/hr) Throw-and-Roll 1.5–5.0 2.6 1.6 Edge Seal 2.5–5.4 3.2 1.4 Semi-Permanent 4.2–27.0 13.3 0.3 Spray Injection 1.9–4.6 2.8 1.7 Source: Wilson and Romine (4).

11 • Installation temperature had minimal effect on perfor- mance except for the longitudinal cracking of polymer and cementitious patching materials in the dry-freeze region. • Type III cement performed comparably to proprietary cementitious patching materials. • Only three combinations of preparation method, patching material, and climate exhibited poor performance com- pared with the other combinations; these were Percol FL with saw-and-patch in the dry-nonfreeze region, Set-45 with chip and patch in the wet-freeze region, and Percol FL with chip and patch in the wet-nonfreeze region. • Differences were observed between the spall prepara- tion techniques but, as noted previously, these differed by climate and patching material used. There were no clear trends in the performance and, since almost all of the patches were performing well, rankings of the differ- ent factors was not possible. The final report published by FHWA (11) confirmed that most of the partial depth repairs and the Type III cement per- formed well. The repairs made with the chip and patch tech- nique performed as well as or better than those with the saw and patch method and were less expensive, resulting in lower annual costs. The waterblast and patch method was effective when done by an experienced operator with properly working equipment. SHRP Development of Automated Pothole Patching Machine Under SHRP contract H-107B, a prototype completely auto- mated pothole patching machine, called the Automated Pave- ment Repair Vehicle (APRV), was developed (14). The machine was intended to reduce the cost of patching by reducing the labor requirements to one or two operators; to improve safety by allowing the operator(s) to work from the cab of the vehicle; to speed the repair process, which would improve safety and reduce delays for motorists; and to allow repairs to be installed in varying weather conditions or at night with a variety of materials. Potholes were identified and repaired using a com- puter vision system and robot. The device was designed to cut around the area to be patched (if desired), clean the hole, heat and dry the interior of the hole, and spray in the patching aggregate and binder. Basically, the patch would be formed using the spray injection method; however, the remainder of the process, specifically preparing to patch, was report- edly improved and automated (14). It was estimated that automated repairs using the APRV could save, on average, about $55 per pothole filled. In addi- tion, it was maintained that the system would be safer, result in fewer traffic delays, and lower vehicle maintenance costs because of the improved road conditions. Summary As with other areas of the program, the SHRP research on pothole patching and spall repair was unprecedented in scope and scale. The results led to increased standardization of terminology; improved materials, tests, and techniques avail- able for implementation; and development of some innova- tive technologies. In later chapters, this synthesis will explore and summarize which of the SHRP recommendations have been implemented.