Pavement Patching Practices (2014)

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12 This chapter summarizes the findings of the literature review regarding pavement patching practices for asphalt and con- crete pavement surfaces. The literature review is presented in three parts: (1) patching as part of a maintenance program, (2) patching asphalt pavements, and (3) patching concrete pavements. There is often considerable overlap in the topic areas covered in individual reports and papers; therefore, these are not absolutely clear-cut distinctions. PAVEMENT PATCHING AS PART OF MAINTENANCE PROGRAMS This section summarizes general, more administrative infor- mation about pavement patching by agencies gleaned from the literature review. Although pavement patching may appear to some to be a simple, routine maintenance activity, the costs associated with patching can be very high in terms of labor, equipment, materials, and user delays. Therefore, the advan- tages of managing the activity effectively can be significant. There have been a number of studies over the years to iden- tify the most cost-effective ways to manage patching, among other maintenance activities. Some of those documents that relate to management programs are summarized here. Management Policies, Costs, and Service Life This section presents the results of some research efforts directed at examining various costs associated with pave- ment patching and the service lives of the treatments to guide management policies. Patch performance in general, from a management perspective, is included here; whereas the per- formance of particular patching materials is discussed later. Management considerations of when and how to patch a pave- ment are also discussed. Prior to the SHRP research described earlier, one of the most comprehensive research efforts on pothole patching was directed by Anderson and Thomas in Pennsylvania. They evaluated pothole patching practices, equipment, and labor productivity to review PennDOT’s patching management through several projects (15–17). One result of this effort was the adoption of a policy to “do-it-right” the first time. The researchers found that using the throw-and-go technique cost approximately three times as much as semi-permanent patches, although the latter take more time to install. The throw-and-go patches typically did not last long and had to be patched repeatedly, increasing costs and inconvenience to the travelling public. The study also concluded that mate- rial costs are a relatively small percentage of the total repair cost; therefore, using more expensive, higher quality patch- ing materials could be justified. Based on the research find- ings, the authors developed a guide for patching for use by PennDOT maintenance personnel (17). This guide included detailed procedures for marking, cutting, cleaning, tacking, filling, compacting, and sealing the patch. Recommendations were also provided on the types of equipment to use for max- imum productivity and longevity of the patch. A paper by Thomas (18) described a procedure for evaluating the effi- ciency of different devices for cutting the patches based on the cutting rate and productivity. Citing a need to evaluate the service life of various mainte- nance activities in order to incorporate maintenance activities into the pavement management system, Feighan et al. (19) researched the costs and service lives of these treatments in Indiana in 1986. This information was deemed essential to allocate maintenance funds, identify the most cost-effective procedures, explore how changes in procedures or materi- als affect longevity, enable planning for future maintenance requirements, and more. One of the activities studied was shal- low patching on asphalt and concrete pavements (see chap- ter five). Surveys and interviews of subdistrict maintenance personnel across the state were used to estimate service life. Records from maintenance crew cards and previous research were used to estimate time requirements and costs. Shallow patching using hot mix, cold mix, cold mix with fibers, and fiber mix heated in a Portapatcher were evaluated. The service lives of these various materials and procedures were com- pared on roadways that were otherwise in good, fair, and poor condition. In general, hot mix was found to have superior per- formance in all cases, and cold mix was less effective. Patches placed on better performing roads also lasted longer. How- ever, it can be noted that these patches were typically placed under the worst conditions and improved materials have been developed since the 1980s. Heating the fiber mix improved the workability and led to better performance than using cold fiber mix (19). For pavement repairs to be efficient technically and finan- cially, it is important to place the right treatment on the right road at the right time. Specifically, if a roadway is sched- uled for replacement or rehabilitation within a few years, extensive semi-permanent or permanent patching may not chapter two LITERATURE REVIEW ON PAVEMENT PATCHING PRACTICES

13 be justified. When performed properly and at the appropri- ate time, patching need not be a temporary fix, but can be an important component of a pavement management system, provided good quality materials and installation techniques are used. Good patching can be an investment in the pave- ment life (20). In a survey of 35 state highway agencies (SHAs) conducted by Peshkin and Hoerner in 2005 (21), the most common approach for selecting a preventative maintenance treatment was “engineering judgment” (28 responses), followed by a selection matrix or decision tree based on pavement distresses (21 responses). This suggests that although many SHAs have a mature system established for decision making, several are relying on past experience and judgment. Although this survey dealt with preventative maintenance in general, the same could be said of patching in particular, as the sur- vey for this synthesis shows (chapter three). Peshkin and Hoerner also noted that the use of pavement management systems, attention to maintenance, and emphasis on pave- ment performance were all increasing (21). These factors also favor increased scrutiny of pavement patching and incorporation of patching activities into overall pavement maintenance programs. Despite the continued reliance on engineering judgment, the use of standardized guidance, such as distress identification manuals, is considered imperative in order to provide a consis- tent, uniform basis for applying treatments. Many states have developed manuals to guide condition ratings. For example, in 2009, the Indiana Department of Transportation (INDOT) recognized that its pavement condition data collection manual was limited owing to a lack of standardized visual methods, measurement methods for severity and extent, and informa- tion on causes of each distress. Knowledge of the causes and mechanisms of distress was identified by INDOT as an impor- tant factor in selecting appropriate pavement treatments. It also acknowledged that an identified pavement distress often has more than one possible cause. Treatment selection without a precise distress diagnostic can result in improper treatment, which may be ineffective in terms of performance and finan- cial value (22). Therefore, INDOT developed detailed treat- ment guidelines on pavement preservation techniques that cover partial-depth patching on concrete pavements. Patching on asphalt pavements is not included because INDOT does not consider this a preservation technique (22). Energy and Cost Considerations Another study in Indiana investigated the fuel consumption associated with equipment used for several maintenance activ- ities. Shallow patching was found to be second only to clean- ing and reshaping ditches in fuel consumption. (Snow and ice removal was not considered.) The researchers concluded that significant fuel savings could be realized by improving the identification of routine maintenance needs and the effective- ness of the maintenance activities to prevent further damage and subsequent re-treatment (23). Energy savings were also identified by increasing the use of pavement preservation techniques. Saito et al. (24) studied the performance of shallow patches and found that the need for shallow patching was reduced in the spring when more sealing had been performed before the preceding winter. The report indicated that the department could realize energy sav- ings through reduced fuel consumption and there could be other benefits, such as reduced pavement damage, improved safety, and lower vehicle operating costs for the public (24). This study emphasized the need to coordinate patching activi- ties with other pavement maintenance, such as sealing, as part of an overall pavement management system. Outreach Another aspect of managing patching operations is public outreach. Informing the public of upcoming patching opera- tions can alert them to potential traffic delays, which may lead them to choose alternate routes. It also lets the public know that maintenance crews will be operating in the right-of-way, and these messages frequently urge the public to slow down for safety (25). This can improve safety for the workers and the traveling public, which is a primary concern in manag- ing roadway operations. Educating the public about the needs and benefits of patching helps them appreciate the importance of the work and, hopefully, instills tolerance. PennDOT has developed a series of cards for distribution to the public to explain the importance of various maintenance activities, including patching (26). Outreach to the public also sometimes takes the form of recruiting drivers to help spot problems. Since 2009, the Dis- trict of Columbia has had an annual program called “Pothole- palooza.” This public relations campaign establishes ways for the public to notify the District Department of Transportation (DDOT) of potholes by phone, smartphone application, e-mail, online, Twitter, and Facebook. Residents can track the progress of filling potholes online (27). In 2014, the department filled nearly 12,000 potholes with the public’s assistance, up from around 4,000 holes filled in 2013 (28). During the campaign the DOT adds crews to enable a faster response time (27). New York City also provides a web-based method for the public to report potholes. The site displays a tally of the number of potholes patched since the beginning of “pothole season”; over the course of the 2013 fiscal year, nearly 250,000 potholes were filled (29). The Missouri DOT initiated a “Missouri Pothole Patrol” campaign in an attempt to encourage quick repair of potholes. The districts in the state compete to see how many potholes they can repair properly during the campaign. The winning district gets a small monetary award to spend on materials and equipment (30).

14 PATCHING ASPHALT PAVEMENT SURFACES This section summarizes the findings of the literature review related to patching pavements surfaced with asphalt mixtures. The results are presented in the categories of Materials and Testing, Techniques and Equipment, and Performance, which includes some discussion of cost-effectiveness. As with the literature on management of patching programs, there is con- siderable overlap in the topics covered in individual papers; for example, much of the literature reporting on materials used for patching also discusses the performance of those materials. Patching Materials and Testing Many states have specifications for locally produced patching materials (as opposed to commercial, proprietary mixtures) or use some of their standard hot mix paving materials, when available. Examples include California (31), Indiana (22), and Pennsylvania (17). In general, clean, angular aggregates are recommended in these specifications for use in produc- ing patching mixtures. The choice of the binder varies; some form of asphalt binder is typically used. Table 3 summarizes several of the state specifications reviewed in this synthesis, some of which focus on the binder used. The Indiana guidelines (22) note that the aggregate size in the hot mix used should be related to the depth of the patch for semi-permanent repairs. If the aggregate size is too small rela- tive to the depth of the patch there is a greater chance of rutting or displacement. If the aggregate size is too large, the material may not be adequately compacted, or seated, into the hole. It is therefore recommended that base material be used for shallow patches 3 to 6 in. deep, and surface mix for patches between 1.5 and 3 in. deep. Intermediate mixes may also be used for patches in the 2 to 5 in. range. For deep patches in asphalt pave- ments, INDOT recommends compacting the patching material in lifts and using surface mix on the top lift. These require- ments are similar to those used in many other states. In 2001, the New Jersey DOT published a research report exploring different patching materials, following the SHRP research protocols. In addition to testing patching materi- als, it also looked at tests for quality assurance and different patching methods, including throw-and-roll, semi-permanent, spray injection, and edge sealing of throw-and-roll patches. The research objectives were addressed through a literature review, laboratory testing, and field trials (32). The lab tests included tests of stability, adhesion/cohesion, durability, workability, and storageability. In addition to con- ventional asphalt tests such as resilient modulus and Mar- shall stability and flow, and binder tests such as penetration and viscosity, two relatively new methods used in the SHRP research were used to evaluate the New Jersey materials. These were the blade resistance test for workability and the rolling sieve test for cohesion. The study concluded that the TABLE 3 EXAMPLES OF MATERIALS SPECIFIED BY STATE DOTs FOR PATCHING FLEXIBLE PAVEMENTS State Relevant Repair(s) Recommended Material(s) Material Selection Guidance ID (34) Hand patch potholes Asphalt cement After consultation with the District Maintenance or Materials Engineer Deep patch (and base repair) Cutback asphalt Asphalt emulsion KY (35) Pothole patching Bituminous mix No guidance Bituminous patching (shoulders) Liquid asphalt (optional) WA (36) Patching HMA (e.g., asphalt concrete Class B) Class B is recommended where possible; no specific guidance. Asphalt pre-mix (cold mix) Fiber-reinforced “winter mix” CA (31) Patching and edge repair Hot mix asphalt (HMA)—preferred Generally HMA materials used to Caltrans DGAC specs. However, the mix type used may vary according to traffic conditions. Cold mix asphalt—temporary only Aggregate/asphalt emulsion combinations Special patching mixtures MT (37) Surface repair Plant mix Choice of materials is dependent on distance from the source of materials to the job, time of year, and the size of the job. Surface patching-hand Emulsions Proprietary (cold weather) mixes TX (38) Potholes Medium-Curing Cutback Asphalt (MC-800) No guidance Special cutback material (SCM I and II) Polymer-Modified Emulsified Asphalt (AES-300S) MN (39, 40) Potholes Cold mix (2381) Repair type; weather; equipment (see Table 6.1) Spray injection Hot mix 2350LV; Type 5 Slurry Mastics Microseal material DGAC = dense-graded asphalt concrete.

15 blade resistance test did not provide any meaningful results and the rolling sieve test did not correlate with field perfor- mance (32). Dong et al. (33), on the other hand, recommended the rolling sieve test at 25°C after compacting specimens with 15 blows of a Marshall hammer as a means to assess patching mix cohesion in a study for the Tennessee DOT. The materials evaluated in the New Jersey study included QPR 2000, UPM, I.A.R., Wespro, SuitKote, and PermaPatch. Although some of these materials did have different perfor- mance in terms of specific behaviors, such as dishing, edge disintegration, and loss of material, overall the materials per- formed similarly. Based on this, the researchers recommended using cost as the determining factor in selecting one of these materials to use for patching (32). The Texas DOT sponsored a research effort to develop a mix design method for what they termed “homemade” patch- ing mixtures, meaning cold patching materials that could be produced locally (41). Locally produced mixtures were com- pared with six packaged, commercial patching materials. A fairly unique set of tests was used in the evaluations. In the lab, a cold patch slump test was used to assess workability, and Hamburg wheel tracking and a less severe Texas stability test were used to assess stability. To assess the ability to store the bagged materials for a period of time, a drop test was devel- oped to drop the bags and determine if the bags split. If the bags do split during handling, material could spill and volatiles could be lost upon exposure to air. Another unique feature of this research was the use of accelerated pavement testing to evaluate patch performance. The Model Mobile Load Simula- tor (MMLS3) was used to test materials in the field. Field test sections on roadways in Lubbock, Lufkin, and other locations were also evaluated (41). Based on the various test results, the research team rec- ommended performance-based specifications for cold patch- ing materials. The specifications require testing workability using the cold patch slump test and stability in the Texas stability test. Upon successfully passing those two tests, the material would be further evaluated under the MMLS3 (41). Another example of an attempt to develop a local patch- ing material is a study by the California DOT (Caltrans) that attempted to modify an existing dense-graded patching material for use in patching open-graded pavement surfaces. The drain- age paths through an open-graded mix can be disrupted by the use of a dense-graded patching material. In this study, a dense- graded urethane polymer-bound patching mix was modified to make it free-draining (i.e., open-graded). The urethane-based patching mix produced was workable and drainable but not durable (42). Studies have also investigated the use of unconventional materials for pavement patching. For example, a study at the Chelsea Center for Recycling and Economic Development looked at using recycled rigid plastic aggregate in a lightweight cold patching mix (43). While the findings were favorable, the material is not known to have been used except experimentally. A study in Minnesota explored the possibility of using taconite mine tailings as aggregate for pavement applications; the report indicated that the use of taconite in asphalt patching materials was an on-going investigation (44). An article in Better Roads (45) indicates the technique of using microwave heating with taconite aggregates has now been commercialized. A Texas study by Estakhri and Button (46) aimed to develop ways to measure the workability of cold patching mixes. The study compared the use of unconfined compression tests and triaxial compression tests on lightly compacted samples of the patching materials. These tests were performed before and after laboratory aging in a forced draft oven at 120°C for 48 or 96 hours. The results suggested that the two types of compres- sion tests gave similar results; therefore, either one could be used to assess workability. The aging for 48 hours was found to best simulate six months of field aging. Criteria for the unconfined compression test, which is simpler to perform than triaxial testing, were established at a maximum of 200 kPa in an unaged condition and less than 1000 kPa after aging (46). Patching Techniques and Equipment The Caltrans Division of Maintenance prepared a maintenance technical guide in 2008 (31), which includes descriptions and diagrams of the causes of potholes and recommendations on patching practices. It endorses using temporary patches when necessary followed by semi-permanent patches using tack and edge sealing. The manual states that merely filling a pot- hole is not enough to stop further damage around or inside the patched area. Better performance is achieved when the hole is cut back to sound pavement. Compaction of the patching material is also critical to good performance. The manual con- tains valuable advice for troubleshooting patching problems, as shown in Table 4 (31). A process for preparing holes for patching was reported in the journal Public Works in May 2004 (47). This was devel- oped through a study, conducted at Brigham Young University, that compared the performance of straight, vertical cut edges on a patch with the rougher surface texture created by a device called an “Asphalt Zipper.” This cutting device produced an “angular scarification” on the cut edge (47). Cores taken one month after patch placement were used to compare the bond strength at the interface of vertical cut faces and the “zipped” face. The results showed that the rough surface texture yielded much higher bond strengths because of the increased mechani- cal interlock between the patch and the surrounding pavement (47). This may be considered to be similar to findings on con- crete pavements that chipping and patching, which produces a rough surface, can perform better than sawing and patching. Another equipment innovation that has found fairly wide- spread adoption is the spray patcher. Many studies since the days of SHRP have evaluated the use of this equipment.

16 Although FHWA considers spray patches temporary (10), some states consider the patches almost as good as semi- permanent patches (see the survey results in chapter three). The Caltrans maintenance manual also mentions spray injec- tion patching as a promising technology, although Caltrans did not use spray patchers at the time and their use by the agency is still limited (31). An article in the journal Better Roads in 2004 described the successful implementation of spray patchers by some agen- cies (20). According to the article, the District of Columbia had purchased four of the devices and found that they were able to repair potholes with smaller crews and less equip- ment; one self-contained spray patcher and a crew of three could replace two or three vehicles used for hauling patching mix, crew, tools, and traffic control devices. The same article reported that South Carolina tested spray patchers in 1997 and was so favorably impressed that they purchased 59 of the units. It was reported that the need for repeat patching was reduced by 50% to 60% when spray injection patches were placed in South Carolina (20). Another technique developed for patching operations uses infrared heat to produce a patch. One process, called HeatWurx, heats and scarifies the existing pavement around the hole, mixes in new material, and compacts the patching material into the hole. A study by Freeman and Epps in Texas (48) evaluated the process and the performance of 83 patches constructed with this process. The study concluded that the process did yield a well-bonded patch. Because the process produces a hot patch, it could be used in cold weather or at locations at a distance from a hot mix plant. On the other hand, concerns were expressed in the report about traffic control, because the bulky equipment requires closure of the adjacent lane; the slow production rate; and the depth of heat penetra- tion, which was reported to be less than 2 in. (48). Other investigations of heating the area to be patched to produce a better repair include the Minnesota study using tac- onite mine tailings (44). As part of that study, the authors also investigated use of a microwave generator to heat the area surrounding a pothole and the reclaimed asphalt pavement material being used to patch the hole. The process took about 50 minutes per hole, which the Minnesota DOT did not find practical at the time (44). The update in Better Roads suggests that the heating time has been shortened and the repair area can be heated in a matter of minutes (45). A Canadian study also looked at heating the area to be patched; in this case, infrared was used to heat and remove material around cracks before patching. The technique was reported to be successful and similar in cost to conventional crack repair (49). Performance Patches may fail because of the materials used, installation issues, or simply because the roadway continues to deterio- rate. The patches themselves may fail in a number of ways, as described by Anderson et al. in 1988 and shown in Table 5 [cited in Rosales-Herrera et al. (2007) (41)]. Some of the less Problem Solution Patching Material Does Not Adhere to Hole Ensure the hole is cleaned properly and not too wet. Ensure sufficient tack coat is applied. Use a self-setting cold mix when holes cannot be dried properly. Ensure the patch is solid before trafficking. Dust patch surface with sand or small aggregate. Wait for better weather. Do not use cutback-based cold mix (unless a temporary repair is being done). For HMA patches, allow to cool before traffic is allowed over the patch. Ensure required compaction is achieved. Surface Flushing/Bleeding Reduce asphalt or emulsion content in the mix. Reduce tack coat application. Allow longer time before trafficking. Ensure the gradation of the aggregate is appropriate. Uneven Surface Ensure cold mix is workable. Ensure HMA is at the right temperature for placement and compaction. Ensure adequate compaction is achieved. Loss of Cover Rock in Seal Coat Patches Ensure surface is clean. Ensure correct emulsion content is sprayed. Ensure aggregate is spread while emulsion is still brown. Ensure emulsion is broken before traffic is allowed. Allow longer cure time before traffic. Traffic Compacts Mix to Below Edge of Hole Ensure finished hole is overfilled 0.1 to 0.2 in. (3 to 6 mm). Ensure adequate compaction is achieved. Ensure mix is workable at application temperatures. Allow longer time before trafficking. After Maintenance Technical Advisory Guide, Vol. 1—Flexible Pavement Preservation (31). • • • • • • • • • • • • • • • • • • • • • • • • • TABLE 4 COMMON PATCHING PROBLEMS AND RELATED SOLUTIONS

17 common terms used in this table were defined by Prowell and Franklin (50) as follows: • Bleeding or flushing—excess asphalt at the surface of the patch. • Dishing—densification of the patch material under traf- fic, resulting in a depression. • Debonding—lack of adhesion of the patch material to the sides or bottom of the patched area. • Raveling—loss of material from the patch. • Pushing and shoving—surface distortion resulting from instability of the patching material. Prowell and Franklin (50) reported on an evaluation of 13 proprietary cold patching mixtures, four of which were already approved under the Virginia DOT’s special provi- sions. It was believed that having more choices of patching materials—provided the performance was the same—would increase competition and lower costs. The materials were eval- uated through test sections and were rated with regard to bleeding, dishing, debonding, raveling, shoving, and track- ing. In addition, tests were performed in the laboratory to assess coating, stripping, draindown, cohesion, workability, and adhesion. The study found that the proprietary cold mix materials performed significantly better than a local Virginia patching mix. The rating system developed in the study could be used to compare the performance of different patching materials. They also concluded that lab tests alone could not predict the field performance and cautioned that conven- tional solvent extractions might yield unreliable estimates of the binder content in these cold mixes (50). A study by Wei and Tighe looked at the typical service lives of various pavement preservation techniques in Canada (51). They found the average life span and costs of patching to be as shown in Table 6. TABLE 5 FAILURE SYMPTOMS AND MECHANISMS Symptom Failure Mechanism In Stockpile Poor Workability Binder too stiff; excessive fines or dirty aggregate; mix too coarse or too fine Binder Draindown Binder too soft; stockpiled or mixed at high temperatures Stripping Inadequate binder coating during mixing; cold or wet aggregate Clumpy Mixture Binder cures prematurely Cold Weather Stiffness Significant binder susceptibility to temperature; excessive fines or dirty aggregate; mix too coarse or too fine During Placement Poor Workability Binder too stiff; excessive fines or dirty aggregate; mix too coarse or too fine Poor Stability Binder too soft or excessive binder; insufficient voids in mineral aggregate; poor aggregate interlock Excessive Softening (when used with hot box) Binder too soft In Service Pushing, Shoving Poor compaction; binder too soft or excessive binder; significant binder susceptibility to temperature; contaminated mixture; slow curing rate; moisture damage; insufficient voids in the mineral aggregate; poor aggregate interlock Dishing Poor compaction Raveling Poor compaction; binder too soft; poor mixture cohesion; poor aggregate interlock; aggregate binder absorption; moisture damage; excessive fines or dirty aggregate; mix too coarse or too fine Freeze-Thaw Deterioration Mix too permeable; poor mix cohesion; moisture damage Poor Skid Resistance Excessive binder; aggregate not skid resistant; gradation too dense Shrinkage or Lack of Adhesion to Sides of the Hole Poor adhesion; tack coat not used or mix not self-tacking; poor hole preparation Source: Anderson et al. (1988), cited in Rosales-Herrera et al. (41). TABLE 6 AVERAGE LIFE AND COST OF ASPHALT PATCHING METHODS Patch Technique Life Span (years) Cost (Canadian $/lane/km) Spray Injection Patching 2 3,375 Machine HMA Patching 4 1,386 Manual HMA Patching 5 1,246 Mill and Patch 10% 6 2,450 Mill and Patch 20% 7 4,900 Source: Wei and Tighe (51).

18 Under the conditions in this study, spray injection was not found to be cost-effective (51). This is in contradiction to some states’ experience and studies, but other states would agree, as discussed in chapter three. Another Canadian study focused on developing a performance-based specification for a particular type of spray patching (52). In this case, dips were observed at transverse cracks on a roadway, causing a rough ride. A repair technique using spray patching was attempted to even out the ride quality by filling in the dips. Based on the improvement in ride qual- ity, as measured by before-and-after International Roughness Index readings, the maintenance contractor would be eligible for an incentive. Overall, the technique did not substantially improve the ride quality. In many cases, the dip at the crack was still present after patching and two bumps were formed by excess patching material immediately before and after the crack (52). PATCHING CONCRETE PAVEMENTS This section parallels the section on patching asphalt pavements and covers the same types of technical details, but specifically focuses on concrete pavements. Overall, there are more options for patching materials, more properties to consider testing, and more potential tests for materials to patch concrete surfaces than asphalt. Therefore, there appears to be more research and more literature on patching concrete pavements. Much of the literature has to do with comparisons of the performance of different types of materials in lab and field settings. Some reports also address types of repairs in the field, their perfor- mance, and most effective practices. More than 70 documents on patching concrete pavements were reviewed. Highlights of some of the most pertinent literature identified are sum- marized here. Patching Materials and Testing As mentioned previously, there are many more options for patching concrete pavements than asphalt pavements. The possible materials available include various types of cementi- tious materials with or without additives, polymer materials, and asphalt mixes. Table 7 summarizes some of the material options allowed by various states. (This is not an exhaustive list, but is intended to show the range of options allowed.) Managed by FHWA through partnerships with SHAs, industry, and academia, the Concrete Pavement Technology Program (CPTP) is an integrated, national effort to improve the long-term performance and cost-effectiveness of concrete pavements. In 2005, the CPTP prepared a technical brief on state-of-the-art concrete pavement rehabilitation and preserva- tion treatments, including partial depth repair (PDR). Recom- mended materials for PDR on pavements that are structurally sound (i.e., no significant fatigue cracking) include cementi- tious (including gypsum-based and magnesium phosphate concretes), polymer-based concrete, and bituminous materials. Conventional portland cement concrete (PCC) is quoted as being the most commonly used PDR material, typically pro- viding opening times of four hours or less. The most common polymer-based materials listed are epoxy, methyl methac- rylate, polyester-styrene, and polyurethane. While typically offering rapid strength gains, these materials are noted as being very expensive relative to conventional PCC. Bitu- minous materials are suggested as being inexpensive, widely used materials, but typically provide temporary patches only. Although no specific guidance is given, material selection is recommended to be based on available curing time, ambient temperature, cost, desired performance, and the size and depth of repairs (53). A 2008 study by Clemson University, sponsored by the South Carolina DOT, identified key factors influencing the compatibility of repair materials with the pavement being patched, including modulus of elasticity, Poisson’s ratio, and tensile strength; porosity and resistivity; chemical resistivity; thermal expansion coefficient; and shrinkage strain (57). A variety of test methods has been used to assess those and other factors (57). Although those tests may be important and useful for research purposes, a review of state specifica- tions and interviews with agency personnel conducted dur- ing this synthesis suggest that relatively few of these tests are used routinely for accepting patching materials by the DOTs. One of the most comprehensive suites of testing is used by the National Transportation Product Evaluation Program (NTPEP). In 2009, NTPEP published its two-year report of field performance and laboratory evaluations of rapid-setting patching materials for PCC (58). Products suitable for consid- eration by the program are cementitious, latex-modified, poly- mer resin, magnesium phosphate, and other materials expressly designed for patching PCC pavements and bridge decks. An extensive suite of laboratory-based testing is undertaken for each material. Field test sites are also monitored for two years (58). NTPEP does not make recommendations, but does pro- vide the data so agencies can draw their own conclusions. In 1999, the University of Central Florida (UCF) under- took research funded by the Florida DOT to identify quality patching materials for the repair of spalls on concrete pave- ments. As part of this work, eight products, three of which were Florida DOT approved, using polymer concrete, elasto- meric concrete, and cementitious mortar were studied as part of this research. Based on material compressive strengths and the fracture patterns observed in this lab-based testing, preferred patch materials were selected for accelerated per- formance testing. The accelerated testing was performed at UCF’s Circular Accelerated Test Track (UCF-CATT)—a 15.2-m (50-ft) diameter test track. The ultimate objective of the work was to evaluate the performance of various advanced materials available on the market for partial depth repair of concrete pavements. Based on the study, UCF developed

19 new guidelines for laboratory testing and material place- ment techniques to enable appropriate material use and field construction practices (59). The accelerated testing showed that after a total of 500,000 repetitions of a 44.5 kN (10,000 lb) load, no signs of major cracking were observed on any of the patches; patch de-bonding was the critical failure mechanism encountered. The elastomeric materials exhibited a higher tendency to fail in comparison with cementitious materials. Notably, the two feather-edged cementitious patches performed well in this study, indicating that a conventional square-cut procedure before patching may not be necessary with appropriate high- strength, fast-set patching materials (59). In 2005, the Iowa DOT undertook a research program to assess the appropriateness of using blended cements for concrete patching operations (60). The impetus for this work TABLE 7 MATERIALS SPECIFIED BY STATE DOTs FOR THE REPAIR OF RIGID PAVEMENTS State (ref.) Relevant Repair(s) Material Material Selection Guidance ID (34) Patching High early-strength concrete To comply with Idaho’s Standard Spec. Book. After consultation with the District Maintenance or Materials Engineer (for volumes greater than 5 cubic yards). Air-entrained concrete IN (22) Partial depth patching HMA Type A Selection of patching materials is based on the curing time, which determines traffic opening conditions. Concrete—Rapid-setting concrete with a non-vapor barrier bonding agent Bitumen HMA with a bonding agent (AE-T) WA (36) Repair/patch ing Portland cement concrete (PCC) Material performance requirements [(see section 9-20.2(1)] WSDOT approved patching mortars (extended with aggregate) WSDOT approved product (rebar coat) CA (54) Isolated partial depth repair Normal concrete mixtures Based on available curing time, climatic conditions, material costs, equipment requirements, mixing and placing time, desired service life, and the size and depth of repair(s). Material properties, such as strength gain, modulus of elasticity, bond strength, scaling resistance, sulfate resistance, abrasion resistance, shrinkage characteristics, coefficient of thermal expansion, and freeze-thaw durability should also be included in the selection process. Specialty concretes: Gypsum-based cement mixtures Magnesium phosphate cement High alumina cement mixtures Accelerating admixtures/additives Alumina powder Specialty: Polymer concrete Epoxy Methyl methacrylate concrete Polyester-styrene concrete Polyurethane concrete Bituminous—temporary fix only Bonding agents: Sand–cement grouts Epoxy bonding agents MN (39, 55) Pop-outs/ scaling Partial depth repairs Concrete (3U18) No guidance Bonding/sealing grout; curing compound Small patches: Cold or hot bituminous mix Proprietary asphalt mixes Epoxy or other modified concrete MT (37) Temporary patching Plant mixed asphalt— temporary patches only Consult material spec for PCC mix design. If using proprietary products, consult product brochures. Permanent patching PCC made (with high early strength cement) Rapid setting proprietary products TX (38) Spalling Rapid-Set Concrete (DMS-4655) No guidance Polymeric Patching Material (DMS- 6170) WY Spalling High-alumina cementitious mortar Preapproved by the Materials Program and (56) (PDR) Epoxy Resin meeting performance spec (Table 810.1.2-1). Injection Material to ASTM C 881, type I, grade 2; Bonding compound to ASTM C 881, type V, grade 2 Bonding agents (as required)

20 was that while many ready-mix producers exclusively made use of blended cements in construction, Iowa DOT specifica- tions did not permit its use in patching operations because of their assumed slow strength gain. (Iowa DOT patching speci- fications required opening at 5 hours on 2-lane or 10 hours on 4-lane pavements.) Ordinary Type I/II portland cements and Type I(SM) blended portland cements were investigated as part of the research. Although the compressive strength gain of the mix- tures with Type I(SM) cement was slower than that of the mixes with ordinary Type I cement, all the results were in excess of the pavement opening requirements. At the curing tempera- tures used in this research, the time difference to achieve the required strength between Type I(SM) and Type I/II cements was approximately one-half hour (60). In 2004, the Wisconsin DOT (WisDOT) published find- ings of laboratory testing of PCC patch materials modified to reduce or eliminate shrinkage (61). In 2001, WisDOT eval- uated several different rapid-setting patch materials on an existing rehabilitation project, all of which exhibited micro- cracking and de-bonding caused by shrinkage within one year. Of the patch materials originally evaluated, only three met all of WisDOT’s requirements for rapid-set concrete patch mate- rials: a proprietary material (Tamms Speed Crete 2028) tested at two different coarse aggregate extension ratios and the Minnesota DOT 3U18 concrete mix (modified with Type III cement in lieu of Type I) (61, 62). The study led to recommen- dations to use appropriate shrinkage-reducing admixtures and curing compounds to enhance the performance of high early strength patch repairs. Also, rather than specifying high strength at a very early age (300 psi at 3 hours), it was recom- mended that this strength level be reached after 24 hours. This would allow use of more conventional repair materials (such as a modified Minnesota DOT 3U18 patch material) providing suitable levels of performance and cost (62). In addition, the study found that the ambient air temperature, temperature of the surrounding concrete, and, in particular, wind speed, have a dramatic effect on the rate of evapora- tion and rate of hydration of concrete patch materials. It was recommended that tighter controls be placed on allowable environmental conditions at the time of placement of concrete patch mixes (62). In 2009, the U.S. Army Engineer Research and Devel- opment Center reported on a research program undertaken to determine rapid-setting material suitability for expedient pavement repairs based on both laboratory and full-scale traf- fic tests (63). The primary objective of the study was to assess commercial, off-the-shelf, rapid-setting, cementitious-based materials currently on the market and to develop appropriate laboratory selection criteria that could be used for selecting expedient repair materials for PCC airfield pavements. Nine different repair materials (belonging to one of four types of base materials: polymeric, ultrafine portland cement, magne- sium phosphate, and high alumina) were assessed (63). Laboratory testing was conducted initially to determine the unconfined compressive and bond strengths of each material. Subsequently, in-field traffic testing was undertaken on 1.5-m (5.0-ft) square repair areas prepared by saw-cutting and removing the surface of an existing PCC pavement. In terms of performance, all the repair materials met the mini- mum traffic level with little to no deterioration. Traffic was then continued to quantify the point at which failure occurred as well as the resultant failure mechanism. Only four repair materials failed to meet the minimum performance level. When failure did occur, the predominant failure mechanism was cracking (63). Based on historical data and the testing undertaken, a correlation between laboratory test results and in-field per- formance under trafficking was established. The proposed laboratory testing protocol for selecting rapid-setting patch materials is shown in Table 8. Although developed primarily for airfield pavements, the authors suggest that these guide- lines can easily be applied to other pavement types (63). The previously mentioned study by Clemson University (57) noted that a wide variety of rapid-set patching materials are available in the industry for repair of concrete, as shown TABLE 8 PROPOSED MINIMUM LABORATORY-BASED TESTING PROTOCOL FOR SELECTING RAPID-SETTING PATCH MATERIALS Property ASTM Requirement Compressive Strength C39 ≥3,000 psi at 2 hours Flexural Strength C78 ≥350 psi at 2 hours Bond Strength C882 ≥850 psi at 1 day (repair bonding to OPC mortar) ≥1,000 psi at 1 day (repair material bonding to repair material) Volumetric Expansion C531 ≤7 × 10−6 in./in./°F (testing begins at 3 days)a C157 <0.03% (testing begins at 4 days)b Source: Priddy et al. 2009 (63). a Test at temperature similar to expected field conditions. b Continue testing according to ASTM requirements following the early age tests.

21 in Table 7. However, the selection of an appropriate material for a particular repair job is challenging as these materials possess a range of physical and mechanical properties and definitive criteria for establishing the compatibility between repair materials and substrate concrete are not adequately defined. Improper selection of repair material, without inves- tigating the compatibility between repair materials and sub- strate concrete, is a common reason for failure. Therefore, compatibility between eight repair materials, which were on the approved list of the South Carolina DOT, and a typical substrate concrete was investigated. Based on the findings from this study, it was concluded that although the prop- erties of repair materials are important from an operational standpoint (i.e., opening the repaired section to traffic), these properties do not correlate well with field performance of the repaired composite sections. As a result of the work under- taken, it was found that flexural strength testing of compos- ite beams better characterized compatibility between repair materials and the substrate concrete (57). In 2003, the Oregon DOT published a spreadsheet-based concrete patching guide to help maintenance personnel deter- mine which product to use. Although state DOT-produced lists of qualified products exist, these typically do not provide information to assist personnel in selecting an appropriate product for a particular job. The tool matches the attributes of specific products to the needs of a particular patching job. An output report is generated providing a list of qualified and con- ditional products (which require field experience before being listed as qualified) from the state Qualified Products List (64). To use the guide, a user checks off on a list statements that describe the requirements for a particular patching job. The patch descriptors include what material the patch will be in contact with, the orientation, size, needed working time, amount of time before the patch is exposed to further con- struction or traffic, need for formwork, and other variables. The selection tool compares the user’s requirements with the attributes of the various patching materials to find matches. It can be noted, however, that the tool was developed based on feedback received from questionnaires completed by mate- rial manufacturers and not on independent performance data or testing (64). Despite all of the tests recommended in the research reports summarized here, a review of state specifications shows that only a few test methods are used routinely by the DOTs to approve or accept patching materials. Patching Techniques and Equipment In August 2005, FHWA published a checklist series, one of which was Partial-Depth Repair of Portland Cement Con- crete Pavements (65). This checklist was created to guide state and local highway maintenance and inspection staff in the use of innovative pavement preventive maintenance processes. The document is brief and provides a checklist covering the key issues relating to: • Preliminary responsibilities, • Document review, • Project review, • Materials checks, • Equipment inspections, • Weather requirements, • Traffic control, • Project inspection responsibilities, • Cleanup responsibilities, and • Common problems and solutions. Last updated in July 2011, the FHWA’s concrete technol- ogy team has published extensive guidance (66) on PDRs. With PDRs defined as repairs involving removal of deterio- rated concrete limited to the top third of a slab’s thickness and replacing it with appropriate repair materials, guidance is given in the following areas: • Selection of candidate projects (based on pavement condition and climatic conditions), • Design considerations (including repair boundaries and selection of materials), • Construction procedures (including repair identifica- tion, preparation, placement, and finishing), • Opening to traffic, • Performance considerations, and • Cost implications. The key output from this document is a generic guide speci- fication for PDRs (66). Another useful guide document was published by the National Concrete Pavement Technology Center at Iowa State University in April 2012 (67). This document, Guide for Partial-Depth Repair of Concrete Pavements, provides information about selecting, designing, and constructing successful PDRs that extend as much as half the depth of concrete pavement slabs. A key departure from previous best practice guidance is the depth of recommended repair, which has increased from one-third to one-half of the pavement depth. In recent times, many deeper PDRs have lasted for 10–15 years or as long as the existing pavement. One technique for PDR construction uses milling machines to excavate the area to be patched. In 1980, Minnesota imple- mented a modified partial-depth repair on a spalled section of pavement that extended deeper than the top one-third of the slab. Milling machines were used to remove the concrete in the distressed area and form a tapered edge around it. The milled surface was cleaned and a cement grout was applied; then a cement-based repair material was applied. In the 1990s, Minnesota’s cost-effective method was copied in Wisconsin and Michigan. In the 2000s, Kansas, Missouri, Colorado, and South Dakota adopted similar milling approaches to PDRs.

22 By using milling equipment and durable concrete mixtures, these states have successfully demonstrated the use of PDRs in pavements where deteriorated areas extend from one-third to one-half the slab depth. As a result, today partial-depth repairs are used for more joint repairs and at less cost than traditional full-depth repairs (67). The Concrete Pavement Technology Program brief (53), mentioned in “Patching Materials and Testing”, suggests that PDR is a suitable strategy for addressing transverse or longitu- dinal joint spalling caused by incompressible or weak concrete and localized surface defects. Distress types not considered as candidates for PDR include crack spalling, joint spalling caused by dowel bar misalignment, lockup, D-cracking, reac- tive aggregate, or other materials-related deterioration. If PDR is selected as the repair technique, it is important that the fol- lowing points be considered (53). • Repair dimensions should be selected by “sounding” a pavement using a hammer, solid rod, or chain, and dete- rioration boundaries marked. A square or rectangular shape is recommended and areas less than 0.6 m (2 ft) apart should be combined into one repair area. To ensure effective performance, generally the area marked for removal should extend 50–150 mm (2–6 in.) beyond the weakened pavement in each direction. Recommended minimum PDR dimensions are 300 mm (12 in.) long, 100 mm (4 in.) wide, and 50 mm (2 in.) deep. • Deteriorated concrete should be removed by sawing using a diamond-bladed saw and chipping out with a light hammer weighing less than 14 kg (30 lb). Alterna- tively, a milling machine, operated either transversely across joints for small, individual spalls or longitudi- nally along the length of joints for larger repair areas, is recommended. • After removal of defective concrete, repair areas should be cleaned to remove all loose particles, dirt, and debris that could inhibit bonding. This is generally accomplished by sand-blasting, followed by air-blasting to remove any residue. • For PDRs placed at joints, a strip of compressible material must be placed in the joint to accommodate horizontal movements, to prevent patching material infiltrating the joint, and to re-establish the joint. Inserts should extend 25.4 mm (1 in.) below and 76 mm (3 in.) beyond repair boundaries. • For most repair materials, application of a thin layer of a cementitious grout bonding agent is recommended before patching. The bonding agent is placed after the repair area has been cleaned and immediately before the placement of the repair material. • In terms of patch material placement and finishing, it is recommended to slightly overfill to allow for a reduc- tion in volume during consolidation. Material should be adequately consolidated with a small spud vibrator to remove entrapped air. A stiff board can be used to screed repair surfaces to ensure surface alignment and bonding with the existing pavement. Repair surfaces should be textured to match that of the surrounding slab (see Figure 12). • Proper curing is very important to prevent rapid moisture loss from PDRs. Commonly a white-pigmented curing compound would be applied as soon as the water sheen has disappeared from the repair surface. Typical cur- ing compound application rates are about 2.5–4.9 m2/L (100–200 ft2/gal). • For early opening to traffic, or in cold-weather condi- tions, insulating blankets may be needed to help accel- erate rates of strength gain. In 2010, Hammons and Saeed published findings of research undertaken to investigate selected methods and equipment for expedient spall repairs constructed with rapid-setting materials (68). With a focus on airfield pavement applica- tions, the main objective of the work was to examine vari- ous methods of excavating concrete and placing a commonly used rapid-setting repair material in 2 ft2 x 4 in. deep spalls within 15 minutes or less. Spalls were prepared using the following methods: • Saw cut and portable pneumatic 30 lb jackhammer (baseline or current standard), • Saw cut and a hydraulic breaker on a skid steer tractor, • Multiple-blade gang saw with saw spacing at ¾ in., • Multiple-blade gang saw with saw spacing at 1½ in., and • Cold planer attachment for a skid steer loader. When compared with the use of a portable pneumatic 30 lb jackhammer (the standard Department of Defense spall repair excavation method), each of the other methods evalu- ated offered significant improvements in production rate. The most efficient method was using a cold planer that, on average, was approximately 58% more efficient than the jackhammer method. Of the methods evaluated, only the cold planer could meet the requirement of excavating the patch in 15 minutes or less (68). The study recommended that the cold planer method be adopted as a standard method of preparing spalls for place- ment of a rapid-setting spall repair material. Although the time to prepare a spall depended on the characteristics of the spall and the skill of the operator, use of this equipment required approximately half the time to prepare the spall compared with manual jackhammer-based approaches. Spalls prepared with this method retained superior bond strength after significant trafficking and were expected to provide superior perfor- mance compared with those prepared using other conventional methods (68). Although partial depths repairs are the subject of much of the literature on field performance and experience, deeper dis- tresses can also be addressed by concrete patching. In 2011, Yuan and Liu reported research undertaken to assess an appro- priate upper size limit for the repair of PCC corner breaks with

23 asphalt concrete. As long as safety and ride quality are not compromised; asphalt concrete patching was proposed by the authors as an appropriate temporary measure to prevent further moisture penetration and performance defects (69). Beginning in 2007, a study was undertaken by Yuan and Liu of the Xiangtan–Leiyang Expressway, where asphalt concrete was applied to 11,441 broken slab corners. The total asphalt patching area was 26,015 m2, with the aver- age patch area of a single broken corner equaling 2.27 m2. Based on statistical and equivalent annual cost analysis, an upper patching area limit of 2.66 m2 was proposed. Beyond this value, full-depth slab replacement was considered to be a more appropriate investment of maintenance funds. Fur- thermore, the authors pointed out that despite the suitability of asphalt for corner break repair, because of its perceived temporary, small-scale applicability, limited corresponding construction specification guidelines had been developed by local highway agencies. Suitable guidance, including con- struction process, materials, and optimum patching areas, was recommended (69). Performance In 1999, research findings were published by the Mississippi DOT aimed at examining the relative performance of propri- etary polymer concrete-based products (RESURF CR and RESURF II) against a standard asphalt-based repair approach (70). In total, 43 punch-out deteriorations on I-55 were repaired using these materials to restore an acceptable riding surface. Rather than adopt the traditional approach of removing failed concrete, re-establishing reinforcing steel as required, and patching with new concrete, the polymer concrete products were used to cement broken concrete pavement pieces together in situ. RESURF CR—a variable viscosity, low shrink, pour- able polyester compound designed for cracks of up to 0.5 in. (12.7 mm)—was used to cement the pieces. RESURF II— a general performance polymer concrete consisting of a sty- rene diluted modified polyester resin with a select aggregate blend—was used to restore a smooth riding surface to patch areas after application of RESURF CR. In summary, the evaluation found that the proprietary materials did not prove to be a long-term solution for punch- out repairs, requiring more effort and time than temporary repairs using asphalt. The proprietary repairs were more than four times as expensive as removing and replacing the con- crete pavement. Based on visual inspections and pavement deflection measurements, 91% of patches surveyed were rated “good” after one year of service, 37% were rated “good” after two years of service, and only one patch lasted three years. In this instance, the use of particular proprietary patch materials was not recommended for punch-out repairs intended to last longer than one year (70). In 2007, Chen et al. reported on field evaluations of vari- ous patch materials used for partial-depth repair of concrete pavements (71, 72). Of the numerous patching materials available on the market, Markey et al. (73) performed exten- sive laboratory and field investigations of ten patch repair materials that have been used in Texas and concluded that polymeric materials performed most favorably. Based on these findings, two types of polymeric patch materials (both polyurethane and epoxy-based resins) were used to repair spalls and cracks on US-290, SH-6, and US-75. The repair materials were used to repair spalls in both continuously reinforced and jointed concrete pavements (CRCP and JCP) and performance was recorded up to a period of six years. Performance was inferred from simple visual observations, distress rating, and ride quality measurements (71). The study found that repairs placed using both chip-and- patch and saw-and-patch methods have performed satisfac- torily over six years. As recommended by FHWA based on the SHRP research, this study confirmed that chip-and-patch is a satisfactory approach provided all delaminated areas of concrete are completely removed. The results showed that polymeric patch materials have performed well in both CRCP and JCP. In particular, the polyurethane-based product was effective at bridging transverse cracks in the CRCP’s vertical direction and resisted the propagation of these cracks through the concrete pavement while maintaining a good bond to the substrate concrete. The use of polymeric-based PDRs has dramatically decreased the frequency of spall repairs under- taken by Texas DOT’s Houston District. Furthermore, this study reported that, compared with full-depth repair, PDRs utilizing polymeric patch materials offer a much more time and cost-effective maintenance strategy (71).