National Academies Press: OpenBook

Microsurfacing (2010)

Chapter: Chapter Seven - Quality Control and Quality Assurance and Performance Measures

« Previous: Chapter Six - Microsurfacing Equipment Practices
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Suggested Citation:"Chapter Seven - Quality Control and Quality Assurance and Performance Measures." National Academies of Sciences, Engineering, and Medicine. 2010. Microsurfacing. Washington, DC: The National Academies Press. doi: 10.17226/14464.
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Suggested Citation:"Chapter Seven - Quality Control and Quality Assurance and Performance Measures." National Academies of Sciences, Engineering, and Medicine. 2010. Microsurfacing. Washington, DC: The National Academies Press. doi: 10.17226/14464.
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Suggested Citation:"Chapter Seven - Quality Control and Quality Assurance and Performance Measures." National Academies of Sciences, Engineering, and Medicine. 2010. Microsurfacing. Washington, DC: The National Academies Press. doi: 10.17226/14464.
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Suggested Citation:"Chapter Seven - Quality Control and Quality Assurance and Performance Measures." National Academies of Sciences, Engineering, and Medicine. 2010. Microsurfacing. Washington, DC: The National Academies Press. doi: 10.17226/14464.
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Suggested Citation:"Chapter Seven - Quality Control and Quality Assurance and Performance Measures." National Academies of Sciences, Engineering, and Medicine. 2010. Microsurfacing. Washington, DC: The National Academies Press. doi: 10.17226/14464.
×
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Suggested Citation:"Chapter Seven - Quality Control and Quality Assurance and Performance Measures." National Academies of Sciences, Engineering, and Medicine. 2010. Microsurfacing. Washington, DC: The National Academies Press. doi: 10.17226/14464.
×
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Page 54
Suggested Citation:"Chapter Seven - Quality Control and Quality Assurance and Performance Measures." National Academies of Sciences, Engineering, and Medicine. 2010. Microsurfacing. Washington, DC: The National Academies Press. doi: 10.17226/14464.
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Page 54

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49 INTRODUCTION A key element of microsurfacing projects is the quality control and quality assurance (QC/QA) philosophy and procedures applied. In both cases, an independent assurance element may be applied. QC/QA is a major issue with the highway agencies that are considering implementing contract pavement mainte- nance. This topic also relates to microsurfacing performance risk allocation that was covered in chapter four. Because micro- surfacing design is laboratory-based and those tests were covered in chapter three, this chapter will confine itself to the construction QC/QA process. Specific QC/QA testing requirements for both the materials and the finished product are summarized and analyzed in this chapter. QUALITY DEFINITIONS For the purposes of this synthesis, Transportation Research Circular E-C074: Glossary of Highway Quality Assurance Terms (Committee on Management of Quality Assurance 2005) will be used to define the quality assurance terms in this report. Quoted here are the major definitions. • Quality. The degree to which a product or service sat- isfies the needs of a specific customer, or the degree to which a product or service conforms to a given requirement. • Quality assurance (QA). All planned and systematic actions necessary to provide confidence that a product or facility will perform satisfactorily in service. (QA addresses the overall problem of obtaining the quality of a service, product, or facility in the most efficient, economical, and satisfactory manner possible. Within this broad context, QA involves continued evaluation of the activities of planning, design, development of plans and specifications, advertising and awarding of contracts, construction, and maintenance, and the interactions of these activities). • Quality control (QC). Also called process control. Those QA actions and considerations necessary to assess and adjust production and construction processes so as to con- trol the level of quality being produced in the end product. • Independent assurance (IA). A management tool that requires a third party, not directly responsible for process control or acceptance, to provide an independent assess- ment of the product and/or the reliability of test results obtained from process control and acceptance testing. (The results of independent assurance tests are not to be used as a basis of product acceptance.) • Verification. The process of determining or testing the truth or accuracy of test results by examining the data and/or providing objective evidence. [Verification sam- pling and testing may be part of an independent assurance program (to verify contractor QC testing or agency accep- tance) or part of an acceptance program (to verify con- tractor testing used in the agency’s acceptance decision).] • Quality Management (QM). The totality of the system used to manage the ultimate quality of the design as well as the construction encompassing the quality functions described above as QA, QC, independent assurance, and verification (Committee on Management of Quality Assurance 2005). MICROSURFACING QUALITY REQUIREMENTS Field quality management in microsurfacing consists of two primary activities. First, the contract for the project will spec- ify a certain amount of QC/QA sampling of materials for test- ing to occur in the field. The primary reason for field sam- pling is to verify that the materials being installed conform to the same standards as in the contract. For example, on large microsurfacing projects where the aggregate and other materials are produced over a series of weeks rather than all at one time, the inherent variability that occurs in nature can change the engineering properties of aggregate and emul- sion (ISSA 2010a). Thus, field sampling seeks to ensure consistency of the mix as it is being applied. The second major quality management activity is the monitoring and correcting of defects in workmanship. A perfect microsurfac- ing mix that has passed all the laboratory tests can still be improperly installed in a manner that prevents it from reach- ing its desired service life. “Therefore, good decisions and careful quality control are necessary from initial selection of the treatment type through final acceptance of the completed project” (Jahren and Behling 2004). Field Testing Practice The survey and the content analysis specifically sampled for information on how public highway agencies distribute the responsibility for conducting various quality manage- ment tasks. At this point it is important to remember from chapter three that most agencies assign the responsibility for CHAPTER SEVEN QUALITY CONTROL AND QUALITY ASSURANCE AND PERFORMANCE MEASURES

developing the job mix formula to the microsurfacing contrac- tor. This changes the classic QC/QA relationships. NCHRP Synthesis 376: Quality Assurance in Design-Build Projects (Gransberg et al. 2008) found that shifting design responsibility from the owner also shifts some of the traditional QA respon- sibility. Therefore, one would expect to see some level of in- volvement of the contractor in the QA as well as the QC process and a higher use of contractor test results in the QA program. Table 33 illustrates the output from the survey and content analysis with regard to the division of responsibilities between the agency and the contractor. It shows that all U.S. and most Canadian agencies retain the traditional inspection responsi- bilities. However, only three agencies in the entire sample require independent verification of the job mix formula based on test results. All U.S. agencies also retain the traditional role with regard to performing their own field tests with either agency personnel or a consultant retained on the agency’s behalf. This is not the case in Canada, where two of five agen- cies assign that task to the contractor. Agencies in Australia and New Zealand use performance-specified maintenance contracts, which make construction testing less important than in a traditional construction or maintenance contract (Manion and Tighe 2007). Laboratory Testing Practice Table 34 is a summary of the microsurfacing-related labora- tory tests that were identified in the survey and the content analysis. No conclusions or effective practices can be drawn from this analysis. Therefore, it is presented for information purposes only. 50 QUALITY OF MICROSURFACING WORKMANSHIP As with all paving contractors, microsurfacing contractors bid their projects based on a calculated rate of production. If the contractor does not complete the number of lane-miles each day that its bid is based on, then the contractor’s profit is at risk. When this happens, the tendency to speed up to catch up becomes almost overwhelming, possibly causing a deepening disregard for the quality of the workmanship. Therefore, it is important to both the agency and the contractor that unnec- essary delays and/or interruptions in production be minimized if possible. The construction of test strips discussed in chap- ter six is a good technique to alleviate technical differences of opinion as to what constitutes acceptable quality before the contractor begins full-scale production. Another tool that is often used is inspection checklists that both the agency’s inspector and the contractor’s QC manager have to allow both parties to check and verify that important details have been accomplished before starting production. A copy of one such checklist authored by the FHWA (2010) is contained in Appendix C. Quality Assurance Focus QA theory advocates identifying those areas that are of par- ticular concern before starting construction and jointly address- ing them in a preconstruction meeting (Austroads 2003b). The ISSA Slurry Systems Inspector’s Manual (2010a) contains a list of preconstruction meeting objectives, which includes a discussion of QC/QA issues. The Minnesota DOT’s micro- surfacing specification (2009) echoes the need for this type of conference and prescribes a “Pre-Paving Meeting” of Quality Management System U.S. Canada Specification Content Analysis Inspection Responsibility? Agency 28 6 18 Consultant 0 1 0 Contractor 0 1 0 Use of Independent Lab to Verify Job Mix Formula? Yes 3 0 0 No 21 8 18 Do not know 4 0 0 Field Sampling/Testing? Yes 20 5 10 No 5 3 8 Do not know 3 0 0 Field Testing Responsibility Agency 15 3 15 Consultant 5 0 0 Contractor 0 2 0 Not specified 0 0 3 Source of Field Acceptance Tests? Source/pit 2 2 10 Stockpile 15 4 6 While transferring to nurse units 1 0 0 Before entering the mixing machine 1 1 0 Do not know/not specified 3 1 4 TABLE 33 SURVEY RESULTS ON FIELD QC/QA PRACTICES

51 similar nature to the one discussed in the ISSA manual. The National Highway Institute’s Pavement Preservation Treat- ment Construction Guide does a thorough job of synopsizing main areas of microsurfacing workmanship quality concern as listed here. • Longitudinal Joints: Longitudinal joints may be over- lapped or butt jointed. They can be straight or curve with the traffic lane. It is important that overlaps not be in the wheel paths nor exceed 75 mm (3 in.) in width. • Transverse Joints: Transverse joints are inevitable when working with truck-mounted batch systems; every time a truck is emptied a transverse joint is required. Transi- tions at these joints must be smooth to avoid creating a bump in the surface. The joints must be butted to avoid these bumps and handwork be kept to a minimum. The main difficulty in obtaining a smooth joint occurs as the microsurfacing machine starts up at the joint, particu- larly when working with microsurfacing that is difficult to work by hand and breaks quickly. Some contractors tend to over wet (add too much water) the mix at start- ups, leading to poor texture and scarring at the joints. Starting transverse joints on roofing felt can eliminate these problems. • Edges and Shoulders: Sealed edges and shoulders can be rough and look poor. This occurs more often with microsurfacing applications that break quickly, making them harder to work by hand than slurry seals. For micro- surfacing, it is important that handwork be kept to a minimum. It is important that the edge of the spreader box be outside the line of the pavement and edge boxes be used when shoulders are covered. • Uneven Mixes and Segregation: Poorly designed microsurfacing mixtures or mixtures with low cement content or too high a water content may separate once mixing in the box has ceased. This leads to a black and flush looking surface with poor texture. Separated mixes may lead to “false slurry,” where the emulsion breaks onto the fine material. In such instances delamination may occur, resulting in premature failure. These types of mixes can be recognized as nonuniform and appear to set very slowly. • Smoothness Problems: Microsurfacing mixtures follow the existing road surface profile and thus do not have the ability to significantly change the pavement’s smooth- ness. However, when using stiffer mixes, the spreader box may, if incorrectly set up, chatter or bump as the material is spread and produce a washboard effect. The chattering may be reduced by making the mixture slower to set, adjusting the rubbers on the box, or adding weight to the back of the spreader box. • Damage Caused by Premature Reopening to Traffic: It is important that the microsurfacing build sufficient cohesion to resist abrasion resulting from traffic. Early stone shedding is normal, but not to exceed 3%. If a mixture is reopened to traffic too early it will ravel off quickly, particularly in high stress areas. It is important that the mixture develops adequate cohesion before it is opened. Choosing the right time to reopen a surface to traffic is based largely on experience. However, a general Test U.S. Canada Specification Content Analysis Total Occurrences Residual Asphalt Content 18 6 18 42 Sand Equivalent 17 3 12 32 Wet-Track Abrasion Test ISSA TB 100 15 4 11 30 Wet Stripping Test ISSA 114 12 5 10 27 Softening Point 14 5 7 26 Penetration 12 5 8 25 Mix Time Test ISSA TB 113 12 4 9 25 Classification Test ISSA TB 144 11 4 8 23 Modified Cohesion Test ISSA TB 139 11 4 6 21 Loaded Wheel Test ISSA TB 109 9 3 7 19 Abrasion Resistance 9 2 6 17 Lateral Displacement Test ISSA TB 147 7 5 5 17 Soundness 11 1 4 16 Cure Time Test ISSA TB 139 6 2 3 11 Tests for the Presence of Clay 6 2 2 10 Percent Sodium Sulfate Loss (resistance to freeze/thaw) 6 0 4 10 Compatibility of Aggregate with Binder 5 3 2 10 Set Time Test 4 1 3 8 Consistency Test ISSA TB 106 3 1 1 5 TTI Mixing Test 1 0 1 2 TABLE 34 SURVEY RESULTS ON LABORATORY QC/QA TESTING PRACTICES

rule of thumb for a microsurfacing is that it can carry traffic when it is expelling clear water (National High- way Institute 2007). • Streaking: Streaking is caused by one of two condi- tions during construction. Insufficient embedment allows larger stones to be caught by the strike-off rubber and dragged along the surface. Excess build-up of material in the spreader box has the same effect (ISSA 2010a). • Delaminating: The major cause of delamination is fail- ure to properly prepare the surface before commencing microsurfacing. It can also be caused by the emulsion breaking too fast, keeping the bond with the substrate from forming (Smith and Beatty 1999; Austroads 2003b). Example Microsurfacing Quality Assurance Specification The Georgia DOT microsurfacing specification (2001) includes a section specifically titled “workmanship” that speaks to the concerns discussed earlier and makes them enforceable contract requirements. The specification is included here as an example of how to articulate these concerns in the contract. Workmanship—Excessive buildup, uncovered areas, or unsightly appearance are not permitted on longitudinal or transverse joints. Place longitudinal joints on lane lines. Excessive overlap is not permitted. Ensure straight lines along the roadway centerline, lane lines, shoulder, or edge lines. Keep lines at intersections straight to provide a neat and uniform appearance. 1. Finished Surface: Ensure that the finished micro-surfacing has a uniform texture free of excessive scratch marks, tears, or other surface irregularities. Excessive tear marks are considered 4 marks that are 1⁄2 inch (13 mm) wide or wider and 6 inches (150 mm) or more long per 100 square yards (85 meters), or any marks 1 inch (25 mm) wide or wider or 4 inches (100 mm) long. Ensure that the edges of the micro-surfacing appear neat and that longitudinal alignment is parallel to the roadway centerline. 2. Joints and Seams: Produce neat and uniform longitudinal and transverse joints. Construct transverse joints as butt-type joints. Place longitudinal joints on lane lines when possible. Do not allow gaps between applications. Joints are acceptable if there is no more than a 1⁄2 inch (13 mm) vertical space for longitudinal joints nor more than 1⁄4 inch (6 mm) for a trans- verse joint between the pavement surface and a 4 ft (1.2 m) straightedge placed perpendicular on the joint. 3. Areas the Mixing Machine Cannot Reach: Surface these areas using hand tools to provide complete and uniform cov- 52 erage. Clean and lightly dampen the area to be hand-worked before placing the mix. Ensure areas that require handwork produce a finished surface that is uniform in texture, dense, and has a neat appearance similar to that produced by the spreader box. Microsurfacing material required to repair defi- ciencies due to unsatisfactory workmanship and the work required to mix and place the materials according to the Spec- ifications will be provided at no expense to the Department (Georgia DOT 2001). This discussion shows agreement between the literature and the specification content analysis and leads to the following effective practice: Holding a pre-paving meeting to discuss quality manage- ment and workmanship issues before full production micro- surfacing provides a forum where both the agency and the contractor can address main areas and concerns about microsurfacing quality. MICROSURFACING PERFORMANCE The purpose of any quality management program is to not only ensure that the product meets the contract requirements but also to ensure that the product is constructed in a manner that permits it to perform as designed. Therefore, connecting the quality management practice discussed previously with agency information about microsurfacing performance allows the analyst to draw inferences about the effectiveness of dif- ferent approaches to this critically important topic. Definition of Microsurfacing Success Just as the term “quality” has many different definitions that depend on who and what it is related to, agency definitions of microsurfacing performance vary among the agencies them- selves. The survey sought to draw out those answers and aggre- gate them to develop a rank ordering of 5+ standard definitions from the literature to identify any trends that might be present in the data. Table 35 shows the results of that analysis, with an interesting trend evident. In chapter three, the reasons why agencies select microsurfacing for a given pavement mainte- nance/preservation project were covered and a number of agen- cies added the comment that their purpose for using microsur- facing was to extend the life of the underlying pavement. This Test U.S. Canada Total Meets expected service life 19 6 25 Meets project specification requirements 14 6 20 Qualitative measures—look, color, etc. 8 8 16 Does not fail shortly after construction 7 5 12 Achieves desired friction/skid number 9 1 10 Meets texture standard (>0.6 mm) 1 0 1 No maintenance expenditures over life 1 0 1 Note: Agencies were asked to check all that applied. TABLE 35 SUMMARY OF AGENCY DEFINITIONS OF MICROSURFACING SUCCESS

53 attitude is validated by the most frequently cited success met- ric; meets expected microsurfacing service life. That leads to the conclusion that microsurfacing is viewed as a valuable pavement preservation treatment rather than merely a pave- ment maintenance treatment. The second most cited success metric was that the treatment met project specifications. This probably relates more to administrative process for contract payment than the long-term quality of the microsurfacing itself. Post-construction visual assessment was the third most common success metric followed by the absence of short-term failure. The friction and texture metrics are the only two post- construction metrics that can be physically measured. The performance-based pavement maintenance contracts in use in New Zealand have as many as 200 post-construction per- formance criteria (Manion and Tighe 2007), many of which involve direct measurements of the pavement’s surface char- acteristics. This explains why the Austroads respondents did not check qualitative measures as part of their success defini- tion and leads to identification of an area for future research: evaluating engineering measurements used by Austroads (2003b) as acceptance tests for microsurfacing projects. Minimizing Post-Construction Microsurfacing Defects The survey also asked respondents to share the types of dis- tresses that they most often found in their microsurfacing proj- ects. Table 36 shows the results of that analysis. One can see that the most common distress found in microsurfacing was reflected cracking. This confirms the conclusion drawn in chap- ter three that microsurfacing is not effective in treating serious cracking. The second most common distress was streaking and it is directly related to the quality of the workmanship. Raveling and delamination are the next two most common distresses in microsurfacing. Raveling can be caused by a number of material, design, or construction quality issues. A list of the most common is as follows: • The aggregate lacks sufficient embedment in the matrix caused from insufficient asphalt quantity to hold the larger aggregate, • Poor quality aggregates may debond from the matrix, • The application rate was too thin to hold larger aggregates, • The matrix has a lack of fines to fill voids between larger aggregates, • Cooler temperatures may result in slowing of the cure necessary for traffic, • Premature opening to traffic, and • Rain fell on the microsurfacing prior to complete setting (ISSA 2010a). Delamination is almost always the result of improper prepa- ration of the substrate surface before microsurfacing (Smith and Beatty 1999; Austroads 2003a; ISSA 2010a). It can also be caused by the emulsion breaking too quickly, which results in a broken mix being placed on the surface that will not form a bond (Austroads 2003b). Finally, improper transverse and lon- gitudinal joints were also cited as post-construction micro- surfacing defects. Both of these are workmanship issues. The ISSA manual describes the cause as follows: • Transverse: The transverse joint was constructed with- out using roofing felt, metal strips, etc., at the start of the placement pass. Similarly, the spreader box was either pulled until empty or ended without stopping on roofing felt or other protective surface meant to ensure a straight transverse joint. Poor joint construction practices result in excessive material build-up, uncovered areas, and un- sightly appearance. Although proper joint construction techniques are followed, occasionally the mixture may not be performing as designed owing to changing envi- ronmental conditions (ISSA 2010a). • Longitudinal: The placement machine may not have driving controls on both sides of the equipment so that the operator can follow existing edge markings, string lines, and previously placed microsurfacing in adjacent lanes. Many times the problem is related to poor planning of the product application process by the contractor. Exces- sive buildup, uncovered areas, or unsightly appearance often results from poor alignment of the longitudinal joint (ISSA 2010a). The survey also asked the agency respondents to rate eight preconstruction factors on their ability to minimize these defects. The results of that analysis are shown in Table 37. It can be seen that the two different population groups Distress U.S. Canada Total Crack Reflection 15 5 20 Streaking 9 2 11 Raveling 6 4 10 Delamination 7 1 8 Transverse Joints 5 3 8 Bleeding 4 1 5 Longitudinal Joints 4 0 4 Corrugation 1 1 2 Note: Agencies were asked to check all that applied. TABLE 36 SUMMARY OF COMMON MICROSURFACING POST-CONSTRUCTION DISTRESS Rated Impact (1 = highest rated factor) U.S. Ranking Canadian Ranking Contractor Experience 1 2 Selecting the Right Project 2 1 Construction Procedure 3 3 Preconstruction Road Preparation 4 7 Better Aggregates 5 5 Better Binder 6 6 Design Method 7 4 QC/QA Program 8 8 TABLE 37 IMPACT OF PROJECT FACTORS ON MICROSURFACING QUALITY

cited the same top three factors: contractor experience, proper project selection, and construction procedures. Cou- pling contractor experience as having the most impact on quality with the finding in chapter four that the availability of qualified microsurfacing contractors was a major concern leads to the conclusion that a certification program for micro- surfacing contractors is not only necessary, but it is also an urgent initiative. This analysis also indicates that project selection is probably the most important step in the microsurfacing design process with regard to impact on the final performance of the micro- surfacing itself. Finally, the relative importance of the material quality, design method, and QC/QA program indicates that the primary focus of the microsurfacing quality management pro- gram needs to be on workmanship rather than materials. By definition, microsurfacing is designed to incorporate high- quality materials (Johnson et al. 2007; ISSA 2010a). Thus, ensuring that the high-quality material is properly installed leads to the following effective practice: Focus agency construction quality assurance efforts on those microsurfacing factors that relate to the quality of the workmanship and other field-related aspects. Microsurfacing Failures Despite the best efforts of quality-conscious contractors and agency inspectors, microsurfacing projects do experience fail- ures. The survey sought to gauge the magnitude and reasons for failures in microsurfacing projects. Table 38 shows the results of those data collection efforts. A trend in the failures is evident. The top reason for failure cited was using an improper application rate. The application rates are developed as part of the job mix formula development process, but need to be adjusted in the field. Assuming that the majority of the time the contractor is furnishing the job mix formula and has control over the application rates in the field, this failure is the contractors’ responsibility. This information further validates the concern expressed in the previous paragraph with the need for qualified and experienced microsurfacing contrac- tors to promote successful microsurfacing projects. 54 The aggregate issues cited in the table could be a function of doing gradation testing at the source (see Table 33). The aggregate will be handled several more times after it leaves the pit and research has shown that every time an aggregate is handled its gradation changes as the handling of the material creates more fines. Although it cannot be determined from this study, a possible fix would be to sample the aggregate gradation as close to its introduction into the mixing machine as possible. Thus, an aggregate that is of marginal quality in terms of soundness and abrasion resistance would be tested in the final gradation that is incorporated into the microsur- facing fix. Finally, project selection comes up once more as a reason for microsurfacing failure, underscoring the impor- tance of that step in the design process. The survey also sampled agency experience regarding com- plaints from the traveling public and their source. Table 39 contains the results. It is gratifying to see that the most com- mon answer was “we don’t get complaints.” That statistic speaks volumes about the ability of microsurfacing to satisfy the needs of the traveling public for a safe, comfortable sur- face upon which to drive. Road noise and appearance were the next most common public complaints. Both of these are perceptional and were discussed in chapter three. Microsurfacing Service Life Finally, the survey asked the respondents to indicate what fac- tor was most critical to microsurfacing achieving its intended service life (Table 40). The overwhelming answer from both groups was essentially selecting the right project for this Cause of Failure U.S. Canada Total Improper application rate 5 5 10 Dirty or dusty aggregate/gradation issues 4 4 8 Wrong road—poor project selection 6 2 8 Improper ambient and/or surface temperatures 3 3 6 Improper binder viscosity 3 3 6 Improper binder temperature 3 3 6 Improper surface preparation 3 2 5 Weather 2 2 4 Field construction procedures 1 0 1 Snow plow damage 1 0 1 TABLE 38 REASONS FOR MICROSURFACING FAILURE Public Complaints U.S. Canada Total No Complaints 5 3 8 Road Noise 8 1 9 Appearance 5 3 8 Loose Stone 1 1 2 Vehicle Ride 1 0 1 Do Not Know 8 0 8 TABLE 39 PUBLIC COMPLAINT SUMMARY

55 treatment’s characteristics. Thus, training in this specific area is vitally important. SUMMARY This chapter reviewed the primary issues associated with microsurfacing construction quality. As a result of the analysis one effective practice, the pre-paving quality meeting, and one area for future research, were derived. The notion that “putting the right treatment on the right road at the right time” (Gale- house et al. 2003) was validated by this analysis of quality man- agement practices. This confirms the idea that agencies that are considering microsurfacing need to invest the appropriate amount of time during the maintenance project programming process to ensure that those roads selected to receive micro- surfacing are indeed good candidates for this treatment. Conclusions The following conclusions were reached in this chapter: 1. Microsurfacing is viewed as a valuable pavement preser- vation treatment rather than merely a pavement main- tenance treatment. 2. Contractor experience was cited as the most important factor affecting microsurfacing quality. With this iden- tified need for competent contractors, a microsurfacing certification program would furnish a means to iden- tify competent microsurfacing contractors. 3. Project selection is probably the most important step in the microsurfacing design process with regard to impact on the final performance of the microsurfacing itself. Effective Practices The following effective practices were identified in this chapter: 1. Holding a pre-paving meeting to discuss quality man- agement and workmanship issues before full produc- tion microsurfacing provides a forum where both the agency and the contractor can address main areas and concerns about microsurfacing quality. 2. Focusing agency construction quality assurance efforts on those microsurfacing factors that relate to the quality of the workmanship and other field-related aspects. Service Life Factors U.S. Canada Total Underlying Pavement Structure 14 6 20 Original Substrate Surface Quality 12 4 16 Traffic Volume 5 0 5 Cold Climate Considerations (freeze/thaw cycles, snowplowing, etc.) 5 2 7 Maintenance Funding 2 1 3 Friction Loss 3 0 3 Construction Quality 0 1 1 Do Not Know 2 0 2 TABLE 40 SUMMARY OF SERVICE LIFE FACTORS

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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 411: Microsurfacing explores highway microsurfacing project selection, design, contracting, equipment, construction, and performance measurement processes used by transportation agencies in the United States and Canada.

Microsurfacing is a polymer-modified cold-mix surface treatment that has the potential to address a broad range of problems on today’s highways.

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