National Academies Press: OpenBook

Microsurfacing (2010)

Chapter: Chapter Nine - Conclusions

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Page 64
Suggested Citation:"Chapter Nine - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2010. Microsurfacing. Washington, DC: The National Academies Press. doi: 10.17226/14464.
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Page 64
Page 65
Suggested Citation:"Chapter Nine - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2010. Microsurfacing. Washington, DC: The National Academies Press. doi: 10.17226/14464.
×
Page 65
Page 66
Suggested Citation:"Chapter Nine - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2010. Microsurfacing. Washington, DC: The National Academies Press. doi: 10.17226/14464.
×
Page 66

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65 INTRODUCTION Chapters one and two set the criteria used in this report for drawing conclusions and identifying effective practices. That process was followed rigorously throughout the entire report. The results are based on the four study instruments used to collect the information contained in the synthesis: a compre- hensive literature review, survey of U.S. and Canadian agen- cies, microsurfacing specification content analysis, and case studies. When two or more independent lines of information from one of those four sources intersected, a conclusion was reached or an effective practice was proposed. Lastly, when a gap in the body of knowledge was revealed, a suggestion for future research was made. Therefore, based on that foun- dation, the conclusions, effective practices, and suggestions for future research are presented in this chapter. CONCLUSIONS The following conclusions were reached in the conduct of this study. They are not listed in any order of importance. • Of all the standard microsurfacing specifications from 50 U.S. states plus the District of Columbia and the FHWA Federal Lands Highway Division, only 18 had sections that specifically contained the word “microsurfacing.” As a result, there is a potential for confusion in the liter- ature about the difference between microsurfacing and slurry seals, which spawns a potential for an inaccurate exchange of technical information on the two treatments. • Only two agencies use microsurfacing on a regular preventive maintenance cycle and a number of survey respondents indicated that their agency uses micro- surfacing to extend the life of the underlying pavement. That approach was validated by the majority of respon- dents, indicating that they use service life as their mea- sure of treatment success. That leads to the conclusion that microsurfacing is viewed as a valuable pavement preservation treatment rather than merely a pavement maintenance treatment. • Microsurfacing is best suited to address rutting, ravel- ing, oxidation, bleeding, and loss of surface friction. Microsurfacing is not appropriate for structurally defi- cient pavements. This makes project selection the most important step in the microsurfacing design process with regard to impact on the final performance of the microsurfacing itself. • Microsurfacing can be expected to provide an average service life of 7 years if the underlying road is in good condition. • Microsurfacing is a pavement preservation and main- tenance tool with very few technical or operational limitations. – Microsurfacing was shown to be effective for all lev- els of traffic, as well as useful in both urban and rural settings. – Microsurfacing was shown to be effective on both asphalt and concrete pavements. – Microsurfacing can be effectively used in locations where the work is to be done at night or in cool weather, as well as where stresses resulting from stopping and snow plowing are present. • The majority of the respondents that use microsurfacing assign the contractor the responsibility for completing the job mix formula. That the majority of the same pop- ulation rates their microsurfacing project performance as satisfactory indicates that contractor-furnished design does not degrade final quality. • Microsurfacing can be procured using a performance- based contract. The content analysis found that a number of agencies are already using performance specifications in their microsurfacing contracts. • Microsurfacing is one of the few pavement preservation and maintenance treatments that can restore the trans- verse geometry of a rutted road. Because U.S. agencies use it primarily as a surface course, they are not maxi- mizing the potential benefits of microsurfacing when they do not use it as the primary tool to fill ruts as their Canadian counterparts do. • Most agencies only use a single microsurfacing emul- sion, and all agencies rated their microsurfacing perfor- mance as satisfactory. Therefore, an agency can select a single emulsion that works best for its specific climatic and traffic environment and achieve satisfactory results. • The majority of maintenance practitioners do not con- sider environmental impact in their microsurfacing proj- ect development process. • Most of the U.S. and Canadian agencies do not perceive that they have an adequate level of competition among qualified microsurfacing contractors for their programs. This may be because most microsurfacing programs do not advertise a consistent amount of work each year, making it difficult for interested contractors to develop the technical capacity and equipment necessary to com- petitively bid on these contracts. CHAPTER NINE CONCLUSIONS

• Most agencies do not prequalify microsurfacing bidders. This may be because the pool of competent and qualified contractors is inherently shallow. Contractor experience was also cited as the most important microsurfacing quality factor. Therefore, the FHWA’s Pavement Preser- vation Expert Task Group initiative to develop a certifi- cation program at the national level is needed. • Requiring warranties for microsurfacing projects is not problematic because the contractor normally furnishes the job mix formula. EFFECTIVE PRACTICES Effective practices are identified when the analyses found mul- tiple instances of microsurfacing success when certain tech- niques or approaches were utilized in the design, contracting, or construction phase of a microsurfacing project. Addition- ally, the case study analysis identified a few other effective practices based on the detailed analysis found in those projects. • Effective Practices in Microsurfacing Project Selection 1. Project selection is critical to microsurfacing success and those agencies that only apply microsurfacing to structurally sound pavements are generally satisfied with its performance. 2. Microsurfacing performs best when applied to correct surface friction, oxidation, raveling, and/or rutting on pavements that have adequate structural capacity. • Effective Practices in Microsurfacing Design 1. Microsurfacing design can be successfully assigned to the microsurfacing contractor with the agency reviewing and approving the final job mix formula. 2. Compounds added to microsurfacing job mix formu- las can be selected by the emulsion manufacturer and the agency can then verify that they are compatible with the approved job mix formula. 3. Microsurfacing programs can be successfully imple- mented with a single binder type with a record of sat- isfactory performance in a given agency’s climate and traffic conditions. • Effective Practices in Microsurfacing Contracting 1. Agencies in northern climates can mitigate potential quality issues induced by a short microsurfacing sea- son by requiring a warranty. 2. It is important that agencies in northern climates let microsurfacing projects as early as possible to permit their completion as early in the season as possible and mitigate the risk that unstable weather at the end of the season will adversely impact microsurfacing quality. 3. Microsurfacing is to be paid for by the ton if the agency is not using a performance specification. 4. Make microsurfacing contract packages as large as is practical to reduce the unit price and increase the number of lane-miles that can be treated each year. • Effective Practices in Microsurfacing Construction 1. When using microsurfacing to improve ride quality on jointed plain concrete pavements, the spreader box 66 can be modified to furnish better support across the joints and the flexible rubber strike-off can be replaced with a rigid strike-off 2. Requiring that a test strip of 500 to 1,000 ft (152.4 to 304.8 m) in length be constructed and inspected allows the agency and the contractor to ensure that microsurfacing equipment is properly calibrated and that any workmanship issues are resolved before full- scale microsurfacing production. If the microsurfacing is scheduled to occur after dark, it is important that the test strip be constructed after dark. 3. 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. 4. Focus agency construction quality assurance efforts on those microsurfacing factors that relate to the qual- ity of the workmanship and other field-related aspects. 5. Scratch coat and full lane-width microsurfacing can use the same size aggregate with no apparent differ- ence in performance. 6. The microsurfacing placement machine is best recal- ibrated every time there is a change in material source or composition. • Case Study Effective Practices 1. Microsurfacing can be effectively employed on roads where routine winter snow removal is a factor if the underlying pavement is structurally sound. 2. Microsurfacing is a proper alternative to enhance skid resistance in areas where the frictional characteristics of the road’s surface are to be restored to safe oper- ating limits. 3. The microsurfacing binder amount can be reduced by 1% to 2% in rut filling and scratch courses upon which a wearing course will be applied. FUTURE RESEARCH NEEDS The synthesis uncovered a number of gaps in the body of knowledge about microsurfacing. The following is a list of future research needs and a brief description of what form that research might take: • Pavement preservation success depends on identifying candidate roadways before they need reactive mainte- nance. The survey found very little information regard- ing trigger points for invoking microsurfacing to extend the underlying pavement’s life and preserve its struc- tural integrity. Thus, research is needed to determine measurable values of distress that can be used in an agency’s pavement preservation program. Additionally, microsurfacing success demands that the road be struc- turally sound. Therefore, research may also include con- solidating agency pavement management system trigger values and furnishing guidance as to appropriate micro- surfacing timing.

67 • There is no clear trend as to whether rolling adds value or not to the microsurfacing process; therefore, research to settle this question is suggested. • Most of the agencies in the survey use the same design for microsurfacing on high-volume roads as they do on low-volume roads. Research is suggested that will either confirm or deny that this is good practice. • The survey results that show that the majority of knowl- edgeable maintenance practitioners do not consider envi- ronmental impact in their project development process. Given the current widespread focus on sustainable design and construction practices, this research would be able to draw from the information currently being developed for other types of highway paving systems. • One of the conclusions reported earlier documented the need for a microsurfacing certification program at the national level. Research to determine the specific content of such a program is suggested. • Because several of the responding agencies are success- fully using warranties, research to determine the appro- priate characteristics of and effectiveness of micro- surfacing warranties is suggested. • Public highway agencies in Australia and New Zealand have long been using performance contracting techniques to procure pavement maintenance and preservation ser- vices. These contracts are based on objective key perfor- mance measures such as skid number, pavement macro- texture, and other criteria. The suggested research would evaluate the current programs used in those and other countries, such as the United Kingdom, South Africa, Portugal, and Spain, and develop a set of key perfor- mance measures that could be used in microsurfacing projects being procured on a performance basis. • The lack of rigorous field tests based on a rational quanti- fication of measurable microsurfacing properties leads to a suggestion for research to develop a series of field tests that allow an inspector to test the microsurfacing mix after it has been laid, as well as tests to identify when the mix has cured to a sufficient degree to open it to traffic without fear of damaging it.

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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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