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OCR for page 65
66 Most agencies do not prequalify microsurfacing bidders. can be modified to furnish better support across the This may be because the pool of competent and qualified joints and the flexible rubber strike-off can be replaced contractors is inherently shallow. Contractor experience with a rigid strike-off was also cited as the most important microsurfacing 2. Requiring that a test strip of 500 to 1,000 ft (152.4 quality factor. Therefore, the FHWA's Pavement Preser- to 304.8 m) in length be constructed and inspected vation Expert Task Group initiative to develop a certifi- allows the agency and the contractor to ensure that cation program at the national level is needed. microsurfacing equipment is properly calibrated and Requiring warranties for microsurfacing projects is not that any workmanship issues are resolved before full- problematic because the contractor normally furnishes scale microsurfacing production. If the microsurfacing the job mix formula. 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- EFFECTIVE PRACTICES agement and workmanship issues before full produc- tion microsurfacing provides a forum where both the Effective practices are identified when the analyses found mul- agency and the contractor can address main areas and tiple instances of microsurfacing success when certain tech- concerns about microsurfacing quality. niques or approaches were utilized in the design, contracting, 4. Focus agency construction quality assurance efforts or construction phase of a microsurfacing project. Addition- on those microsurfacing factors that relate to the qual- ally, the case study analysis identified a few other effective ity of the workmanship and other field-related aspects. practices based on the detailed analysis found in those projects. 5. Scratch coat and full lane-width microsurfacing can use the same size aggregate with no apparent differ- Effective Practices in Microsurfacing Project Selection ence in performance. 1. Project selection is critical to microsurfacing success 6. The microsurfacing placement machine is best recal- and those agencies that only apply microsurfacing to ibrated every time there is a change in material source structurally sound pavements are generally satisfied or composition. with its performance. Case Study Effective Practices 2. Microsurfacing performs best when applied to correct 1. Microsurfacing can be effectively employed on roads surface friction, oxidation, raveling, and/or rutting on where routine winter snow removal is a factor if the pavements that have adequate structural capacity. underlying pavement is structurally sound. Effective Practices in Microsurfacing Design 2. Microsurfacing is a proper alternative to enhance skid 1. Microsurfacing design can be successfully assigned resistance in areas where the frictional characteristics to the microsurfacing contractor with the agency of the road's surface are to be restored to safe oper- reviewing and approving the final job mix formula. ating limits. 2. Compounds added to microsurfacing job mix formu- 3. The microsurfacing binder amount can be reduced by las can be selected by the emulsion manufacturer and 1% to 2% in rut filling and scratch courses upon which the agency can then verify that they are compatible a wearing course will be applied. with the approved job mix formula. 3. Microsurfacing programs can be successfully imple- mented with a single binder type with a record of sat- FUTURE RESEARCH NEEDS isfactory performance in a given agency's climate and traffic conditions. The synthesis uncovered a number of gaps in the body of Effective Practices in Microsurfacing Contracting knowledge about microsurfacing. The following is a list of 1. Agencies in northern climates can mitigate potential future research needs and a brief description of what form quality issues induced by a short microsurfacing sea- that research might take: son by requiring a warranty. 2. It is important that agencies in northern climates let Pavement preservation success depends on identifying microsurfacing projects as early as possible to permit candidate roadways before they need reactive mainte- their completion as early in the season as possible and nance. The survey found very little information regard- mitigate the risk that unstable weather at the end of the ing trigger points for invoking microsurfacing to extend season will adversely impact microsurfacing quality. the underlying pavement's life and preserve its struc- 3. Microsurfacing is to be paid for by the ton if the tural integrity. Thus, research is needed to determine agency is not using a performance specification. measurable values of distress that can be used in an 4. Make microsurfacing contract packages as large as agency's pavement preservation program. Additionally, is practical to reduce the unit price and increase the microsurfacing success demands that the road be struc- number of lane-miles that can be treated each year. turally sound. Therefore, research may also include con- Effective Practices in Microsurfacing Construction solidating agency pavement management system trigger 1. When using microsurfacing to improve ride quality values and furnishing guidance as to appropriate micro- on jointed plain concrete pavements, the spreader box surfacing timing.

OCR for page 65
67 There is no clear trend as to whether rolling adds value priate characteristics of and effectiveness of micro- or not to the microsurfacing process; therefore, research surfacing warranties is suggested. to settle this question is suggested. Public highway agencies in Australia and New Zealand Most of the agencies in the survey use the same design have long been using performance contracting techniques for microsurfacing on high-volume roads as they do on to procure pavement maintenance and preservation ser- low-volume roads. Research is suggested that will either vices. These contracts are based on objective key perfor- confirm or deny that this is good practice. mance measures such as skid number, pavement macro- The survey results that show that the majority of knowl- texture, and other criteria. The suggested research would edgeable maintenance practitioners do not consider envi- evaluate the current programs used in those and other ronmental impact in their project development process. countries, such as the United Kingdom, South Africa, Given the current widespread focus on sustainable design Portugal, and Spain, and develop a set of key perfor- and construction practices, this research would be able to mance measures that could be used in microsurfacing draw from the information currently being developed for projects being procured on a performance basis. other types of highway paving systems. The lack of rigorous field tests based on a rational quanti- One of the conclusions reported earlier documented the fication of measurable microsurfacing properties leads need for a microsurfacing certification program at the to a suggestion for research to develop a series of field national level. Research to determine the specific content tests that allow an inspector to test the microsurfacing of such a program is suggested. mix after it has been laid, as well as tests to identify Because several of the responding agencies are success- when the mix has cured to a sufficient degree to open it fully using warranties, research to determine the appro- to traffic without fear of damaging it.