National Academies Press: OpenBook

Microsurfacing (2010)

Chapter: Chapter Two - Summary of Information Collected

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Suggested Citation:"Chapter Two - Summary of Information Collected." 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 Two - Summary of Information Collected." National Academies of Sciences, Engineering, and Medicine. 2010. Microsurfacing. Washington, DC: The National Academies Press. doi: 10.17226/14464.
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Page 11
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Suggested Citation:"Chapter Two - Summary of Information Collected." National Academies of Sciences, Engineering, and Medicine. 2010. Microsurfacing. Washington, DC: The National Academies Press. doi: 10.17226/14464.
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Page 12

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11 INTRODUCTION This report is the result of a comprehensive literature review, a survey of both U.S. and Canadian public highway agencies, a content analysis of DOT microsurfacing specifications, and case studies of DOT-specific experiences with microsurfac- ing. The resulting information is merely a recitation of infor- mation found by each of those instruments and conclusions drawn are based on multiple confirmations from two or more study instruments. It must be noted that the synthesis repre- sents a “snapshot” in time with respect to the state of the prac- tice. Wherever possible, seeming conflicts between survey responses and other information, such as the literature, were verified by a third source. However, when no conflict arose, the information reported in the survey was accepted and car- ried into the analysis. SYNTHESIS METHODOLOGY The synthesis employed the following major study instruments: 1. Comprehensive literature review, 2. Survey of U.S. state and Canadian province transporta- tion agencies, 3. Content analysis of U.S. microsurfacing specifications, and 4. Case study analysis of selected U.S. and Canadian microsurfacing programs. The structure and content of each of the instruments was developed to integrate with all other instruments, which allows the output of each instrument to be mapped with the output of the others identifying trends in the data. The survey was issued to the maintenance engineers in 50 U.S. state DOTs and 13 Canadian provincial or territorial MOTs (see Appendix A for details). A survey on microsurfac- ing practices provided responses from 44 U.S. state DOTs and 12 Canadian provincial MOTs, resulting in an overall response rate of 89%. The survey respondents are shown in Figure 4. This analysis separated the U.S. and Canadian responses to account for the difference in the construction contracting reg- ulatory environment that exists in both countries and also to highlight potential innovative Canadian microsurfacing prac- tices, keeping them from being lost in the total survey popula- tion. It can be noted that local agencies at the municipal and county levels are also known to use microsurfacing. However, no effort was made to survey these agencies, as it was beyond the scope of this synthesis. Finally, the reader must under- stand that because the survey results are presented in tabular form throughout the report that attempting to add up the vari- ous responses and get them to sum to the same number for the United States and Canada cannot be done. Many of the ques- tions asked respondents to check all answers that applied. A number of the questions were follow-up questions answered only by those respondents that answered in a prescribed man- ner on the previous questions and some of the surveys were not totally completed. Therefore, the survey results are reported exactly as they were observed. Standard microsurfacing specifications from all 50 U.S. states plus the District of Columbia and the FHWA Federal Lands Highway Division (FLHD) were assembled. Of that group, 18 contained sections that specifically contained the word “microsurfacing.” The others may have been used for microsurfacing under another term such as “surface treat- ment” or even “slurry seal.” Other section titles found were: “Cold-Laid Latex Modified Emulsion Pavement Course” (Pennsylvania) and “Paver-laid Surface Treatment” (Alabama). An example of the indeterminate state of micro- surfacing terminology is the FLHD specification, which states in Section 410—Slurry Seal: “This work consists of applying an asphalt slurry seal or a polymer modified microsurfacing mix on an existing pavement surface” (FLHD 2003, italics added). The word “microsurfacing” is found only in this sen- tence and the remainder of the section does not differentiate between the two treatments, effectively giving both treatments the same specification. As a result of the potential for inaccu- rate analysis, only the 18 specifications that contained a refer- ence to microsurfacing were included in the content analysis. A case study analysis was also undertaken to furnish spe- cific information on microsurfacing as experienced by selected agencies. Each case study was selected for a specific focus, which furnishes a unique perspective on an agency’s micro- surfacing program. Table 4 shows the case studies and the rea- son each was selected. GENERAL AGENCY MICROSURFACING INFORMATION To put the information in this report in proper context, the reader needs to understand the relative magnitude of micro- surfacing programs in the United States and Canada. Table 5 CHAPTER TWO SUMMARY OF INFORMATION COLLECTED

12 FIGURE 4 Survey responses from U.S. DOTs and Canadian MOTs. Agency Reason for Inclusion Georgia DOT Agency with successful demonstration project but does not use in program. Also included road noise analysis. Kansas DOT Microsurfacing on jointed concrete pavement. Maine DOT Agency uses microsurfacing to maintain both roads that are built to DOT standards and roads that are not built to DOT standards. Minnesota DOT Agency has robust internal microsurfacing research program, including trials of softer binders to reduce cracking. Oklahoma DOT Agency has 9-year field performance monitoring program and an ongoing rigorous field test that focuses on microsurfacing skid resistance and macrotexture. Ontario MTO Agency has completed rigorous studies relating microsurfacing to traffic safety. TABLE 4 CASE STUDY SUMMARY Characteristic U.S. DOT Canada Percent of Rural Local Roads with Microsurfacing 2.2% 0.0% Percent of Rural Interstate Roads with Microsurfacing 5.6% 9.1% Percent of Urban Local Roads with Microsurfacing 6.0% 0.0% Percent of Urban Interstate Roads with Microsurfacing 10.7% 0.3% Percent Total Network with Microsurfacing 3.1% 6.9% Average Microsurfacing Approxi mate Annual Volum e $3.0 mi llion $4.0 mi llion* High Reported $12.0 m illion $10.0 m illion* Low Reported $0.5 mi llion $0.06 m illion* Average Microsurfacing Annual Program Size 60 mi les (96.6 km) 57 mi les (92 km) High Reported 150 m iles (241.4 km) 124 m iles (200 km) Low Reported 12 miles (19.3 km) 10 mi les (16 km) Agencies with Microsurfacing Installed by In-house Crews 1 2 Agencies with Microsurfacing Installed by Contractor Crews 30 6 *These are Canadian dollars, which at the time of this writing is trading at roughly par to the U.S. dollar. TABLE 5 SUMMARY OF MICROSURFACING PROGRAM STATISTICS FROM SURVEY RESPONDENTS

13 summarizes the survey responses from those respondents that indicated that microsurfacing was used in their organizations. Table 5 shows that microsurfacing constitutes a relatively low percentage of most agencies’ programs. Texas ($12 mil- lion), Tennessee ($9.3 million), Louisiana ($6.3 million), and North Dakota ($6.3 million) had the largest U.S. micro- surfacing programs. In Canada, Saskatchewan ($10 mil- lion) and Manitoba ($9 million) led the provinces. The table shows that microsurfacing is largely installed by contract crews. Only one U.S. DOT and two Canadian MOTs have the capability to apply microsurfacing using agency per- sonnel. Minnesota puts approximately 5% of its annual program down with DOT maintenance crews. Quebec and Saskatchewan agency personnel install 2% and 5%, respec- tively. The study found no specific information as to why microsurfacing constitutes such a small percentage of the typical agency’s pavement preservation and maintenance program. However, a check of the bid tabulations for a May 2010 letting by the Utah DOT shows roughly equiva- lent quantities of microsurfacing and chip seal being bid at $2.07 per square yard and $1.72 per square yard, respec- tively, roughly a 20% difference in price. Therefore, eco- nomics may be the factor, as an agency can preserve 20% more lane-miles of its roads each year by using the lower priced treatment. Finally, because microsurfacing can be used as a tool in an agency’s preventive maintenance program, the survey respon- dents were asked if they applied it on a regular cycle as well as the length of the cycle if they did. The Indiana and Utah DOTs reply affirmatively and Indiana stated that the preventive maintenance cycle averaged 8 years. Nova Scotia was the only other respondent to reply yes to this question and it reported that it used a 6-year cycle. The written comments on this issue suggest that microsurfacing is viewed primarily as a pavement preservation tool in North America. Several respondents stated that their agencies use it specifically to extend the underlying pavement’s surface life when asked to estimate microsurfacing service life. Figure 5 summarizes the survey responses. The service life reported by U.S. DOTs averaged 6 years within a range of 1 year to 15 years. Canadians agencies reported an average microsurfacing service life of 7 years, with a low of 3 years and a high of 10 years. SUMMARY AND CONCLUSIONS Microsurfacing is an effective tool for pavement preservation and maintenance programs in North America. It is not used in large amounts nor is it a technology that is kept in-house by public highway agencies. Overall, the survey respondents were satisfied with their microsurfacing contractors’ perfor- mance and depend on the technology to extend pavement ser- vice life. The output from the study instruments discussed in this chapter will be used to present a more detailed discussion of the state of the practice in microsurfacing in the following chapters. It will also be used to identify effective practices that can be implemented by both agencies with extensive micro- surfacing experience or agencies that are contemplating adding it to their pavement preservation toolbox. The following conclusion was found in this chapter: Microsurfacing is fundamentally viewed as a tool to extend the service life of the existing pavement and thus it is used primarily as a pavement preservation treatment. 1 11 1 7 6 6 3 11 2 2 1 1 0 2 4 6 8 2 3 4 5 6 7 8 9 10 11 12 13 14 15 N um be r o f S u rv ey R es po ns es Microsurfacing Service Life (years) US Canada FIGURE 5 Summary of survey microsurfacing service life responses.

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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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