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33 MICROSURFACING CONTRACT PROVISIONS to be above 60F (16C) and Louisiana uses 70F (21C). The functional effect of lower temperature requirements is to Often contracting provisions can have a large impact on pave- extend the microsurfacing season, which is necessary for agen- ment preservation and maintenance treatment performance. cies in northern climes such as the three mentioned. Louisiana For example, a Texas study found that agencies that paid for is the only southern agency that does not use that specifica- crack sealing by the linear lane-mile rather than by the pound tion. No explanation could be found for the reason that the of sealant had fewer flushing issues in their seal coat programs Louisiana Department of Transportation and Development because the unit price by weight created an incentive for the uses 70F (21C). Wyoming's use of a higher than standard crack sealing contractor to use as much crack seal as possible temperature (60F; 16C) stems from the concept that it is the to boost the total amount paid (Senadheera et al. 2001), Rocky Mountain state where temperature gradients are much whereas paying by the lane-mile had the opposite effect, but steeper than those found in northern states in the Midwest and required a higher level of quality assurance to make sure all farther east. In the Rockies, the temperature can vary 40F cracks were sealed. Another example from that study was the (4.4C) in mid-summer and more if the road is at a high alti- finding that seals installed early in the season had less early tude. Therefore, the Wyoming DOT is building a safety factor raveling than the ones placed late in the season because early into its specifications to meet the demands of local climate. seals had more high surface temperature traffic compaction, which kept the binder softer (Senadheera et al. 2001). There- Research has found the surface temperature affects the fore, it is important to evaluate key contract provisions to look rate at which an emulsion breaks (Moulthrop 2007). Figure 13 for similar trends in microsurfacing. shows the relationship between temperature and emulsion breaking time. One report indicated that it would be necessary This section will look at the following contract provisions: that surface temperatures be within a range of 50F (10C) and 140F (60C) to ensure a proper break (Gransberg and James Seasonal restrictions 2005). When the emulsion breaks too fast, wash-boarding can Pay units occur, and if it breaks too slow, the product becomes suscepti- Incentive/disincentive clauses ble to raveling (Moulthrop 2007; ISSA 2010a). All the specifi- cations reviewed also contained a further requirement to the Seasonal Considerations effect that the minimum temperatures needed to occur in conjunction with a period of no fog, rain, drizzle, or forecast of Microsurfacing is an asphalt-based product and as a result is freezing temperatures within the next 24 h. Therefore, it is sensitive to ambient air temperature, humidity, wet conditions, important the microsurfacing contract include air and surface and surface temperature. "The basic prerequisite for success is temperature requirements that match both the materials to be that the emulsion needs to properly break and cure. As a result, used and the climatic conditions in which they will be applied. humidity, wind conditions, and temperature (both surface and air) are important and need to be considered" (ISSA 2010a). The other common climatic constraint found in the speci- Therefore, the microsurfacing contract needs to account for the fications was a definition of the microsurfacing season. Most restrictions that the material places on the environment in run from May to September, with the season being shortened which it can be applied with good results. The specification as the location of the agency moved north. The survey asked content analysis accumulated weather-related provisions. the respondents to identify the months in which they authorize Table 25 shows the most typical climate-related contract microsurfacing operations. Figure 14 is a histogram show- provisions regarding temperature limits within which micro- ing the frequency of response for the United States, Canada, surfacing can be applied. Most revolve around the typical tem- and the total population. When the combined population is perature for hot-mix paving operations: 50F (10C) and summed, 63% of all microsurfacing occurs in June, July, and rising. The three that were lower than that limit were the Ohio August, with 100% being completed from April to October. DOT at 40F (4C) and Michigan DOT and FLHD at 45F None of the responding agencies applied microsurfacing from (7C). Kansas and Wyoming DOTs require the temperature November through March. TABLE 25 SUMMARY OF CONTENT ANALYSIS SPECIFICATION TEMPERATURE LIMITS States Using Specified Air States Using Specified Surface Specification Limit Temperature Limit Temperature Limit None No states AL, KS, NE, NM, PA >45 (7.2C) FLHD, MI FLHD, MI >50 (10C) AL, GA, MN, MO, NE, NM, OH, AL, GA, MN, MO, OK, OH, TN, OK, PA, TN, TX, UT, VA TX, UT, VA >60 (15.6C) KS, WY No states >70 (21.1C) LA LA

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34 140 120 100 Break time (min) 80 60 40 20 0 60 80 100 120 140 160 180 Emulsion Temperature (degrees F) Aggregate at 85 degrees F Aggregate at 70 degrees F FIGURE 13 Relationship between temperature and emulsion breaking time (ISSA 2010a). Figure 15 shows the distribution if the respondents are 1. Agencies in northern climates can mitigate potential split between northern and southern climates. It reveals that quality issues induced by a short microsurfacing season microsurfacing is more intense in the shorter northern season, by requiring a warranty. whereas the southern states are able to spread their program 2. Scheduling microsurfacing project letting as early as out over a several more months. This puts the issue of qualified possible will permit their completion as early in the sea- microsurfacing contractor availability into a time context. The son as possible and mitigate the risk that poor weather northern agencies complete their annual programs between at the end of the season will adversely impact micro- mid-May and mid-September; therefore, it is essential that the surfacing quality. number of new lane-miles of microsurfacing be placed at a faster rate in the north, creating a seasonally higher demand for qualified contractors in the north than in the south. Contract Payment Provisions Taking the location of those agencies in North America that "Unit price contracts are used for work where it is not possi- require microsurfacing warranties shown in Table 23 into ble to calculate the exact quantity of materials that will be account, one finds that 12 of 15 are northern states or Canadian required. Unit price contracts are commonly used for heavy/ provinces. The common trend in these three sources leads to highway work" (Schexnayder and Mayo 2004). When an two identified effective practices: owner selects unit price contracting, it is doing so to share the FIGURE 14 U.S. and Canadian microsurfacing season comparison.

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35 FIGURE 15 Northern and southern agency microsurfacing season comparison. risk of the final quantities of work with the contractor to the pay unit follows the type of specification used for the pay reduce the price. This happens because the contractor does not item (Schexnayder and Mayo 2004). Microsurfacing that is have to bid the worst possible case if the quantities of work delivered using a performance specification can then be paid are not finite as it would be driven to do in a lump sum con- for by the area, because the amount of material installed to tract where it bore the entire quantity risk (Schexnayder and meet the performance requirements is left to the contractor Mayo 2004). The owner assumes the risk of quantity over- (Erwin and Tighe 2008), whereas an agency using a method runs by agreeing to pay for the actual units applied, rather than specification would pay by the ton, because the agency has paying a premium for transferring the risk of quantity over- taken control of the specified application rates (Price 2010). runs to the contractor through a lump sum price. Given that Based on the literature and survey results, the following effec- microsurfacing projects usually are limited to a defined area tive practice is identified: of pavement, quantity surveys are fairly straightforward and not highly variable. Thus, lump sum contracts, including the Microsurfacing is to be paid for by the ton if the agency is total cost of the project with mobilization and traffic control, not using a performance specification. could be used without the agency incurring a substantial cost increase. For instance, the British Columbia MOT reported The second parameter that affects unit prices is the quantity getting excellent results since the mid-1980s from lump sum of work on the project being bid. As the amount of work microsurfacing contracts (Miquel and Condron 1991). That that is packaged in a single contract increases, its unit price being said, no survey respondents indicated that they pro- decreases because the contractor is able to spread the fixed cured microsurfacing with lump sum contracts. costs, such as mobilization and traffic control across more units (Schexnayder and Mayo 2004). The survey found that The survey found an almost even split between specifying the average U.S. microsurfacing project was 7.4 lane-miles pay units by area and by weight (see Table 26). Most respon- (11.9 lane-km), with the low of 2 lane-miles (3.2 lane-km) and dents added a note to the effect that they do not differenti- a high of 17 lane-miles (27.4 lane-km). In Canada, the average ate between the binder and the aggregate, but rather use a microsurfacing project was roughly the same at 6.8 lane-miles single pay measure for microsurfacing. It also found that these (11 lane-km), with the low of 3.7 lane-miles (6 lane-km) and a were used because of perceived fairness and the ability to high of 17 lane-miles (12.4 lane-km). The point made here is accurately measure pay quantities. The literature shows that that pavement managers can stretch microsurfacing budgets TABLE 26 SUMMARY OF MICROSURFACING UNITS OF MEASURE AND THEIR RATIONALE Easier to Do Not Know Fairest to the Accurately Why We Use Pay Item Unit of Measure Reduces the Cost Contractor Estimate Them Binder U.S. Canada U.S. Canada U.S. Canada U.S. Canada Units of Area (SY/SM) 1 0 3 2 4 3 3 0 Units of Weight (ton/tonne/MG) 2 0 4 0 4 2 2 0 Aggregate U.S. Canada U.S. Canada U.S. Canada U.S. Canada Units of Area (SY/SM) 2 0 2 1 4 4 3 0 Units of Weight (ton/tonne/MG) 1 0 7 0 7 2 1 0