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From page 23... ... 23 This chapter summarizes the results of the surveys of agencies and industry. As noted previously, a total of 45 state DOTs responded to the survey, a 90% response rate. Read the entire page →
From page 24... ... 24 Impact of Asphalt Thickness on Pavement Quality Responded No Response Figure 6. States responding to the agency survey. Read the entire page →
From page 25... ... Survey Results: Current Practices Regarding Lift Thicknesses 25 and 4×NMAS for all sizes except 37.5 (which they do not use) Read the entire page →
From page 26... ... 26 Impact of Asphalt Thickness on Pavement Quality • For scratch or leveling courses; • To limit drop-offs; • Shoulders and transitions; and • To control costs. Some states indicated they might allow thicker lifts to be placed (especially deeper in the pavement) Read the entire page →
From page 27... ... Figure 11. Are target densities the same if compaction is limited to static mode? Read the entire page →
From page 28... ... 28 Impact of Asphalt Thickness on Pavement Quality Figure 14. Have you observed paving contractors having more difficulty in obtaining required field densities since implementing the Superpave mix design system? Read the entire page →
From page 29... ... Survey Results: Current Practices Regarding Lift Thicknesses 29 Figure 15. If the situation has improved, what changed? Read the entire page →
From page 30... ... 30 Impact of Asphalt Thickness on Pavement Quality three are experimenting. These other options include things like the use of material transfer devices, modified mix designs like Superpave 5 in Indiana and balanced mix design in Texas, segregation checks with a nuclear gauge, and minimum mix temperatures. Read the entire page →
From page 31... ... Survey Results: Current Practices Regarding Lift Thicknesses 31 unstable bases or first lifts, high gyration mixes, dry mixes, and some source-specific combinations of materials. There are many strategies that reportedly have been used to address some of the difficulties mentioned. Read the entire page →
From page 32... ... 32 Impact of Asphalt Thickness on Pavement Quality responses were increased permeability (23) , increased cracking (23) Read the entire page →
From page 33... ... Survey Results: Current Practices Regarding Lift Thicknesses 33 (21%) were unsure; this may be because they were not in the research divisions in their agencies or had not been around long enough to know about past research. Read the entire page →
From page 34... ... 34 Impact of Asphalt Thickness on Pavement Quality options, intelligent compaction, improved permeability tests, lightweight deflectometer testing, and ways to determine uniformity of compaction. Finally, respondents were given the opportunity to offer other comments. Read the entire page →
From page 35... ... Survey Results: Current Practices Regarding Lift Thicknesses 35 • New Brunswick routinely assesses workability using visual cues, like checking, cracking, pushing, and shoving, and they are experimenting with using mat temperature. Ontario is using a permeability test experimentally. Read the entire page →
From page 36... ... 36 Impact of Asphalt Thickness on Pavement Quality most often. In Appendix D, industry responses are identified by both all the states they work in as well as the most common one. Read the entire page →
From page 37... ... Survey Results: Current Practices Regarding Lift Thicknesses 37 About a third (20 or 34% as shown in Figure 27) of the industry representatives reported having difficulties attaining density when Superpave was first implemented but having an easier time now (Q4) Read the entire page →
From page 38... ... 38 Impact of Asphalt Thickness on Pavement Quality Most of the industry respondents (50 of 57, 88%, see Figure 30) report that they are able to use WMA technologies as compaction aids. Read the entire page →
From page 39... ... Survey Results: Current Practices Regarding Lift Thicknesses 39 When asked if they had encountered situations where they would request exceptions to the required lift thicknesses (Q7) , the contractors were pretty evenly split. Read the entire page →
From page 40... ... 40 Impact of Asphalt Thickness on Pavement Quality Figure 33. Have you encountered situations during project planning or construction where you have requested exceptions or waivers to the lift thickness requirements? Read the entire page →
From page 41... ... Survey Results: Current Practices Regarding Lift Thicknesses 41 roller patterns and types of rollers have been only marginally successful. Use of intelligent compaction and thermal imaging were seen as being not very successful. Read the entire page →
From page 42... ... 42 Impact of Asphalt Thickness on Pavement Quality • "I believe the performance issues in [my state] are related more to low/inadequate asphalt binder content (as allowed by the specifications) Read the entire page →
From page 43... ... Survey Results: Current Practices Regarding Lift Thicknesses 43 3.4 Analysis and Summary of Survey Findings As shown in the preceding sections of this chapter, there are similarities and differences between the agencies' and industry's awareness and perceptions of issues regarding lift thicknesses and the related issues of density and pavement performance. • Most states and provinces have policies and guidelines regarding allowable lift thicknesses. Read the entire page →

From page 23...

... 23 This chapter summarizes the results of the surveys of agencies and industry. As noted previously, a total of 45 state DOTs responded to the survey, a 90% response rate.