Impact of Asphalt Thickness on Pavement Quality (2019) / Chapter Skim
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6 This chapter summarizes the findings of the literature review regarding lift thickness, mix type and size, and pavement performance. It opens with a discussion of the basics of asphalt mix compaction and the factors that influence the level of compaction.
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Literature Review: Effects of Lift Thickness on Pavement Performance 7 (Williams et al., 2015)
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8 Impact of Asphalt Thickness on Pavement Quality Technology (NCAT) Test Track, they found that it took more energy (ACP)
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Literature Review: Effects of Lift Thickness on Pavement Performance 9 The main product of the asphalt research program under SHRP was a new mix design system dubbed Superpave, for SUperior PERforming asphalt PAVEments. Superpave included • A new binder specification and tests, now known as performance grade (PG)
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10 Impact of Asphalt Thickness on Pavement Quality national specifications in the early 2000s, as shown in Figure 3, though some states continued to specify it. The RZ had also been used to differentiate between fine and coarse mixes.
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Literature Review: Effects of Lift Thickness on Pavement Performance 11 As shown later in this chapter, compaction difficulties were often encountered with coarse graded Superpave mixtures. Some states that had required coarse graded mixes, such as Florida (see Chapter 4)
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12 Impact of Asphalt Thickness on Pavement Quality fine graded 9.5-mm mix was compacted to 96.5% of laboratory density at the optimum t/NMAS ratio of 4.6:1 but the density was only 94.3% when the ratio was 2:1. For coarse gradations the impact was even greater -- a decrease of 4.8% (Brown et al., 2005)
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Literature Review: Effects of Lift Thickness on Pavement Performance 13 aggregates were being crushed; no significant crushing was observed in any of the mixes tested. Laboratory results indicated lift thickness ratios should be between 4 and 6 times the NMAS.
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14 Impact of Asphalt Thickness on Pavement Quality overall air void content is not sufficient to predict whether a pavement will exhibit excessive permeability. For example, Vardanega (2014)
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Literature Review: Effects of Lift Thickness on Pavement Performance 15 (or porosity)
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16 Impact of Asphalt Thickness on Pavement Quality Concerns about the coarse gradations of early Superpave mixes prompted the Colorado DOT to explore the possibility of using an air permeameter developed by Marquette University to test the in-place permeability of asphalt pavements to identify those that may develop performance problems related to high permeability (Retzer, 2008)
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Figure 4. Method for selecting critical in-place air voids and field permeability (Cooley et al., 2001)
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18 Impact of Asphalt Thickness on Pavement Quality Florida is another state where significant differences between nuclear and core densities were noticed (NAPA, 1999, Musselman et al., 1998)
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Literature Review: Effects of Lift Thickness on Pavement Performance 19 Lifts thinner than 1.5 in. should be avoided because of a tendency to cool too quickly.
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20 Impact of Asphalt Thickness on Pavement Quality benefits as well. Possible means of reducing costs have also been reported, though not in quantified dollars and cents.
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Literature Review: Effects of Lift Thickness on Pavement Performance 21 angular aggregates, and no use of reclaimed materials. In terms of material costs, they are quite expensive, but since they are placed at about half the lift thickness, they are considered competitive and may even be up to 30% less expensive in initial costs.
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22 Impact of Asphalt Thickness on Pavement Quality Failure to achieve adequate density, which can be caused by insufficient lift thickness, can cause rutting under traffic, increased cracking, moisture damage, and more. Excessive permeability allows air and water to enter the pavement, accelerating binder oxidation (embrittlement)
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