A Manual for Design of Hot-Mix Asphalt with Commentary (2011) / Chapter Skim
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Pages 91-100
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From page 91... ...
The structural HMA layers are usually referred to as surface, intermediate, and base courses depending on their location in the pavement structure. The intermediate course is sometimes called the binder course.
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From page 92... ...
Prior to constructing the overlay, areas of the pavement that exhibit alligator or fatigue cracking must be repaired to full depth because the base of the existing pavement remains the primary load-carrying element in the flexible pavement after construction 92 A Manual for Design of Hot Mix Asphalt with Commentary HMA wearing course HMA intermediate course crushed aggregate base prepared subgrade HMA wearing course HMA intermediate course crushed aggregate subbase prepared subgrade HMA base course HMA wearing course HMA intermediate course prepared subgrade HMA base course HMA wearing course HMA leveling course crushed aggregate subbase prepared subgrade PCC (a) Conventional HMA Pavement (b)
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From page 93... ...
Alternatively, as shown in Figure 7-2c, the PCC slab may be broken or rubblized to control reflective cracking. In this case much thicker HMA layers are placed over Selection of Asphalt Concrete Mix Type 93 full-depth repair HMA overlay HMA leveling course existing HMA pavement subgrade crushed aggregate subbase joint repair HMA overlay HMA leveling course existing PCC pavement subgrade crushed aggregate subbase HMA overlay HMA leveling course Rubblized PCC base subgrade crushed aggregate subbase (a)
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From page 94... ...
Smaller nominal maximum aggregate size mixtures can be placed in thinner layers, have higher binder contents, and, when compacted to the same in-place air void content, have lower permeability than larger nominal maximum aggregate size mixtures. Surface courses contain highly angular aggregates and an appropriate performance-graded binder to resist traffic and environmental forces.
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From page 95... ...
Since intermediate courses are close to the surface of the pavement, they must be resistant to rutting. However, they can be constructed with mixtures having lower binder contents than surface courses because the intermediate course is not directly subjected to traffic loading or the damaging effects caused by water and oxidative hardening of asphalt binder.
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From page 96... ...
The use of dense-graded mixtures with higher effective binder content should be considered for base courses in perpetual pavements. One of the structural 96 A Manual for Design of Hot Mix Asphalt with Commentary Traffic Level, ESAL Description < 300,000 Applications include roadways with very light traffic volumes such as local roads, county roads, and city streets where truck traffic is prohibited or at a very minimal level.
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From page 97... ...
The effective binder content of GGHMA mixtures is very high due to the gap-graded structure of these mixtures. OGFC mixtures typically incorporate modified binders and fibers to increase the binder content of these mixtures and improve their durability.
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From page 98... ...
98 A Manual for Design of Hot Mix Asphalt with Commentary Mixture Type Minimum Ratio of Lift Thickness to Nominal Maximum Aggregate Size Maximum Ratio of Lift Thickness to Nominal Maximum Aggregate Size Fine, Dense-Graded 3.0 5.0 Coarse, Dense-Graded 4.0 5.0 GGHMA 4.0 5.0 Table 7-2. Recommended lift thicknesses as given in NCHRP Report 531.
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From page 99... ...
OGFC is a gap-graded mixture with a high air void content. The high air void content and open structure of the mixture provides macrotexture and high permeability to drain water from the tire-pavement interface.
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From page 100... ...
(2004) NCHRP Report 531: Relationship of Air Voids, Lift Thickness, and Permeability in Hot-Mix Asphalt Pavements, TRB, National Research Council, Washington, DC, 48 pp.
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