Evaluation of HMA Lift Thickness
Record Type: DOT
Proper compaction of hot mix asphalt (HMA) mixtures is vital to ensuring that a stable and durable pavement is constructed. There are many factors that can affect the compaction of HMA. One of these factors is lift thickness. Previous work by the Florida DOT and the National Center of Asphalt Technology showed that for a given compactive effort, an increase in lift thickness results in an increase in compacted density.
MDOT’s current lift thickness requirements for a single lift of HMA is based on nominal maximum aggregate size (NMAS), with maximum lift thickness limited to generally 4 times the NMAS. Most current gravel sources in Mississippi are producing particle sizes that are in the range of 1 ½ to 2 inches. Once crushed to provide the needed particle angularity for HMA, most of the aggregate particles are less than ½ inch in diameter. This means that the most rut resistant mixes (mixtures containing the most angular aggregates) have a relatively small NMAS. Under the current Mississippi aggregate requirements, the highest quality HMA mix used in Mississippi, a 9.5 mm NMAS, can not be used in 2 inch mill and fill overlay projects, and a high quality 12.5 mm NMAS mix cannot be utilized in a 2 ½ or 3 inch upper binder layer.
The proposed research evaluates the use of 9.5 mm NMAS aggregate HMA in a 2-inch maximum lift thickness and a 12.5 mm NMAS aggregate HMA in a 3-inch maximum lift thickness in a total of 12 field projects. For each of these projects the compaction process will be monitored for roller types and pavement temperature and pavement density between roller passes. The collected data will be used to estimate the relative ability to compact the lift and provide information on whether the thicker lifts result in better density using a typical compactive effort. Uniformity of compaction throughout the depth of the compacted layer and the permeability of the layer will also be addressed. Based upon the research findings, MDOT would be provided with the requisite information to modify the current allowable lift thickness for HMA.
Start date: 2006/10/1
End date: 2008/9/30
Status: Active
Contract/Grant Number: State Study No. 193
Total Dollars: 80000
Source Organization: Mississippi Department of Transportation
Date Added: 10/11/2006
Index Terms: Hot mix paving mixtures, Asphalt mixtures, Durability, Stability (Mechanics), Pavements, Thickness, Aggregates by shape and surface texture, Compaction, Research projects,
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Mississippi Department of Transportation
http://www.mdot.state.ms.us/
P.O. Box 1850, 500 North West Street
Jackson, MS 39215-1850
USA
Federal Highway Administration
http://www.fhwa.dot.gov/
1200 New Jersey Avenue, SE
Washington, DC 20590
USA
Phone: (202) 366-4000
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Battey, Randy L.
Phone: (601) 359-7650
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