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Heading: 1.2Re-compating HMA - Research Papers and Experience?
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Please tell me your experience and/or any research paper references about re-compacting HMA one or more days after initial lay-down. This would be for various state and interstate roadways.

I was told of a case where this was done and a 2% gain in density was seen. As I understand it, a nuclear density gauge was used in the same locations to verify the increase. I have a hard time believing that that much gain could be seen unless the density gauge was off or significant base problems occurred.

I guess there are two schools of thought for this practice. (1) It should not be allowed since the pavement could be damaged. (2) It should be allowed. No damage would occur and it would help long term performance by closing the air voids faster.

It would be hoped that if this were done, a pneumatic rubber tired roller (RTR) would be used. If used, what would be an average ESAL loading for that RTR? The web site below lists several RTR's. With so many ballists, tire widths and spacing, computing an average ESAL loading is difficult.

http://www.constructionequipment.com/article/CA6359275.html

My fear is that this practice could be detrimental to the performance of the roadway. More than the standard 18 kip loading may cause micro-fractures that would hurt the long term performance of the pavement.

Many DOT's have a requirement that compaction be obtained before the HMA cools to 175 to 180 degrees Fahrenheit. Of course the time for compaction with warm mix HMA’s would be extended. I am more concerned about standard HMA’s. Software programs like PaveCool give a limited time to obtain compaction. Additional compaction either has no effect or becomes detrimental and decreases density.

I know of one other state DOT that has allowed re-compacting HMA.

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Kenneth Ray Hobson, P.E.
QA Engineer
Oklahoma DOT


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Kenneth Hobson


Kenneth,

I experienced similar proposals on projects in India. There was a neglible improvement in degree of compaction and the the use of RTR resulted in loss of surface texture in the short term. Achieving the degree of compaction at time of placing is by far preferable to trying to achieve it by remedial rolling.

PG
Senior Materials Engineer
CBI
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Philip Gilburt
 
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