FHWA Highways For LIFE Technology Partnerships Program

Intelligent Asphalt Compaction Analyzer October 01, 2007 – September 30, 2009

Haskell Lemon Construction CompanyP.O. Box 75608, Oklahoma City,  OK 73147BLemon@haskelllemon.com(405) 947-6069

University of OklahomaNorman, OK

Volvo Road MachineryShippensburg, PA

EST Inc.,Norman, OK

University of OklahomaIntelligent Asphalt Compaction Analyzer (IACA)

The IACA display (above right) provides real-time information on the density and the mat temperature to the roller operator at each location on the pavement during each roller pass.

The Intelligent Asphalt Compaction Analyzer is a roller-mounted device that continuously senses the vibrations of the compactor and estimates the level of compaction (density) achieved during the construction of an asphalt pavement.

Principle of Operation of the IACA

• During the compaction of an asphalt pavement, the vibrations of the compactor depend not only on the rotation of the eccentric weights in the drum, but also on the stiffness of the asphalt mat being compacted. The density of the asphalt mat is related to its stiffness and is commonly used as an indicator of the level of compaction.

• The IACA is based on a novel Neural-Network based technology that can classify the vibrations of the roller during compaction into classes corresponding to different density levels for a given mix type and construction parameters (base/intermediate/ surface course, 2/3/4 inch lift, full depth construction or overlay, etc).

• The IACA is first trained using vibrations observed at different levels of compaction. During operation, the IACA observes the vibrations and estimates the corresponding density of the mat.

Comparison of IACA and Conventional QA Methods

• Point-wise density measurements using a nuclear or a non-nuclear density gauge. Typically, 3-5 readings are taken per lane mile of the pavement.

• Detailed density measurements can only be taken after the mat has cooled down.

• Measurements using a nuclear gauge require about 5 minutes for each reading. Non-nuclear gauges are easily affected by the amount of moisture on the pavement.

• Cannot detect site preparation issues or problems in the underlying subgrade.

• Density is estimated continuously over the entire pavement. The measurements have been shown to be of accuracy better than those obtained using conventional tools.

• Density estimates are available in real-time during each roller pass.

• The functioning of the IACA is unaffected by ambient moisture. Density estimates are instantaneous.

• IACA can be used to detect variations / failure in the subgrade. Addressing the problems in the subgrade can minimize the early degradation of pavements due to poor site preparation.

Conventional IACA

IACA ‘As-Built’ Density Map

• Density information from the final pass of the roller can be used to compile the final density of the entire pavement. The color coded map ( 90%, 92%, 94%,) portrays the uniformity of compaction that was achieved.

• Areas in green (in the figure above) indicate inadequate compaction or uncompacted areas resulting from relief features on the pavement surface (concrete manhole covers, in this case).

• Uneven compaction can be investigated to determine the cause. In this case, soft subgrade had resulted in uneven compaction on the North Lane.

N

Conclusions

• Intelligent compaction techniques provide

•continuous monitoring of the compaction process

•can help prevent under/over compaction of the pavements

•instantaneous and complete evaluation of the pavement being compacted

•tools to identify problems in the subgrade before they manifest themselves

in the pavement.

• Intelligent Compaction can help improve efficiency of the construction crew and improve productivity through the reduction in labor and fuel costs, and in the number of conventional spot tests.

• The IACA technology demonstrates the possibility of retrofitting existing rollers for real-time monitoring of compaction quality.