Researchers Study the Effects of Increased Asphalt Pavement Density

Featured in Technology Today (Volume 34, Issue 3), a quarterly publication of the Louisiana Transportation Research Center.

In-place density is essential to measuring the durability and long-term performance of asphalt pavement. If pavement doesn’t have satisfactory in-place density, the effectiveness of the pavement can be reduced. This may lead to shortened service-life, including reduction in fatigue performance and rut resistance. Researchers Louay Mohammad, Ph.D., P.E., and Moses Akentuna, Ph.D., P.E., explored how to prevent such negative effects by testing the initial increase of in-place density during pavement design and construction. This is reflected in their report, “Demonstration Project for Enhanced Durability of Asphalt Pavements through Increased In-Place Pavement Density.”

“There have been significant advancements in technology and techniques for pavement design and construction. These advancements have the potential to increase asphalt pavement density and improve both durability and cost-effectiveness,” explained Dr. Mohammad. “Many of these advancements are already being employed; however, in many instances, standards for in-place density have remained unchanged.”

Using already-adopted practices, researchers sought to identify a cost-effective, safe method for increasing in-place density of asphalt pavements by partnering with FHWA in a demonstration project conducted in Louisiana. The project took place on Route US 190 near the city of Walker in Livingston Parish.

Dr. Mohammad said, “The rehabilitation project consisted of milling off approximately 4-in. of existing asphalt pavement and replacing it with a 2-in. Level 2 binder course mixture followed by a 2-in. Level 2 wearing course mixture meeting the '2016 DOTD Standard Specifications for Roads and Bridges.'”

Two approaches for increasing in-place density were explored: (1) the addition of an Evotherm warm mix asphalt (WMA) additive at a dosage rate of 0.6% by the weight of mix, and (2) the addition of 0.2% asphalt binder (Plus AC) to the design optimum asphalt binder content of standard dense-graded mixtures. The field component of the research involved three 4,000-ft. long test sections representing control hot-mix asphalt mixtures (HMA), Evotherm WMA mixtures, and the Plus AC HMA mixtures. Each test section included a binder and wearing course for a total of six mixtures. Test sections were constructed to meet current requirements for in-place density (control) as well as a test section that had a 1.5 percent in-place density increase (WMA, Plus AC).

After this, an array of tests, such as the Hamburg loaded wheel tracking and semi-circular bending tests, were used to accurately gauge performance and density measurements.

Results showed the two techniques to improve in-place density were successful, and other observations were noted as well—one being that the two approaches for increasing in-place density also resulted in better expected resistance to cracking and rutting.

As a result, researchers recommend that DOTD adopt these two technologies (Evotherm WMA and Plus AC HMA) in order to improve in-place density of asphalt pavements in Louisiana. They also recommended long-term monitoring of the pavement test sections to further validate increased in-place density. Researchers anticipate the results from this study will be used as guidance for DOTD in updating current density requirements for asphalt pavements. This study may also be used by the FHWA to provide guidance for improving asphalt pavement durability at a minimal cost.

Learn more

To learn more, you can read Final Report 628 or Technical Summary 628 in full or contact Dr. Mohammad at (225) 767-9126 or louaym@lsu.edu.


Photo by Alex Woods on Unsplash