July 2008 Focus - Improving Pavement Performance with the Asphalt Mixture Performance Tester

Improving Pavement Performance with the Asphalt Mixture Performance Tester

A pooled-fund study launched this year by the Federal Highway Administration (FHWA) offers State transportation agencies the opportunity to obtain and learn how to use the new Asphalt Mixture Performance Tester (AMPT) to evaluate Superpave mixtures.

The widespread implementation of the Superpave mix design system over the past decade is one of the great success stories of the Strategic Highway Research Program (SHRP), with the majority of State transportation departments now using the Superpave performance grade (PG) binder and volumetric mix design process developed under SHRP. While the Superpave system was designed to also include prediction models and performance tests, these aspects of the system were not complete when SHRP implementation efforts concluded in 2000. Developed through two subsequent National Cooperative Highway Research Program (NCHRP) projects (NCHRP Projects 9-19 and 9-29), the AMPT now offers an improved method of predicting the performance of Superpave mixes, including the likelihood of rutting.

The Asphalt Mixture Performance Tester now offers an improved method of predicting the performance of Superpave mixes, including the likelihood of rutting.

The AMPT is a computer-controlled hydraulic testing machine that submits a compacted asphalt mixture specimen to cyclic loading that mimics traffic loading. The device then measures the deformation of the mixture to assess performance. Among the tests that can be performed are dynamic modulus, flow number, and flow time. “The AMPT can be used to identify inferior mixes and perform quality control, as well as in the structural design of flexible pavements,” says Audrey Copeland of FHWA’s Office of Pavement Technology. The AMPT can replace existing, less accurate test methods and models, offering potential time and cost savings, and can be used in a variety of climates and with different materials, without the need for extensive calibration. Its dynamic modulus test can also help provide the data input needed to use the new Mechanistic-Empirical Pavement Design Guide.

Figure 1. Photo. A close-up view of the Asphalt Mixture Performance Tester (AMPT). The AMPT can be used to evaluate Superpave mixtures.

The new Asphalt Mixture Performance Tester can be used to evaluate Superpave mixtures.

The 3-year pooled-fund study, “Implementation of the Asphalt Mixture Performance Tester (AMPT) for Superpave Validation,” (Study No. TPF-5(178)) has the following objectives:

Purchase and deliver the AMPT for highway agencies.
Provide training in using the AMPT to perform proposed American Association of State Highway and Transportation Officials standard practices for measuring dynamic modulus and flow number and developing dynamic modulus master curves.
Evaluate the nationwide implementation and use of the AMPT to assess performance over a wide range of climatic conditions, materials, and structures.

Three manufacturers currently produce the AMPT, with the average cost of the device ranging from $75,000 to almost $90,000 (including shipping, set up, and initial training). The pooled-fund study will provide the means to purchase the device for participants in bulk at a discounted price. Participating agencies are asked to contribute a minimum of $105,000 to the study ($35,000 a year for 3 years). In addition to the equipment purchase, the study will provide for:

Technical support.
Development of a National Highway Institute (NHI) course, “National Training Course for the Asphalt Mixture Performance Tester.”
Travel and course expenses for two representatives from each participating agency to attend the NHI course.
Implementation assistance.

The study may also sponsor additional testing of the AMPT. Agencies that would like to participate in the study without purchasing the equipment can join for a minimum contribution of $30,000 ($10,000 a year for 3 years).

Seventeen State departments of transportation have joined the study to date, with five additional agencies having expressed interest in participating.

Utah, Virginia, Florida, and Minnesota have already purchased the AMPT. The Utah Department of Transportation has five AMPTs and has been exploring the use of the technology for the past 2 years to understand more about how it can best use the equipment, as well as the limitations of the device. The Florida Department of Transportation (FDOT) plans to start using its AMPT after holding training sessions led by FHWA personnel in August 2008. “We believe it will be a useful tool, particularly as we implement the Mechanistic-Empirical Pavement Design Guide,” says Greg Sholar of FDOT. Florida, Utah, and Virginia have all committed to participating in the pooled-fund study.

For more information on the AMPT or to learn more about joining the pooled-fund study, contact Audrey Copeland at FHWA, 202-493-0341 (email: audrey.copeland@fhwa.dot.gov). Information on the pooled-fund study is also available at www.pooledfund.org (search under Study No. TPF-5(178)).

		July 2008
		FHWA-HRT-08-015