Traditionally, pavement engineers around the world, and mainly in the United States, design flexible and rigid pavements based on the American Association of State Highway and Transportation Officials (AASHTO) method. This methodology was developed in the late 1950s in Ottawa, Illinois, under what was called then the AASHO Road Tests. The AASHO Road tests are considered by many road engineers to be one of the first references of experimental data that takes into consideration the interaction between the vehicle and the road in the design of the pavement, and aid in determining how traffic influences the deterioration of roadways. For this reason, the AASHO Road Tests can be considered as one of the very first accelerated pavement testing (APT) facilities.
With the help of the AASHO Road tests from the 1950s, the performance of the pavement structures of known thickness under moving loads of known magnitude and frequency was observed, and the results obtained were the source to develop the pavement design guides that pavement engineers use to design flexible and rigid pavement structures. The first version of what is known today as the AASHTO Pavement Design guide was published in 1961, with major updates issued in 1972 and 1993. In 1998, a supplement to the 1993 guide was published and its use continues nowadays in the United States and around the world.
One of the shortcomings of these conventional pavement design guides is that they are based on empirical relationships derived from observations of loading and distresses, experience, and field tests on pavements with local materials and weather. New methodologies have been developed since the early 2000s based on mechanistic-empirical principles. This methodology consists of combining the observed performance from the empirical methods with the measured physical and mechanical characteristics of the used materials under local traffic load and weather.
The initial development of the Mechanistic-Empirical Pavement Design Guide (MEPDG) used data collected under the Long-Term Pavement Performance (LTPP) program. LTPP is a collaborative research project develop by the Federal Highway Administration (FHWA) and AASHTO with the objective of collecting and analyzing pavement data from the United States and Canada. The data collected on the LTPP program provides an important tool in pavement design because it uses pavement mechanistic response parameters, such as stress, strain, or deflection, to estimate pavement damage.
Today, data collected at accelerated pavement testing (APT) research facilities from testing equipment and instrumentation plus traffic counts and local weather aid engineers in analyzing temperature, moisture, dynamic strain data, freeze and thaw, and frost depth behavior as they relate to pavement design and performance. The analyzed data, together with observations made by experience engineers, scientists, and technicians, is the basis for continuing the development of the Mechanistic-Empirical Design Guides (MEPDG).
The MEPDG pavement design methodology is considered a step forward in pavement design because it allows pavement engineers to optimize pavement designs based on engineering mechanics and validate it with extensive road test performance data. This has an impact on the end user as it can translate to more cost-effective and reliable pavement designs with lower initial and life cycle costs to state agencies.
About the Author:
Dr. Emil G. Bautista, PE is a Civil Engineer with over 10 years of experience in research construction materials with a special interest dealing with highways design and construction and the use of sustainable materials such as Recycled Asphalt Pavement (RAP) and Coal Combustion Products (CCP) in pavement structures. He is currently working as one of MnROAD Project Engineers for the Department of Transportation of Minnesota (MnDOT). He is responsible for working on contracted research with major pavement research partnerships that MnDOT is leading or participating in. These research efforts include many research partners national, regional, and Minnesota research efforts going on in MnDOT’s Road Research Section at the Maplewood Lab. These partnerships include the current National Road Research Alliance (NRRA), National Center of Asphalt Technologies (NCAT), Minnesota DOT, and the Minnesota Local Road Research Board (LRRB) and new partnerships in the future. He provides support to research contracts with NCAT related to asphalt mix and pavement preservation and takes an active role in the leadership and support of these initiatives. He also provides an expert level of knowledge on concrete/asphalt mixtures, performance testing, construction, and pavement performance as it relates to the research efforts going on with each partnership that typically relates to the MnROAD research facility and assist in the review of MnROAD database, providing input on future development and implementation of data quality checks to insure the data being shared with research partners is of the research quality expected from the MnROAD facility.
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Anthony Fasano, P.E.
Engineering Management Institute
Author of Engineer Your Own Success