NON-CONTACT SENSOR FOR THE REAL-TIME MEASUREMENT OF STIFFNESS OF ASPHALT PAVEMENTS DURING COMPACTION

Abstract

The development of a non-contact sensor capable of determining the quality of asphalt pavements during their construction is addressed in this dissertation. Adequate compaction of asphalt pavement during its construction is necessary for the proper functioning of the pavement over its design life. Rutting, cracking, pot holes and other forms of distress in asphalt pavements can be attributed partly to improper compaction during the construction process. While the mechanism of pavement failure is well understood, there are no widely accepted tools that can determine the quality of the entire pavement during its construction. Furthermore, quality control and acceptance criteria require the extraction of roadway cores from the finished pavement. Such tests are destructive in nature and also contribute to the early deterioration of the pavements. The complexity of the compaction process and the limitations of the spot tests have led researchers to develop advanced compaction technologies, such as Intelligent Compaction (IC).

Intelligent Compaction is an emerging area of research that attempts to extend mechanistic-empirical design principles to the compaction of bound and unbound aggregate materials and soil subgrades. Intelligent Compaction is based on the hypothesis that the vibratory compactor and the underlying pavement layers form a coupled system whose response characteristics are influenced by the changing properties of the pavement material. IC techniques estimate the stiffness of the pavement layer by observing the vibratory response of the roller during compaction. One of the limitations of IC technologies is that the measurement values reported by these devices cannot be easily verified through in-situ measurements of density or dynamic modulus. The lack of established theoretical foundations has also limited the widespread acceptance of these technologies.

In this dissertation, the problem of ensuring adequate compaction of asphalt pavement during construction is addressed through the development of a mathematical model that can replicate the compaction process in the field. The asphalt pavement is first modeled as a Visco-Elastic-Plastic (VEP) material and the equations governing the motion of the coupled system comprised of the vibratory compactor and the asphalt mat are developed. The parameters of the model are shown to depend on the properties of the asphalt mix, as well as the type of vibratory compactor. Numerical simulations show that this model can not only capture the effects of static rolling, but can also accurately predict the effects of vibratory compaction. The VEP model can also account for the effect of asphalt mat thickness and temperature on the quality of compaction. The simulation results along with the data recorded during the construction of asphalt pavements are used to validate the hypothesis of Intelligent Compaction.

The theoretical results of this dissertation are central to the development of verifiable Intelligent Compaction technology. The Intelligent Asphalt Compaction Analyzer (IACA) prototype that was developed during the course of this dissertation is the first step in this direction. This prototype was successfully tested on several types of dual drum vibratory compactors such as IR DD110, IR DD118, IR DD132, and IR DD138HF, manufactured by Volvo Construction Equipment Company, Shippensburg, Pennsylvania (formerly Ingersoll Rand). The field evaluation of the IACA was carried out at six different construction sites between June 2009 and April 2010. These results conclusively show that the IACA can not only be used for effective quality control during the construction of asphalt pavements but can also serve as a non-destructive quality assurance tool.

It is anticipated that the research carried out in this dissertation will pave the way towards closed-loop control of vibratory compactors for intelligent compaction of aggregate materials and soil subgrades. Improving the quality and consistency of pavements during their construction will increase the life span of the roads, reduce the cost of their maintenance, and reduce the impact of road construction and traffic on the environment.