Integration of NDT data for the development of in-situ asphalt dynamic modulus master curve

In recent years, a growing trend has emerged towards sustainable pavement infrastructure. Six key pavement life-cycle phases are considered for sustainability best practices: materials, production, design, construction, use, preservation / maintenance / rehabilitation, end of life. As much of the road network is completed, road authorities are focused on ensuring and/or extending the original intended life of the pavements through maintenance or rehabilitation measures. Pavement preservation is inherently a sustainable activity. It often employs low-cost, low-environmental- impact treatments to prolong the life of the pavement by delaying major rehabilitation activities. However, any form of pavement treatment should be done at an early stage of deterioration and should be limited to the asphalt layers. In this way, pavement life will be continuously extended, which is the desired outcome since pavements, as an integral part of the transportation network, function virtually forever (long-life pavements). Therefore, it is important to timely assess the structural condition of the pavement so that road authorities can plan and implement proactive strategies.

The structural condition depends on the structural properties of the pavement and the mechanical properties of the mixtures of the layers. In flexible pavements, the asphalt layers are the most important structural element of the pavement, as they are in direct contact with traffic loads and play the most important role in transmitting stresses to the underlying layers and especially to the subgrade. For this reason, the mechanical properties of the asphalt mix and, in particular, the stiffness modulus are an important factor that determines to a large extent not only the performance of the asphalt layers but also of the pavement. On this basis, the viscoelastic behavior of the asphalt mix can be described by the master curve of the dynamic modulus (E*).

The Mechanistic-Empirical Pavement Design Guide (MEPDG) proposes a practical method that involves the development of an E* master curve that is reliable for field conditions and is based on field Non-Destructive Testing (NDT) data and an algorithm for estimating E*. The present work deals with the implementation of the methodology developed within the MEPDG for the determination of the E* field master curve. The objective is to evaluate the individual steps, to identify possible weaknesses and to make suggestions on how to overcome them, and finally to make a statement on the accuracy of the methodology in terms of performance characteristics (fatigue cracking and rutting in the asphalt layer). For this purpose, an experimental study was conducted, which included two stages: (1) in-situ acquisition of FWD and GPR data and coring, (2) laboratory testing of the cores taken. The performance indices for fatigue cracking and rutting were used for validation. The results show that, under certain conditions, the methodology is sound and can provide accurate results for the E* field. As such, in the frame of preventive maintenance, the accurate assessment of the structural condition of in-service pavements provides road authorities the ability of planning the necessary activities to improve the structural condition at the right time before its rapid deterioration.