Experimental and theoretical investigation on road pavements and materials through ground-penetrating radar

Abstract

Ground-penetrating radar (GPR) is being increasingly used over the last years in a wide range of applications, due to its flexibility and high potential to provide characterization and imaging of structures and materials. Overall, several reasons are contributing to increase the demand for the use of this tool and non-destructive testing techniques (NDTs) in general. Amongst all, it is worth citing technological advances of both hardware and software elements, an intrinsic lower significance of measurements provided by traditional monitoring techniques along with their greater invasiveness in measuring processes and, last but not least, the impacts of Global Economic Crisis on the use of economic resources affecting for years countries worldwide. The combination of such factors has led the interest of several skill profiles spanning from researchers, practitioners and end-users in general, and focused the attention of governments and local authorities on the high capabilities to gather a large amount of information in a relatively short time of surveying. In the field of pavement engineering, GPR has been used since the early 1980s mostly focusing on the geometrical characterization of road structure, by evaluating layer thicknesses. Minor care has been given to the analysis of the main causes of damage and performance properties of pavements, in order to improve management of infrastructural asset through effective and efficient maintenance and rehabilitation actions, as well as to provide best conditions in design of new roads. In that regard, this thesis is aimed to give a useful contribution also in the perspective of road safety issues by improving current processes of management and maintenance of road asset, along with the design of new roads, and provide effective support for the application and practical use of the tools described. Efforts have been spent in order to detect and quantify those physical and strength characteristics of road materials and subgrade soils that are relevant causes of damage, such that an effective planning of supporting actions for maintenance, rehabilitation and design of new roads may be timely performed. Three main topics are addressed, namely: i) the evaluation of moisture spatial field in subgrade soils through a self-consistent frequency-based technique and the analysis of radar support scale in small-scale measurements of water content; ii) the potential to detect and quantify clay content in load-bearing layers and subgrade soils through different GPR tools and signal processing techniques, and iii) the possibility to infer strength and deformation characteristics of both bound, unbound pavement structures, and subgrade soils from their electric properties. The results are encouraging for applications in the field of pavement engineering.