Analysis of the Behavior of Asphalts with and Without an Optical Measurement System in Cyclic Indirect Tensile Tests (CITT)

The aim of the investigations is to establish a non-destructive testing method for the condition of asphalt roads. For this purpose, a sensor system is inserted into the asphalt layers during construction. In the recent developments, Rayleigh scattering-based distributed optical-fiber sensors (DOFS) have been used increasingly for measurements at barely accessible locations, for which the base layer of a road is an example. This paper explores the feasibility of embedded distributed optical-fiber sensors in asphalt roads to record the fatigue behavior. To confirm the validity of the measurement results, extensive preliminary tests and comparative measurements are carried out. The cyclic indirect tensile test [CITT, in accordance with (FGSV, 2018)] has been used to determine the fatigue behavior of asphalt, where modified Marshall Specimen (MS) with integrated DOFS has been used. It is shown that the modifications have no influence on the fatigue behavior. The DOFS allows to measure with a high spatial resolution, where the conventional method only acquires one value per time step. The horizontal strain function of an undamaged MS in dependence of time and space in the CITT can be perfectly matched to a Gausian-sinusoidal-3D-fit, which subsequently can be applied to Young-modulus calculations. Obvious deviations from the fit could be used for crack detection in asphalt structures. Furthermore, it is discussed how the lab-scale results can be used for the implementation of DOFS in asphalt roads.