Abstract
Ground Penetrating Radar (GPR) technique is commonly used in the nondestructive evaluation of pavement structures. In particular, this method is used to estimate thicknesses of pavement layers as well as it can be utilized in advanced studies of pavement structures. The device presented in this paper comprise the high frequency impulse antennas that allow for investigating the interlayer zones in terms of their electromagnetic properties (e.g. dielectric constant). In some cases these electromagnetic responses can be suitable in the assessment of layer bonding in the pavement structure. This paper discusses the assessment of the quality of asphalt pavement interlayer bonding with the use of high frequency GPR techniques. The preliminary laboratory measurements were performed using an impulse antenna in the zero-offset configuration combined with the large-scale models simulating an idealized horizontal delamination. These measurements allowed to estimate the antenna sensitivity to detect interlayer connection under dry and wet conditions. Analysis of collected results led to formulating practical conclusions regarding critical limitations of the measuring system and adequate methods of signal processing and interpretation. The field investigations consisted of the GPR measurements along selected road sections and collection of the core samples at the locations associated with the specific reflexes. Inspection of the cores provided some real insights into the structure of different delaminations associated with characteristic reflexes. Analysis showed the reflection properties are able to expresses some important features of the interlayer zone, such as delaminations, presence of alien material at the interface, insufficient compaction occurring at the base of layer, and water penetration.
Highlights
The bonding of asphalt layers is a significant factor that directly influences the strength and durability of pavement structures
He states that cracks in asphalt pavement occur because of insufficient bonding of asphalt layers and reports that an optimal bonding is necessary in order to obtain a sufficient asphalt pavement strength to prevent rutting
Raposeiras [7] have determined that the deformation of asphalt pavement layers increases significantly if the layer bonding decreases from 100% to 90%, which results in a premature deterioration of asphalt pavement
Summary
The bonding of asphalt layers is a significant factor that directly influences the strength and durability of pavement structures. According to the authors' opinion the following causes and phenomena, simultaneously present in the studied section of pavement are responsible for the lack of connection between the layers: - insufficient compaction of upper layers; adverse weather conditions (wind and low temperature) during the laying of asphalt concrete in the base layers (dual layer) and the bonding layer, causing premature increase in viscosity of asphalt in the mix and hindrance to compaction; increased number of voids at the bottom of the layer (strong porosity of the floor of the top layer near the contact) - no effect of interlock of contacting layers due to inefficient compaction of upper layer, - the segregation of the mixture in the upper layer; reduction of the contact area of layers due to the presence of clusters of coarse aggregate particles at the bottom of the top layer, - lack of or inadequate spraying of the interlayer surface, the lack of bonding between layers, - increasing insufficiency of bond or an increase of the area of lack of bond between the layers resulting from the presence of water penetrating through micro fissures, insufficient compaction of the bottom layers, leaky longitudinal and transverse joints; intensified penetration of water due to interruption of the watercourse in the surrounding area, - dirt in the interlayer space, failure to clean layers during the incorporation of successive layers The knowledge about these phenomena is very useful in explaining presence of strong, specific reflections on the recorded echograms. Possibility of water penetration, presence of foreign material at the interlayer connection, porous base of the layer and change of particle size at the boundary have crucial importance in interpretation of the type, sign and amplitude of the resulting reflections
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