Antonio D’Andrea

Reliance of pavement texture characteristics on mix-design and compaction process

The surface texture in Hot Mix Asphalt (HMA) pavements has an important role respect to all functional performances: wet and dry friction, rolling noise generation, tire wear, and so on. The texture of a new pavement is a consequence of HMA composition (mix-design) and of construction techniques, especially considering the compaction process. While numerous studies have investigated the effect of mix design on texture, it is still unclear the effect of construction techniques. In this research, some experimental results coming from on-site investigations during the HMA construction, were processed, in order to determine the texture characteristics of pavement surfaces, in terms of mega, macro and micro-texture, using both volumetric and profilometric measures. Furthermore, the asphalt mix composition (grain size, void ratio, bulk density, percentage of bitumen, etc.) were assessed on pavement cores. Some statistical correlations between texture and asphalt mix composition were also carried out. The results confirm that the main influence on the pavement texture level is related to the aggregate maximum dimension, but also the void percentage has a significant influence. The compaction conditions, instead, seem to determine a lower effect, but nevertheless some observations can be deducted. More general, the presented research proposes some considerations, useful to improve the design of mixtures and the compaction techniques of HMA, especially in order to obtain a reduction of rolling noise generation.

Prediction of Fatigue Failure at Asphalt Concrete Layer Interface from Monotonic Testing

This study investigated the characterization of interface shear behavior in asphalt concrete through the estimation of the stress ratio (SR). This parameter, originally identified as the ratio between predicted interface stress from a finite element model (FEM) and interface shear strength at the corresponding normal stress, was assumed to be dynamic. As part of the experimental plan, monotonic tests on double-layered asphalt specimens were performed. Dynamic evaluations of the number of repetitions to failure under several stress conditions, equal to or higher than stresses computed from an FEM of the pavement structure, were also performed. The failure curves of the two testing modalities show similar patterns on the Mohr plane. The Hoek–Brown shear strength failure criterion and the three-dimensional surface that best fits the dynamic outcomes were considered. In this scenario, the SR referred to the proportion between the applied shear stress conditions in the dynamic modality and the maximum stress from monotonic tests. For the same predicted failure repetitions, SR assumed a constant value. Correlating monotonic and dynamic results could be an important approach both in furthering knowledge of interface shear strength and in predicting information about failure under repetitive loading applications based on simple monotonic tests.

Recycling Dredged Sludge in Asphalt Pavement

An experimental investigation of an innovative recycling method to reuse dredged sludge in asphalt pavements is presented. According to this method, semifinished products or agglomerates, made of dried sludge and bitumen, are produced. These products may be used to partially substitute fine sand and bitumen in the asphalt mix. In this paper, the practical aspects of the manufacture, storage, and transportation of these agglomerates are simulated in order to demonstrate the feasibility of the method. The technical properties of asphalt mixes prepared with these new products are compared to those of a reference asphalt mix, in terms of Marshall characteristics, stiffness, complex modulus, permanent deformation, and water sensibility. Environmental and economic issues are also analyzed. A simplified cost factor analysis shows that this method is economically advantageous compared to the disposal of contaminated sludge.

Investigation of Dilatancy Effects on Asphalt Interface Shear Strength

Dilatancy is described as the shear-induced volume change in granular materials. An inclined shear test was used in this study to measure dilatancy on double layer asphalt specimens, where, due to the configuration of the device, dilatancy cannot be inhibited. Under monotonic loading conditions, three angles of 30°–45°–60° between the specimen axle and the horizontal were considered, so as to set different ratios between normal and shear force. A guillotine shear test was used to compare allowed and inhibited dilatancy at different levels of applied normal stress. The dilatancy angle ψ and the dilatancy speed were introduced as useful parameters to characterize the phenomenon. The results proved that, by inhibiting dilatancy, the interface shear strength increases of a constant amount regardless of the applied normal pressure. Moreover, the comparison of the test outcomes between the two devices highlighted the non-contemporaneity between the dilatancy speed peak and the shear stress peak in the inclined shear test. It can be attributed to the fact that the volumetric expansion of the specimen is countered by the normal stress, which increases proportionally to the shear stress during the test.