Felice Giuliani

Moisture Susceptibility and Stripping Resistance of Asphalt Mixtures Modified with Different Synthetic Waxes

Wax modification of asphalt binders represents an actual resource in warm-mix asphalt technology. Despite its benefits in reducing plant temperatures and atmospheric emissions, the presence of wax can be associated with side effects on the quality and durability of asphalt pavements. A simple procedure to evaluate the influence of wax on asphalt stripping resistance and moisture susceptibility is proposed. An unmodified asphalt binder was blended with waxes having different chemical structures (paraffinic and polyamidic); wax-modified asphalt mixtures were then prepared with various aggregate types. Moisture sensitivity was initially studied using conventional methods, such as indirect tensile strength measured after water conditioning. The stripping resistance of bitumen-coated aggregates was then quantitatively evaluated by identifying the stripped surface with a digital image analysis method. In contrast with expectations, results indicated that enhanced performances can be obtained in the presence of wax-modified asphalts. However, the type of wax was found to be decisive. In the same way, results of contact angle and adhesion measurements performed on bitumen–wax blends indicated that changes in asphalt–water affinity occur according to the type and content of wax.

In Plant Production of Hot Recycled Mixtures with High Reclaimed Asphalt Pavement Content: A Performance Evaluation

Nevertheless hot recycling process is nowadays a widespread technique, many doubts related to the in plant recycling process effects on the performance of recycled mixtures still exist and limit the maximum allowable amount of Reclaimed Asphalt Pavement (RAP). Therefore, the feasibility of an efficient production of plant hot recycled mixtures characterized by high RAP content and suitable performance should be properly addressed. To this aim, the overall performance of hot recycled asphalt mixtures produced in asphalt plant and containing high RAP content were assessed in this study. The mixtures were prepared with two different bitumens (high and low content of SBS polymer modifier) and 40 % of RAP only deriving from asphalt layers containing polymer modified bitumens. The aggregate grading curve was previously optimized through a specific laboratory study by applying the Bailey Method and using selected RAP. A third mixture, currently used for binder layers in motorway pavements, was also studied for comparative purposes. Compactability, stiffness, cracking and rutting resistance and fatigue behavior were investigated. Results of the mechanical tests suggest that mixtures containing 40 % RAP are suitable for the production of new asphalt pavements, especially when low modified bitumens are used. In fact, the performance of such mixtures were comparable or even higher than those of the reference mixture. In particular, the specific and accurate mix design allowed the potential drawbacks due to higher RAP content to be balanced.

Structural transitions and physical networks in wax-modified bitumens

This research focuses on the characterisation and evaluation of wax-modified bitumens for use in warm mix asphalt (WMA). Wax-modified bitumens were produced by addition of different types of wax to a 50/70 unmodified bitumen. Five different waxes were used, including synthetic hydrocarbons Fischer–Tropsch wax, Montan waxes and amidic-functionalised waxes. A basic structural picture of wax-modified bitumens was initially derived from the analysis of the thermal properties and morphological arrangements. The mechanical properties of the binders were then evaluated by rheometry, which indicated that bitumen modification with synthetic and functionalised waxes provides significant alteration in the overall colloidal structure. A comprehensive analysis of linear viscoelastic spectra depicted the existence of a sequence of structural transitions and relative behavioural processes, which deeply alter the behaviour of the original binder at in-service temperatures. All the rheological dynamics were interpreted in the light of the concept of residual crystallinity. The presence of physical networks generated by contiguous microcrystalline segments was finally hypothesised to explain the gel-like behaviour of the materials.

The odour fingerprint of bitumen

Bitumen is a very complex material with chemical composition and properties highly dependent on the crude oil source and refinery processes. Several analytical procedures were developed to understand the relationship between bitumen composition, microstructure and physical properties. Nevertheless, these techniques are expensive, time-consuming and involve significant drawbacks. Moreover, advanced research and industrial research have often different purposes and timing perspectives. Several bitumen operators require simpler and more suitable techniques for research and technology development, production and acceptance control and above all polymer modification. This necessity has led the authors to propose a new approach based on the artificial olfactory system (AOS), also known as electronic nose or e-nose. AOS is an instrument consisting of an array of partially selective sensors coupled to a suitable pattern-recognition system capable of recognising complex odours. The warm-up study highlighted the possibility of AOS to discriminate, already at room temperature without the need of sample pre-treatments, between bitumen produced with different origin crude oils and to verify the production stability in the same plant. Thus, these results indicate that the e-nose method may be used for quality assurance and quality control applications and for the fingerprinting of bitumen, showing a number of advantages over classical analytical instruments.

Chromatic and Rheological Characteristics of Clear Road Binders

Clear asphalt pavements provide specific functional characteristics to improve safety and climatic conditions in urban areas. The technological development of clear pavements refers to the formulation of special binders with particular chromatic characteristics. This research evaluated three clear binders with different chemical formulations with the aim of establishing the effectiveness of their mechanical properties and chromatic characteristics. Mechanical properties were analyzed by rheological methods. All clear binders were found to have specific dependence on stress levels, time, and temperatures. Different behaviors emerged, depending on the chemical origin of the binders. Chromatic characteristics were quantitatively evaluated by means of a digital image analysis. Red–green–blue as well as hue, saturation, and brightness models were used to determine and compare the chromatic performances of the three binders. The stability of the chromatic characteristics was also estimated with a laboratory aging process. Relationships were found between the chemical origin of the clear binder and its chromatic performance.

Kerosene-Resistant Asphalt Binders Based on Nonconventional Modification

The development of bituminous binders with an intrinsic fuel resistance is required to limit pavement damage and maintenance operations in those areas, such as airport systems and industrial areas and filling stations, where the risk of fuel spilling exists. This paper focuses on the study of the interactions between bitumen and fuel to attain a composition of modified binders with enhanced fuel resistance. Several different modifiers, including polymeric materials, recycled crumb rubber, and synthetic waxes, were added to a base bitumen. All blends were studied with special reference to their chemical composition and subjected to a solubility test consisting of a controlled immersion in kerosene (jet fuel A-1). The results were interpreted on the basis of the compositional characteristics which determine the interactions occurring between bitumen and modifiers. Among the formulations with enhanced fuel resistance, those based on synthetic waxes appeared to be the most interesting ones.

Advanced Characterization of Clear Chip Seals

Chip seals are widely used throughout the world for the construction and preventive maintenance of asphalt pavements because they are recognized as cost-effective solutions able to improve skid resistance while creating a waterproof surface. On the other hand, chip seals are often affected by early stone loss because of several, not always easily manageable, material-related and traffic-related factors. It is, therefore, in the interest of researchers to develop scientific methods able to predict the aggregate retention performance of chip seals. Given this background, in the present paper, a performance-based evaluation of chip seals with regard to aggregate retention properties is carried out through a laboratory test based on the Ancona shear testing research and analysis equipment. In this study, a chip seal prepared with a clear emulsion derived by emulsifying a synthetic clear binder was analyzed and compared with two traditional chip seals manufactured with a plain cationic bituminous emulsion and a styrene butadiene styrene polymer-modified asphalt emulsion, respectively. Specifically, six chip seals obtained by combining the three selected emulsions with two types of aggregates (crushed limestone and basalt) were tested at three different temperatures. Moreover, a rheological characterization of emulsion residues was also carried out through the dynamic shear rheometer and the binder bond strength adhesion tester. Results mainly showed that the investigated clear synthetic emulsion can be successfully used for the construction of clear chip seals in combination with aggregates of different mineralogy.

DEM modelling analysis of tree root growth in street pavements

The coexistence of urban green spaces and infrastructure is often difficult. Trees find inhospitable environments in urban areas, whereas tree root systems can damage sidewalk, street and parking lot. The main form of failure concerns the growing of tree roots beneath the pavements, which produce upheavals and displacements on wearing course. The main objective of this study was a distinct element method modelling analysis of the potential interactions between tree root systems and street pavements. This calculation code allowed us to simulate the dynamic behaviour of the ground-pavement system as result of the roots growth. The performed modelling, representative of various planting strategies commonly used in urban contexts, have highlighted the progressive reduction of deformations with the increase of the roots penetration depth. Such displacements were strongly influenced by other factors such as the porosity and the grain-size distribution of the soil and the type of pavement considered.

Street-Crossing Behavior of People with Disabilities

AbstractPhysical disability is as a multifaceted phenomenon, whose manifestations may be difficult to realize and properly address when designing or improving urban built environments. The mere application of technical requirements cannot account for designing accessible public spaces and infrastructures for pedestrian mobility. In this perspective, unsignalized crosswalks are emblematic. Design recommendations for them are prevalently focused on purely technical aspects, such as pedestrian walking speed and visibility problems. Apprehension and nervousness experienced by pedestrians when attempting to traverse the roadway is usually neglected, but this uneasinesses may weaken the autonomy and comfort of pedestrians with disabilities. Interaction with approaching drivers is a decisive factor. It is known that unimpaired pedestrians attempt hazardous crossings if they realize that drivers do not observe their right-of-way. The question arises of investigating street-crossing behavior of people with differe...

Model of Potential Crash Rates of Rural Roundabouts with Geometrical Features

In recent years, there has been a widespread diffusion of roundabout intersections in the Italian road network; their undoubted popularity is attributable not only to their proven performance in terms of safety but also to their guarantee of smooth traffic flow. However, safety-related requirements of geometric designs are occasionally placed in a subordinate position; therefore, the success achieved by some foreign experiences has not been reached in every area. A model of potential crash rates may indicate how to modify the geometry of intersections to ensure safety. With regard to this, an example model based on the conflict opportunity technique has been developed for estimating crash rates at rural roundabouts. The model appears to respond well to traffic conditions and the geometry of roundabouts. Development of the model and results are described and analyzed in this paper.