1,721,018 research outputs found
Caratterizzazione reologica del danneggiamento per fatica e dell'autoriparazione dei leganti bituminosi
No full textPerformance-Related Characterization of Bituminous Binders and Mixtures Containing Natural Asphalt
Full text linkNatural asphalt as an additive in bituminous mixtures was subjected to evaluation by means of performance-related laboratory tests carried out on materials sampled from a production plant and a test section. Compaction issues were discussed by referring to binder viscosity and by considering the volumetrics of laboratory-compacted specimens. Mixture stiffness was assessed by means of repeated load indirect tensile tests carried out on field cores and by constructing pseudo master curves. Models were employed for the quantification of effects associated to enhanced compaction and binder ageing. Fatigue was also investigated by means of indirect tensile test
VARIABLES INFLUENCING SPEED DISTRIBUTION ON URBAN ARTERIALS AND COLLECTORS
No full textSpeeds are affected by several variables such as driver characteristics, vehicle performance, road geometrics, environmental conditions and driving regulations. A knowledge of the relationship between speed and such variables allows conscious speed management on existing and planned roads, with the aim of constraining drivers to select a speed consistent with the posted speed limit. This relationship is of great interest to those who wish to achieve roadway functionality and improve overall safety. Focusing on this objective, some contributions concerning urban roads are already available in literature with the caveat that they can be applied only to specific road types and recently built-up areas. Moreover, they refer mainly to the 85th percentile of speed. Lastly, they can only be applied in locations which are homogeneous in terms of environment, driving regulations and vehicle type. The research aims to establish the correlation of roadway features to operating speed by elaborating panel-data models for the urban environment. The paper presents the results of an investigation carried out on Italian urban arterials and collectors within the municipality of Torino (Italy). The fact that this area is characterized by dissimilar geometric features facilitated the inclusion and study of a fully representative range of variables. Models were calibrated by combining the complete dataset and disaggregating it for the different road typologies. The results showed that, when consideration was given to all the selected variables, some variables were found to be ever present and statistically significant for all model
FIELD INVESTIGATION ON THE EFFECTS ON OPERATING SPEED CAUSED BY TRAPEZOIDAL HUMPS
No full textThe most effective way to reduce vehicle speed on urban low volume roads, such as residential streets, is the installation of traffic calming systems such as speed humps and tables. In those roads in which these measures are applied, a reduction in traffic volume and accidents is generally observed, with clear benefits for pedestrians, bicyclists and residents. A study was undertaken in order to investigate the effectiveness of trapezoidal speed humps in reducing the operating speed and to highlight the main factors influencing this type of traffic calming system. An urban residential street 1.8 km (1.12 miles) long, characterized by the presence of 12 humps, was monitored during two months (between October and December 2006) and several speed profiles were collected with different measuring systems. All data were processed in order to present a statistical discrete operating speed profile, making it possible to derive a model which links hump spacing, lane width and operating speed. Such a model can be a valuable tool for road engineers in predicting, for design purposes, the effectiveness of trapezoidal speed humps in similar situation
Rutting Behaviour of Wearing Course Mixtures in Severe Temperature and Loading Conditions
Full text linkFollowing the construction of a major motorway pavement in Northern Africa, relevant rutting phenomena were observed after opening to traffic. Preliminary investigations showed that permanent deformations were limited to the upper wearing course layer which was designed according to set requirements. In order to define the most appropriate rehabilitation strategy, investigations were carried out by focusing on the volumetric and mechanical properties of the employed wearing course mixture. Compaction properties were assessed by making use of a gyratory shear compactor and of a rubber-wheeled roller. Moreover, simulative wheel-tracking tests were carried out in severe temperature and loading conditions. Additional tests were performed on an alternative bituminous mixture containing polymer granules. Based on the obtained results the possible causes of the above described distress phenomena were identified and the use of the alternative bituminous mixture as a technical solution to adopt for rehabilitation was considere
Experimental Investigation on the Fatigue Damage Behaviour of Modified Bituminous Binders and Mastics
No full textWith respect to the minimization of fatigue cracking in flexible pavements, it is widely recognized that current SUPERPAVE specification criteria do not allow a reliable ranking of the fatigue resistance of bituminous binders. Thus, an alternative characterization procedure, based on the use of time sweep testing protocols and on the concept of Dissipated Energy Ratio (DER), has been proposed within NCHRP Project 9-10. However, the true significance of test results still needs to be thoroughly understood in order to define new acceptance and grading criteria. In this paper the Authors present the results obtained during an experimental investigation which addressed the issue of fatigue damage of modified binders and mastics. In particular, the objective of the study was to highlight, by means of time sweep tests, the effects on the fatigue behaviour caused by variations of the type and dosage of the polymer used as a chemical modifier. Moreover, the same kind of test was carried out on bituminous mastics in order to gain a better understanding of the role played by mineral filler in the fatigue performance of the binding matrix. In the analysis of test results, for a more complete description of the damage behaviour of the materials during cyclic loading, a new parameter, based on dissipated energy data, was introduced. Such a parameter, called Relative Crack Propagation Amplitude (RCPA), proved to be especially useful in highlighting the peculiar effects caused by the creation within the binder mass of an effective fatigue-resistant polymer network, in differentiating the consequences deriving from the use of different polymer types and dosages, and in comparing the performance of mastics with that of the corresponding binder
Rheological Characterization of Bituminous Binders Modified with Carbon Nanotubes
No full textThe study presented in this paper focused on the use of carbon nanotubes (CNT) in bituminous binders. By employing a single reference base bitumen and multiwall CNTs, several bitumen-CNT blends were prepared at various concentrations and were subjected to rheological characterization in different aging conditions. Results indicate that when CNTs are added with a sufficiently high percentage to base bitumen, they can significantly affect rheological properties. CNTs provide an enhancement of rutting resistance potential and of resistance to thermal cracking. Moreover, susceptibility to oxidative aging is reduced with further advantages that are expected in the long-term performance of bituminous mixture
Evaluation of self healing properties of bituminous binders taking into account steric hardening effects
Full text linkSteric hardening is a time-dependent phenomenon that can affect the healing properties of bituminous binders. In the experimental investigation reported in this paper, the rheological test method proposed for the evaluation of healing involved the use of a prolonged rest period included between two continuous oscillatory loading phases. A simple model was developed to subtract the contribution of steric hardening to the total stiffness gain attained during rest and thus to evaluate the recovery in mechanical properties due to self healing only. Analysis of the results indicated that cumulated damage of binders is composed by a reversible and a non reversible part. True self healing potential of the materials, as evaluated by means of the relative reversible damage index (RRD) and the relative index of fatigue life increase (RFIHEALING), was found to be a function of imposed damage, binder source and polymer modificatio
The effects of road geometrics and traffic regulations on driver-preferred speeds in northern Italy. An exploratory analysis
No full textSpeeds are affected by several variables such as driver characteristics, vehicle performance, road geometrics, environmental conditions and driving regulations. It is therefore important to study the relationships between speed and such variables in order to facilitate conscious speed management on existing and planned roads, and to induce drivers to select a speed consistent with the posted limit. This relationship is of great interest to those who wish to achieve roadway functionality and improve overall road safety. A small number of studies have focused on this objective; however, few of them concern urban roads and they are limited to specific road types and recently built-up areas. These studies often refer to the 85th percentile of the speed distribution and are relevant to locations which are homogeneous in terms of geometry, environment, driving regulations and vehicle type. This paper presents results obtained from a study carried out on urban arterials and collectors characterized by dissimilar geometric features which facilitated the inclusion of a fully representative range of variables. A general model able to predict operating speed for a generic percentile was calibrated using three different strategies: (a) a simple multiple regression analysis in which the variables were selected using the Bayesian Information Criterion (BIC); (b) the analysis of covariance method including random effects on the same set of variables as in (a); and, finally, (c) the analysis of covariance method with random effects and a new selection of variables (again using BIC). The analysis shows a dramatic variation in results depending on the method selected. In particular, when random effects are considered, almost all the variables are found to be statistically significan
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