1,720,993 research outputs found
A New Step Towards Performance Based Specifications for Asphalt Pavements
No full textTechnical specifications of many Agencies are quickly moving from prescriptive to performance based, that requires field compliance tests of the constructed pavement, such as in situ pavement stiffness measurements by the Falling-Weight Deflectometer (FWD). This creates a number of issues for material suppliers, constructors, consultants, designers and end users who are now required to rely on data produced from such devices for design and compliance checks in the field. Whilst there is wide experience on the use of such devices, issues remain such as optimisation of test methodology, data interpretation and use, comparison between laboratory and in situ measured moduli.
The aim of this work is to define a data interpretation procedure and a framework for the analysis of results obtained by using such device to ensure high quality data and decision making, particularly for their role in performance based specifications. In a previous work, a particular testing and data interpretation procedure have been proposed in order to evaluate strains in pavement layers directly from FWD deflections and pavement layer thickness; here the values of elastic modulus back-calculated in the previous work are compared with those of resilient modulus MR evaluated by laboratory tests carried out on cores taken from pavement.
Stiffness Master Curves (SMC) have been developed by using the resilient modulus data determined at various test temperatures and loading frequencies, and they have been used for shifting data to the in-situ asphalt pavement conditions. The frequency spectrum of FWD load has been calculated in order to assume a representative loading frequency for this device. For this loading frequency, the back-calculated asphalt modulus has shown excellent correlation with the corresponding values of the SMC. This illustrates that reasonable estimates of the in situ asphalt modulus can be provided by using the Indirect Tensile Test for Cylindrical Specimens (IT-CY) protocol to determine resilient modulus on cores or specimens compacted in laboratory; values obtained by this test must be shifted to in situ test conditions in order to be related to in situ asphalt modulus values, and to be used with elastic theory in pavement design
Measurements of Pavement Macrotexture with Stationary and Mobile Profilometers
No full textThe ISO 13473-1 provides an equation to estimate Mean Texture Depth (MTD) from Mean Profile Depth (MPD) measurements. Many studies on determination of relations between MTD and MPD have been conducted, but they have not always given the same results.
The aim of this work is to describe a data analysis procedure that can estimate MTD values by analysing pavement profiles recorded with stationary and mobile profilometers. For this purpose, a statistical analysis of MPD values obtained with a mobile profilometer was carried out in order to determine the right data analysis procedure; the directional properties of the surface texture were evaluated by analysing profiles recorded in directions: parallel, perpendicular and at 45° to the direction of traffic
A Statistical Model for Prediction of Critical Strains in Pavements from Deflection Measurements
No full textExisting pavements of collector rural roads are often characterized by a strong dishomogeneity in pavement layer thicknesses and mechanical properties of materials. In order to evaluate structural conditions of these pavements, they must be delineated in homogeneous sub-sections with regard to variations both in the thickness and the mechanical properties of pavement layers, but this task is often very difficult. For this purpose, this paper proposes a statistical model for the straight evaluation of critical strains in pavements by using the deflections measured by the Falling Weight Deflectometer and the layer thicknesses without backcalculating layer moduli. The model is calibrated on the basis of experimental data and it is useful to evaluate statistical parameters of the homogeneous sub-sections with the aim to evaluate the residual pavement life taking into account the reliability concepts
Mechanical and Performance-related Properties of Asphalt Mixes Containing Expanded Clay Aggregate
No full textThe use of artificial aggregates such as expanded clay in the production of asphalt concrete makes it possible to reduce both natural aggregate extraction and the use of non-renewable raw resources, giving considerable environmental benefits. Moreover, the expanded clay production process allows non-dangerous waste materials to be reclaimed, thereby avoiding disposal as landfill or dumping, with consequent environmental and economic advantages. This paper reports on the results of laboratory and in situ tests carried out to evaluate the feasibility and advantages of using expanded clay in producing asphalt mixes for use in urban areas with the aim of reducing traffic noise. Some experimental low noise asphalt surfaces were laid, using 15 % of expanded clay by weight, and mechanical as well as performance properties were evaluated. The mechanical characteristics, friction and acoustic performance obtained, in comparison to results with traditional asphalt surfaces, showed that considerable benefits derive from use of expanded clay in asphalt mixes for surface layers. In particular, interesting results in terms of friction increase and noise spectrum reduction were observed
Monitoring and Evaluating Performance Requirements of Flexible Road Pavements
No full textThis paper presents key findings of a research project which is entrusted with setting up guidelines for monitoring and evaluation of pavement performance requirements with the aim of improving durability and both road safety and environmental sustainability.
The study has investigated some techniques for monitoring structural and surface characteristics of asphalt pavements, such as Ground Penetrating Radar, Falling Weight Deflectometer, Laser Profilometer, Skiddometer, and has addressed problems arising from the use of these techniques; the paper describes some measures needed to overwhelm them and for optimizing data collection procedures. In order to enhance the evaluation of asphalt pavements, the study has focused on data analysis and interpretation methodologies; it proposes refinements to the existing procedures for both data processing and interpretation
Empirical rolling noise prediction models based on pavement surface characteristics
No full textTyre/road noise is a complex phenomenon which is function of tyre, surface properties and speed. This study aims to define a rolling noise prediction model for a reference tyre, as a function of speed, on dense asphalt surfaces with medium-low macrotexture levels. The model was defined by relating texture levels of pavement profiles and rolling noise levels recorded at different speeds. The study also defines an extension of the model valuable for semi-porous surfaces, as a function of only surface characteristics. Both of the models serve as a support tool for mix design of low noise asphalt pavement surface
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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