1,355,426 research outputs found
Preliminary study of an energy harvesting system for road pavements made with marginal aggregate
No full textThe progressive reduction of available energy resources and the continuous increase in demand are providing strong incentives for the use of renewable energies. Asphalt solar collectors are efficient energy harvesting systems for roads, able to extract thermal energy from pavements and convert the heat collected by their surfaces. Indeed, the possible reuse of waste materials in road construction, converted into valuable resources, has a strategic importance and could surely enhance the environmental sustainability of road pavement applications. This paper presents a preliminary experimental study aimed at evaluating the feasibility of a pipe-based energy harvesting system, which allows fluid circulation on a coil embedded in asphalt concrete manufactured with marginal aggregates. For this purpose, two-layer dense-graded asphalt slabs (AC8) were prepared in the laboratory, using different aggregate types (limestone and steel slag). A steel coil positioned at the interface was utilized to establish water circulation below the wearing course. The collected thermal energy was measured varying the water flow characteristics; the system was monitored through thermographic analysis while being subjected to a selected radiative power. Main results indicated that water flow rate was crucial in determining the temperature mitigation effect on asphalt concrete surfaces and the efficiency of the energy harvesting system. Some concerns about the operative approach were evinced (mainly related to the scale of the test); however, steel slag inclusion did not seem to compromise nor enhance the thermal conductivity of mixtures
Transversal stability of road profiles in urban contexts: a case-study
No full textThe survey of the longitudinal profile of road pavements is a crucial operation when evaluating the superstructure conservation state. For a correct and accurate verification of evenness, it is necessary that the alignment chosen for the acquisition of profilometric data is as representative as possible of the real road surface, which doesn’t always prove to be the case, especially in urban areas. This emerges more clearly in profilometric surveys conducted with the ARRB Walking Profiler (characterised by a preset data acquisition step of 24 cm, in correspondence to the mega-texture wavebands), the sensitivity of which requires detailed attention.
The study reported in this paper investigated the effects of randomness or stability of the profilometric surveys of road surfaces along parallel longitudinal alignments in different urban road contexts. The acquisition, and successive numerical processing of the profilometric data also allowed the variability and stability to be verified of the evenness indexes currently used in a transverse direction with respect to the platform (IRI, RN, MRI, RMS, PSD).
The profilometer used was the Walking Profiler, an instrument produced by ARRB Transport Research following the World Bank specifications for Class I profilometers. The profilometric data acquired using the ARRB Walking Profiler were then downloaded and analysed using the software ProVAL (Profile Viewing and AnaLysis), an application sponsored by the US Department of Transportation, as well as the Federal Highway Administration (FHWA) and the Long Term Pavement Performance Program (LTPP), and specifically built to allow the users to make a diversified analysis of the longitudinal profiles of pavements
A reduced-order model for Monte Carlo simulations of stochastic groundwater flow
No full textWe explore the ability of the greedy algorithm to serve as an effective tool for the construction of reduced-order models for the solution of fully saturated groundwater flow in the presence of randomly distributed transmissivities. The use of a reduced model is particularly appealing in the context of numerical Monte Carlo (MC) simulations that are typically performed, e.g., within environmental risk assessment protocols. In this context, model order reduction techniques enable one to construct a surrogate model to reduce the computational burden associated with the solution of the partial differential equation governing the evolution of the system. These techniques approximate the model solution with a linear combination of spatially distributed basis functions calculated from a small set of full model simulations. The number and the spatial behavior of these basis functions determine the computational efficiency of the reduced model and the accuracy of the approximated solution. The greedy algorithm provides a deterministic procedure to select the basis functions and build the reduced-order model. Starting from a single basis function, the algorithm enriches the set of basis functions until the largest error between the full and the reduced model solutions is lower than a predefined tolerance. The comparison between the standard MC and the reduced-order approach is performed through a two-dimensional steady-state groundwater flow scenario in the presence of a uniform (in the mean) hydraulic head gradient. The natural logarithm of the aquifer transmissivity is modeled as a second-order stationary Gaussian random field. The accuracy of the reduced basis model is assessed as a function of the correlation scale and variance of the log-transmissivity. We explore the performance of the reduced model in terms of the number of iterations of the greedy algorithm and selected metrics quantifying the discrepancy between the sample distributions of hydraulic heads computed with the full and the reduced model. Our results show that the reduced model is accurate and is highly efficient in the presence of a small variance and/or a large correlation length of the log-transmissivity field. The flow scenarios associated with large variances and small correlation lengths require an increased number of basis functions to accurately describe the collection of the MC solutions, thus reducing significantly the computational advantages associated with the reduced model. © 2013 Springer Science+Business Media Dordrecht
Cold recycling with bitumen emulsion of marginal aggregates for road pavements
No full textThe paper deals with a laboratory study of bitumen emulsion bound mixtures for road pavements with an aggregate structure totally composed of waste materials, i.e. reclaimed asphalt pavement (RAP), steel slag, coal ash and glass wastes, combined in different ratios. The investigation was divided into a preliminary environmental and physical analysis of each waste material and a subsequent mechanical characterization of the bitumen emulsion bound mixtures, by means of indirect tensile strength, stiff-ness modulus and repeated load axial tests. Indirect tensile strength tests were also performed in wet conditions to evaluate the moisture resistance of the mixes. The main outcomes of the trial (indirect tensile strength at 25 °C on dry samples up to 0.37 MPa; stiffness modulus at 25 °C and 2Hz up to 4,266 MPa, depending on the mixture) were compared with the requisites for acceptance of the main Italian Contract Specifica-tions, which demonstrated that the analyzed marginal materials are suitable for use as integral substitutes of natural aggregates in the production of bitumen emulsion bound mixtures for road pavements
Guidelines for the control of transportation systems' environmental noise level: « euphonic» road infrastructures
No full textIncreasing environmental awareness has made it necessary to plan new civil engineering projects according to sustainable development criteria. As regards the more specific case of transportation infrastructures, the major environmental impact of roads is undoubtedly that caused by traffic noise.
Obviously, the simple physical distancing of the sensitive receptors most exposed to the sources of noise is in itself a sure method of self-mitigation. However, both for economic reasons (costs of expropriation) and the scantiness of non-urbanised territories bordering with the infrastructures, it is clear that the hypothesis of direct physical distancing between source and receptor is impractical.
Any analysis of the phenomenon of acoustic impact must also include discussion on the need to extend the width of the strip pertaining to road noise, which is currently on the agendas of governments in Europe and other parts of the world. In Italy, for example, a recent government decree has laid down the widths of noise-abatement strips (varying from 250 m for major extra-urban roads and motorways, to 30 m for urban and local roads), extending the width of the limit of the true territorial impact of transportation infrastructures.
The aim in the near future must therefore be to design road infrastructures with “euphonic characteristics”, acting both on road geometry (sections in a natural or artificial cutting, tunnels, etc.) and materials (eco-technical, sound-absorbing, euphonic pavements, etc.). The objective might be more easily reached once the roadside strips are included within the concept of “road”, with the potential to mitigate the environmental impact of the infrastructure itself. A “widened road system” can thus reasonably be referred to, no longer meaning just the roadway but also strips of land of an adequate width on either side of the infrastructure, with truly self-mitigating characteristics with respect to the local environmental context.
This discussion also covers the debate on the renewal of anti-noise systems for road infrastructures, specifically orientated towards minimising the environmental impact of the actual noise abatement systems and aimed at systematically increasing the sustainability of the new transportation infrastructures during the preliminary design stage
Economic evaluation of external costs in the project cycle
No full textThe economic evaluation of a project is nowadays a delicate task: the new cost items deriving from consideration of the socio-environmental externalities have to be added to the calculation of the more traditional technical costs. The monetary quantification of the former, together with the advancing of scientific knowledge on the environment, is subject to constant reappraisal. The literature in the field of environmental evaluation is still quite recent and sporadic, so, although some important estimative references already exist for the assessment of external costs of transport, the discipline is still evolving.
As things stand today, a top priority will be to correctly consider and calculate all the budget items involved, in terms of both costs and benefits, in order to be able to evaluate the true economic advisability of the investments in terms of an environment oriented approach.
Quantification of the economic consistency of the perturbative effects on the state of the environment ante quam by means of the external costs of transport (or socio-environmental costs) is the responsibility of that branch of estimation known as environmental and territorial evaluation.
In order to fully integrate the environmental problems with the technical-constructive needs when building new highways, it is necessary to calculate both the technical and socio-environmental costs in the project budget on equal terms and internalize the latter within the design criteria, given that the redirecting of funds within the budget is, in reality, an environmentally-oriented investment.
The assessment of the advantage of including works of environmental mitigation and then, the choice of the most suitable solutions for the context, generally both depend on the amount of the external costs of transport. However, the “environmental question” (in terms of both costs and works of mitigation) currently plays an exclusively secondary role and generally subsequent to the technical design of the infrastructures, in common practice being reflected in a clear distinction between the technical-construction costs and the external ones associated with the environment. In the same way, the environmental study on “mitigation” of the impacts produced comes after and it is separated from the technical study of designing the work.
On the contrary, the new frontier of infrastructural design and, in line with this, of transport economics that justify the choices made, is to integrate at all levels the technical-economic requirements of the projects with those of the environment to be preserved, re-orientating and redirecting the economic-financial investments required anyway towards more sophisticated design solutions
Guidelines for the "euphonic" road infrastructures project
No full textIncreasing environmental awareness has made it necessary to plan new civil engineering projects according to sustainable development criteria. As regards the more specific case of transport infrastructures, the major environmental impact of roads is, undoubtedly, that caused by traffic noise. Obviously, the simple physical distancing of the sensitive receptors most exposed to the sources of noise is in itself a sure method of self-mitigation. However, it is clear that the hypothesis of direct physical distancing between source and receptors is impractical both for economic reasons (costs of expropriation) and the scantiness of non-urbanised territories bordering with the infrastructures.
Any analysis of the phenomenon of acoustic impact must also include discussion on the need to extend the width of the strip pertaining to road noise, which is currently on the agendas of governments in Europe and other parts of the world. In Italy, for example, a recent government decree has laid down the widths of noise-abatement strips (varying from 250 m for major extra-urban roads and motorways, to 30 m for urban and local roads), extending the width of the limit of the true territorial impact of transport infrastructures.
Therefore, the aim in the near future must be to project road infrastructures with “euphonic characteristics”, acting both on road geometry (sections in a natural or artificial cutting, tunnels, etc.) and materials (eco-technical, sound-absorbing, euphonic pavements, etc.). The goal may be more easily reached once the roadside strips are included within the concept of “road”, with the potential to mitigate the environmental impact of the infrastructure itself. A “widened road system” can be reasonably referred to, no longer means just the roadway but also strips of land of an adequate width on either side of the infrastructure, with truly self-mitigating characteristics with respect to the local environmental context.
This discussion also covers the debate on the renewal of anti-noise systems for road infrastructures, specifically oriented towards minimising the environmental impact of the actual noise abatement systems and aimed at systematically increasing the sustainability of the new transport infrastructures during the preliminary project level
The "human" factor in the verification of the optical performances of materials for road marking with post-spraying
No full textSafety is a priority for all management authorities of road networks. The factors that act together to reach high safety performance standards are the correct design of the axis geometry, the maintenance of functional levels of the pavement surface, the organization of adequate systems aimed at reducing accidents. Another safety factor is represented by the road marking. Basic requisites for a correct perception of the information supplied by the road marking are recognizability, visibility and readability, especially when driving conditions are unfavorable.
In Italy, the test standard for verification of the performances of road marking is European regulation UNI EN 1436:2004, in which the testing methods of the functional parameters characteristic of the marking material are specified (Qd, RL, β chromaticity coordinates x and y, SRT). However, nothing is specified about the criteria which are necessary to guarantee the representativity, reproducibility and stability of the values obtained.
This paper reports the results of a series of trials aimed at the definition of a new standard for testing horizontal road marking materials, which also takes into account the road user’s awareness and perception of the road space as a function of the category of road and speed of travel
Analysis of the operative safety conditions in the road curvilinear elements
No full textRoad Safety Audits strongly depend on the operative conditions roads are exposed to, in terms of both influence of local environmental parameters (light, visibility, troubling elements, etc.) and vehicle dynamics related to driver behaviour. This is particularly important in the case of circular curves, where the influence of the “human” factor becomes highly determinant in the road safety assessment: both the choice of trajectory and transit speed along the geometric element unavoidably rebound on vehicle behaviour and, with this, on the tyre-road friction characteristics.
These aspects are reflected in Road Safety Audit procedures, mainly through the integration of the “human” factor in road safety assessment. The border-line conditions to be used in safety audits must reflect the real road geometry covered by drivers (free geometry or free trajectories), the transit speed accepted by drivers (in terms of S85) and the real dynamic conditions undercurrent between tyres and road pavement.
Road Safety Audits conducted considering the “human” factor will show a different safety degree between the operative conditions and the theoretical ones forecast for the geometric element, especially in terms of required skid resistance. The adoption of higher transit speeds than the theoretical ones, united with the choice of trajectories not coinciding with the road axis, unavoidably involves higher friction properties than those foreseen by designers. In particular, comparing required friction and offered friction in both cases (operative and theoretical), a different safety coefficient can be found for the considered geometric element.
This paper discusses the importance of the interaction among the three factors “driver-vehicle-road” in Road Safety Audits in the case of circular curves
Sustainability and integration for environmental control of linear transportation infrastructures : the Italian case
No full textNowadays, the planning of road infrastructures that will pass across the territory is certainly no easy task. This is because of the obvious dichotomy between the requirements for development and the need to protect our environmental heritage. The apparently hyperstatic condition of the road design sector arises from the necessity to pursue so many different objectives (safety, quality, efficiency and efficacy), all of which are subject to a rapidly escalating complexity of constraints.
The expansion to the east of the European Union area of influence and the foreseeable logistic facilities due to the opening of frontiers between the countries involved are reflected, at this moment in time, in the dire need to update and develop transport networks at a European level. Even more so in Italy, which is at a crossroads for the principal commercial and tourist routes of international importance. The “infrastructure question”, regulated by Law no. 443/2001, is an extremely topical subject, both for its technical-economic (this is the most relevant element) and the more strictly environmental connotations. Currently however, following an opposite trend to that registered in the recent past, the item of environmental impact connected to transportation systems represents a reality that is inescapable if it does not actually condition the territorial and transport policies in Italy. In parallel, the new laws on environmental subjects all converge towards bringing the evaluations of “impact” forward to the early stages of planning and designing new roads (SEA, EIA on the preliminary project, etc.), thus necessarily raising the level of the importance of the territorial system involved and, consequently, the technical level required for new infrastructures. Last, but not least, the 2002/49/EC directive, on the subject of noise pollution, stresses the need to pay increasing attention to the question of “environmental noise”, especially that due to transport infrastructures.
All of this means that an integrated approach must be used for the planning of transportation systems, matching the technical-constructional requirements to those of environmental protection in order to raise the eco-sustainable nature of the latest generation infrastructures.
This work does not aim to provide “the” answer to the question but rather to stress the importance of identifying the design alternatives at a preliminary stage, which take the items of environmental impact into account and can combine, as far as possible, technical efficiency with the economic and environmental sustainability of the project
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