1,720,974 research outputs found
Electric arc furnace slags in cement-treated materials for road construction: Mechanical and durability properties
Full text linkElectric arc furnace (EAF) slags are by-products of a widespread steelmaking process. The recycling of these materials as artificial aggregates in different road applications is a well established practice, which has allowed to reduce the consumption of natural resources and to minimize waste production and costs of landfilling. However, these aggregates are still underutilized in cement-treated materials (CTMs), which consist of mixtures of aggregates blended with small amounts of cement and water that harden after compaction to form a strong paving material. In the light of these considerations, different cement-treated materials, each containing different percentages of natural and artificial aggregates were analyzed. After a preliminary characterization of chemical, physical and durability properties of EAF slag aggregates, a mix design procedure based on both moisture-density approach (gyratory compactor) and mechanical testing (unconfined compression test and indirect tensile test) was performed to identify the optimum cement and water content of CTMs. The design mixtures were then subjected to 5 different accelerated aging procedures in order to study the influence of some factors (temperature, pressure and humidity) on the durability of the cement-treated materials. The results highlighted how the EAF slags represent suitable aggregates for cement-treated materials. The use of these aggregates produced a greater compaction difficulty, but guaranteed excellent mechanical performances, above all in terms of indirect tensile strength. The durability analysis demonstrated that the recycled mixtures showed a worse behavior than the reference one, composed only by limestone aggregates. However, if correctly designed, balancing the percentage of natural aggregate replacement, these mixtures could represent suitable and durable solution for base and sub-base pavement layers
Swelling behavior of electric arc furnace aggregates for unbound granular mixtures in road construction
No full textThermomechanical behaviour of airfield concrete pads supporting joint strike fighter F-35B
No full textThe Lockheed Martin F-35B Lightning II is the Short Take-Off/Vertical Landing (STOVL) aircraft variant of the joint strike fighter. The new dual-cycle propulsion system, which permits the STOVL operations, exposes the airfield pavements to extremely critical thermal conditions (temperatures exceeding 930°C and heating rate of about 85°C s−1). This study permitted to analyse the thermomechanical behaviour of an ordinary concrete pad during the F-35B aircraft vertical landing. The numerical analysis provided a detailed picture of the pavement stress state generated by the jet gases, opening the scenario to different planning solutions. The results highlighted how the damage, in the form of thermomechanical spalling, occurred in the top 2–5 mm of the pavement surface. One of the possible design solutions for high-performance vertical landing pads, supporting the F-35B aircraft, could be a two-layered pavement characterised by a thin (2.5 cm) fibre-reinforced Very High-Strength Concrete overlay
Phyto-based sodium chloride hydrogel for highway winter maintenance of porous asphalt pavements
Full text linkThe need of the highway agencies to customize their winter maintenance operations on porous asphalt pavements prompted the authors to develop an innovative anti-icing technology based on the hot liquid spray application of a saline hydrogel. A bio-based (phyto-based) thermo-sensitive sodium chloride (NaCl) brine, that has the ability to form a gel simply by coming into contact with a very cold surface, was conceived. The increase in viscosity and the formation of a gel-like structure would make this anti-icing product able of filling the surface voids without permeating through the mixture (longer residual deicing effectiveness), while maintaining at the same time the pavement frictional resistance. In view of adopting sustainable winter maintenance strategies, this innovative blend was formulated by exploiting the thickening and gelling properties of wall-cell polysaccharides contained in seaweeds fibers. The mechanisms of gel formation were experimentally studied in laboratory, analyzing in detail the thermal and rheological properties of the salt hydrogel during the different phases of preparation, storage and application. On the basis of this characterization, a full-scale validation was carried out on an existing highway porous asphalt pavement. For this purpose, a tank truck prototype was equipped with a heating capacity tank and a customized specific spraying system
The Parma University Campus as major trip attractor. Traffic microsimulation for modelling vehicle access scenarios
No full textUniversity campuses are multi-modal and major trip attractors, facing strong interactions of several transport modes within a unique system. Although campuses may share common features, they have different transport needs. The development of policies that encourage active mobility and transit service and the improvement of road infrastructures are main strategies to accomplish sustainable transportation goals. While many universities devote efforts to reducing drive-alone commute trips, private vehicles often remain the most affordable and convenient choice for many employees and students. In addition to discourage or apply strict restrictions to vehicular traffic, the optimization of the inbound and outbound flows is a necessary approach to reduce congestion and safety issues on and near campus Micro-simulation models are increasingly popular for examining these complex traffic problems at detail level, emulating traffic behavior in a transport network over time and space to predict a system performance. In this perspective, the article describes the case study of the mitigation of motorized traffic problems of the University Campus of Parma (Italy), which is implementing multiple sustainability strategies towards modal shift to non-motorized systems and optimization of public transport. Specifically, a traffic micro-simulation modelling was implemented to study the vehicle access at the main entrance to the Campus delimited area from the public road network via a multi-lane roundabout. Different scenarios, that do not involve any investment in infrastructure but only interventions in the management of the scheduled educational activities and services, were presented for increasing the users' safety and level of service. Following a description of the software calibration process and its validation to match the locally observed conditions, some operational solutions based on the re-planning of the lesson timetable were presented to reduce the current congestion levels within the campus and in its vicinity during peak hours
Photoluminescent road surface dressing: A first laboratory experimental investigation [Revêtements routiers photoluminescents: étude expérimentale préliminaire en laboratoire]
No full textThe main objective of this experimental research was to analyze the possible use of afterglow photoluminescent pigments for road wearing courses. Thanks to their natural color or their glowing color, depending on their emission spectra, photoluminescent pigments could allow a better identification of different pavement zones in the darkness. We studied two type of pigments (masterbatches and powders), based on zinc sulfide (ZnS:Cu) or on strontium aluminate phosphors (SrAl2O4:Eu2+,Dy3 +), in different experimental conditions. Firstly, experiments were performed to determine the crystals' luminescent properties. Next, we investigated possible application of these materials in asphalt concrete and slurry seal, prepared by using clear binder and synthetic bitumen emulsion. The representative samples of photoluminescent Strontium Aluminate surface dressing were able to re-emit energy in the form of visible light for significant period of time, after exposure to daylight or artificial light. Assuring good performances in different condition, they could be having interesting suitable applications in a wide variety of contexts: low-volume roads, footpaths and bicycle lanes. © EDP Sciences, 2014
DEM modelling analysis of tree root growth in street pavements
No full textThe 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. © 2015 Taylor & Franci
Airborne emissions of asphalt/wax blends for warm mix asphalt production
Full text linkDuring the asphalt heating process in the various stages of hot mix asphalt (HMA) production and paving operations a complex mixture of hydrocarbon aerosols, vapors and gases, generally composed of products of combustion, volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs), is emitted into the atmosphere. The reduction of these airborne asphalt emissions is a continuous issue and challenge for asphalt industry and road agencies. Thus, a number of new sustainable and cleaner technologies, generally referred to as warm mix asphalts (WMA), that significantly reduce the manufacturing and application temperatures, had been developed. Despite the great number of reported WMA methodologies, organic waxes are widely used for reducing the binder viscosity and for enhancing the asphalt mixture workability already at lower temperatures (90â140 °C). The manuscript presents a detailed laboratory investigation, based on headspace gas chromatography-mass spectrometry (HS-GC/MS) and photoionization detection (PID), which aimed to assess the content of VOCs and PAHs in the asphalt emissions, taking into account the effective contribution of binder or binder/wax blend. The characterization of asphalt fume composition has allowed the identification of more than 200 volatile compounds, highlighting at the same time a hierarchy of their appearance in relation to the temperature. The detection of the less volatile compounds was feasible only at temperatures higher than 160 °C, temperature range in which the HMA is generally produced. The study of the binary asphalt/wax mixtures highlighted the twofold way in which the waxes perform in reducing emissions: on the one hand they act as flow improvers (reduction of production and paving temperatures) and on the other as fume suppressants
The odour fingerprint of bitumen
No full textBitumen 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
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