1,720,970 research outputs found
THE ALKALI-ACTIVATION OF CONSTRUCTION AND DEMOLITION WASTE COMPONENTS FOR STABILIZATION PURPOSES
No full textThis study investigates the potential of the different components of CDW (recycled concrete RC, recycled asphalt RA, crushed bricks and tiles BT, natural aggregate NA, and undivided CDW UND) to undergo alkali activation (AA) when mixed with an appropriate alkaline solution (AS). The feasibility of the AA of CDW fines for the stabilization of CDW aggregates was evaluated for particles smaller than 0,125 mm. A preliminary chemical characterization was carried out on different components of CDW aggregates to identify the main crystalline phases and ascertain the presence of aluminosilicates needed for the AA process. Particles of each component were afterwards mixed with three concentrations of the same AS, cast in prismatic moulds, and cured at room temperature without any thermal treatment. Mechanical tests after 3, 7, and 28 days of curing demonstrated that CDW fine powders tend to react positively in a basic environment, showing an increase in strength without any thermal treatment. These results can be translated into practical applications in the form of a methodology for improving pavement layers made up of CDW aggregates without the addition of any cementitious binders
How the position of a cycle lane installed on an urban residential street impacts on the behaviour of young drivers
No full textIn this driving simulation study, we evaluated the change in driver behaviour of forty young drivers (20 females) following the conversion of a 2-way local street into a 1-way one with a cycle lane in a typical residential neighbourhood. Twenty drivers who were also used to commuting/travelling by bicycle were selected for the study. We compared three road layouts: (i) a standard 2-way urban street with no cycle lane (baseline), (ii) a 1-way street with a cycle lane on the right side, and (iii) a 1-way street with a left-side cycle lane. Driver behavioural metrics when interacting with cyclists including overtaking speed, lateral position in the lane, and vehicle-cyclist clearance were analysed using linear mixed-effect models. Speed and lateral position in the lane were also analysed in the non-overtaking phase. Significantly better driver behaviour was observed in layouts with a dedicated cycle lane, manifesting itself in greater lateral distance values for safer overtaking and better trajectory control. Drivers were more likely to stay within their lanes, eliminating the need to alter trajectory when passing cyclists, thus promoting better longitudinal and lateral control. The presence of a cycle lane significantly improves the interaction between drivers and cyclists, regardless of the position of the cycle lane, i.e., left vs. right side with respect to the vehicle lane. While the results do not favour a particular side, designers should also consider cyclist preferences and driver expectations at intersections. Further research is crucial to validate findings and explore lane positioning effects near intersections, and greater emphasis should be placed on determining cyclist preferences in terms of infrastructure design
A preliminary investigation into the use of alkali-activated blast furnace slag mortars for high-performance pervious concrete pavements
No full textPervious concrete (PC) pavements are water control systems for infiltrating storm water, reducing runoffs, contrasting heat-island effects and noise diffusion in urban environments. Their poor strength and stiffness, which stem from their porosity, limit their application for use in sidewalks and residential streets. To overcome this limitation, the research aimed at developing an alkali-activated blast furnace slag binder (AA-BFS) which, when added to the concrete mixture, would enable it to attain the characteristics required for application in trafficked road pavements. A Portland cement (CEM-I) and a blast furnace cement (CEM-III/C) were included for comparison purposes. Standard and high-performance pervious concrete (HPPC) mortars were tested with the same mix ratio of binder, sand, and admixtures. The effects of a latex polymer admixture were also analysed. After 2, 7, and 28 days of curing, AA-BFS mortars exhibited the greatest flexural and compressive strengths. As expected, CEM-III/C needed more time to achieve strengths comparable to those recorded for CEM-I. The addition of latex failed to result in any discernible benefits in terms of the stress-strain behaviour of mortars. The results confirm that AA-BFS is a sustainable option for HPPC production
How cognitive distraction affects motorway short-term work zone safety along curves: A driving simulation study
Full text linkThis study investigates how cognitive distraction affects driver behaviour on a two-lane motorway reduced to one lane (the left) in a short-term work zone along a left-hand curve. Forty-two participants were divided into two groups: undistracted and cognitively distracted drivers - with the latter required to perform mental calculations. Drivers had to react to the sudden and unexpected appearance of stationary vehicles in a queue. Distracted drivers started braking at higher speeds and released the accelerator later than undistracted ones. Their reaction times were significantly longer, and five of them could not avoid a collision with the last vehicle in the queue. Heat maps of eye fixations show that distracted drivers focused their gaze on a few elements of the road section, predominantly on the inside of the carriageway, while undistracted drivers looked at a wider area of the road scenario. Distracted drivers exhibited delayed responses to unexpected events, highlighting the importance of addressing cognitive distraction in road work zones. Given the high frequency of roadworks on motorways, specific safety countermeasures are needed to compensate for the objective risk posed by unexpected events in scenarios where distracted drivers operate with limited available sight distance
Life cycle economic and environmental impacts of cdw recycled aggregates in roadway construction and rehabilitation
Full text linkThe use of recycled materials in roadway construction and rehabilitation can achieve significant benefits in saving natural resources, reducing energy, greenhouse gas emissions and costs. Construction and demolition waste (CDW) recycled aggregate as an alternative to natural one can enhance sustainability benefits in roadway infrastructure. The objective of this study was to quantitatively assess the life cycle economic and environmental benefits when alternative stabilizedCDW aggregates are used in pavement construction. Comparative analysis was conducted on a pavement project representative of typical construction practices in northern Italy so as to quantify such benefits. The proposed alternative sustainable construction strategies considered CDW aggregates stabilized with both cement and cement kiln dust (CKD) for the base layer of the roadway. The life cycle assessment results indicate that using CDW aggregate stabilized with CKD results in considerable cost savings and environmental benefits due to (i) lower energy consumption and emissions generation during material processing and (ii) reduction in landfill disposal. The benefits illustrated in this analysis should encourage the wider adoption of stabilized CDW aggregate in roadway construction and rehabilitation. In terms of transferability, the analysis approach suggested in this study can be used to assess the economic and environmental benefits of these and other recycled materials in roadway infrastructure elsewhere
Effect of Degradation on Mechanical Strengths of Alkali-Activated Fines in Stabilized Construction and Demolition Waste Aggregates
Full text linkRecent works have demonstrated that construction and demolition waste (CDW) aggregates for subbase road pavement applications can be stabilized via the alkali activation of their fine fraction (d<0.125 mm). Despite the promising results with this method, the durability of alkali-activated (AA) CDW fines (which act to stabilize CDW aggregate mixtures) need to be investigated. To this end, the effects on pavement materials of the typical degrading actions of water, deicing salts, and the freeze-thaw process were investigated. Samples of AA fines were subjected to water, deicing salt, and freeze-thaw treatments and assessed based on the variation in 28-day flexural and compressive strength values with respect to not-degraded materials. In addition to the fines normally present in CDW aggregate mixtures (i.e., the undivided fraction), samples with fines of the main CDW constituents (concrete, asphalt, bricks and tiles, aggregates and soil) were also prepared for comparison purposes. One set of specimens was cured at 20°C to replicate field conditions, and another was treated at 80°C to replicate optimal conditions for AA materials. Although 80°C heat-treated specimens achieved higher strength values, those values fell sharply following the degrading action of water and deicing salts. In contrast, the specimens cured at 20°C retained their mechanical property values even after exposure to water and deicing salt degradations
Effects of quantity and plasticity of fine particles on the workability and resilient behaviour of aggregate-soil mixtures for granular pavement layers
Full text linkThe paper presents the results of a laboratory investigation seeking to quantify the effects of fine quantity and type on the workability and resilient response of aggregate-fine soil mixtures for subbase formation. Laboratory devices were used to simulate in-field conditions and compact samples and evaluate their resilient response under pulsing loads. Four different types of fines passing through a 63mm sieve (one non-plastic silt and three silty-clays exhibiting plastic behaviour) in three different quantities (5.4, 10.8 and 16.2%) were combined with coarser aggregates while maintaining the same grading distribution. A variant of the generalized model proposed in the Mechanistic Empirical Pavement Design Guide was calibrated to distinguish the contribution of fine type to resilient modulus from that of moisture content and suction. The results evidenced an improvement in mixture workability during the compaction process when using plastic fines instead of non-plastic ones. However, the quantity of plastic fines should be limited (lower than 10.8% within the aggregate skeleton) in order to achieve a high compaction level and to attain a hardening resilient behaviour ratherthanthesofteningoneobservedinthecaseofgranularmaterialscontainingnon-plastic fines
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
Do driver monitoring technologies improve the driving behaviour of distracted drivers? A simulation study to assess the impact of an auditory driver distraction warning device on driving performance
Full text linkBeing distracted while driving is a major cause of road crashes. To help prevent this particular type of crash, new driver monitoring technologies track ocular and head movement and alert drivers when periods of prolonged distraction are detected, thus preventing hazardous situations on the road. In this mixed-factorial multi level experiment, the behaviour of drivers was measured as they performed a secondary task while being monitored via an auditory Driver Distraction Warning (A DDW) device which reminded them to look at the road ahead and cease the activity which was the source of distraction. Here, we evaluated the effectiveness of this type of DDW device by measuring longitudinal and lateral behaviour in situations where the driver is intentionally distracted for a significant period of time, and when the device repeatedly reminds the driver of his/her primary task.
Forty-two participants were randomly stratified into three groups and subjected to the following distraction levels: (i) not distracted (baseline), (ii) distracted, and (iii) distracted but interacting with the A DDW device. All participants drove in (i) free flowing and (ii) stable traffic conditions along straight motorway segments. Speed and speed deviation values for distracted drivers were lower than for undistracted ones but they also experienced a significant deterioration in vehicle lateral control. Conversely, drivers assisted by the A DDW device experienced a considerable improvement in their lateral control even though their speed and speed deviation values were higher. The reaction times of distracted drivers interacting with the A DDW device deteriorated as revealed in cognitive tests conducted before and after the driving task
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