Use of Life Cycle Cost Analysis and Multiple Criteria Decision Aid Tools for Designing Road Vertical Profiles

The current design practice for the vertical profile of roads in rolling and mountainous terrains is to follow the existing grades in order to minimize earthwork costs. This means that the only criterion considered during the design phase is the initial cost. It would be preferable to include other criteria that are directly related to sustainability, particularly fuel consumption and CO2 emissions. Therefore, this paper describes a proposed design procedure that starts by finding feasible alternatives with different grades. Then, a microsimulation traffic tool is used to simulate the movement of predicted vehicles (volume and type) over the different alternatives. The microsimulation tool provides reliable estimates of travel times, fuel consumption, and CO2 emissions for the different alternatives. With these data, it is possible to use life cycle cost analysis (LCCA) or multiple criteria decision aid (MCDA) tools to select the “optimal” alternative. The proposed procedure was used on a case study involving a 6-km highway section with different proposed grades ranging from 2% to 8%. Using LCCA and an MCDA tool, it was revealed that the current design alternative is not the optimal alternative in most considered scenarios (various fuel values for LCCA and different “Cost” weights for MCDA)

Analysis of moving bottlenecks considering a triangular fundamental diagram

A significant number of research efforts have studied and analyzed the case in which a vehicle is moving slower than the traffic stream. This phenomenon, known as a moving bottleneck, results in a disruption of traffic flow and may significantly impact the traffic stream behavior upstream, downstream and abreast the slow moving vehicle. In this paper, a macroscopic approach for modeling moving bottlenecks is developed using microscopically derived data considering a triangular fundamental diagram. The passing flow rates of different moving bottleneck scenarios are determined using a previously developed microscopic model based on simulated data derived from the INTEGRATION software. Using the simulation results, an explicit expression of the bottleneck diagram, a flow-density relationship that defines the phenomenon macroscopically is proposed and the behavior of the traffic stream downstream and abreast the moving obstruction is depicted. It is demonstrated that the behavior of the traffic stream downstream of the slow vehicle as well as the acceleration behavior while passing is governed by the demand level. Such a result is coherent and consistent, to a significant extent, with two decades of research related to modeling moving bottlenecks and constitutes a potential feasible and more detailed description of the phenomenon in the case of a triangular fundamental diagram. Finally, it is noteworthy that the research subject of this paper could be considered as a first step in developing a numerical and practitioner-friendly framework for the analysis of moving bottlenecks that does not involve approaching the problem from its theoretical perspective

Steady-State Car-Following Time Gaps: An Empirical Study Using Naturalistic Driving Data

The time gap is defined as the time difference between the rear of a vehicle and the front of its follower, which affects both safety and the saturation flow rate of a roadway segment. In this study, naturalistic driving data were examined to measure time gaps from seven different drivers in a car-following scenario within steady-state conditions. The measurements were taken from a 13-km section of a Dulles Airport access road in Washington, DC. In total, 168,053 time gap samples were obtained covering seven speed intervals. Analysis of the data revealed a large variation in time gaps within individual drivers’ driving data, with coefficients of variation as high as 63.8% observed for some drivers. Results also showed that the variability within drivers was more significant at speeds higher than 54 km/h. In addition, there was a large variability between drivers. At speeds above 108 km/h, minimum time gaps left by some drivers could be 1.6 times longer than those left by others. Several statistical distributions were used to fit the data of the seven drivers as well as the data for all drivers combined for each speed interval. The selected distributions passed the goodness-of-fit (Kolmogorov-Smirnov, Chi-square, and Anderson-Darling) criteria only when the number of samples was reduced. Data reduction was not performed randomly, but rather in a manner intended to maintain the same observed distribution when all the samples were used. It is therefore recommended that empirical measures of distributions be used in traffic microsimulation software rather than theoretically fit distributions obtained based on statistical tests. This will lead to better naturalistic traffic behavior simulations, resulting in more precise predicted measures of performance (travel time, fuel consumption, and gas emissions)

Durability of self-compacting rubberized concrete exposed to external sulphate attack

This study evaluated the performance of self-compacting rubberized concrete against external sulphate attack (ESA). cylinders 100 mm in diameter and 220 mm in length of control concrete (no rubber) and rubberized concrete were prepared and tested by visual inspection to identify visible degradation, length and mass variations of specimens, compressive strength, water-accessible porosity, mercury intrusion porosimetry (MIP), and thermal decomposition obtained from thermogravimetric analysis (TGA). Results show that the incorporation of up to 15% rubber enhances the performance against ESA. Rubber reduced the expansion strains and compressive strength. All immersed specimens did not have visible cracks around them. Water porosity was found to increase or decrease versus the time of sulphate immersion. As a result, the impact of rubber on porosity variation is significantly less than the effect of the sulphate-hydrate reaction. Thermogravimetric analysis showed a decrease in portlandite, which is not related to rubber incorporation

Experimental Investigation of PCC Incorporating RAP

Abstract Rehabilitation and repair of flexible pavements produce huge amounts of reclaimed asphalt pavement (RAP) material. Using RAP in the formulation of portland cement concrete (PCC) is a technique that is part of a sustainable development approach since it reduces on the consumption of new aggregates and reuses a material that is considered as waste. This paper describes the semi-adiabatic calorimetry test performed on a concrete mix incorporating RAP material as aggregate. Results showed that the cement hydration process is not affected by the presence of asphalt coated on the surface of RAP material. Classical tests (compressive strength, flexural and indirect-tensile strengths, elastic modulus, and free-shrinkage) were also performed on PCC mixes incorporating different percentages of RAP. It was found that as the percentage of RAP increases, the PCC mechanical properties decrease. This is mainly attributed to the presence of voids in the transition zone between the asphalt-coated aggregates and the hydrated cement paste as confirmed by scanning-electron microscope images. Unrestrained shrinkage testing showed statistically insignificant change in shrinkage strain with RAP content. The strength and shrinkage results lead to conclude that as much as 40% of RAP could be incorporated into the formulation of PCC and achieve properties that are acceptable for the construction of rigid pavements

Implementation Phase Safety System for Minimising Construction Project Waste

The construction sector is a key component of a nation’s gross domestic product, but its inherent nature results in potentially dangerous conditions that affect the safety of all workers on construction projects (CPs). Therefore, the original idea of the research is to determine the relationship between safety system (SS) during the implementation phase (IPh) of CPs and the minimisation of waste (materials, time and cost). Achieving a lean construction work requires suitable planning, safety considerations and waste resource minimisation throughout the project cycle. This research aims to identify and rank the safety factors during the IPh of a CP, which will have positive effects on minimising waste. Information and data were gathered from the existing literature and the structured interviews and questionnaire survey conducted among 111 randomly selected construction companies. Questionnaire results were evaluated using statistical tools, such as hypothesis testing, analysis of variance and linear regression. This research identified and ranked 24 important safety factors with positive effects on minimising waste in CPs during IPh. The seven most important safety factors that should be considered to minimise material, time and cost wastage are as follows: handling, management, external factors, workers, procurement, site condition and appropriate scaffolding for SS. The best linear model was developed on the basis of the importance index of the identified factors. This model can predict the minimisation of waste (materials, time and cost) in CPs by using SS. Thus, the safety criteria and SS should be used during IPh to minimise waste on the basis of the developed model

Etude comparative de la cinétique de la réaction d’hydratation des bétons autoplaçants et des bétons vibrés

Les bétons autoplaçants (BAP) sont des bétons très fluides, absolument homogènes, mis en place sans vibration externe ou interne et présentant des résistances analogues à celles des bétons vibrés, ordinaires et à hautes performances (gamme de 25-80 MPa). De telles caractéristiques sont directement liées à leurs composition, qui en plus du ciment, de l’eau et des granulats (sable et gravillons) renferment des fines, un fluidifiant et assez souvent un agent de viscosité. Ces bétons présentent deux intérêts : Le premier économique par la simplification de la mise en oeuvre, l’amélioration de la sécurité et la réduction des nuisances sur et autour du chantier ; Le second est technique par l’amélioration de la qualité et coulage de zones fortement armées. Les BAP sont des solutions bien adaptées à des nombreuses applications, notamment des ouvrages telles que les dallages, les parois, les radiers, les planchers etc. Ces ouvrages généralement considérés comme ouvrages massifs sont soumis à plusieurs types de déformations pendant le processus d’hydratation du béton. En effet, la nature exothermique de la réaction chimique du ciment peut induire des déformations de dilatation et de contraction. Par ailleurs, la dépression capillaire crée par la consommation d’eau due à l’hydratation du ciment entraine un retrait de dessiccation. Ces déformations peuvent entrainer des micros fissurations pouvant affecter la durabilité de l’ouvrage à long terme surtout pour les ouvrages épais. D’où l’importance d’étudier la cinétique d’hydratation de ses bétons non conventionnels et de les comparer à celle des bétons vibrés traditionnels. L’évolution de la température adiabatique ainsi que la variation en fonction du temps du degré d’hydratation sont déterminées pour le béton autoplaçant et le béton vibré. L’analyse des résultats expérimentaux obtenus montre que le changement de composition modifie considérablement la cinétique de la réaction d’hydratation

Modification of bending beam rheometer specimen for low-temperature evaluation of bituminous crack sealants

It is difficult to evaluate effectively the low-temperature stiffness of bituminous hot-poured crack sealants with existing test methods. The standard bending beam rheometer (BBR) was found to be inappropriate for testing soft bituminous-based hot-poured crack sealant, even at a temperature of -40\ub0C. To address this issue, the moment of inertia of the tested beam was increased by doubling its thickness (from 6.35 mm to 12.7 mm). For the new beam dimensions, only 4% of the beam center deflection is due to shear, a value deemed acceptable for sealant evaluation and comparison. On this basis, the BBR stiffness of hot-poured sealants was obtained at several discrete temperatures between -10\ub0C and -40\ub0C to assess the repeatability of the method for the evaluation of the low-temperature stiffness of bituminous sealants. Ten different sealants were tested at -40\ub0C; three of these 10 were further tested at -35\ub0C, -30\ub0C, -28\ub0C, -25\ub0C, and -20\ub0C; and the three "hard" sealants were tested at -10\ub0C. A minimum of three replicates were used. The coefficient of variation on the measured stiffness after 60 s of loading was always lower than 18%, with almost 75% of the measurements having a coefficient of variation less than 10%. A pairwise comparison showed that the modified BBR could be used to classify sealant products according to their measured stiffness. As to the effect of temperature, it was found that the stiffness varies exponentially with temperature in the range of -40\ub0C to -20\ub0C. A statistical analysis of the results indicated that the modified BBR method could be used to classify sealants based on low-temperature stiffness.Il est difficile d'\ue9valuer efficacement la rigidit\ue9 \ue0 basse temp\ue9rature des scellants \ue0 fissures bitumineux coul\ue9s \ue0 chaud en employant les m\ue9thodes d'essai existantes. En effet, on a d\ue9couvert que le rh\ue9om\ue8tre de flexion (RF) standard \ue9tait inad\ue9quat pour la mise \ue0 l'essai de ces produits, m\ueame \ue0 une temp\ue9rature de -40 \ub0C. Au bout de seulement quelques secondes de chargement, la flexion mesur\ue9e d\ue9passait la limite du RF. Pour r\ue9soudre ce probl\ue8me, on a augment\ue9 le moment d'inertie de la poutre test\ue9e en doublant son \ue9paisseur (de 6,35 mm \ue0 12,7 mm), ce qui permet de tester le mat\ue9riau le plus mall\ue9able (\uab mou \ubb) qui soit actuellement disponible sur le march\ue9. Pour les nouvelles dimensions de poutre, on a d\ue9couvert que seulement 4 % de la flexion de la poutre en son milieu est attribuable \ue0 l'effort tranchant, valeur jug\ue9e acceptable aux fins de l'\ue9valuation et de la comparaison des scellants. Partant de ceci, la rigidit\ue9 au RF des scellants a \ue9t\ue9 obtenue \ue0 plusieurs valeurs de temp\ue9rature discr\ue8tes comprises entre -10 \ub0C et -40 \ub0C pour d\ue9terminer la r\ue9p\ue9tabilit\ue9 de la m\ue9thode aux fins de l'\ue9valuation de la rigidit\ue9 \ue0 basse temp\ue9rature des scellants bitumineux. Dix (10) scellants diff\ue9rents ont alors \ue9t\ue9 test\ue9s \ue0 -40 \ub0C; trois (3) de ceux-ci ont \ue9t\ue9 test\ue9s subs\ue9quemment \ue0 -35 \ub0C, \ue0 -30 \ub0C, \ue0 -28 \ub0C, \ue0 -25 \ub0C et \ue0 -20 \ub0C; et les trois (3) scellants \uab durs \ubb ont \ue9t\ue9 test\ue9s \ue0 -10 \ub0C. Un minimum de trois (3) r\ue9p\ue9titions ont \ue9t\ue9 r\ue9alis\ue9es. Le coefficient de variation de la rigidit\ue9 mesur\ue9e apr\ue8s 60 s de chargement \ue9tait constamment inf\ue9rieur \ue0 18 %, pr\ue8s de 75 % des mesures pr\ue9sentant un coefficient de variation de moins de 10 %. Une comparaison par paire a r\ue9v\ue9l\ue9 que le RF modifi\ue9 pourrait ainsi \ueatre utilis\ue9 pour classifier les produits scellants en fonction de leur rigidit\ue9 mesur\ue9e. L'incidence de la temp\ue9rature sur la rigidit\ue9 a \ue9t\ue9 examin\ue9e pour trois (3) scellants. Il s'est av\ue9r\ue9 que la rigidit\ue9 varie de fa\ue7on exponentielle avec la temp\ue9rature dans la plage de -40 \ub0C \ue0 -20 \ub0C. Une analyse statistique des r\ue9sultats a indiqu\ue9 que la m\ue9thode avec RF modifi\ue9 peut servir \ue0 une classification des scellants qui soit fond\ue9e sur la rigidit\ue9 aux basses temp\ue9ratures.Also published in "Transportation Research Board 84th Annual Meeting: Compendium of Papers CD-ROM.(2005)"Aussi publi\ue9 dans "Transportation Research Board 84th Annual Meeting: Compendium of Papers CD-ROM.(2005)"Peer reviewed: YesNRC publication: Ye