Search

This work focuses on the reuse of reclaimed asphalt pavement (RAP) in the production of self-compacting concrete (SCC) for usage in the construction of rigid pavements. The article first describes an experimental study where five SCC mixtures incorporating 0%, 20%, 40%, 60% and 100% volumetric substitutions of natural aggregates by RAP were formulated. Several characterisation tests in the fresh and hardened states were then performed. The results of all performed tests showed that RAP has a slight negative effect on SCC performance in the fresh state. The most significant reduction observed does not exceed 18% for slump-flow and 10% for L-shaped box values when total substitution is applied. Furthermore, the mechanical properties noticeably decrease with an increase in RAP content, with reductions of up to 37% in 28-d compressive strength and 23% in 28-d indirect tensile (IDT) strength observed in the case of full replacement. However, it is possible to formulate SCC mixtures even with 100% RAP substitutions and meet specifications for rigid pavement construction. In addition, modelling of the various mechanical characteristics made it possible to find out the reason behind the reduction in these properties with RAP content. In fact, the thin bitumen film around RAP particles weakens their surface adhesion with the hydrated cement paste. With the intrinsic RAP properties found, the hardened-state characteristics of any other SCC mixture incorporating RAP could be predicted. [ABSTRACT FROM AUTHOR]

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)., 1. Introduction Time headway between vehicles is an important microscopic traffic flow property. It is used in many areas of traffic engineering, as it is directly related to traffic safety, [...]

One of the 12 instrumented sections of the Virginia Smart Road was used to compare measured vertical compressive stress and measured transverse horizontal strain under the hot-mix asphalt (HMA) layer induced by a 25.8 kN (5.8 kip) single tire and a 39.5 kN (8.9 kip) set of dual tires to those calculated using layered linear elastic theory. The pavement section is composed of 38 mm (1.5 in.) HMA wearing surface, 150 mm (6 in.) of HMA base mix, 75 mm (3 in.) of asphalt stabilized open graded drainage layer, 150 mm (6 in.) of cement stabilized aggregate layer, and 175 mm (7 in.) of unbound aggregate base. The subgrade is a fill material composed mainly of rocks. Measured stresses were obtained using pressure cells embedded in the pavement during construction. Horizontal transverse strain was measured using H-type strain gauges that were also embedded during construction. Temperature in the pavement layers was measured using embedded T-type thermocouples. Theoretically calculated stresses and strains were obtained using software based on the layered-elastic theory (Kenpave, Bisar 3.0, Elsym5, and Everstress 5.0). In addition, two finite-element approaches were used. Results indicated that the layered elastic theory overestimates pavement responses at low and intermediate temperatures, but significantly underestimates the pavement responses to vehicular loading at high temperatures. CE Database subject headings: Flexible pavements; Stress; Instrumentation; Finite element; Elasticity; Measurement.

The objective of this study was twofold: (1) quantify the benefits of a specially designed geocomposite membrane [a low modulus polyvinyl chloride (PVC) layer sandwiched between two nonwoven geotextiles] to act as a moisture barrier in flexible pavement systems; and (2) quantitatively measure the moisture content of unbound granular materials nondestructively. The geocomposite membrane was installed over half the length of a pavement test section at the Virginia Smart Road, while the other half of the test section consisted of the same design without the interlayer system. An air-coupled ground penetrating radar (GPR) system with 1 GHz center frequency was used to monitor and detect the presence of moisture within the pavement system over different periods of time corresponding to different levels of water accumulation. Results of GPR data analysis indicated that the use of the geocomposite membrane reduced water infiltration to the aggregate base layer by as much as 30% when measurements were performed after rain. It was also found that the moisture content underneath the interlayer was almost constant and therefore independent of the amount of rainwater, which is the primary source of moisture in pavement systems that have a low water table. The impact of moisture in the granular layers was investigated using the results of a deflection monitoring program. The results indicate that the area with the geocomposite membrane always showed less deflection than the area without the interlayer. The study recommends that any pavement drainage layer must be backed by an impermeable interface, given that the water table is low. CE Database subject headings: Surface drainage; Moisture content; Flexible pavements.

Ground-penetrating radar has been used successfully to predict layer thicknesses in flexible pavements. Currently, a time-domain method is used to measure the two-way travel time between reflections from which the layer thickness is predicted. In this method, the dielectric constants are assumed to be real and are calculated from simplified equations. This paper presents a new method to measure layer thicknesses in flexible pavements. The method is based on predicting the reflected frequency spectrum through a multiple reflection model. The dielectric constants of the materials are assumed to be constant over the entire frequency range of the radar system, although dielectric and conduction losses are considered in the model. An optimization procedure is used by first calculating the reflected frequency spectrum using several values for the thicknesses and the complex dielectric constants, then choosing the solution with the minimum root-mean-square error between the predicted and measured frequency spectrums. The method was used in three pavement sections with known layer thicknesses. A percentage error of less than 3.6% was found between the measured and predicted values. CE Database keywords: Radar; Flexible pavements; Thickness; Nondestructive tests.

The paper develops an analytical formulation that quantifies the effect of vertical grade on vehicle fuel consumption and then illustrates the use of the developed procedure in the identification of the fuel efficient freeway layouts. Specifically, the Virginia Tech Comprehensive Power-based Fuel consumption Model (VT-CPFM) was used to develop the formulation and then applied using 2015's 10 most-sold vehicles in the U.S. and Europe to quantify the vertical grade effect on vehicle fuel consumption rates. An increase in fuel consumption of approximately 140% was found when the roadway grade increased from 0.5% to 6%. The proposed selection procedure uses Geographical Information System (GIS) applications in the design phase to evaluate possible freeway layouts. A multi-criteria analysis is performed to rank the feasible alternatives. The yearly fuel consumed by cars traveling on each feasible layout is then predicted and the alternatives are sorted in ascendingly. If the alternative selected by the multi-criteria analysis gives the least yearly fuel consumption, then that alternative should be constructed. If not, then the alternative that results in the least yearly fuel consumption should be re-evaluated with respect to the one selected by the multi-criteria analysis tool. The proposed procedure is validated using a real case study involving the construction of a new freeway in Cameroon. As much as a 12% difference in fuel consumption was found between the alternative with the least estimated yearly fuel consumption and that selected based on a multiple-criteria decision analysis. [ABSTRACT FROM AUTHOR]

Numerous research efforts have attempted to study the impact of a slow moving vehicle on the surrounding traffic stream behavior, also known as a moving bottleneck. However, none of the previous studies succeeded in developing a theory that is applicable to the breadth of traffic conditions that the phenomenon may occur in. Specifically, they are either based on intuition and mathematical reasoning or oriented towards very specific situations that do not reflect empirical behavior. Consequently, the research presented in this paper proposes and calibrates a flow–density relationship that takes into account all the parameters defining the state of traffic on the underlying fundamental diagram. The developed relationship, namely a bottleneck diagram, contains all the information necessary for the analysis of moving bottlenecks such as the traffic stream states directly upstream, downstream, and abreast the moving bottleneck (the passing rate and the average passing speed). A major contribution of the study resides in the fact that it reveals that the behavior of the traffic stream downstream abreast the moving bottleneck is governed by the arrival rate. [ABSTRACT FROM AUTHOR]

The accuracy of existing theoretical models to predict the compressive strength of concrete relies mainly on the accuracy of the used properties of its constituents. However, these models could be used at first to backcalculate the properties of aggregates from a given rock formation. Then, the compressive strength of any type of concrete made using those aggregates could be accurately predicted, using the already established properties. In this research, the compressible packing model and its extension to include non-optimised mixes (containing more than 10% filler) was used to mechanically characterise aggregates. Two procedures are described to backcalculate the parent rock compressive strength from compressive and/or indirect tensile strengths of concrete mixtures. Five different rock formations were used (three limestone, one marly limestone, and one dolomitic limestone). The first procedure uses compressive strength data for a concrete mixture at two different ages, while the second procedure uses compressive and indirect tensile strengths data from two concrete mixtures. Results show that both procedures provide a good estimate of the parent rock compressive strength. [ABSTRACT FROM AUTHOR]

This paper presents the findings of an experimental study performed on sand concrete reinforced with polypropylene fibres, which is a fine concrete containing only sand as aggregate. The material is intended to be used for the construction of rigid pavements for secondary roads. This material is considered ecological since it saves on the consumption of coarse aggregates, which natural resources are getting scarce, and it is based on two materials that are considered as wastes, namely sea-dredged sand and quarry sand. The performed tests include compressive strength, indirect tensile strength, three-point bending flexural strength, modulus of elasticity and free shrinkage. It was found that polypropylene fibres slightly reduce the mechanical properties of the material but significantly enhance its shrinkage behaviour as well as its toughness and therefore ductility. It was concluded that sand concrete reinforced with 1% (by weight of cement) polypropylene fibres is a suitable material for constructing rigid pavements for low-traffic roads. [ABSTRACT FROM AUTHOR]

The paper develops an analytical formulation that quantifies the effect of vertical grade on vehicle fuel consumption and then illustrates the use of the developed procedure in the identification of the fuel efficient freeway layouts. Specifically, the Virginia Tech Comprehensive Power-based Fuel consumption Model (VT-CPFM) was used to develop the formulation and then applied using 2015's 10 most-sold vehicles in the U.S. and Europe to quantify the vertical grade effect on vehicle fuel consumption rates. An increase in fuel consumption of approximately 140% was found when the roadway grade increased from 0.5% to 6%. The proposed selection procedure uses Geographical Information System (GIS) applications in the design phase to evaluate possible freeway layouts. A multi-criteria analysis is performed to rank the feasible alternatives. The yearly fuel consumed by cars traveling on each feasible layout is then predicted and the alternatives are sorted in ascendingly. If the alternative selected by the multi-criteria analysis gives the least yearly fuel consumption, then that alternative should be constructed. If not, then the alternative that results in the least yearly fuel consumption should be re-evaluated with respect to the one selected by the multi-criteria analysis tool. The proposed procedure is validated using a real case study involving the construction of a new freeway in Cameroon. As much as a 12% difference in fuel consumption was found between the alternative with the least estimated yearly fuel consumption and that selected based on a multiple-criteria decision analysis. [ABSTRACT FROM AUTHOR]