Many different test methods are used in practice to evaluate the surface infiltration performance of permeable pavements. This has led to inconsistency in reporting of test results. This study ...recognizes the differences in nature between a soil infiltration study and the surface infiltration evaluation of permeable pavements, and identifies the main issues associated with the current practice of surface infiltration testing. It proposes that hydraulic conductivity be adopted as the flow property for measurement and reporting instead of the commonly used infiltration rate. The advantages of measuring hydraulic conductivity are elaborated from both theoretical and practical implementation points of view. The theoretical merits of providing a consistent and integrated treatment of surface infiltration performance of a permeable pavement during the design, construction and maintenance phases are presented. The practical benefits are addressed from the following aspects: consistency between laboratory and field testing, uniformity in reporting of test measurements, rationality in construction quality control and acceptance checking, effectiveness in surface infiltration performance monitoring, and enhanced ability in implementing effective maintenance management. It is emphasized that the techniques and methods needed for measuring hydraulic conductivity of permeable pavement materials, for laboratory testing as well as on-site field testing, are already readily available and have been used by researchers and some practitioners for surface infiltration testing. Two falling-head test methods are recommended: one applies Darcy's law and determines hydraulic conductivity in the conventional way; another measures the time history of falling head and calculates hydraulic conductivity using a modified Darcy equation. It is also highlighted that the measurement of hydraulic conductivity offers a convenient platform for assessing the durability of a permeable pavement against clogging.
•Permeable pavement surface infiltration capacity governs stormwater management.•Conventional infiltration rate inadequately addresses stormwater management needs.•Consistent laboratory and field test methods of surface infiltration is proposed.•Proposed test methods measure hydraulic conductivity instead of infiltration rate.•Proposed tests permit integrated framework of design, construction and maintenance.
•Three skidding modes on horizontal curves are analyzed.•Computer simulation model predicts maximum safe speeds against skidding.•Key skidding potential factors are vehicle speed, water depth, and ...pavement state.•Other factors include curve radius, superelevation and vehicle parameters.
High crash rates on horizontal curves during wet weather are a major road safety concern. Among the various causes of crashes on horizontal curves, wet-weather skidding is a major contributing factor. This study analyzed the mechanisms of three possible modes of vehicle skidding on horizontal curves based on theories of mechanics. The three modes of skidding analyzed were: (i) forward skidding of front steering wheel, (ii) sideway skidding of front steering wheel, and (iii) sideway skidding of rear wheel. The main objective was to provide useful information to researchers and practitioners in identifying the important factors that contribute to horizontal curve crashes. A computer simulation procedure was developed to evaluate the maximum safe vehicle speeds against the three modes of skidding on wet horizontal curved pavements. This offers a much improved method for skidding potential evaluation compared to the conventional approximate method using estimated coefficient of friction. The skidding potential of a vehicle is defined as the difference between its speed and the maximum safe speed against skidding. The smaller the difference, the higher is the skidding potential. The relative magnitudes of skidding potential for the three skidding modes were considered for different operating conditions. Different operating conditions were represented by different values of pavement curve radii, super-elevations, and wet-weather conditions represented by the thickness of pavement surface water-film. The analysis identified five key factors that affect the skidding potential of vehicles negotiating a horizontal curve. They are: vehicle speed, curve radius, superelevation, water film thickness and pavement skid resistance state.
The Concept of Skid Resistance State for highway pavements is introduced in this paper. The Concept states that at a given point in time, each unit length of a pavement has a fixed deterministic skid ...resistance value under a given set of pavement, environmental and vehicle operating conditions. A set of the operating conditions is defined by the following parameters: Vehicle tyre geometric and structural properties, wheel load, tyre pressure, vehicle speed, tyre slip ratio, tyre slip angle, pavement microtexture and macrotexture properties, ambient temperature, and pavement surface water film thickness. It is demonstrated in this study that, according to the proposed Concept, the skid resistance characteristics of a pavement can be fully described by a computer simulation model that analyses tyre-pavement-fluid interaction based on solid mechanics and fluid dynamics theories. Once the computer skid resistance model of a pavement section has been established, its skid resistance value under any vehicle-pavement-environmental operating condition can be calculated. Currently, there are already a number of computer skid resistance models developed by pavement researchers. Using one of these models for illustration, this paper explains how the Concept of Skid Resistance State is applied. The rationale, calibration process of the model, and input parameters are described; followed by a numerical demonstration of the establishment of the Skid Resistance State of an example pavement section. The significance and potential applications of the Concept on functional pavement mix design, pavement friction maintenance management, and harmonising of skid resistance measurements by different devices are also described.
•Sand-patch test of mean texture depth (MTD) is unsuitable for field monitoring.•Existing methods to predict MTD from digital images contain incorrect assumptions.•New digital image-based method is ...proposed using concept of planation surface.•New method provides realistic simulation of standard sand-patch test.•New method gives more accurate MTD predictions than existing methods.
The conventional manual sand-patch method of mean texture depth (MTD) measurement is unsuitable for network level pavement condition monitoring. Relying on 2-D mean linear profile depth (MPD) to estimate 3-D MTD is also unsuitable because MTD-MPD regression relationship varies from one pavement mix type to another. This problem of network level MTD measurements and monitoring can be overcome if MTD could be numerically determined from 3-D digital laser images. All the numerical MTD determination methods proposed by researchers in recent years made a common invalid assumption that the MTD top surface was defined by the high texture peaks of the test surface. This study presents evidence to show that the top surface defining MTD actually lies below the highest peaks of the test surface. Next, applying the concept of planation surface, a novel numerical procedure is proposed to identify a reference surface for MTD calculation by means of a second-derivative plot of peak-height percentiles. The validity of the proposed method was verified experimentally with measured MTD values of both laboratory fabricated specimens and in-service pavements. For four different surface course materials, the errors in the predicted MTD values range from 0.20 to 7.31 %. The proposed method produced improved accuracy in MTD predictions compared with the existing methods which were based on incorrectly assumed MTD top surfaces.
Different infiltration tests of permeable pavements provide different measurements of the infiltration capacity. These measurements often do not represent the fundamental flow properties, and hence ...cannot be directly compared. This presents an undesirable obstacle to the sharing of experience and to obtaining a better understanding of the infiltration performances of different permeable pavements. This problem is especially acute in the case of interlocking-block permeable pavements (IBPPs), owing to the presence of joints and the different sizes, shapes, and laying patterns of paving blocks. To overcome this problem, the present study proposed a new approach for evaluating the infiltration capacity of an IBPP while retaining the same measuring devices in use today. This approach makes use of a finite-volume computational fluid dynamic method to develop a simulation model for an infiltration test. Once calibrated to define the hydraulic parameters of the IBPP being tested, the model can be applied to calculate the saturated infiltration capacity of the IBPP under actual rainfall conditions. The model also permits the calculation of a conventional infiltration capacity measurement, such as the average infiltration rate in mm/h as measured by a particular infiltration test, or the time required to drain the tested water depth. Thus, the proposed approach provides a meaningful common basis for comparing the infiltration capacities of different permeable pavements, including porous asphalt, pervious concrete, and IBPPs.
•New calculated measure of permeable pavement infiltration capacity IC is proposed.•New approach resolves the current issue of inhomogeneous reporting of IC.•No changes are needed to the measuring devices and methods in use today.•The issue of measuring localized IC faced by current devices is eliminated.•The approach is theoretically sound.
The British pendulum test is commonly used to measure low-speed pavement friction and provide a measure of the quality of pavement surface micro-texture in terms of skid resistance contribution. ...Generally, it is considered an empirical test, and the measured British Pendulum Number (BPN) taken as an index value. The present study shows that this interpretation is a misrepresentation of the test, and that the British pendulum test is a theoretically sound test, and there exists a unique one-to-one mechanistic relationship between the measured BPN and friction coefficient. By means of a three-dimensional finite-element simulation model developed using theories of physics, it is demonstrated mechanistically that for each test surface with a known coefficient of friction, there is a unique corresponding BPN value. That is, BPN is not an empirical index, but an engineering quantity that has a mechanistic relationship with the friction coefficient of the test surface. The theoretical model makes it possible to interpret mechanistically the results of tests conducted in the field and laboratory. The theoretical soundness of the test has high practical significance in evaluating the low-speed friction coefficients of pavement materials during mix design in the laboratory, and friction management of in-service pavements.
Traffic-induced wear of road pavements is known to possess directional characteristics. Quantitative characterization of wear directionality in terms of surface texture properties has practical ...significance in the study of wear mechanisms and driving safety analysis. However, the pavement texture parameters and indices in use today are unable to reveal the directional characteristics of pavement wear. This study proposed a texture statistic, the Directional Wear Index (DWI), to measure pavement wear directionality based on a laser scanned image of a pavement surface. First, macrotexture peaks that were likely to be subjected to traffic abrasive actions were identified as primary peaks using the concept of topographic prominence. Next, a slope ratio was calculated to characterize the shape of a primary peak. DWI was determined as a function of the prominence-weighted sum of the shape codes of all the primary peaks of the surface analyzed. The calculated value of DWI defines both the direction and the magnitude of directional wear of the pavement wear. The proposed concept and DWI calculation procedure were validated using field measured data of actual in-service pavement segments with known directional wear characteristics.
•All existing texture descriptors cannot reveal directionality of traffic-induced wear.•A texture statistic DWI was proposed to measure pavement wear directionality.•The concept of prominence and slope ratio was adopted to calculate DWI.•DWI is able to differentiate directions and degrees of wear of actual pavements.
Knowing the maximum safe driving speed on a pavement curve under wet condition is crucial in achieving safe driving in wet weather. This information is valuable for pavement engineers in paving ...materials selection, mix design, drainage design and pavement maintenance treatment design to meet the skid resistance requirements for the safe driving speed. Unfortunately, due to the complex variables involved (including pavement surface material properties, tire properties and water film thickness), currently there is no practical working procedure that allows pavement engineers to determine the maximum safe driving speed of a vehicle on a horizontal curve under wet weather condition. To bridge this gap, this paper presents a finite element simulation model that predicts the maximum safe driving speed for a vehicle on a horizontal pavement curve (with known pavement material properties) in wet weather when there is a layer of water on the pavement surface. The maximum safe driving speed was derived by first calculating the available tire-pavement frictional resistance using the finite element simulation model, followed by a tire skidding potential analysis considering the available tire-pavement frictional resistance and the centrifugal force acting on the tires. The development and validation of the simulation model are described in this paper, and numerical examples are presented to illustrate its application in the determination of maximum safe vehicle speed. The procedure and input data (including pavement material properties and drainage data) required for calculating the maximum safe vehicle speeds on actual in-service pavement curves are presented and explained.
Asphalt mixture is a multi-phase material composed of coarse aggregate, asphalt mortar and air voids. It is of interest to study how the distribution of internal phases of asphalt mixture would ...affect pavement surface texture. This is an area that has not received much attention. In an attempt to establish a relationship between the internal structure of an asphalt mixture and its surface texture, this paper employs a 2-dimension image-based internal structure analysis method (2D-IISAM) to characterise the aggregate arrangement, voids distribution and mortar distribution of an asphalt mixture. The internal structure properties of 28 different asphalt mixtures were evaluated by 2D-IISAM, and their corresponding surface texture properties were evaluated by sand patch method and 2-Dimension Image-based Texture Analysis Method (2D-ITAM), respectively. The relationships between the surface texture and the internal structure parameters of the asphalt mixtures studied were established by the Levenberg-Marquarat and generalised global optimisation algorithm. The results suggest that the surface texture of an asphalt pavement is significantly influenced by its internal structural properties. Regression relationships were developed to predict surface texture from the internal structure of an asphalt texture, and vice versa.
•Each scanned area by commercial laser scanners is too small for pavement studies.•A setup was proposed to provide larger and accurate pavement texture images.•Reverse-twin scanning procedure was ...proposed to reduce occlusion effects.•Software application was developed for efficient implementation of the new setup.•Experimental verification confirmed the efficiency and accuracy of the new setup.
Commercial laser scanners that have the required measurement resolutions, cover too small an area per scan for pavement texture studies. Time and skill demanding image splicing tends to introduce errors. To overcome the limitation, this study developed the laboratory Chang’an University 3D Laser Scanning Device (CUSD) to cover a single-scan area of up to 800 × 325 mm, with the capability to perform a reverse-twin scanning procedure to reduce occlusion effects. To verify the advantages of CUSD, twelve asphalt mixtures were tested by CUSD and a commercial scanner AMES HD9400. CUSD took 19 min to scan and process the image of an area measuring 750 mm long, compared to more than 3 h by AMES HD9400. The experimental verification showed that the mean profile depth (MPD), root-mean-square height (RMS) and height deviation index (Ra) obtained from CUSD images were all within 5% of the values by AMES HD9400.
