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Abstract

Accidents increase during the first rain after a long dry period due to the accumulation of fine particles, which contaminates the road surface and induces a friction loss. This paper presents new experimental evidences that help to understand how the particulate contaminants lubricate the tire–road interface. A laboratory test method is developed to reproduce the deposit of contaminant particles on the road surface and measure the friction coefficient on dry and wet contaminated surfaces. Test protocol is described with respect to the contaminant collection, the spreading of contaminant particles on the road specimen and their compaction to simulate the effect of the traffic, the wetting of the test surface to simulate precipitations, and the friction measurement. Friction tests are conducted in dry and wet conditions (by adding successive known quantities of water). Results show that dry particles can induce friction loss and the friction coefficient of dry contaminated surfaces is always lower than that of a dry and clean surface. The dry lubrication mechanism is attributed to shearing and sliding of the particle layer. Water induces first a significant friction drop, attributed to the viscosity of the particles–water mixture, then a friction increase due to a washing effect. Weight analysis shows a tight relationship between the friction coefficient and the mass of contaminants (particles in dry condition and particles–water mixture in wet conditions). There is a minimum in the friction versus water weight variation. Interpretation is made by considering fine particles as a wet granular material. Discussions are made with respect to the influence of particle concentrations and surface texture.

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... This is due to the fact that the lubricant particles are added more condensed inside the contact in the present study, leading that the tribofilms are well formed inside the contact. As observed in the previous studies including experimental, simulation and modeling ones [22,[55][56][57], the COF shows the lower value for the fully covered rough surface than for the unfulfilled covered one. The COF strongly depends on the type of the oxide particles, as seen in Fig. 2d; however, there are the ranges of the oxide types that show the same the COF, for example, the range of from CuO to Fe 2 O 3 . ...
... It is clear from the observation of the N film in Fig. 4a that lubrication should be increasing in the range ordered from SiO 2 to Bi 2 O 3 . This result is agreeable with the previous reports as the better lubrication with the better formed tribofilm [22,55,56,63]. The increase of the N film also results in the increase of the interaction strength between the oxide particles and the slider, as seen the above. ...
... The size and percentage, which are 1-20 µm and 5% in Ref. [66] and 0.5 µm and 100% in here, of the SiO 2 particles can be the reason causing the discrepancy of the COF. Friction can better improved with the smaller size [22,33,34] or the higher percentage [22,[55][56][57] of the lubricant particles inside the contacts. The single quartz sand particle against the N80 casing steel has the COF of 0.279-0.399, ...
Article
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The paper carries out the smoothed particle hydrodynamics simulations of lubrication for the micronscale iron contact by the 20 types of the spherical solid oxide particles. The iron slabs and oxide particles of micrometer sizes are modeled by the elastic particle lattice coarse-graining and discrete element method, respectively. Motion of the iron particles is presented by the governing equations of the smoothed particle hydrodynamics approach. The interactions between the particle pairs such as iron-oxide and oxide-oxide ones are presented by the Hertz repulsive contact and van der Waals attractive noncontact forces. Furthermore, the oxide particle dissipates its kinetic energy into the environment containing it through the Stockes damping force. It is found that stability and shear of the tribofilm are the main factors influencing friction reduction in all the behaviors. The interactions between the oxide-oxide particles and between the oxide-asperity iron particles mainly contribute to formation and maintainability of the tribofilm. The oxide with the higher density or the heavier oxide particle results in the lower friction coefficient. The friction reduction also strongly depends on the water/diesel environment containing the particles; however, the relative lubrication ability among the oxides is almost independent of the environment. It is also found that in the contacts with the highly condensed situation of the oxide lubricant particles the van der Waals force can be neglected due to its very slight contribution to the detected forces and the rolling of the lubricant particles almost has no contribution to friction, in contrast to the strong influence of temperature of the environment.
... Therefore, this result predicts that the friction of a rough substrate added condensed by elastic lubricant particles can increase with time. The present observations very well match close to the experimental reports of Hichri et al. that showed the dry and wet friction behaviors of the rough road surfaces contaminated by the fine particles [55][56][57]. The particle- contaminated surface at each given initial particle concentration always shows the lower value of the COF than the dry-clean one during the test for both the behaviors [55][56][57]. ...
... The present observations very well match close to the experimental reports of Hichri et al. that showed the dry and wet friction behaviors of the rough road surfaces contaminated by the fine particles [55][56][57]. The particle- contaminated surface at each given initial particle concentration always shows the lower value of the COF than the dry-clean one during the test for both the behaviors [55][56][57]. In each certain test with the given initial particle concentration, the COF increases with the testing time due to the decrease of the number of the fine particles inside the contact caused by the particle ejection outside the studied sample by the slider [55][56][57]. ...
... The particle- contaminated surface at each given initial particle concentration always shows the lower value of the COF than the dry-clean one during the test for both the behaviors [55][56][57]. In each certain test with the given initial particle concentration, the COF increases with the testing time due to the decrease of the number of the fine particles inside the contact caused by the particle ejection outside the studied sample by the slider [55][56][57]. This results in the decrease of the height of the fine particles on the rough surface and the change of the lubrication mechanism from the protective film to the surface mending, as obviously shown in Fig. 17 in Ref. [55] or Fig. 14 in Ref. [56]. ...
Article
The present study uses the smoothed particle hydrodynamics (SPH) and discrete element method (DEM) coupling to investigate influence of the hexagonal boron nitride (hBN) particles on friction of the elastic coarse-grained micronscale iron. The hBN lubricant particles significantly improves the friction performance of iron in various simulation behaviors. The particle size, the air/water background containing the particles and its temperature result in reduction of the friction coefficient. The surface mending, the protective film and the energy dissipation are the main mechanisms related to the friction reduction. Additionally, it is worthy to note that the static friction and the kinetic friction can be clearly observed by this elastic coarse-graining.
... Nevertheless, Mills et al. [12] and more recently Y. Hichri et al. [13,14] have observed that friction is already reduced on dry contaminated roads. These authors measured the friction by means of a Skid Resistance Tester (SRT) Pendulum which is widely used on roads field as a reference. ...
... The same testing procedure as the one of Y. Hichri et al. [14] was followed. Friction was measured on a clean and dry aluminium slab, as indeed Y. Hichri et al. [13] showed, roughness parameters of the aluminium slab are similar to road aggregates polished by the traffic. The friction was measured after the deposit of particles, then the measurement of friction was repeated until stabilisation of the friction coefficient. ...
... During friction tests, carbon adhesive discs were placed 50 mm away from the slab to capture particles ejected from it at passages 1,2,3,5 and 12. In accordance with Y. Hichri et al. [13], the passages 1,2 and 3 correspond with the fastest variation of the friction. Passage 5 corresponds with the slow increase of the friction and it is the passage at the half of the test. ...
Article
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Previous studies highlighted that friction value measured on real road surface textures covered by particles depends on particle sizes. This paper focuses on identification of particles behaviours at the tyre/road interface in the presence of particles. Identification is made by visual observations through high-speed camera, focus-variation microscopy and Scanning Electron Microscopy on the contaminated surface as scratch analysis on the surface. Two particle types were collected into samples picked next to roads. They are composed of clay and quartz which have different behaviours at the interface and affect the friction. Clay has a lasting effect due to its adhesive behaviour. Quartz has a scratching and rolling behaviour and is quickly ejected to the contact area due to a pinching effect.
... Similar results that the skid resistance of Stone Mastic Asphalt (SMA) covered by thin particles ( ∼ 1 mm) of ash slightly lower than those observed on wet surfaces in Blake et al. (2017). Hichri and Changarnier et al. (Changarnier et al., 2018;Hichri et al., 2017;Hichri et al., 2020) observed dry fine particles (less than 0.1 mm) behaviour at the slider/road interface, they found that the friction starts from a minimum value and then increases with successive passes of the rubber slider on the road surface covered by particle contaminants. Dry particles can induce friction loss attributed to the shearing and sliding of the particle layer. ...
... In Scenario 2, the pendulum test is also used as a means of evaluating the skid resistance of pavement in the Field Test Methods of Highway Subgrade and Pavement (JTG3450-2019). Previous studies (Hichri et al., 2017;Hichri et al., 2020; have mainly considered the lubrication effect of fine particles (less than 0.6 mm) on the road surface. Based on the experimental results of this study, when fine particles interact with a surface with small roughness (such as sand particles with a size below 0.6 mm and AC surface), the pavement friction even decreases by 40%, which has a significant potential hazard. ...
Article
To understand the effect of particulate contaminants on pavement skid resistance, the friction numbers of three surfaces under different pollution conditions (particle size, coverage fraction, and shape factor) were measured using a British Pendulum Tester (BPT). The results show that less than 45% coverage fraction of the particles above 0.3 mm even results in almost 50% friction loss at a low speed of 10 km/h. In this situation, the rougher surface has a stronger holding particles capacity. Moreover, the particle size determining the lowest friction level gradually increases as the surface roughness increases. The particle size of 1.18-2.36 mm is the most typical size range leading to a low friction level. In addition, the friction first drops sharply and then increases slowly with the coverage fraction increases, which also conforms to the Stribeck curve. Highlight • The skid resistance of road surfaces covered with particles was tested. • Effects of particle size, coverage fraction, and shape on friction were analysed. • Potential hazard scenarios with particulate contaminants were discussed. ARTICLE HISTORY
... In a previous study (Hichri et al 2017a), a test protocol to assess dry friction on road surfaces contaminated by particles was developed. These authors showed that particles lubricate the tire/road interface Effect of particles' characteristics and road surface's texture on the tire/road friction 2 Y Hichri et al and confirmed the particles trapping-as a lubrication mechanism-stated by Mills et al (2009). ...
... This is due to the fact that the distribution of particles evolves at each friction run. Nevertheless, to assess the repeatability of the test method, some test series were repeated and it was found that values of the friction coefficient at every step are very repeatable (coefficient of variation-ratio standard deviation/ mean-less than 4% at each step) (Hichri et al 2017a). ...
Article
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This paper presents a laboratory study to investigate the lubrication induced by particles deposited on road surfaces which is responsible for the increase of accidents at the first rain after a long dry period. Particles are extracted from sediments collected at a catchment area and characterized by their chemical composition and size distribution. Protocol to simulate the particle deposit on the road surface and their compaction by the traffic is described. The test program includes variables such as particle concentrations, particles’ size fractions and surface textures. Dry friction tests are conducted using the Skid Resistance Tester which simulates the sliding friction between a rubber slider and the test surface. Friction is lowered when the surface is covered by particles, compared with a clean surface. Repeated passages of the slider induce an increase of friction coefficient until reaching a stable value. Particles’ flows during a friction run are separated into those ejected from the sample, those stored by the surface macrotexture and those that stay on the test surface; this study demonstrated that the friction coefficient is closely related to the quantity of particles available on the test surface. SEM analysis shows on the other hand that these particles are mainly trapped by the surface microtexture. Similar behavior between fine particles and powder in terms of lubrication mechanisms is observed.
... Un calibrage du système de mouillage a permis de définir le meilleur emplacement de l'échantillon dans la chambre de mouillage en termes de répétabilité de la quantité d'eau reçue (coefficient de variation de 6%) et de durée de précipitation nécessaire (10s pour simuler une profondeur d'eau moyenne de 0,015 mm avec un coefficient de variation de 7% ; on simule donc une pluviométrie de 6,3 mm/h). Les essais de calibrage sont détaillés dans [12]. ...
Article
nte une étude en laboratoire visant à reproduire les conditions de contamination par des particules fines d’une surface de chaussée. Un protocole expérimental a été développé pour simuler le dépôt des particules sur un échantillon de chaussée, leur lessivage par l’eau de pluie ainsi que mesurer le frottement sur la surface contaminée. L’évolution du coefficient de frottement est comparée à celle de la masse des particules présentes sur la surface de l’échantillon. Des observations visuelles mettent en évidence le piégeage des particules par des creux de surface. Un modèle simple, intégrant la fraction de surface recouverte de particules, permet de reproduire les observations expérimentales en condition sèche.
... -The recirculation flow, which represents the particles that are raised and fall back onto the surface as well as the particles that remain trapped by the texture. In [2] and [22], it was thought that the passage of the SRT pad induces a shear in the particle layer that thins to the point where the rubber-surface asperity contact is established; during this shearing process, the particles are either ejected from the contact or trapped by the surface texture. This reasoning induces in turn the idea following which the surface coverage should decrease continuously with the repetition of the passages of the rubber pad and can be modelled by, for example, an approach based on a removal process as developed in [11]. ...
Article
This paper deals with the modeling of the coverage of surfaces contaminated by fine particles, the objective being the prediction of the skid resistance of road surfaces when it rains after a long dry period. The research methodology is based on the identification of particles' flows in the tribological circuit composed of the particles (3rd body) and the tire and the road (1st bodies). Experiments are conducted in laboratory where sliding friction is measured between a rubber pad (simulating a tire tread block) and a sandblasted aluminum surface (simu-lating a microtextured road surface) covered by particles. The test program includes particle concentrations representative of deposits of particles on the road surface at different dry periods and different particle size fractions. The test protocol consists in repeating passages of a rubber pad on the test surface and visualizing the particles' movements by means of high-speed cameras. Two particles' flows are identified: particles ejected from the contact and those raised by the rubber pad then fall back to the surface. Similarities are established with the removal and deposition of gas species in vapor-phase lubrication. An analytical model was derived to express the surface coverage as a function of the number of passages and two parameters (values between 0 and 1) called respectively the ejection and recirculation ratios. The proposed model is included in a linear rule-of-mixtures equation for the calculation of friction. Calculated friction coefficients compare favorably to experimental data and the model's parameters are determined. A master curve for different particles' sizes is obtained when relating the surface coverage to the mass of particles. Relationships between the ejection and recirculation ratios, the particles' characteristics and the surface texture are presented. Discussions are made in terms of transposition of the model to real road surfaces.
... With this device, it is also possible to study the rav-103 eling resistance of a surfacing material [10] .104In another study Hichri et al. are developed a laboratory test method to reproduce the 105 deposit of contaminant particles on the road surface and measure the friction coefficient on 106 dry and wet contaminated surfaces[11] . ...
Article
The existence of any liquid on the pavement surface causes a decrease in skid resistance. Heavy rain storm or improper surface grading leave a water film on the pavement surface. By increasing water film and vehicle velocity, there is a moment in which hydroplaning phenomenon can occur and causes the vehicle linear speed to become disproportionate to wheel rotational speed. In this study, a new laboratory-scale simulator is designed and manufactured that can simulate the occurrence of hydroplaning on asphalt pavements, facilitating the study of different parameters on the occurrence of this phenomenon such as vehicle speed, water film thickness, tire thread, pavement surface physical properties, etc. The lack of proportion between the linear movement of vehicle shaft and wheel rotation was considered as an important principle in designing of this machine. The designed apparatus involved electrical, mechanical, water transfer and asphalt mixture parts. The obtained results showed that the ratio of wheel rotational speed to its longitudinal speed is a proper index for identifying hydroplaning threshold. The results showed that by increasing frequency from 27.5 to 35 Hz, the ratio of wheel rotation to axle rotation in rpm is reduced by almost 10% in wet condition and hydroplaning occurred.
... On the surface covered by particles, as the contamination state evolves after each pass of the rubber pad, the reported friction coefficient corresponds to one run. Tests reported in a separate paper [12] have shown ...
Article
This paper presents a laboratory study using SEM observations to provide new insights into the behavior of fine particles at the tire/road interface. Similarities with the concepts of third-body and tribological circuit, on which the research methodology is based, are presented. The test protocol allows following the variation of the friction coefficient with the depletion of the particles on the test surface and collecting the particles ejected from the surface. Observations at different contamination phases reveal mechanisms like the coverage of the surface by the particles and the trapping of the particles by the surface voids. An analytical model, based on mass balance, is developed to explain the particles’ source and ejection flows and the effect of the particles’ size.
... The superhydrophobic functionalization was already developed in asphalt mixtures with polytetrafluoroethylene (PTFE) with water contact angle up to 166° [9] and with copolymer fluoroacrylate modified with CaO nanoparticles with water contact angle 163° [8]. The presence of oil, grease and dirty particles on the pavement also reduces significantly friction [10,11]. The self-cleaning property can reduce accidents in oil spilled areas and also in dusty areas. ...
Article
Although the noise and wear of frictional pairs in third-body behaviour have been widely researched, the dynamic characteristics of the frictional force under third-body intrusion behaviour are seldom studied. In this study, a spring–block structure driven by a conveyor belt with third-body particles is established. The results indicate that the interference of third-body particles changes the positive correlation between the frictional force and velocity to a negative correlation. A multi-contact frictional model is established using a cellular automata modelling approach to estimate the distribution of particles. The results reveal that this model can effectively predict the negative correlation under particle intrusion. This correlation may be attributed to the decrease in the third-body particle number with velocity. SiO2 third-body intrusion complicates the frequency characteristics; however, the intrusion of PVC particles lead to a smaller amplitude of the frictional force. Altering the size of the interface has a certain effect on the fluctuation mode of stick–slip under an extremely small surfaces separation.
Article
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We show experimentally that the sliding friction on sand is greatly reduced by the addition of some-but not too much-water. The formation of capillary water bridges increases the shear modulus of the sand, which facilitates the sliding. Too much water, on the other hand, makes the capillary bridges coalesce, resulting in a decrease of the modulus; in this case, we observe that the friction coefficient increases again. Our results, therefore, show that the friction coefficient is directly related to the shear modulus; this has important repercussions for the transport of granular materials. In addition, the polydispersity of the sand is shown to also have a large effect on the friction coefficient.
Article
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Solid particles on the floor, both dry and wet, are common but their effects on the friction on the floor were seldom discussed in the literature. In this study, friction measurements were conducted to test the effects of particle size of solid contaminants on the friction coefficient on the floor under footwear, floor, and surface conditions. The results supported the hypothesis that particle size of solids affected the friction coefficient and the effects depended on footwear, floor, and surface conditions. On dry surfaces, solid particles resulted in friction loss when the Neolite footwear pad was used. On the other hand, solid particles provided additional friction when measured with the ethylene vinyl acetate (EVA) footwear pad. On wet surfaces, introducing solid particles made the floors more slip-resistant and such effects depended on particle size. This study provides information for better understanding of the mechanism of slipping when solid contaminants are present.
Article
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The effects of particle shape and size distribution on the constitutive behavior of composite soils with a wide range of particle size were investigated. Two comparable sets of specimens were prepared: (1) mixtures of fines (clay and silt) and an ideal coarse fraction (glass sand and beads), and (2) mixtures of fines and natural coarse fraction (river sand and crushed granite gravels). Direct shear box testing was undertaken on 34 samples and the structure of the shear surfaces, change in volume and water content and the particle shape coefficient of the sheared specimens were examined. The results indicate that the contraction/dilation a specimen exhibits is restrained within the shear zone while the outer zones remain unchanged during shearing. An increased coarse fraction leads to an increase in constant volume shear strength. In addition, increasing elongation or decreasing convexity of the coarse fraction increases the constant volume friction angle. The overall roughness of the shear surface at constant volume state is negatively related to particle smoothness (convexity) and positively related to the area of the shear surface occupied by particles with particular shapes. Two equations are proposed for the estimation of constant volume friction angle based on the proportion and shape coefficient of the coarse fraction. It is hoped this will assist in considering the shear strength of mixed soils when the size of the coarse fraction makes laboratory testing difficult.
Article
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The strength of different wet granular materials is investigated as a function of the liquid volume fraction by measuring the elastic shear modulus, G'. We show that the optimum strength is achieved at a very low liquid volume fraction of 1–3%. Surprisingly we find that the macroscopic strength of different wet granular materials depends with a power of 2/3 on the microscopic elastic modulus of the individual grains, with a power of - 1/3 on the radius, and with a power of 1/3 on the surface tension. This can be explained by assuming that the attractive capillary force between two grains deforms the grains elastically, yielding a "spring constant" for further deformation. Averaging over many grain-grain orientations allows us to predict the macroscopic shear modulus in excellent agreement with our experiments.
Article
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Accurate and reliable estimations are the most important factors for the development of efficient stormwater pollutant mitigation strategies. Modelling is the primary tool used for such estimations. The general architecture of typical modelling approaches is to replicate pollutant processes along with hydrologic processes on catchment surfaces. However, due to the lack of understanding of these pollutant processes and the underlying physical parameters, the estimations are subjected to gross errors. Furthermore, the essential requirement of model calibration leads to significant data and resource requirements. This underlines the necessity for simplified and robust stormwater pollutant estimation procedures. The research described in this thesis primarily details the extensive knowledge developed on pollutant build-up and wash-off processes. Knowledge on both build-up and wash-off were generated by in-depth field investigations conducted on residential road and roof surfaces. Additionally, the research describes the use of a rainfall simulator as a tool in urban water quality research. The rainfall simulator was used to collect runoff samples from small-plot surfaces. The use of a rainfall simulator reduced the number of variables which are common to pollutant wash-off. Pollutant build-up on road and roof surfaces was found to be rapid during the initial time period and the rate reduced when the antecedent dry days increase becoming asymptote to a constant value. However, build-up on roofs was gradual when compared to road surfaces where the build-up on the first two days was 66% of the total build-up. Though the variations were different, it was possible to develop a common replication equation in the form of a power function for build-up for the two surface types with a as a multiplication coefficient and b as a power coefficient. However, the values for the two build-up equation coefficients, a, and b were different in each case. It was understood that the power coefficient b varies only with the surface type. The multiplication coefficient varies with a range of parameters including land-use and traffic volume. Additionally, the build-up observed on road surfaces was highly dynamic. It was found that pollutant re-distribution occurs with finer particles being removed from the surface thus allowing coarser particles to build up. This process results in changes to the particle size composition of build-up. However, little evidence was noted of re-distribution of pollutants on roof surfaces. Furthermore, the particulate pollutants in both road and roof surfaces were high in adsorption capacity. More than 50% of the road and more than 60% of the roof surface particulates were finer than 100 μm which increases the capacity to adsorb other pollutants such as heavy metals and hydrocarbons. In addition, the samples contained a significant amount of DOC which would enhance the solubility of other pollutants. The wash-off investigations on road and roof surfaces showed a high concentration of solid pollutants during the initial part of events. This confirmed the occurrence of the 'first flush' phenomenon. The observed wash-off patterns for road and roof surfaces were able to be mathematically replicated using an exponential equation. The exponential equation proposed is a modified version of an equation proposed in past research. The modification was primarily in terms of an additional parameter referred to as the 'capacity factor' (CF). CF defines the rainfall's ability to mobilise solid pollutants from a given surface. It was noted that CF varies with rainfall intensity, particle size distribution and surface characteristics. Additional to the mathematical replication of wash-off, analysis further focused on understanding the physical processes governing wash-off. For this, both particle size distribution and physicochemical parameters of wash-off pollutants were analysed. It was noted that there is little variation in the particle size distribution of particulates in wash-off with rainfall intensity and duration. This suggested that particle size is not an influential parameter in wash-off. It is hypothesised that the particulate density and adhesion to road surfaces are the primary criteria that govern wash-off. Additionally, significantly high pollutant contribution from roof surfaces was noted. This justifies the significance of roof surfaces as an urban pollutant source particularly in the case of first flush. This dissertation further describes a procedure to translate the knowledge created on pollutant build-up and wash-off processes using small-plots to urban catchment scale. This leads to a simple and robust urban water quality estimation tool. Due to its basic architecture, the estimation tool is referred to as a 'translation procedure'. It is designed to operate without a calibration process which would require a large amount of data. This is done by using the pollutant nature of the catchment in terms of buildup and wash-off processes as the basis of measurements. Therefore, the translation procedure is an extension of the current estimation techniques which are typically complex and resource consuming. The use of a translation procedure is simple and based on the graphical estimation of parameters and tabular form of calculations. The translation procedure developed is particularly accurate in estimating water quality in the initial part of runoff events.
Article
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Rubber friction on wet rough substrates at low velocities is typically 20-30% smaller than for the corresponding dry surfaces. We show that this cannot be due to hydrodynamics and propose a novel explanation based on a sealing effect exerted by rubber on substrate "pools" filled with water. Water effectively smoothens the substrate, reducing the major friction contribution due to induced viscoelastic deformations of the rubber by surface asperities. The theory is illustrated with applications related to tire-road friction.
Chapter
Description 40 papers on the characteristics of pavement surfaces, methods of measuring and interpreting them, and how to apply the resulting data in pavement management. Chapters include: Skid Resistance and Texture; Pavement Roughness, Field Economy, Noise, and other Related Subjects.
Chapter
The portable skid-resistance tester can carry out a wide variety of measurements on the road and in the laboratory. This paper outlines the basic principles underlying the design of the tester and describes the laboratory and field trials conducted during the development of the instrument. The factors influencing its performance are emphasized. In its performance, the instrument behaves as a patterned tire skidding at 30 mph. It is particularly well suited for testing rough-textured surfaces, and readings are independent of gradient, camber, or crossfall on the test surface.
Article
The research conducted to study the effect that unbonded material that lies on the road surface has on the short-term variation of skid resistance and polishing is described. This research included the design and construction of a device that can be mounted on a moving vehicle that is traveling at a speed of 16 km/h and can remove, collect, and separate according to size unbonded material on the road surface. For this study, daily skid-resistance measurements were taken on the road surface according to ASTM E274-77 and a sample of dust and debris was collected from the road surface and analyzed for size distribution.
Article
The portable skid-resistance tester can carry out a wide variety of measurements on the road and in the laboratory. This paper outlines the basic principles underlying the design of the tester and describes the laboratory and field trials conducted during the development of the instrument. The factors influencing its performance are emphasized. In its performance, the instrument behaves as a patterned tire skidding at 30 mph. It is particularly well suited for testing rough-textured surfaces, and readings are independent of gradient, camber, or crossfall on the test surface.
Article
Suspension rheology is of widespread importance to industry and research. Hard spheres represent a benchmark by which to compare other particle suspensions, and there are a variety of analytical and numerical models available to describe their rheology. However, it is experimentally challenging to produce ideal hard spheres, where surface forces are negligible between particles, and where phase volume is precisely defined. Beyond the dilute regime, the model by Maron and Pierce [1] and Quemada [2], which we refer to as the MPQ model, is commonly used analytically to describe the relative viscosity of hard sphere suspensions as a function of phase volume and a maximum packing fraction (ϕ m). We show that obtaining ϕm from empirical fits can lead to misinterpretation of experimental data. We reveal that reasonable prediction of the viscosity is obtained using the MPQ model when ϕm is set to the geometric random close packing fraction ϕ rcp, which is independently defined from the particle size distribution using the packing model of Farr and Groot [3]. This 'theoretical' approach is tested using a wide variety of experimental data on colloidal and non-colloidal hard spheres without need for any fitting parameters or empiricisms. In addition, plotting the inverse of the square-root of viscosity as a function of phase volume, which linearises the MPQ model, provides a convenient means by which to clearly see where suspensions deviate from the model due to such effects as particle aggregation, particle softness and measurement errors. We also demonstrate the necessity of this approach by accurately predicting the viscosity of microgel suspensions up to ϕ rcp; empirical fits across the full data set are erroneous because particle deformation and viscoelasticity lead to values of ϕ > ϕ rcp. This approach provides a suitable unambiguous theoretical baseline for comparison to experimental studies on suspension rheology involving polydisperse size distributions.
Article
The effect of contaminants has been overlooked and yet plays a significant role in driver safety and road maintenance. A laboratory test method is developed to reproduce the deposit of contaminant particles on the road surface and measure the friction coefficient on dry and wet-contaminated surfaces. It simulates in this way the variation of skid resistance of the road surface due to contaminants during a dry period–precipitation event and the washoff effect of the rain. Protocols are described with respect to the contaminant collection on site and the subsequent preparation in the laboratory, the spreading of contaminant particles on the road specimen and their compaction to simulate the effect of the traffic, the wetting of the test surface to simulate precipitations, and the friction measurement. Values of friction coefficient on clean and dirty dry surfaces as well as during the surface wetting (simulation of precipitations) are plotted. Comparison with the literature shows that the developed test method reproduces remarkably well qualitative graphs used to highlight the loss of skid resistance with time during a rain preceded by a long dry period. The effect of contaminant concentrations and traffic is shown. Explanations are given in terms of the masking of the road surface microtexture; they are supported by visual observation of the road surface before and after the contaminant deposit.
Article
This paper is the second part of an investigation of the mechanism and performance of powder lubrication. In the first part of the investigation (this volume pp. 508–517), the basic features of the quasi-hydrodynamic nature of particulate lubricants were conceptualized and the experimental setup for testing was described. In the tests described herein, load capacity, friction levels, and, most importantly, rates of wear were recorded for a wide range of operating conditions and various surface geometries, materials, and powder lubricants. The test results demonstrate the viability of powder lubrication. The results also corroborate the postulated quasi-hydrodynamic nature of particulate films. In addition, features specific to powder lubrication were brought to light, such as the onset of starvation with time, and the phenomenon of film adhesion. Based on these findings, design requirements for the proper functioning of practical powder-lubricated systems are described. Finally, a hydrodynamic model consisting of a mating surface, intermediate films, and a particulate lubrication film is presented. With these tools developed, analytical or semi-empirical relations should become available for the design of full-scale, powder-lubricated tribosystems.
Article
Samples of sediment found on an urban road in Aberdeen (Scotland) were collected by washing designated surfaces. This method, called the "wet" method, was capable of collecting sediment of the smallest particle size range that is normally left behind by traditional sampling techniques using dry vacuuming. Over 17 months (mainly on a weekly basis), 66 samples were collected and analyzed for sediment loading, particle size distribution, concentration of heavy metals (Zn, Cu, Pb, Cd) in four sediment size fractions, and several dissolved pollutants in the effluent collected from washing (NO3-, SO42-, PO43-, Cl-, F-, NH4+, total organic carbon, total carbon). Standard statistical methods, including multiple regressions, were used to determine relationships amongst different sediment characteristics. It was found that sediment loading, as well as concentrations of Cl- and SO42-, were highest in the winter months, 4 especially when snow was present on the road surface. It was observed that 66% of total road sediment loading was found within a 0.5 m strip next to the curb. The average sediment particle sizes found were smaller than those previously recorded in the literature. As expected, the concentrations of heavy metals were highest in the smallest particle size fraction analyzed (<63 mum), and this occurred during the summer months when less sediment was available on the street surface. The antecedent dry weather period had a very weak and negative influence on the loading rate of the smallest particle size fraction next to the curb.
Article
Statistics by the UK Health and Safety Executive (HSE) suggest that slips, trips and falls account for up to one in three major workplace accidents. The vast majority of these accidents are the result of contaminant (fluid or solid) within the shoe–floor contact. Though the lubrication mechanisms for liquid contaminants within the contact are well understood, the same cannot be said for particulate contaminants. This paper considers the key parameters controlling friction in a shoe–floor contact contaminated with various particles of different diameters and shape factors and floors with different roughness values (Rz). Experiments were conducted using a Stanley Pendulum Tester, which is the floor friction tester recommended by the HSE. Results suggest that the adhesive friction is significantly affected by particulate contaminants, while the hysteretic component is not. Three lubrication mechanisms identified as sliding, shearing and rolling have been observed depending on floor roughness, particle size and shape factor and have been plotted in a simple map to predict behaviour.
Article
A general method to optimize a wet powder agglomeration process for achieving desired properties of granulated products is suggested. The different states of a wet powder are characterized by a cohesion function, i.e. the evolution of the torque of the stirred system as a function of the moisture content. Two different types of agglomeration behaviours are shown: Stepwise Growing Behaviour (SGB) and Continuous Growing Behaviour (CGB). The influence of various parameters such as the particle-size distribution and the wettability of the solid surface on the cohesion function are highlighted. Such functions are shown to be very helpful to define the granulation process and the properties of the granulated products, revealing a promising methodology.
Article
Many laws already exist for wear, but few are really predictive. In order to better understand the wear process, classical wear models are compared to the third body concept. This concept emphasizes that particle detachment mechanisms, the flow of these particles inside the contact, and their ejection from the contact have to be considered in order to describe wear effectively. An analytical demonstration is proposed, that considers the particle detachment process and the particle ejection process separately. These two processes are then linked by a mass equilibrium equation. In continuous sliding, a steady-state wear process can be identified in which the mass of third body particles in the contact remains constant. The source flow and the wear flow (representing, respectively, particle detachment and particle ejection) become equal and constant in time. Initially presented via numerical investigations, this analytical model is then confirmed by simple experiments.
Article
An understanding of pollutant characteristics on impervious surfaces is essential to estimate pollutant washoff characteristics and to design methods to minimise the impacts of pollutants on the environment. This paper presents data on surface pollutant characteristics on an urban road surface in Melbourne, Australia, from samples collected over a 36 day period. The data indicate that buildup over the dry days occurs relatively quickly after a rain event, but slows down after several days as redistribution occurs. The surface pollutant also becomes finer over the dry days as it is disintegrated. The washoff of surface pollutant is dependent on the rainfall and runoff characteristics, but the results here show that common storms only remove a small proportion of the total surface pollutant load. The data also show that street sweeping may have an adverse impact on pollutant washoff because the street sweeper releases the finer material but only removes some of them, making the fine sediment available for washoff by the next storm. The data also show that most of the nutrients are attached to the finer sediments, and to effectively reduce nutrient loads in particulates, treatment facilities must be able to remove the finer particles (down to 50 μm for TP and down to 10 μm for TN), and not just the total sediment or suspended solid load.
Article
The quality of stormwater runoff from the urban environment is of increasing concern to urban communities and, consequently, greater emphasis is now being placed on the management of stormwater quality. An essential need for this management is information about the drainage system and the impacts of alternative management approaches. This information, typically, is obtained through the use of catchment model systems which simulate the processes which influence both the quantity and quality of stormwater runoff. These model systems consist of a number of components with information flowing from one component to another; each of these components in turn comprised of process models. An important component of these systems for water quality modelling is the generation component where the mass of pollutant constituent available for transport during the storm event is estimated. Available information for use in the models applied to this task is extremely limited and, consequently, the poor reliability of this initial information is reflected in the reliability of the predictions obtained from the catchment model system. Presented herein are the results of a study investigating the build-up of pollutant constituents on a suburban road in the eastern suburbs of Sydney, Australia. It was found that the pollutant constituents available for transport during storm events were significantly different from previously published data for North America. Furthermore, it was found that both rain and wind events lowered the available pollutant constituent mass on the road surface.
Thesis
Specific appreciation (as outlined below) is given to the significant industry partners/supporters that have helped support the research in many different ways. Firstly, I must give special thanks to Works Infrastructure Limited who have supported the research both financially and with resources almost from the outset of the research programme. The field testing data collection in the Northland Region of New Zealand would not have been possible without the support of the Whangarei Works Infrastructure team which included Peter Houba, Peter King, Matthew Findlay, Glen Kirk and the temporary traffic control team headed by Derek Phillips. Thanks also go to the Auckland Works Infrastructure testing laboratory which supplied aggregate supplies for laboratory sampling and testing and whose technicians also undertook Polished Stone Value tests on the aggregate samples. Special thanks are also given to Michael Haydon and David Hutchison from the technical management team of Works Infrastructure who have always been willing to listen to my requests and the many discussions that we have had on aspects of skid resistance, policy and technical matters. Pavement Management Services and especially Dr John Yeaman and Daniel Rich for their support for the research programme from the beginning, and secondly for financially contributing to the purchase of the Dynamic Friction Tester for the static field testing and the laboratory tests. Achnowledgement is also given to The Ports of Auckland and especially Jo Campbell of the AXIS Intermodal group that allowed access to the rail grid site as a field-testing site outside of normal port operation hours. Transit New Zealand head office staff (Mark Owen, David Cook and Chris Parkman) are also thanked for their support of the research and in enabling access to historic SCRIM and RAMM data on the Transit New Zealand state Highway network. Land Transport New Zealand (formerly Transfund New Zealand) are acknowledged for their significant financial support of the research, in terms of the Land Transport New Zealand Research project that allowed the field research data collection and analysis programme to continue for a further year and for the extension to the controlled laboratory testing. It has been well proven that as the skid resistance of a road surfacing decreases, the number of loss of control type crashes increases, causing road death and injuries. However, the management of skid resistance of road surfacings continues to be difficult due to the inherent and sometimes random variation in skid resistance levels over time. This study is an investigation and analysis of seasonal and short term variation of measured skid resistance in two phases. Phase 1: Regular field monitoring was undertaken using the GripTester and the Dynamic Friction Tester measurement devices on seven sites in the Auckland and Northland Regions of New Zealand was undertaken over a three year period. The effects of temperature, rainfall, contaminants, new surfacings, geometric elements and aggregate properties were analysed to investigate factors that initiate changes in the measured skid resistance of pavement surfacings. Phase 2: Laboratory prepared samples were constructed for accelerated polishing and skid resistance testing of four different aggregates (two greywackes, a basalt and an artificial iron-making melter slag aggregate). The samples were polished in an accelerated polishing machine to an ‘equilibrium skid resistance’ level (Stage 1 polishing). Contaminants were then added to the accelerated polishing process to determine the effect of varying additive, particle size and hardness in an attempt to simulate seasonal and/or short-term variations that occur in the field. The results have demonstrated that significant and previously unpredictable variations (greater than 30%) in measured skid resistance can occur over short time periods. These variations cannot be explained by any one factor. They are the result of a number of inter-related factors, including the geological properties of the aggregates and the contaminants themselves, the previous rainfall history, the road geometry, the calendar month of the year and (depending upon the measurement device), the temperature during testing. The laboratory tests demonstrate that accelerated polishing tests of aggregate samples could be prepared for testing by the Dynamic Friction Tester and that significant variations in measured skid resistance could be simulated on various aggregates in the laboratory by the addition of contaminants. The results of the testing and addition of contaminants on various aggregates resulted in significant behavioural differences which were related to the geological properties of the aggregates themselves, as well as the contaminants used in the accelerated polishing process. The findings of the research have specific relevance to three areas of industry; Road Controlling Authorities who are primarily interested in skid resistance policy, standards and management, Road Asset Managers who operate, maintain and manage condition level and the safety aspects of the road network and Crash Investigators who collect and analyse crash data primarily for legal proceedings. All three of these industry organisations need to clearly understand the inherent variability of skid resistance, the factors involved and the effects that geological and environmental variations have on skid resistance measurement.
Article
Materials commonly found on street surfaces have been determined to contribute to urban pollution when washed into receiving waters by storm runoff. A study was performed that provides a basis for evaluating the significance of this source of water pollution relative to other pollution sources. The study was designed to include information from communities having a broad range of sizes, geographical locales, and public works practices. Information was developed for major land use areas within the cities. In general, street runoff was a greater pollutant than sanitary wastewater, at least during storms.
Article
This paper investigates the relationship between precipitation and traffic crashes in the US during the period 1975-2000. Traffic crashes represent the leading cause of death and injury for young adults in the US, and the ninth leading cause of death for the overall population. Prior studies have found that precipitation raises the risk of traffic crashes significantly. A negative binomial regression approach is employed. Two different units of analysis are examined: state-months and state-days. The sample includes all 48 contiguous states. A surprising negative and significant relationship between monthly precipitation and monthly fatal crashes is found. However, in the daily level analysis, a strong positive relationship is estimated, as in prior studies. The source of the contrasting results appears to be a substantial negative lagged effect of precipitation across days within a state-month. In other words, if it rained a lot yesterday, then on average, today there are fewer crashes. Additional analysis shows that the risk imposed by precipitation increases dramatically as the time since last precipitation increases. For example, 1cm of precipitation increases the fatal crash rate for a state-day by about 3% if exactly 2 days have passed since the last precipitation and by about 9% if more than 20 days have passed. This basic pattern holds for non-fatal crashes as well. The lagged effects of precipitation across days may be explained by the clearing of oil that accumulates on roads during dry periods or by the conditioning of people to drive more safely in wet conditions. Either way, policy interventions that prepare drivers more adequately for the risks of precipitation following dry periods are likely to be beneficial.
Article
In the context of stormwater quality modelling, an in-depth understanding of underlying physical processes and the availability of reliable and accurate mathematical equations, which can replicate pollutant processes are essential. Stormwater pollutants undergo three primary processes, namely, build-up, wash-off and transport, before accumulating into receiving waters. These processes are expressed mathematically by equations in stormwater quality models. Among the three processes, wash-off is the least investigated. This paper presents the outcomes of an in-depth investigation of pollutant wash-off processes on typical urban road surfaces. The study results showed that a storm event has the capacity to wash-off only a fraction of pollutants available and this fraction varies primarily with rainfall intensity, kinetic energy of rainfall and characteristics of the pollutants. These outcomes suggest that the exponential equation commonly used for mathematically defining pollutant wash-off would need to be modified in order to incorporate the wash-off capacity of rainfall. Consequently, the introduction of an additional term referred to as the 'capacity factor'C(F) is recommended. C(F) primarily varies with rainfall intensity. However, for simplicity three rainfall intensity ranges were identified where the variation of C(F) can be defined. For rainfall intensities less than 40 mm/h, C(F) varies linearly from 0 to 0.5. For rainfall intensities from 40 to around 90 mm/h, C(F) is a constant around 0.5. Beyond 90 mm/h, C(F) varies between 0.5 and 1.
Guide for pavement friction. NCHRP Web-Only Document
  • Jw Hall
  • Kl Smith
  • L Titus-Glover
Effect of water-film thickness on tire-pavement friction Surface characteristics of roadways: International research and technologies, ASTM STP 1031
  • Bt Kulakowski
  • Dw Harwood
Atomic emission spectrometry methods for determination of heavy metals (As, Cd, Co, total Cr
  • L Prevedello
  • Salvagio Manta
  • D Sprovieri
Prevedello L, Salvagio Manta D and Sprovieri M. Atomic emission spectrometry methods for determination of heavy metals (As, Cd, Co, total Cr, Cr(VI), Cu, Hg, Ni, Pb, Se, V, Zn) in marine sediments. Technical Report (http://eprints.bice.rm.cnr.it/1239/), IAMC-CNR di Napoli, 2008.
Guide for pavement friction
  • J W Hall
  • K L Smith
  • L Titus-Glover
Hall JW, Smith KL, Titus-Glover L, et al. Guide for pavement friction. NCHRP Web-Only Document, 2009, http:// onlinepubs.trb.org/onlinepubs/nchrp/nchrp_w108.pdf.
Method for measurement of slip/skid resistance of surface -Part 4: The pendulum test
European Committee for Standardisation. Method for measurement of slip/skid resistance of surface -Part 4: The pendulum test. European Standard, prEN 13036-4, 2009.