Anti‐Slip Material‐Based Strategies and Approaches

A comparison of results from portable and laboratory floor slipperiness testers

Like all test devices, a British pendulum tester has to be calibrated to ensure that its measurements are correct and accurate within acceptable limits. The ASTM E303 and BS EN 13036-4 standards present two established and widely followed calibration procedures for the British pendulum tester. Though similar in most aspects, there are some differences in the two calibration procedures. This study examines the impacts on British pendulum test (BPT) results of the calibration requirements of the two standards by means of a finite element BPT simulation model developed based on theories of mechanics. The simulation model is applied to analyze the range of variations in the test values of BPT devices with different operating parameter values within the allowable limits of the two standard procedures. It is found that two BPT devices both satisfying the ASTM E303 calibration requirements could produce measurements with a difference of more than 60 % of their mean test value, and for BS EN 13036-4 it is more than 25 %. It means that different BPT devices, all meeting necessary calibration and precision requirements of either of the two standards, could give different test values that might lead to different skid resistance assessments of the pavement tested. This is unsatisfactory for practical applications in skid resistance evaluation of pavements. Based on analyses of the simulation model, this study proposed revised calibration limits to achieve more acceptable magnitudes of differences between the measurements made by different BPT devices.

The conventional British pendulum tester (BPT) utilises a cuboid rubber slider and measures the skid resistance between its front slider edge and a test surface. This standard test method is known to produce erroneous skid resistance measurements on grooved pavements, owing to impacts between the straight slider edge of BPT and the vertical walls of pavement grooves. To overcome the problem, this study replaced the cuboid slider with a curved slider having an external radius of 100 mm, constructed of the same rubber material as the standard BPT rubber slider. The ability of the proposed improved device to eliminate the vertical-wall impact problem and provide correct skid resistance measurements of a grooved surface was verified experimentally and numerically. A full-scale prototype was fabricated for this purpose. Experimental validation tests involving the standard cuboid-slider BPT and the curved-slider BPT were conducted, and the test results were analysed with the aid of finite-element numerical models. The results confirmed that the proposed curved-slider BPT can provide more consistent and accurate skid resistance measurements compared to the standard BPT, for both grooved and ungrooved pavements.

Mechanistic harmonization of British pendulum test measurements

Skid resistance and surface friction of pavements is an essential consideration in pavement performance and traffic safety. The British pendulum tester (BPT) is widely used to measure the skid resistance of pavements worldwide both in the field and laboratory. Diamond grinding and grooving is a commonly used surface rehabilitation technique for concrete pavements to improve their surface friction. At the laboratory scale, polishing of concrete pavement surfaces by diamond grinding and grooving using the three-wheel polishing device creates a smaller available test area compared to the test area required by the standard test method for the British pendulum test. This study presents a modified test method for the use of BPT on diamond ground surfaces with small test areas. To evaluate the feasibility of this method, the effect of different levels of polishing on the BPT measurements were analyzed. Results suggest that the BPT using the modified method described in this study is not a reasonable tool to evaluate the skid resistance of diamond ground surfaces at the laboratory scale.

Testing and evaluation for skid resistance of steel slag asphalt wearing course based on surface texture characteristics

The British pendulum test is one of the most common laboratory test methods for the determination of low-speed microtexture-related skid resistance properties of pavement surface materials. This paper presents the development of a three-dimensional finite-element model that simulates the British pendulum test. The procedures for determining different model parameters are described. Besides the constant parameter values representing the characteristics of the British pendulum tester, only a relatively simple static friction test is needed to provide the necessary input to the computer model. Three different pavement materials were studied in the model validation program. Results of the validation program showed that there was very good agreement between the laboratory measured British pendulum test data and the computed values by the finite-element model. The output variables verified included the energy loss, British pendulum number (BPN), sliding distance, time taken to cover the sliding distance, inclination of rubber slider, and contact pressure. The findings suggest that the skid resistance BPN of a pavement material can be determined without having to physically perform the British pendulum test.

Low-speed skid resistance tests provide useful information not available from the normal high-speed skid resistance testing of road pavements. There are known limitations of the two commonly used measuring devices of low-speed skid resistance, i.e. British Pendulum Tester (BPT) and Dynamic Friction Tester (DFT). This study develops a Walking Friction Tester (WFT) to offer a practical alternative to measure low-speed pavement skid resistance. This paper compares WFT with BPT and DFT measurements in the following three aspects: correlation relationship, measurement variability, and speed comparison of field tests. Tests were also performed to examine the variability of WFT test results with respect to walking speed and water film thickness, respectively. The study showed that there was a good correlation coefficient of 0.80 between BPT and WFT measured data, and 0.70 between DFT and WFT friction coefficients. WFT measured data were found to have smaller variability than those of BPT and DFT. In field tests performed over a length of pavement section, WFT generated continuous friction data in much shorter times compared with the spot measurement mode of either BPT or DFT. The results also showed that WFT tests were independent of changes in walking speeds of operators and variations of water film thickness applied.

The British pendulum tester (BPT) provides a method to measure the skid resistance of pavement, which possesses both theoretical and practical engineering significance. This article aims to establish a numerical hysteresis friction model for BPT to reproduce the dynamic motion of the slider and estimate the pavement friction based on surface texture roughness, rubber viscoelasticity property and contact characteristics. The analytical hysteresis friction model was introduced based on one of the modern rubber friction theories. As an input parameter of this model, the average penetration depth of rubber was calculated based on the interfacial separation assumption. A numerical model was established by combining the geometric and motion characteristics of BPT. To validate the model, the self-affine characteristics of texture from four types of asphalt pavement were analysed; simultaneously, the storage and the loss modulus of rubber slider at various frequencies were obtained using the Zener constitutive model. As a result, the velocity of the slider decreases gradually with the dynamic fluctuation of the friction coefficient. A significant linear correlation was found between the predicted values and the measured data. This numerical friction model performs some potential for friction estimation. However, more conditions need considering for the improvement and practicability of the model.

Laboratory investigation of the effect of temperature on frictional properties of concrete pavements containing crushed glass

Pavement frictional behavior affects pavement performance in terms of vehicle safety, fuel consumption, and tire wear. Comprehending and interpreting pavement friction measurements is a challenging task, because of friction sensitivity to several uncontrollable factors. These factors include: pavement surface conditions, such as the type and thickness of contaminants and fluids on the surface and their interaction with friction forces; and the device operating conditions, such as sliding speed, material properties and geometry of the rubber slider used, and operating temperature. Despite the efforts to describe and quantify the impact of varying conditions on pavement friction, which ultimately will allow for a better harmonization of friction measurements, there is a need to better understand the link between the surface texture and physical friction measurements. In this paper, Persson’s friction model is used to analyze and understand the impact of surface texture on frictional behavior of dry pavement surfaces. The model was used to analyze 18 test locations, which were compared with the dry kinetic coefficients of friction (COF) estimated using a British pendulum tester (BPT). The results show that Persson’s friction model could predict the COF estimated from the BPT results with relatively high accuracy. In addition, the model could provide a profound explanation of the frictional forces mechanism. Finally, it was found that the mean profile depth (MPD) cannot provide a full picture of the frictional behavior. However, combining MPD with the Hurst exponent, texture measurements can potentially provide a full physical explanation of the frictional behavior for road surfaces.

The British pendulum test is a common procedure for laboratory as well as field measurement of the low-speed friction of a road surface material. It is widely suggested that the measured low-speed friction is largely governed by the surface microtexture of the road material, and many researchers and practitioners have considered the friction measurements made by the British pendulum test to be an indirect form of measurement of available microtexture of the road material. The experimental results presented in this paper show that this general view is not always correct. This study investigated the effects of test surface macrotexture represented by the following two geometric parameters: the size of subcontact areas and the magnitude of gaps between subcontact areas. The test results demonstrated that the low-speed friction measurements by the British pendulum tester were significantly affected by test surface macrotexture. This finding also implies that the closely packed aggregate condition required for the laboratory British pendulum test may not produce a correct assessment of the skid resistance of the true road surface. Laboratory measurements are likely to overestimate the skid resistance of a road surface if the surface aggregate spacing is wider than the spacing of the manually-packed laboratory specimens.

Runway surface friction is critically important to safe aircraft operations and mostly depends on the surface texture, which provides grip in the presence of contamination and directly affects the friction coefficient in general. Microtexture assessment is the most challenging part of texture assessment since there is no standardised pavement microtexture control method in runway maintenance and management practice. The purpose of this study was to develop a simple laser profilometer and analysis model and subsequent validation for use in runway friction surveys. To that end, a simple laser profilometer was developed, and a profile picture analysis and macrotexture filtration method were designed. Test results were compared to the stylus-based roughness tester and the British Pendulum Tester. The proposed profile picture analysis and profile smothering and filtration methodology, based on linear approximation, is simpler and more effective for the case of macrotexture filtration for the friction survey. The laser profilometer model results were highly correlated with the stylus-based roughness tester results (R2 = 0.99). The average roughness of the microtexture profile, after smothering and macrotexture filtration, also showed good correlation with the British Pendulum results (R2 = 0.78). The results from this study confirm the possibility of texture assessment for routine runway friction surveys using a simple and economical laser profilometer, which is not routinely available in current airport surface friction management.

Providing sufficient pavement surface friction (i.e., skid resistance) between vehicle tires and pavement surface throughout the pavement service life is considered to be one of the main objectives of highway design. Moreover, vehicle safety, the amount of consumed fuel, and the wearing rate of vehicle tires generally are influenced by pavement surface friction. In this study, a comprehensive experimental testing program was conducted on different aggregate sources, including calcined bauxite and five alternative local sources, to assess their friction characteristics. The testing program included a British pendulum tester (BPT) and a dynamic friction tester (DFT), which were used to evaluate the friction characteristics of the proposed aggregates, along with basic and durability properties tests. The aggregate imaging measurement system (AIMS) technique was applied to evaluate the aggregate characteristics due to Micro-Deval degradation. This study provides two empirical models for the friction characteristics of high-friction surface treatment (HFST)-application aggregates based on the experimental results. The first model correlates the friction coefficient at 20 km/h (DFC20) with the British pendulum number (BPN). The second model expresses DFC20 as a function of polishing resistance of aggregates, which is represented by the initial and terminal aggregate texture and angularity values measured using the AIMS device with an overall coefficient of determination (R2) of 0.949. The aggregate characteristics (i.e., particle angularity and surface texture) align well with the microtexture characteristics of the investigated sources.

This paper reports the influence of nanosilica on friction and sound absorption responses of concrete for application in rigid pavements. The paper also discusses the feasibility of applying nano-lotus leaf as a coating for concrete material. Previous research on friction and sound absorption characteristics of concrete pavement primarily emphasized creating different surface textures through macrotexture modifications. The microstructure can also have a significant effect on surface texture, friction, and sound absorption characteristics of concrete. This research studied the friction and sound absorption properties of concrete on the basis of microtexture modification that used nanomaterials such as nano-silica and nano-lotus leaf. Several laboratory concretes were produced by using different proportions of nanosilica, which partially replaced cement by weight. The fresh concretes were tested for workability, wet density, and air content. The hardened concretes were tested for compressive strength, friction, and sound absorption. The British pendulum test was used to determine the friction number. An impedance tube was used to determine the sound absorption coefficient. Preliminary results indicate that nanosilica can increase friction and sound absorption of concrete pavements. In addition, the results show that nano-lotus leaf can be applied as a coating on concrete material for rigid pavements to improve retention of their friction properties during the wet season.