British Pendulum Research Articles

Theoretical and practical engineering significance of British pendulum test

ABSTRACT 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.

Investigating the Relation among British Pendulum Number, Mean Texture Depth and Asphalt Content in Hot Mix Asphalt

Pavement surface texture and its skid resistance are two key safety parameters of highways, which both are influenced by pavement characteristics. In the present study, a newly constructed asphalt pavement (Qom-Garmsar freeway) in Iran is examined. The goal is to inspect the relation between skid resistance and pavement texture in order to asphalt content changes in Hot Mix Asphalt. Mean Texture Depth (MTD) and British Pendulum Number (BPN) are being applied to quantify pavement texture and skid resistance, respectively. The results show that the asphalt content has a significant effect on MTD and consequently, BPN in loaded pavements, as well as non-loaded pavements. The result revealed that the lowest BPN value obtained, when the asphalt content is about the optimum value. Moreover, it is demonstrated that using asphalt contents less and more than the optimum value, results in BPN improvement. Asphalt content increasing, around optimum value, leads to MTD decrease. The results also reveal that by increasing the MTD, the BPN decreases to 75 (in MTD value of 0.62 mm) and then increases.

How Can Sustainable Materials in Road Construction Contribute to Vehicles’ Braking?

Vehicles’ braking is a key factor towards safer driving. In particular, tyre–pavement friction is connected with both industry and infrastructure requirements in terms of tyre characteristics and frictional properties of pavement surfaces respectively that both contribute to safe braking. For this reason, tyre–pavement friction is considered as one of the most pressing emergencies in roadway assets in order to reduce skidding related accidents. At the same time, sustainability aspects have been raised in modern infrastructure engineering. Hence, an issue is introduced on how sustainable materials used for pavement construction may contribute to tyre–pavement and consequently vehicles’ braking. For this reason, a laboratory process is developed to investigate the frictional properties of several utilized in pavement wearing courses including both traditional and sustainable materials (reacted activated rubber—RAR and reclaimed asphalt pavement—RAP). Environmental conditions (seasonal temperature changes, rainfall effect and contamination caused by dust formation) are simulated in the laboratory and vehicles’ braking is investigated using the British Pendulum Tester (BPT). Results provide a good explanation for the vehicles’ braking ability under the investigated conditions for both traditional and sustainable materials. Ultimately, it is proved that asphalt mixture types with RAR modifier or RAP material exhibit a satisfactory performance towards providing a safe road surface for the moving vehicles.

Correlate aggregate angularity characteristics to the skid resistance of asphalt pavement based on image analysis technology

The impact of aggregate morphological characteristics plays a key role in the skid resistance of road surface due to driving safety and cost benefits. The 2nd generation of the Aggregate Imaging Measurement System (AIMS II) and X-ray Computed Tomography (CT) were utilized to evaluate the shape of particles and capture the change in their morphological characteristics. The Los Angeles Abrasion (LAA) Test was also conducted in this paper to investigate the influence of variations in aggregate angularity on the resistant performance of asphalt mixtures. Before and after 100, 300, 500, and 1000 rotations of LAA polishing process, 48 particles from each different size were adopted and measured using AIMS II and XCT to obtain the value of their morphological properties. The parameter gradient angularity (GA) with AIMS II and three-dimensional angularity (3DA) with XCT of aggregate surface area were proposed from these tests. Analysis of Variance (ANOVA) was employed to compare these two image analysis systems. Conventional experiments including the sand patch test and British pendulum test, were applied using the prepared aggregates to establish a correlation between the morphological properties of grains and the parameters related to the skid resistance of asphalt mixtures. It was found that the resistance performance of asphalt mixtures can be well described with a function using the value of morphological properties through regression analysis. The efficacy of the X-ray CT analyzing system was verified to evaluate the performance of asphalt mixture pavement precisely. The changes in morphological characteristics of particles are the main causes for degradation in the skid resistance of asphalt pavement.

Fraction Factorial Design of a Novel Semi-Transparent Layer for Applications on Solar Roads

Solar roads are transportation infrastructures able both to generate electricity thanks to solar cells placed under a semi-transparent layer and to ensure heavy traffic circulation. In this paper, a novel transparent top layer made of glass aggregates bonded together using a polyurethane glue is presented. The goal is to design a composite material able to support traffic load, guarantee vehicle skid-resistance, allow the passage of sunlight, and protect the solar cells. For this purpose, the authors investigated the effect of different variables (thickness, glue content, and glass aggregate distribution) on the mechanical and optical performances of the material applying the factorial design method. The semi-transparent layer was characterized by performing the three-point bending test and measuring the power loss. Regarding the vehicle friction, experimental tests with the British Pendulum were conducted in order to measure the skid resistance of the surface and compare it with the specifications of a typical road infrastructure. According to the fraction factorial design and the British Pendulum test, the following mixture was developed: 42.8% of 4/6 mm; 42.8% of 2/4 mm, 14.4% of glue in volume, and a thickness of 0.6 cm. The first results are encouraging, and they demonstrate the feasibility of a semi-transparent layer for future applications in full scale.

Chemical Frost Protection of Road Surfaces: A Laboratory Investigation

Anti-icing chemicals are commonly used to protect against hoar frost formation on roadways and bridges. Because of their negative impact on both environment and infrastructure, their use should be optimized. During conditions for hoar frost formation, this means that good knowledge is needed about when it is necessary to apply chemicals, and the corresponding protection time. A laboratory setup has been used to study the freezing process for a salted road surface during conditions for hoar frost formation, and a description of the process is given. It has been observed that freezing starts in the top layer of the applied solution, indicating the occurrence of a concentration gradient owing to accumulation of water molecules in the top layer. A British pendulum was used to simulate the mechanical load of traffic. The pendulum successfully destroyed the ice up to a certain ice fraction. This ice fraction was seen to depend on the amount of salt solution applied to the test sample. Finally, it has been illustrated how the maximum ice fraction can be used to calculate the amount of water allowed to be added to the road surface, and estimates of the protection time are given.

Long‐Term Skid Resistance Evaluation of GAC‐16 Based on Accelerated Pavement Testing

In this paper, four antiskidding surface test sections were paved to investigate the long‐term skid resistance of the improved dense‐graded asphalt concrete in Guangdong Province (GAC) using diabase fine aggregate instead of limestone. Four test sections were tested by the accelerated loading equipment (MLS11, mobile load simulator). The reduction law of the long‐term skid resistance of GAC‐16 was analyzed based on the accelerated pavement testing results. Prediction models of the GAC‐16 skid resistance were also established and verified. The evaluation indexes of the long‐term skid resistance of the asphalt pavement were introduced, and the antiskidding durability of different sections was evaluated. Results show that the initial British pendulum number (BPN) and mean texture depth (MTD) of the asphalt pavement cannot completely characterize its long‐term skid resistance. With increasing loading cycles, the attenuation law of the BPN and MTD of GAC‐16 denotes a fast reduction during the early stage, which gradually stabilizes. The relation between the skid resistance index and accelerated loading cycles was analyzed by nonlinear fitting according to the least‐squares‐method principle. The attenuation law of the BPN and MTD of GAC‐16 with loading cycles was in accordance with the exponential and logarithmic models, respectively. The long‐term antiskidding performance of the asphalt pavement could be accurately characterized using a stable BPN, loading cycles while reaching a stable BPN, the initial MTD value, and the MTD reduction rate as the evaluation indexes of the skid resistance of asphalt pavement. Compared with limestone fine aggregate, diabase fine aggregate can improve the long‐term skid resistance of the asphalt mixtures.

Influence of the Skid Resistance of Ultrathin Wearing Course with Various Types of Asphalt Binders

Ultrathin wearing course (UTWC) has been widely applied in both asphalt pavements preventive maintenance and functional overlay. This study’s objective is to evaluate the influence of different modified asphalt binders with warm mix additives on the skid resistance of UTWC and to reveal the attenuation law of skid resistance of UTWC. Three types of modified asphalt binders (Styrene‐Butadiene‐Styrene‐ (SBS‐) modified asphalt, Acrylester Rubber‐ (AR‐) modified asphalt, and SinoTPS‐modified asphalt) and sasobit warm mix asphalt additive were selected to prepare asphalt mixtures. The Model Mobile Load Simulator 3 (MMLS3) was used to simulate repeated vehicle loading and abrasion. The British Pendulum Number (BPN) and Mean Texture Depth (MTD) were chosen to evaluate the skid resistance of the UTWC. The Analysis of Range (ANOR) and Analysis of Variance (ANOVA) were used to verify the significance of asphalt binder on the antiskid performance of the UTWC. ANOR and ANOVA show that the influence of different modified asphalt binders on the skid resistance of the UTWC is significant. The SinoTPS modified asphalt mixture can maintain high texture roughness before and after abrasion, providing excellent and durable skid resistance. The influence of the addition of a warm mixing additive on the skid resistance of UTWC is not significant, and changes in microtexture mainly reflect its impact on antiskid performance. The decay curve of three modified asphalt binders of the skid resistance of the UTWC can be well fitted into an exponential function. The conclusion will play an essential role in selecting the asphalt binder in a UTWC to improve the antiskid performance.

Performance of Waterborne Epoxy Emulsion Sand Fog Seal as a Preventive Pavement Maintenance Method: From Laboratory to Field

To preserve the existing asphalt pavement and extend its service life, various preventive maintenance methods, such as chip seal, slurry seal, fog seal, and microsurfacing, have been commonly applied. Sand fog seal is one of such maintenance methods, which is based on the application of bitumen emulsion and sand. Thus, its performance is largely dependent on the properties of the bitumen emulsion and sand. This study aims to develop an improved sand fog seal method by using waterborne epoxy resin as an emulsion modifier. To this end, both laboratory tests and field trials were conducted. In the laboratory, the wet track abrasion and British pendulum test were performed to determine the optimum sand size for the sand fog seal, and the rubbing test was carried out to evaluate the wearing resistance of the sealing material. In the field, pavement surface regularity before and after the sand fog seal application was measured using the 3 m straightedge method, and the surface macrotexture and skid resistance were evaluated with the sand patch method and British pendulum test, respectively. The laboratory test results indicated that the optimum sand size range is 0.45–0.9 mm, and the sand fog seal with waterborne epoxy resin showed good wearing resistance and skid resistance. The field test results verified that both the pavement texture and skid resistance were substantially improved after sand fog sealing.

Effect of surface texture, size ratio and large particle volume fraction on packing density of binary spherical mixtures

Packing density is a key factor in governing the properties of materials such as concrete, asphalt, ceramic etc. Therefore, determination of packing density of a particulate mixture accurately, is of great importance. However, involvement of many external and internal factors such as surface texture, shape, method of packing etc. has made it very complicated and tedious to determine the packing density. The study investigated the combined effect of particle surface texture, size ratio and large particle volume fraction on packing density and developed a descriptive model to predict the packing density. Further, design graphs were also developed for the convenience. The study revealed that the British pendulum number value of the surface texture linearly varies with the packing density. The rougher the surface, the lower the packing density. The interparticle friction hinders the particle rearrangement. Hence, the ability to achieve a higher packing state is reduced. Further, irregularities in the surface boundary create void spaces, increasing the total voids in the mix. Thus, the packing density reduces. The increase of the size ratio decreases the packing density linearly. The packing density variation with a large particle volume fraction follows a 3rd order polynomial curve. The trend analysis was conducted to develop the descriptive model and design graphs to predict the packing density of binary mixtures.

Evaluation of skid resistance of pervious concrete slabs under various winter conditions for driver and pedestrian users

Skid resistance of pervious concrete (PC) in comparison with traditional portland cement concrete (PCC) was investigated in the laboratory and in the field. Dry, wet, and iced PC surfaces were tested using the British Pendulum Tester (BPT) with two rubber sliders to represent driver and pedestrian users. Also, iced PC surfaces were treated with de- and anti-icing chemicals and then tested using BPT. Skid resistance values were recorded as the British Pendulum Number (BPN). PC slabs cast from one mix design in three compaction levels revealed that minimal correlation existed between PC porosity and BPN. Laboratory-cast PC slabs showed 23%, 27% and 97% higher BPN values relative to PCC slabs under dry, wet and icy surface conditions, respectively. After one icing event, the one-time application of anti- and de-icing agents on PC slabs improved their friction to the allowable BPN level using both MgCl2 and CaCl2. Field testing of five PC installations with various mix designs and surface conditions showed similar or slightly higher BPN than adjacent PCC slabs. Overall, the laboratory testing in this study showed it is possible to produce PC with significantly higher skid resistance relative to traditional concrete, the field testing revealed the importance of regular maintenance, aggregate type and mixture design on the skid resistance of pervious concrete.

Skid resistance of gap graded hot-mix asphalt with added crumb rubber

Road surface condition is a critical factor that determines road safety. The paved surface of the road should have sufficient skid resistance to enable a vehicle passing over it to accelerate and stop/brake safely and comfortably. Gap graded hot-mix asphalt is generally used as a non-structural and an impermeable layer to protect the structural layers. The hot rolled sheet (HRS) asphalt mixture has larger cavities that require more asphalt compared to other asphalt pavement types. The addition of crumb rubber (CR) to the asphalt mixture was carried out using the dry mixture method, and the resulting mixture was added to the aggregate. This study utilizes gap graded asphalt pavements containing natural asphalt from a processed product called Asbuton Retona blend 55. CR was added to the asphalt mixture in proportions of 0.5%, 1%, 1.5%, and 2%. This added material improves the performance of the asphalt mixture. The skid resistance of the paved surface layer studied herein used the British pendulum tester for pavement surface temperature variations of 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, and 50 °C. Utilization of CR derived from used tire rubber powder provides the benefit of reusing waste materials that can help preserve the environment. The gap graded hot-mix asphalt with added CR and asphalt modified Asbuton Retona blend 55 has shown an improvement in the skid number. These results show that the hot-mix asphalt pavement with modified asphalt is more impermeable and provides better slip resistance.

Thermal changes in concrete pavement skid resistance

Concrete pavements comprise a considerable portion of pavements that are currently in use. This paper presents the results from a laboratory investigation on the effect of temperature and surface texture on the skid resistance of concrete pavements. Briquettes representative of concrete pavements were created and textured in the laboratory. Readings of skid resistance on laboratory specimens were obtained using a portable British pendulum tester. Water and liquid hand soaps were used as lubricants in an attempt to separate the adhesion and hysteresis components of friction. In order to simulate the wear and ageing of concrete pavements, several cycles of polishing were applied to the briquettes. Tests were conducted at five different temperatures. The results showed that there is a correlation between the magnitude of friction components and temperature. A normalisation procedure for friction measurements based on temperature was developed, which can be used to normalise measurements to a standard temperature of 293·15 K.

Effect of Pavement Friction Factors on Skid Resistance of Highway Pavements using Prediction Models

There are many features for road pavements, in which the most significant feature is skid resistance. Skid resistance is referred to as the contact (friction) among the pavement surface and automobile tires. Essentially, this feature is vital to guarantee adequate road secureness and it takes a fundamental part during specific climatic conditions. The aim of this research is targeted at distinguishing the primary attributes that impact skid resistance, so that the rates of traffic collisions that occur as a result of insufficient skid resistance specifically in wet climate conditions, are minimized. Throughout this research, designs to calculate the association of surface texture form, automobile velocity, tire type and the type of asphalt mixture on skid resistance were created and applied to evaluate the significance of each attribute as well as enhancing the secureness of roads. Hence, the attributes influencing skid resistance were chosen and evaluated utilizing the SPSS program. Also, the British Pendulum Skid Resistance Tester was utilized in order to evaluate the skid resistance of various surface textures. The outcomes obtained by this study proved that there is a strong association among surface texture, wheel form, type of mixture and automobile velocity, where R2=96.5%. Moreover, the outcomes advocated the necessity of applying operating method designs to minimize duration and exertion as well as computing the influence of these attributes on skid resistance. The ingenuity of this research is in its concept which advocates that the manipulation of skid resistance operation method results in enhanced road security and minimizes collisions, which respectively diminishes fatality rates.

Experimental Investigations on Tire/Road Friction Dependence from Thermal Conditions Carried out with Real Tread Compounds in Sliding Contact with Asphalt Specimens

The understanding of tire’s adherence with a rough surface is a common goal for several fields in the automotive sector. In fact, grip is synonym of safety and performance, playing a decisive role for braking distance and vehicle stability, fuel consumption, wear rate [1], noise generation and for the vehicle dynamics control system (e.g. ABS, TCS, AYC and other) [2]. This paper deals with tire tread grip experimental investigation and evaluation under different conditions that influence it during the sliding contact [3]. In this regard the test campaign involves the use of different tire compounds (in terms of viscoelastic characteristics), tested in several conditions: different contact pressure, sliding speed, temperature, sliding contact length and road surface. The test bench employed by the UniNa Vehicle Dynamic Research Group is an upgrade of the British Pendulum, an instrument for outdoor tribological tests on road sections. The principal sensors installed on the test bench are an encoder, for the evaluation of the sliding speed of the tire specimen, and a load cell, for the measurement of the force arising at tire/road interface in the longitudinal and vertical directions [4]. In fact, the grip shall be determined as the ratio of the longitudinal force and corresponding load on the tire. The paper's aim is the description of the experimental campaign after an accurate introduction on the test setup and an illustration of the equipment. Finally, the preliminary results and the methodologies used to process the acquired data are described.

Prediction of frictional characteristics of bituminous mixes using group method of data handling and multigene symbolic genetic programming

A safe road transport requires adequate friction between vehicle tires and pavement surface for safe travels. Adequate friction is essential for a vehicle to safely maneuver. Inadequate friction is directly correlated to the accident hazard, particularly in wet weather conditions. Quality of pavement materials has a prodigious effect on skid resistance and high-quality materials allow adequate pavement frictional resistance for an extended period. Science evaluation of frictional characteristics depends on physical, chemical, and mineralogical properties of the aggregate, type of mix, binder/bitumen content, water film thickness, etc., and it necessities a costly and time-consuming test protocol. In the present research, a model is developed for the evaluation of skid resistance in terms of the British pendulum number (BPN), using experimental observations, with the aid of machine learning tools. In the present work, group method of data handling (GMDH) and multigene symbolic genetic programming (MSGP) have been used to model the BPN. Developed model is capable to simplify extremely nonlinear deviations in data as well as forecast the frictional performance from experimental data. It is also found that the performance of the MSGP (R2 = 0.99) is more encouraging and better than that of the GMDH model (R2 = 0.98) for the prediction of BPN. The analytical expression obtained through MSGP in the present study has been also subjected to sensitivity analysis to assess the effect of individual parameters in prediction of BPN.

Photocatalytic asphalt mixtures: semiconductors’ impact in skid resistance and texture

Photocatalytic asphalt mixtures have the capability of mitigating air quality problems and degrade oils/greases by using semiconductors. The techniques to do so can change their functional characteristics. This study aimed to analyse the functionalization effect on the essential surface characteristics, such as macrotexture, skid resistance, and microtexture. AC 14 and AC 6 mixtures were functionalised with nano-TiO2 and micro-ZnO by spraying and bulk incorporation. Mean Profile Depth, British Pendulum and microtexture amplitude parameters were evaluated. TiO2 application seemed to smooth the surface slightly. In dry condition, the skid resistance of functionalised asphalt and control mixtures was similar. In wet condition, the functionalization caused a maximum decrease of 7% in skid resistance. The amplitude parameters were not affected by any functionalization technique except the skewness of AC 14 with 6% TiO2 by bulk incorporation. Furthermore, the application of the semiconductors can be used without high impacts in texture and skid resistance.

Directional Skid Resistance Characteristics of Road Pavement: Implications for Friction Measurements by British Pendulum Tester and Dynamic Friction Tester

The British pendulum tester (BPT) and the dynamic friction tester (DFT) are commonly used to evaluate the polishing effect of traffic on pavement skid resistance. The present study was conducted to answer two questions: (i) whether the directional moving traffic action results in significant directional differences in skid resistance of the pavement, and (ii) if so, whether BPT and DFT are effective tools for evaluating the skid resistance performance of polished pavements with significant directional skid resistance characteristics. Five in-service pavement sections with different degrees of polishing were examined in this study. The following findings were obtained from the study: (a) There were statistically significant differences between the longitudinal and transverse skid resistance of the polished pavements tested; (b) there were no statistically significant differences between the longitudinal and transverse skid resistance of the newly paved unpolished pavement tested; (c) BPT was able to differentiate the directional skid resistance differences of the polished pavements tested; and (d) DFT was unable to differentiate the directional skid resistance differences of the polished pavements tested. DFT produces one skid resistance value for a circular path at each test point. The test results found that DFT over-estimated the traffic-direction skid resistance of in-service pavements. The over-estimation errors ranged from 0.001 to 0.023 DFT units, and the corresponding percent errors were from 0.4% to 11.1%. This finding suggests that the over-estimation effect of skid resistance directionality of polished pavements on DFT measurements should be recognized in pavement skid resistance evaluation and pavement safety studies.

Mobile Light Detection and Ranging for Automated Pavement Friction Estimation

Rapid detection and maintenance of pavement friction is essential for roadway crash prevention. Traditional measurement methods are time-consuming, labor-intensive, and inefficient. This paper proposes a new method to rapidly estimate pavement friction by using a light detection and ranging (LiDAR) sensor. Eight parameters are developed to capture the texture and material information of pavement. The British pendulum number is adopted as the reference of pavement friction with the data collection and processing approaches stated. An ordered logit regression model is utilized to estimate the level of pavement friction, with an average accuracy of 75.86%. The model shows that both textures and material information contribute to pavement friction. Some experimental tests are conducted to explore the potential impact of illumination, showing that lighting and road shading do not affect measurements. The proposed LiDAR-based method is able to assist for rapid, economical, and automatic estimation of pavement friction.

An Evaluation of Relationship with Polished Stone Value and Skid Resistance Value Based on a Laboratory Investigation

Aggregates which are the main component of asphalt concrete play a major role in loading transfer and skid resistant performance of asphalt concrete. Therefore, reduction in friction resistance of aggregate would lead to a decrease in overall skid resistance of asphalt concrete which is a commonly used road pavement surface material. This research aims to evaluate relationship of aggregate friction capacity through the polished stone value and asphalt concrete skid resistance. In this study, a series of polished stone value tests on the study aggregate of limestone and sandy mudstone and British pendulum tests for skid resistance value of polished hot mix asphalt (HMA) slab. An accelerated polishing machine was used to create reduction of skid resistance of HMA slabs. Test results showed that reduction of polished stone value (PSV) of limestone 47.6% leads to a decrease of skid resistance value (SRV) approximately 43.8% of HMA slabs. Furthermore, 14.5% reduction of PSV of sandy mudstone causes a decrease of 20.3% SRV of HMA slabs. Finally, a relationship linear regression between PSV of aggregates and SRV of HMA slab was established.