Dynamic Friction Tester Research Articles

Exploring the texture–friction relationship: from texture empirical decomposition to pavement friction

This paper investigates the pavement friction–texture relationship, using a decomposition method of the pavement texture that is part of a new signal processing technique called ‘Hilbert–Huang transform’ to develop a texture parameters–friction relation. This method allows the empirical decomposition of the texture profile to a set of basic profiles in a limited number, called ‘intrinsic mode functions’ or IMFs. From the obtained IMFs, a set of four new functions called ‘base intrinsic mode functions’ or BIMFs, are introduced and are characterised from the density and sharpness of the peaks contained in the individual BIMFs. Then these two parameters are correlated with the pavement friction using different combinations. This procedure is applied to a set of texture and friction data measured through test roads in France. The textures and frictions are measured using, respectively, the Circular Texture Meter and the Dynamic Friction Tester in France and also on a number of test sites in the USA. The obtained results show a good correlation between some of the BIMF parameters (density and sharpness) and friction.

Effect of aggregate shape on the surface properties of flexible pavement

One of the most important properties of flexible pavements in terms of tire-pavement interface is surface texture. The texture of a pavement surface and its ability to resist polishing effect of traffic is of prime importance in providing skidding resistance. Pavement surface texture greatly contributes to tire-pavement skid resistance which has a direct effect on traffic operation and safety particularly at high speeds. Doubtless, there exists a close relationship between pavement surface texture and aggregate angularity within the wearing course. This paper is aimed to determine the effect of aggregate shape on the surface properties of Hot Mix Asphalt (HMA). Two different mineralogical types of aggregate (basalt and limestone) have been crushed with impact, jaw and roll type of crushers. Various types of aggregate with different shapes have been mixed with 50/70 penetration grade bitumen to form dense graded mixtures. Test methods related with the evaluation of shape and texture characteristics have been utilized to characterize the geometrical properties of aggregates. The texture and friction properties of asphalt slabs have been evaluated by means of sand patch test, 3D laser scanner and dynamic friction tester respectively.

An initial attempt to develop an empirical relation between texture and pavement friction using the HHT approach

Pavement friction, one of the main factors contributing to road safety, depends mainly on surface texture. However, despite its importance having been well corroborated by the numerous investigations attempting to predict it, the manner in which texture is related to friction remains widely unknown. The current paper will explore the friction-texture relationship based on a new signal processing method called Huang–Hilbert Transformation, or HHT. This method allows empirical decomposition of a texture profile to a set of basic profiles in a limited number, called Intrinsic Mode Functions, or IMFs. Each IMF contains a given interval of amplitudes and frequencies. From the obtained IMFs, a set of four new functions called Base Intrinsic Mode Functions, or BIMF are computed based on the frequency and power content of the underlying IMFs and are characterized using the Hilbert Transformation technique to obtain the scale-dependent norm frequency and amplitude profiles. Then these two parameters are correlated with the pavement friction from a multiple regression analysis. This analysis is applied to a set of texture and friction data measured through test track surfaces in France and lab samples of concrete in the United States. The textures and frictions are measured with the Circular Texture Meter (CTMeter) and the Dynamic Friction Tester (DFTester), respectively. The obtained results show a good correlation between the BIMF's parameters to friction, thus opening a promising new means for characterizing texture in relation to friction.

EVALUATION AND COMPARISON OF SURFACE MACROTEXTURE AND FRICTION MEASUREMENT METHODS

Two- and three-dimensional macrotexture characteristics of various surfaces were measured using five different testing methods including sand patch method, laser profiler, laser texture scanner, circular texture meter, and x-ray computed tomography (CT) scanning. A dynamic friction tester was also used to measure the friction resistance of the same surfaces. Asphalt and Portland cement concrete samples of various mix designs and finishes and other commonly manufactured textured samples were used. Relationship between the macrotexture and friction was investigated. Mean texture depth (MTD) of 26 laboratory specimens was obtained from volumetric sand patch tests. Two-dimensional profiles and mean profile depth (MPD) of specimens were measured by a laser profiler. A laser texture scanner and a circular texture meter were also used to calculate the MPD of sample surfaces. Three-dimensional rendering of the surfaces were obtained from laser texture scanner and x-ray CT scans. Using the experimental data collected in this study, relationships between friction resistance and macrotexture obtained from different methods were investigated. The estimated texture depths predicted from laser profiler, laser texture scanner, and CT meter were comparable to the MTD obtained from sand patch tests. Also, the friction resistance increased with increasing surface macrotexture.

Evaluating Frictional Characteristics of Typical Wearing Course Mixtures in Louisiana

Abstract In this study, the frictional characteristics of a number of Louisiana wearing course mixtures were evaluated through a suite of laboratory tests. Aggregates of different levels of micro-textures were used in the mix design. Asphalt concrete slab samples were prepared using a kneading compactor and were accelerated polished using a three-wheel polishing device developed by the National Center of Asphalt Technology for simulating the traffic-polishing effect on the surface texture of the pavement. After different numbers of polishing cycles, the frictional characteristics of asphalt concrete slabs were evaluated using a dynamic friction tester (DFT) and a circular texture meter (CTM). A comprehensive statistical analysis was conducted to investigate the effects of aggregate type and mix type on the frictional characteristics of the asphalt concrete mixtures. The international friction index F(60) values (calculated from the DFT and the CTM test results) were used to characterize the overall frictional performance of the asphalt concrete mixtures considered. The experimental results showed that aggregates with higher levels of micro-texture generally performed significantly better than those with lower levels of micro-texture in the DFT test. The open grade friction course and stone matrix asphalt showed better macro-textures than the Superpave mixtures in the CTM tests. A statistical grouping based on the terminal F(60) values of different mixtures showed that it is possible to achieve the same level of F(60) using different combinations of mix and aggregate types. This study demonstrates that blending low- and high-friction aggregates together can possibly produce an asphalt mixture with adequate field skid resistance.

Development of Design Procedure to Predict Asphalt Pavement Skid Resistance

A laboratory design procedure was developed to evaluate the skid resistance of asphalt pavement with laboratory test results. For the development of the procedure, twelve typical asphalt wearing course mixtures with different combinations of aggregate sources and mix types were considered. The frictional performance of asphalt mixtures was evaluated with an accelerated polishing and testing procedure developed at the National Center for Asphalt Technology. The circular texture meter and the dynamic friction tester at various predetermined polishing cycles were used to evaluate the variations in surface texture and friction characteristics of asphalt testing slabs during accelerated polishing. The skid resistance of asphalt mixtures attributable to accelerated polishing was quantified with the international friction index number F60, which was computed with the friction numbers measured with the dynamic friction tester at 20 km/h and the obtained mean profile depth values. The analysis of F60 results led to the development of a set of friction prediction models and a laboratory friction-resistant mix design procedure. The developed procedure, which allows estimation of asphalt pavement skid resistance based on laboratory measured micro- and macrotexture results, is a useful tool for laboratory evaluation of a mixture's friction resistance. The procedure can also facilitate the use of locally available aggregates with lower skid resistance in a wearing course mix design and thereby produce both cost-effective and skid-resistant surface mixtures.

Polish Resistance of Fine Aggregates in Portland Cement Concrete Pavements

Many state agencies have limited the use of some sources of fine aggregates in portland cement concrete pavements because of possible skid issues related to the incorporation of such sands. The Texas Department of Transportation, for example, has adopted the acid-insoluble residue (AIR) test to identify polish-resistant aggregates. Because calcium carbonate is soluble in acid, no carbonate sand passes the AIR test, which has a minimum limit of 60% AIR in Texas. This paper describes research that evaluated the polish resistance of aggregates with a laboratory concrete performance test. Concrete slabs made with different fine aggregates were evaluated for skid with the use of a circular track meter, a dynamic friction tester, and a three-wheel polishing device. For each concrete slab tested, the change in texture and friction was monitored for 160,000 polishing cycles. To ensure that the values obtained in the laboratory related to field performance, test sections constructed with 100% limestone sand and blended sands were also evaluated. Results show that some aggregates that failed the AIR test performed as well as some siliceous fine aggregates that passed the AIR test. Other aggregate tests such as the fine aggregates micro-Deval have been shown to relate more closely to the concrete performance tests performed under laboratory conditions. Results obtained from laboratory and field testing showed that blending small quantities of siliceous sand with limestone sands considerably increased the skid resistance of concrete.

Harmonization of Texture and Friction Measurements on Florida's Open-Graded and Dense-Graded Pavements

A study was initiated to harmonize the dynamic friction tester and a locked-wheel tester on Florida's typical open-graded and dense-graded surfaces under various speed conditions. In addition, two texture measuring devices, the circular track meter and a high-speed 64-kHz laser mounted to the locked-wheel tester, were evaluated. These devices were first harmonized at a standard test speed of 40 mph (65 km/h). Because of the increased level of macrotexture in the open-graded mixtures, the open- and dense-graded surfaces were assumed to show different frictional behavior under different speed conditions. As a consequence, the harmonization equations for the open- and dense-graded surfaces were developed separately. Harmonization of different test speeds was also performed for each given test method to allow for converting the friction measured at a range of speeds—30 mph (50 km/h) to 60 mph (95 km/h)—back to that of the standard speed. The flexibility provided by these harmonization efforts is of great practical use and provides an alternative to the international friction index for Florida's conditions.

Development of a Model for Asphalt Pavement Skid Resistance Based on Aggregate Characteristics and Gradation

Many research studies and field experiences have shown a strong relationship between wet-weather accidents and pavement skid resistance. Therefore, measurement methods and models are needed to evaluate the safety level of driving on an asphalt pavement surface during its service life. The objective of this study was to develop a skid resistance prediction model based on measurable quantities such as aggregate shape characteristics, aggregate gradation, aggregate resistance to polishing, and traffic level. To achieve this objective, the skid number (SN) of asphalt pavement sections and traffic data were acquired and analyzed. In addition, statistical analysis was conducted to determine the relationship between different aggregate properties, pavement surface characteristics, and the measured SN values. The aggregate properties were measured using conventional test methods (acid insolubility, magnesium soundness, micro-Deval, and British polish value), and the Aggregate Imaging System (AIMS). The pavement surface characteristics were measured using the dynamic friction tester and circular texture meter. The statistical analysis led to the development of a new model for predicting the asphalt pavement SN as a function of traffic level, initial and terminal aggregate texture values measured using AIMS, and aggregate gradation described using the two-parameter Weibull distribution function.

Revised Methodology for Computing International Friction Index

An investigation evaluated the principles underlying the concept of the international friction index (IFI) to revise the current ASTM methodology for calibration of the IFI model parameters. The current ASTM standard for computing the IFI assumes a linear correlation between speed-corrected measurements of all friction-measuring devices that operate at different slip ratios with those of the standard device, the dynamic friction tester (DFT), which operates at 100% slip. This investigation revealed that a linear correlation existed between measurements converted to the standard slip speed of 60 km/h (FR60 values) obtained from devices that operate at 100% slip conditions and those of the DFT. However, the relationships between FR60 values obtained from friction-measuring devices that operated in the slip range of 10% to 20% and those of the DFT were observed as nonlinear. The FR60 values obtained with the latter category of friction-measuring devices when transformed by a power transformation produced a linear relationship with the standard F60 values obtained by using the DFT. A revised methodology for computing the IFI was proposed. This revised methodology yielded higher predictive capability than the current ASTM procedure and calibration parameters A and B that were speed invariant. The revised methodology also captured the actual friction–speed relationship of any given friction-measuring device on a given pavement surface by incorporating not only surface characteristics but also device-specific characteristics into the definition of the speed constant.

The Research on Dynamic Friction Tester of Pavement

As to the pavement test, with the slip-based control method, a new pavement mobile type of measuring device was designed to obtain the continuous friction coefficient parameters in this paper. The operation principles and the concrete completion methods of slip ratio control were introduced in detail. 89C52 was adopted as the center chip to achieve the system design of hardware and software. After the pavement tests, the prototype is of high reliability, low cost, and simple operation, meanwhile, meets the requirements of pavement skid resistance.

Measuring Friction of Patterned and Textured Pavements

The Florida Department of Transportation initiated a field study to compare the suitability of two friction-testing devices for measuring the friction characteristics of patterned and textured crosswalks: (a) a site-specific dynamic friction tester (DFT) and (b) a semicontinuous locked wheel tester. The locked wheel testing was performed with both ribbed and smooth tires at 20, 30, and 40 mph (30, 50 and 65 km/h), respectively. Ten test sections were randomly selected to include the different types of patterned and textured processes currently approved for use in Florida. The results of this study indicated that the smooth tire measurements were, generally, in good agreement with the DFT, regardless of test speed. The correlation between the DFT and the ribbed tire test improved with the increasing speed of the locked wheel testing. In addition, for a given test method, harmonization of different test speeds was also performed to allow for the speed conversion of the friction coefficients. The flexibility provided by these harmonization efforts is of great practical use in evaluating the frictional characteristics of patterned and textured crosswalks, especially when dealing with constraints such as speed limits. The testing program, the data collection effort, and the subsequent analyses and findings are described, as well as the lessons learned from Florida's experience with patterned and textured pavements.

The skid resistance performance of natural New Zealand aggregates using a dynamic friction tester

Abstract Research has clearly shown that as the skid resistance of a road surface decreases, the road-based transport crash rate increases. In recognizing the importance of providing safe pavement surfacings for travel during wet weather, most highway controlling authorities in developed countries have skid resistance standards. However, recent research has demonstrated that there is significant variation in performance between natural aggregates where supposedly high-quality surfacing aggregates (as measured by the Polished Stone Value Test) have not performed well or predictably over an economic asset life in areas of high demand for friction. A comparison is made between the performance of six natural aggregates (greywackes, felsic volcanic rocks and basalts) used in New Zealand as road surfacing dressing. The comparison includes surface friction test results of prepared samples that have undergone accelerated polishing using a new laboratory test method. The coefficient of friction is measured at various stages of polishing by the Dynamic Friction Tester. Scanning electron microscope (SEM) photographs show the characteristics of the microtexture of the aggregate surface before and after accelerated polishing, correlating the degree of surface polishing to the measured skid resistance performance and relating this to the aggregate mineralogy, grain size, and degree of lithification and diagenesis.

Assessment of Precision of Circular Track Meter and Dynamic Friction Tester

As part of the evaluation of the potential use of the international friction index as the standard for the reporting of friction measurements, the Florida Department of Transportation (FDOT) conducted an assessment of the precision of the dynamic friction tester (DFT) and circular track meter (CTM) test methods. The FDOT CTM equipment and DFT equipment were compared with similar portable equipment owned and operated by the National Center for Asphalt Technology (NCAT) in an attempt to quantify both the repeatability and the reproducibility of the test data obtained. The FDOT portable equipment was mobilized to Auburn, Alabama, for side-by-side testing with the NCAT equipment. This paper summarizes the results of an assessment of the precision of the DFT and CTM equipment on 10 different test surfaces at the NCAT Pavement Test Track. Tests with DFT and CTM were performed at five different locations within each of the 10 different test sections by using both NCAT and FDOT equipment. On the basis of the results of this comparison testing, proposed precision statements are presented for both the repeatability and the reproducibility of the data for the respective pieces of equipment. Correlation relationships are also presented for the portable equipment and the full-scale equipment currently used by FDOT and others.

Field Calibration of an Analytical Model for Pavement Friction Testing Applications

Abstract Regular evaluation and maintenance of skid resistance (friction) of highway and runway pavements is an essential task in improving transportation safety. Various measuring devices operating under different mechanisms have been developed for friction evaluation. Generally, there is a significant variation of friction measurements provided by different devices on the same surface, requiring reliable guidelines for comparison of devices. This paper presents the results of a study conducted to verify whether the LuGre model, an existing dynamic friction model composed of physically significant parameters, would satisfy the above need. A revised formulation which would enhance the applicability of the average lumped version of the LuGre model to model real-world dynamic friction problems is also presented. The original LuGre model was applied to two widely used pavement friction measuring devices; the locked wheel skid trailer and the dynamic friction tester (DFT). In the work presented here the characteristic equations for each device have been formulated based on the LuGre model. In addition an analytical treatment of the kinetics of the DFT is performed to facilitate the application of the LuGre model to the DFT. For each device, the LuGre model parameters were tuned to match a part of the field data collected during a field test carried out by the authors. It was seen that the obtained parameters are reasonably comparable with those reported in the literature. Moreover, the calibrated model equations were seen to predict the observed data that were not used in model fitting, with acceptable accuracy. The results obtained in this study clearly show that the LuGre model can be utilized as an efficient physically intuitive tool with possible applications in: (1) predicting the three-dimensional variation of friction (with wheel slip and traveling speed) as measured by selected friction measuring devices, (2) providing physical interpretations to friction data from different devices, (3) regular self-calibration of friction devices, and (4) comparing pavement friction measurements from different devices.

Evaluation of International Friction Index Coefficients for Various Devices

This paper presents a research effort to compare and harmonize measurements of texture and skid resistance taken with various devices at the Virginia Smart Road in May 2008 by the members of the Virginia Consortium for Pavement Surface Properties. There have been numerous efforts by different countries and agencies to understand better the relationship and behavior of different friction-testing devices and the influence of texture, speed, and other external conditions on these measurements. Measurements obtained with different types of equipment on 24 pavement sections with a wide range of textures were compared, and the relationship between friction and speed for the different pavement sections and devices was studied. Data were collected with two locked-wheel skid trailers, a Griptester, and a dynamic friction tester. Nine asphalt sections were tested; six were Superpave® mixes, two were stone matrix asphalt, and one was an open-graded friction course. The concrete sections tested included one continuously reinforced concrete pavement with tined finishing and two epoxy overlays. Even though all steps included in the specifications derived from the experiments by the Permanent International Association of Road Congresses (PIARC) were followed, the results obtained were not satisfactory. From a theoretical standpoint, all the values computed with the international friction index (IFI) F60 should be equal, but this was not the case. Discrepancies in the IFI values calculated for the different devices suggest that the original coefficients determined during the PIARC experiment may need to be adjusted for the devices evaluated, before the IFI can be implemented by the participating agencies.

Predicting Asphalt Mixture Skid Resistance by Aggregate Characteristics and Gradation

The objective of this study was to investigate the influence of aggregate characteristics and gradation on the skid resistance of various asphalt mixtures. Asphalt mixture slabs with different combinations of aggregate sources and gradations were fabricated in the laboratory. These slabs were polished with a wheel-polishing device developed by the National Center for Asphalt Technology. The frictional characteristics of each slab were then measured by the sand patch method, British pendulum, dynamic friction tester, and circular texture meter. Aggregates used in these mixtures were characterized by petrographic analysis, conventional test methods (acid insolubility, magnesium soundness, Micro-Deval, and British polish value), and the aggregate imaging system (AIMS). In addition, the aggregate gradation of each mixture was described by the two-parameter cumulative Weibull distribution function. Statistical analysis of test results led to the development of a function for predicting the International Friction Index, which is a measure of skid resistance of asphalt mixtures, after different intervals of polishing. The parameters of this function were found to be related to ( a) initial and terminal aggregate texture measured by using AIMS, ( b) rate of change in aggregate texture measured by using AIMS after different polishing intervals in the Micro-Deval, and ( c) the Weibull distribution parameters describing aggregate gradation. This function can be useful for estimating the frictional characteristics of an asphalt mixture surface during the mixture design stage.

Development of Portable Tester for Measuring Skid Resistance and Its Speed Dependency on Pavement Surfaces

Skid resistance is an important factor in a rational maintenance program for pavement surfaces. Therefore, the skid resistance of a road surface is monitored by maintaining skid resistance inventories; in addition, spot checks are made at high accident sites. The equipment, called the dynamic friction tester (DF tester), is a disc-rotating-type tester that measures the friction force between the surface and three rubber pads attached to the disc. The disc rotates horizontally at a linear speed of about 80 to 20 km/hr under a constant load, so the DF tester can measure the skid resistance at any speed in this range with a single measurement. At the same time, the results provide speed dependency of skid resistance that will be as close as possible to the results obtained by other testing modes. The DF tester can measure on flat as well as rutted surfaces, the depths of which are less than 6 mm. In that case, the coefficient of variation is found to be less than 10 percent. The long-term characteristics of ...

Development of Portable Tester for Measuring Skid Resistance and Its Speed Dependency on Pavement Surfaces

Skid resistance is an important factor in a rational maintenance program for pavement surfaces. Therefore, the skid resistance of a road surface is monitored by maintaining skid resistance inventories; in addition, spot checks are made at high accident sites. The equipment, called the dynamic friction tester (DF tester), is a disc-rotating-type tester that measures the friction force between the surface and three rubber pads attached to the disc. The disc rotates horizontally at a linear speed of about 80 to 20 km/hr under a constant load, so the DF tester can measure the skid resistance at any speed in this range with a single measurement. At the same time, the results provide speed dependency of skid resistance that will be as close as possible to the results obtained by other testing modes. The DF tester can measure on flat as well as rutted surfaces, the depths of which are less than 6 mm. In that case, the coefficient of variation is found to be less than 10 percent. The long-term characteristics of the coefficient of friction were measured by the DF tester, the British pendulum tester and the mini-texture meter. The coefficient of friction increases moderately with the traffic service period (up to 35 weeks) and decreases with increasing speed. The test results showed a significant speed dependency on the coefficient of friction measured by the DF tester although there was a high relationship between the coefficient of friction of the DF tester and the British pendulum number at each point and at each measuring speed. A weak relationship was found between the coefficient of friction and the sensor-measured texture depth values produced by the texture meter. Results of the Permanent International Association of Road Congresses experiment to compare and harmonize texture and skid resistance measurements indicate that the DF tester is capable of reporting the friction component (F60) of the international friction index using the friction coefficient at 60 km/hr.