Dynamic Friction Tester Research Articles

A Comparative Study on the Texture of Exposed Aggregate Concrete (EAC) Pavements Using Different Measurement Techniques.

This paper presents issues related to the assessment of the texture of aggregate concrete (EAC) surfaces using various methods for its verification. Microtexture was assessed using the British Pendulum Tester (BPT) and Dynamic Friction Tester (DFT). Two laser profilometers were used to assess macrotexture, circular texture meter (CTM) and stationary laser profilograph (SPL), as well as the commonly known volumetric method. Measurements were carried out on left and right tracks and in between them on five test sections of expressways. Based on the analyses performed, it was found that the results obtained by the DFT were less sensitive to changes in microtexture between individual tracks compared to the results obtained by the BPT. The BPN values in the left track were lower than those in the right track. However, the difference between the DFT20 results in these spots was insignificant. Both MPD and MTD values did not show significant differences between the right and left tracks. However, some differences were observed between the MPD parameters obtained using the CTM and SPL. This resulted from the different frequency and length of the scanned surface profile. However, the differences were at an acceptable level. A very high linear correlation was obtained in the case of BPN and DFT20 values (r - 0.719), and in the case of MPD and MTD values, the correlation was almost certain (r above 0.900). Based on a comparative analysis of the models estimating mean texture depth (MTD/ETD), a significant difference was observed between models based on EAC pavement results and those based on asphalt surfaces.

Field Study of Asphalt Pavement Texture and Skid Resistance under Traffic Polishing Using 0.01 mm 3D Images

Pavement texture and skid resistance are pivotal surface features of roadway to traffic safety, especially under wet weather. Engineering interventions should be scheduled periodically to restore these features as they deteriorate over time under traffic polishing. While many studies have investigated the effects of traffic polishing on pavement texture and skid resistance through laboratory experiments, the absence of real-world traffic and environmental factors in these studies may limit the generalization of their findings. This study addresses this research gap by conducting a comprehensive field study of pavement texture and skid resistance under traffic polishing in the real world. A total of thirty pairs of pavement texture and friction data were systematically collected from three distinct locations with different levels of traffic polishing (middle, right wheel path, and edge) along an asphalt pavement in Oklahoma, USA. Data acquisition utilized a laser imaging device to reconstruct 0.01 mm 3D images to characterize pavement texture and a Dynamic Friction Tester to evaluate pavement friction at different speeds. Twenty 3D areal parameters were calculated on whole images, macrotexture images, and microtexture images to investigate the effects of traffic polishing on pavement texture from different perspectives. Then, texture parameters and testing speeds were combined to develop friction prediction models via linear and nonlinear methodologies. The results indicate that Random Forest models with identified inputs achieved excellent performance for non-contact friction evaluation. Last, the friction decrease rate was discussed to estimate the timing of future maintenance to restore skid resistance. This study provides more insights into how engineers should plan maintenance to restore pavement texture and friction considering real-world traffic polishing.

Alternative Approaches for Rapid Evaluation of Frictional Resistance of Aggregates

Skid resistance of pavements plays a crucial role in ensuring the safety of road users, particularly under wet weather conditions. The standardized method for evaluating the skid resistance of aggregates, AASHTO PP103, requires using a three-wheel polishing device. That test procedure requires significant time for specimen preparation, testing, and monitoring of aggregate stockpiles. This study aims to propose alternative test methods to reduce the time required for the evaluation of skid resistance of aggregates. Two approaches were examined as alternatives to the AASHTO PP103 method. The first approach involved using a micro-deval abrasion device to polish the aggregates before evaluating the skid resistance of the aggregates using a dynamic friction tester. In the second approach, a multiple linear regression equation was proposed that uses conventional mechanical performance test results as independent variables to predict skid resistance. Twenty-one aggregate samples were collected from various sources in Texas for this study. The study results indicate that both approaches can be used as surrogate methods for AASHTO PP103 for rapid screening of the skid resistance of aggregates, which could help manage aggregate quality control and assurance.

Influence of Morphological Characteristics of Coarse Aggregates on Skid Resistance of Asphalt Pavement.

This research aims to improve the durability of skid resistance of asphalt pavement from the perspective of coarse aggregates based on on-site investigation. Firstly, the skid resistance of six representative actual roads was tested during two years by employing the Dynamic Friction Tester and the attenuation characteristics of skid resistance of different types of asphalt pavements were analyzed. Secondly, core samples were drilled onsite and coarse aggregates were extracted from the surface layer of the core samples. The morphological parameters of coarse aggregates were collected by a "backlighting photography" system and three-dimensional profilometer, and the variation rules of angularity and micro-texture of coarse aggregates were investigated. Finally, the correlation between the morphological characteristics of coarse aggregates and the pavement skid resistance was established based on the grey correlation entropy. The research results show that with the increase in service time, the attenuation rate of skid resistance of asphalt pavement gradually slows down; the angularity of coarse aggregates gradually decreases, and the micro-texture on the wearing surface gradually wears away. The grey correlation entropy between all the micro-texture indexes of coarse aggregates and dynamic friction coefficient, as well as between the roundness and skid resistance is more than 0.7, whereas the correlation between other evaluation indicators and the dynamic friction coefficient is poor, indicating that compared with the angularity of coarse aggregates, the micro-texture affects the skid resistance of actual asphalt pavement more greatly. In engineering applications, the use of coarse gradation, coarse aggregates with high roughness or high anti-wear performance can slow down the attenuation of pavement skid resistance, so that the pavement can maintain superior long-term anti-skidding performance.

Using bauxite as alternative for coarse aggregate in asphalt mixture: Improving skid resistance

The depletion of natural resources promotes to search for alternative of virgin pavement materials with the aim of ensuring the performance of pavement especially skid resistance, which is often linked to financial and health services of the country. To solve the issues, the paper attempts to employ bauxite as alternative for coarse aggregate of surface layer to improve skid resistance. To this end, the performance of calcined bauxite aggregate was characterized on the basis of some laboratory tests. Thereafter, radar chart method was used to evaluate the comprehensive skid resistance of different aggregates, followed by preparing asphalt mixture based on optimization results. Currently, the skid resistance of asphalt mixture composed of different aggregate was examined by the three-wheel polishing device (TWPD) combined with dynamic friction tester (DFT). After the process, the multiple linear regression model was performed considering the morphological, mineral and chemical characteristics of aggregate with the aim of predicting the long-term skid resistance. As for physical and mechanical properties, the different grades of calcined bauxites show an increase about 20%∼200% compared with limestone. From the radar chart method, it was observed that calcined bauxite, especially 88# calcined bauxite, was found to exist highest comprehensive skid resistance. It is obvious that the model involving mineral and chemical properties is able to exist higher accuracy, adjusted R2 having values even exceed 0.9. In addition, it was found that the cost-benefit of 88# calcined bauxite and 75# calcined bauxite were 22.82 and 12.70 respectively. Herein, the study allows us a feasible approach to ensure the demand of pavement and mitigate the challenge for environment.

Predicting the Friction Coefficient of High-Friction Surface Treatment Application Aggregates Using the Aggregates’ Characteristics

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.

Experimental analysis of long-term skid resistance of steel slag asphalt mixture based on differential wear

ABSTRACT This study aimed to analyse the attenuation law of skid resistance of steel slag asphalt mixture (SSAM) based on differential wear. In this study, an indoor accelerated wear instrument was used to accelerate the wear of the SSAM surface. A pavement laser scanner and a dynamic friction tester measured the three-dimensional morphology and dynamic friction coefficient (μ) of SSAM. Then, the improvement mechanism of steel slag on the skid resistance of SSAM was expounded by analysing the surface microtexture, mineral composition, and chemical composition of aggregates. The results showed no linear relationship between the amount of steel slag and the improvement of SSAM skid resistance. The SSAM with 50% steel slag maximised the differential wear effect and had the largest μ and the richest surface macrotexture. It was recommended that the steel slag content in the SSAM should not exceed 50%. The more mineral composition and higher average hardness of steel slag were the sources of its excellent skid resistance. In addition, it is suggested that the differential wear between mixed aggregates should be considered in the design of skid resistance pavement, and the proportion of different aggregates should be reasonably distributed.

Friction Characteristics of Open Graded Asphalt Friction Courses with BOF and EAF Steel Slag Aggregates

Friction properties of open graded asphalt friction course (OGAFC) mixtures play an essential role in ensuring traffic safety, especially under wet weather conditions. This study evaluated the friction characteristics of basic oxygen furnace (BOF) and electric-arc furnace (EAF) steel slag aggregate incorporated OGAFC mixes. Nine sets of OGAFC mixes were fabricated using five percentage replacements (0%, 25%, 50%, 75%, and 100%) of the coarse natural aggregate fraction by BOF and EAF steel slags. The effect of modified binder type (polymer and crumb-rubber modified) on the frictional characteristics of OGAFC mixes was also examined. The principal friction test devices used were the British pendulum tester and dynamic friction tester. Multiple friction performance aspects were studied: (1) effect of surface condition (dry, wet, and ponding) on the measured friction coefficient; (2) separate evaluation of adhesion and hysteresis friction components; (3) variation of friction coefficient with varying slip speeds, and (4) friction performance later in the OGAFC service life using artificially polished aggregates, and comparison of the performance with unpolished aggregates. Results revealed that the use of steel slags in OGAFC mixes considerably enhanced the frictional characteristics and that the skid resistance of OGAFC-BOF mixes was better than that of OGAFC-EAF mixes. Frictional resistance of the mixes was found to increase with an increase in steel slag content. OGAFC mixes comprising polished steel slag aggregates also showed promising results with the increment in steel slag content. The findings also indicated that OGAFC-CRMB mixes perform better than OGAFC-PMB mixes.

Life Cycle Cost Analysis of High Friction Surface Treatment Applications

Life cycle cost analyses for high friction surface treatment (HFST) applications were executed relying on a Microsoft Excel program developed by the researchers. Calcined bauxite (CB), five CB alternatives, and epoxy binder were utilized in the HFST applications. The aggregates’ performances were evaluated through the aggregate image measurement system (AIMS) before and after Micro-Deval polishing. The performance of the HFST applications was evaluated by the dynamic friction tester (DFT) and British pendulum (BP). The major purpose of this program was to present a rational method for converting different input data (project and material specifics) to comparable output data (net present value [NPV]) that facilitated comparison between different alternatives. The project specifics included traffic data, highway classification, and geometric design data. The material specifics data were AIMS results, DFT results, BP results, and materials and shipping costs. Three prediction models were selected to relate the performance test results to skid number (SN). The rehabilitation matrix, proposed by the researchers, was used to make the decision to maintain the HFST. This was conducted by comparing the predicted terminal SN and the recommended terminal SN (controlled by the user). The program output showed that Meramec River Aggregate and Flint HFST applications had the lowest NPVs, followed by Steel Slag HFST application, and then Earthworks HFST application. Nevertheless, Rhyolite HFST application showed the highest NPVs followed by the CB HFST application. The cost of the resin was dominant over the total cost of the HFST application.

Practical Specimen Preparation and Testing Protocol for Evaluation of Friction Performance of Asphalt Pavement Aggregates with Three-Wheel Polishing Device

AASHTO has provisionally endorsed the use of a three-wheel polishing device (TWPD) for polishing and the dynamic friction tester (DFT) for measuring the friction of the coarse aggregates used in hot mix asphalt (HMA). Despite ample studies showing the feasibility of such a system for HMA specimens, research efforts related to quantifying the coarse aggregates that are used in those mixes have been less common. The results of a study to accelerate the test and to decrease the tedium of specimen preparation for aggregates are reported here. Three identical TWPD devices that complied with the AASHTO provisional specification were fabricated. A new specimen preparation method was introduced to reduce the associated time and cost. Several operational parameters that can impact the repeatability and reproducibility of the process, such as tire type and tread condition, specimen preparation, and DFT rubber pad thickness, were investigated. This study verified that the TWPD/DFT test method can delineate the polishing/friction performance of different aggregates with acceptable repeatability and reproducibility. The TWPD/DFT test time and cost can potentially be decreased considerably by using the proposed practical and analysis modifications.

Influences of alternative friction aggregates on texture and friction characteristics of high friction surface treatment

High friction surface treatment (HFST) is commonly used to improve surface friction of asphalt pavements at high crash rate locations, and the objective of this study is to assess the feasibility of using alternative friction aggregates in HFST. Three-wheel polishing device (TWPD) was used to simulate the actual traffic polishing in the laboratory. Firstly, the texture and friction properties of HFSTs with 12 friction aggregates were characterized using circular track meter (CTM) and dynamic friction tester (DFT) after various TWPD polishing cycles (0 k, 70 k, and 140 k). The laboratory results showed that both DFT60 and mean profile depth (MPD) decreased with TWPD polishing cycles, and the DFT60 and MPD results after 70 k TWPD polishing cycles had no significant difference with those values after 140 k TWPD polishing cycles. In addition, a good linear correlation was observed between DFT60 and MPD. Based on the DFT60 results, two bauxite HFSTs showed the best friction performance, and taconite was found to be a suitable alternative aggregate source for HFST. This study also found that slag, silica, and quartz were not good candidates for HSFT application due to the poor texture and friction properties of the corresponding HFSTs. Based on the laboratory evaluation results, eight friction aggregates were selected to pave the HFST sections at the National Center for Asphalt Technology (NCAT) Test Track, which was subjected to 2.6 million equivalent single axle loads (ESALs) in six months. The CTM, DFT, and lock-wheel skid trailer (LWST) were used to characterize the texture and friction properties of field HFST sections, and both DFT and LWST results showed that the bauxite HFST exhibited better friction performance than the granite and flint HFSTs. In addition, there were good linear correlations existing between laboratory DFT60 and MPD results with the corresponding field measurements. Lastly, the influences of aggregate properties (i.e., particle size, durability, angularity, and shape index) on the texture and friction properties of HFST were investigated. The statistical analysis indicated that particle size had significant effects on the MPD and DFT60 of HFST. Meanwhile, only angularity showed a linear relationship with the MPD results of HFST.

Linear friction tester design and validation

Due to the complexity of friction phenomena, empirical analysis is the best way to predict the friction coefficient. To accomplish this, laboratory test rigs are needed. Although a rotary dynamic friction test bed was available to the authors, it had its limitations, such as low speed, inducement of lateral force, and the limitation of testing samples with different shapes. This paper will explain the process of designing and manufacturing a novel test setup for measuring friction and wear of the tire. The newly designed test rig can apply dynamic loading during the tests, and it can automatically measure the wear rate and temperature between cycles. In addition, it can be used for measuring the wear rate of rubber samples sliding on different types of surfaces. Therefore, experiments can be run under more controlled conditions. The designed linear friction tester can slide flat and round rubber samples approximately three meters across a large flat surface. The frictional force of rubber samples can be measured for various normal loads, velocities, and surface conditions. The new setup can automatically control the applied normal load on the sample using proportional–integral–derivative controller control. The important difference between this novel design and the existing testers used by other researchers is implementing the ball screw technology and the servo motor with high accuracy encoder to achieve highly accurate test results. In this design, the new mechanism for the ball screw is designed to increase the speed limit and eliminating vibrations while keeping the precision. In addition, in this design, the sample's mass can be measured automatically after each test cycle, thus providing a measure of the rate of wear of the rubber. In this study, the data collected by the linear friction tester is validated by comparing the data to the data collected by the dynamic friction tester (a validated rotary friction tester that exists in CenTiRe Lab). The data collected by the new setup was later used to benchmark the Persson analytical friction model.

High Friction Surface Treatment Deterioration Analysis and Characteristics Study

High friction surface treatment (HFST) is used to improve friction on curved roadways, especially on curves that have a history of wet pavement crashes. Observations on the long-term performance monitoring of HFST sections at the National Center for Asphalt Technology (NCAT) Test Track showed friction (skid number, SN) dropped significantly at the end of service life of HFST, creating unsafe driving conditions. There is no clear, observed friction deterioration trend to predict the friction drop when using friction performance measures like SN. Therefore, there is an urgent need to explore and develop supplementary HFST safety performance measures (such as aggregate loss) that can correlate to friction deterioration and provide predictable, cost-effective, and easily measurable results. The objectives of this paper are to (i) analyze the correlation between HFST aggregate loss percentage area and friction value using a dynamic friction tester (DFT), and (ii) study the characteristics of HFST deterioration associated with aggregate loss, at the NCAT Test Track and at selected HFST curve sites in Georgia (using 2D imaging and high-resolution 3D laser scanning). Results show a strong correlation between HFST aggregate loss percentage area and DFT friction coefficient. Where friction measurement is used as the primary safety performance measure, it is recommended that HFST aggregate loss be used as a supplementary performance measure for monitoring the HFST safety performance deterioration. Aggregate loss can be easily identified by characteristics such as color and texture change. Preliminary texture analyses of 3D HFST surface profiles show lower mean profile depth (MPD) and ridge-to-valley depth (RVD) texture indicators can also identify loss of aggregate spots on HFST surface.

Influence of shotblasting treatment on asphalt pavement performance

ABSTRACT The objective of this study was to examine the effectiveness of using shotblasting treatment to improve surface friction of asphalt pavements. This study selected six pavement sections with low skid resistance from the National Center for Asphalt Technology Test Track for shotblasting abrasion. These sections included three surface mixture types (open-graded friction course and dense-graded asphalt with and without reclaimed asphalt pavement material) and four coarse aggregate types (limestone, granite, dolomite and sandstone). The dynamic friction tester and lock-wheel skid trailer were used to measure the surface friction of these sections at the different traffic polishing cycles. In addition, the pavement performance including rut depth, cracking and surface roughness were periodically monitored. The test results indicated that shotblasting treatment was effective in improving the friction performance of asphalt pavements and had no detrimental impact on pavement performance in terms of cracking, rutting and surface roughness. The friction improvement by shotblasting treatment was significantly dependent on surface mixture type and coarse aggregate type.

Laboratory Evaluation of Aggregate Friction and Texture Properties

Aggregate shape, texture, and angularity are important physical properties for the development of high-quality adhesive systems with asphalt binder, and a good quality aggregate skeleton in asphalt and concrete mixtures. These properties are commonly measured using systems that employ images of aggregate samples taken with a digital camera. In practice, macro-texture measurements are commonly conducted nondestructively at highway speed using high-frequency lasers. There is a need to investigate the application of these optical sensors for measuring aggregate texture in the laboratory. Researchers used a laser-based scanning system to test aggregates from five sources before and after Micro-Deval abrasion. The aggregate specimens were embedded in a ring-shaped polyester material and tested with the aggregate ring texturing system (ARTS) along with the dynamic friction tester (DFT) to characterize micro-texture and frictional properties. Researchers analyzed the laboratory test data to evaluate the relationship between DFT friction at 60 km/h (DFT60) and the micro mean profile depth obtained with the ARTS. This analysis showed that the igneous and gravel aggregates had better micro-texture and frictional characteristics compared with the dolomite and limestone aggregates. The results from this implementation project showed the potential for using the ARTS to improve the Texas Department of Transportation’s existing surface aggregate classification system. Further testing is needed to characterize aggregates from other sources and compile a more comprehensive and representative database with which to establish meaningful aggregate classification criteria that include surrogate statistics for expected field performance.

Analysis of High-Friction Surface Texture with Respect to Friction and Wear

High Friction Surfaces (HFS) are applied to increase friction capacity on critical roadway sections, such as horizontal curves. HFS friction deterioration on these sections is a safety concern. This study deals with characterization of the aggregate loss, one of the main failure mechanisms of HFS, using texture parameters to study its relationship with friction. Tests are conducted on selected HFS spots with different aggregate loss severity levels at the National Center for Asphalt Technology (NCAT) Test Track. Friction tests are performed using a Dynamic Friction Tester (DFT). The surface texture is measured by means of a high-resolution 3D pavement scanning system (0.025 mm vertical resolution). Texture data are processed and analyzed by means of the MountainsMap software. The correlations between the DFT friction coefficient and the texture parameters confirm the impact of change in aggregates’ characteristics (including height, shape, and material volume) on friction. A novel approach to detect the HFS friction coefficient transition based on aggregate loss, inspired by previous works on the tribology of coatings, is proposed. Using the proposed approach, preliminary outcomes show it is possible to observe the rapid friction coefficient transition, similar to observations at NCAT. Perspectives for future research are presented and discussed.

Random Forest–Based Pavement Surface Friction Prediction Using High-Resolution 3D Image Data

Abstract Many studies have concluded that pavement micro- and macro- texture characteristics have significant contributions to pavement friction and thus roadway safety. This study explores novel three-dimensional (3D) areal texture parameters to represent pavement texture characteristics at both micro- and macroscales and their usage for friction prediction. Three rounds of pavement friction and texture data were collected from 2015 to 2017 at a testing site in Oklahoma with six different mixture designs. Pavement friction was acquired by a Dynamic Friction Tester, and the corresponding texture data were collected by a portable ultrahigh-resolution 3D laser scanner. Each 3D texture datum is decomposed into micro- and macroscales with predesigned Butterworth filters. Twenty-seven 3D texture parameters falling into five categories are calculated at both texture levels. Subsequently, the random forest algorithm is implemented to determine the most important texture parameters for friction predictive model development. The selected macro- and micro-texture parameters account for 48.8 % and 39.6 % contributions to high-speed friction and 50.0 % and 14.1 % contributions to low-speed friction. The temperature during testing also exhibits a significant impact, with 11.6 % and 35.9 % contributions to high- and low-speed friction, respectively.

Effect of aggregate type and polishing level on the long-term skid resistance of thin friction course

• Thin friction course with 88# calcined bauxite shows satisfactory skid resistance. • Aggregate mineral/chemical compositions affect the long–term skid resistance of TFC. • The attenuation rate of aggregate’s PSV has a strong correlation with that of μ 40 . This study was attempted to investigate the influence of aggregate type and polishing level on the long–term skid resistance of thin friction course particularly with calcined bauxite. The PSV (Polished Stone Value) test, self-designed three wheel polishing device (TWPD) and dynamic friction tester (DFT) were applied to examine the friction performance of asphalt mixture and aggregate at different polishing cycles in laboratory. The mineral hardness of aggregate was linked with the skid resistance of aggregate and thin friction course by regression analysis. The grey correlation and t -test were utilized to evaluate the factors that influenced the skid resistance of thin friction course. It is found that better skid resistance value is observed for thin friction course by 88# calcined bauxite than by limestone, basalt and 75# calcined bauxite at each polishing level. PSV presents most significant influence for both terminal value and initial value of μ 60 . The PSV attenuation rate of aggregate has a strong correlation with the attenuation rate of μ 40 . The aggregate hardness parameter presents the ability of the aggregate and asphalt mixture to keep long–term skid resistance. In addition, calcined bauxite aggregate owns extensively applied potential in the thin friction course in China.

Friction and Texture Retention of Concrete Pavements

In the late 1980s and early 1990s, the Alabama Department of Transportation (ALDOT), U.S., noticed a decline in skid trailer numbers on concrete pavements shortly after grinding operations. The engineers at the time suspected that the coarse aggregate caused the decline in these numbers and the resulting conclusion led to a ban of carbonate aggregates in mainline concrete pavement in Alabama that is still in place. This detailed laboratory study re-examines the fundamental friction issues that led to this policy. A total of 48 aggregate, grinding, and grooving combinations were tested as part of this study. Three aggregate sources were examined: a siliceous source, a “hard” limestone source, and a “soft” limestone source. Two blade spacings were examined for grinding operations: 52 blades/ft and 60 blades/ft. Some ground specimens were also grooved. Finally, a set of specimens had the Next Generation Concrete Surface (NGCS) applied to them. The specimens were polished with the National Center for Asphalt Technology (NCAT) three-wheel polishing device (TWPD). The dynamic friction tester was used to evaluate friction values at various points through the polishing process. After the polishing, the macrotexture was characterized using the circular track meter. Across the board, the highest performing texture was that with no grooves and 52 blades/ft. Very generally, the loss of friction decreased with increasing siliceous content. However, some of the trends were extremely minor and, in a few cases, siliceous aggregates caused higher friction loss. There were numerous instances when blended carbonate/siliceous concrete pavement surfaces performed better than sole siliceous concrete pavement surfaces.

Development of predictive models for skid resistance of asphalt pavements and seal coat

ABSTRACT Skid resistance is a key factor in road safety. Surface friction characteristics of roads are dependent on the microtexture and macrotexture of the surface. The decay of skid resistance with time is a function of traffic level and aggregate characteristics. This study developed predictive models for skid resistance of asphalt pavements and seal coat surfaces. The researchers examined the surface friction characteristics of 35 asphalt pavement test sections and 35 seal coat test sections. The skid number was measured using a skid trailer, while the microtexture and macrotexture of the test sections were measured using a dynamic friction tester and a circular texture meter, respectively. The Aggregate Image Measurement System (AIMS) and Micro-Deval test were also used to evaluate the aggregate shape properties and its resistance to polishing and abrasion. The developed skid prediction models express the skid number over time as a function of aggregate gradation, aggregate resistance to abrasion and polishing, and traffic level. The models showed good correlations with skid numbers measured in the field. These models can be used to optimise the mix design to provide adequate level of friction and estimate the skid number of asphalt pavements and seal coat surfaces over time.