Abstract
Surface friction is currently the most common metric for evaluating the performance of high friction surface treatment (HFST). However, friction test methods such as the locked wheel skid tester (LWST) commonly provide a spot measurement. Large variations may arise in the LWST testing on curves. Based on 21 actual HFST projects, a study was performed to use a macrotexture metric, i.e., the mean profile depth (MPD) to evaluate HFST’s performance and improve its quality control (QC)/quality assurance (QA) procedures. The material properties were presented to understand the aspects of HFST. The method for calculating MPD was modified to account for the variations of macrotexture measurements. A vehicle-based test system was utilized to measure MPD periodically over an 18-month period since HFST installation. Statistical analysis was performed on the MPD measurements to identify the effects of influencing factors. Compared with the friction from LWST, MPD was equally effective in evaluating HFST performance. However, the use of MPD eliminated the errors as arisen in LWST testing and made it possible to detect surface distresses, including aggregate loss, delamination, and cracking. The expected overall MPD may be calculated by combining the MPD measurements made three months after installation at different HFST sites and used as a metric for evaluating HFST performance and QC/QA.
Highlights
Pavement friction plays a critical role in reducing vehicle skid crashes, especially when pavement surface is wet
Great efforts have been made to broaden the understanding of high friction surface treatment (HFST) surface texture, especially the gaps existing in the knowledge, effective measures, data needs, limitations of field testing, and performance requirements
For a standard HFST composed of epoxy resin binder and calcined bauxite aggregate, surface friction and macrotexture metrics such as skid number (SN) and mean profile depth (MPD) are equivalent when used to evaluate the surface friction of HFST
Summary
Pavement friction plays a critical role in reducing vehicle skid crashes, especially when pavement surface is wet. The conventional friction treatments are not capable of providing long excellent, durable surface friction performance. At friction-prone locations such as horizontal curves, interchange ramps and intersections, pavement surface is likely to become polished more rapidly due to frequent braking of vehicles, and friction demands may exceed the friction capability of conventional friction treatments. High friction surface treatment (HFST) has been promoted as a cost-effective solution to the extreme friction demands in the United Sates [2,3]. HFST consists of a thin layer of polymer binder topped with polish-resistant aggregate and can be installed by either mechanical or manual methods. The polymer binders commonly used in HFST are epoxy resin binders specially engineered for use in bonding skid resistant materials to roadway surface. The aggregate is typically calcined bauxite with an aluminum oxide (A2 O3 ) content of 87% [4]
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