Asphalt pavements surface texture and skid resistance

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Asphalt pavements surface texture and skid resistance — exploring the reality

Can. J. Civ. Eng. Downloaded from www.nrcresearchpress.com by Renmin University of China on 05/28/13 For personal use only.

M. Alauddin Ahammed and Susan L. Tighe

Abstract: Wet pavement skidding due to inadequate surface texture or friction contributes to 20% to 35% of all wet weather crashes. Many of the past studies of pavement surface texture and friction have deficiency in selecting the model forms or variables and interpreting the models and (or) the findings or have recommended further investigation. These pose a challenge for the highway agencies in selecting the appropriate surface layer and (or) measuring tools. This study was undertaken to re-examine some of the pavement surface texture and skid resistance related issues and aid the highway agencies in this area. Pavement surface texture and skid resistance aspects were carefully examined using the data collected from nine asphalt concrete (AC) surfaces. Pavement surface texture was measured using the sand patch method and a high speed texture laser. Skid resistance was measured using a British Pendulum and a skid trailer. The analysis has reinstated that aggregate quality is the predominant factor for AC surface skid resistance. Both texture depth and ribbed tire skid resistance was shown to increase with an increase in coarse aggregate (CA) content proving their interdependency. Neither the voids in mineral aggregate (VMA) or air voids (AV) contents showed a meaningful or statistically significant correlation with the surface texture or skid resistance. Fairly good correlations were found among the British Pendulum number (BPN), ribbed tire skid number (SN) and mean texture depth (MTD) rejecting the hypothesis that BPN is a measure of only surface microtexture and ribbed tire skid number is insensitive to surface texture. Key words: asphalt concrete, British Pendulum, mean profile depth, mean texture depth, mix constituents, skid number, surface texture. Résumé : Le dérapage sur chaussée mouillée en raison d’une texture ou un coefficient de frottement à la surface inadéquat contribue à 20 % – 35 % de tous les accidents par temps de pluie. Plusieurs études antérieures sur la texture et le coefficient de frottement des chaussées présentent des manques dans la sélection des formes ou des variables des modèles et l’interprétation des modèles et/ou des conclusions ou encore recommandent de nouvelles études. Cela pose un défi aux ministères des transports quant à la sélection de la couche de surface et/ou des outils de mesure appropriés. La présente étude a été entreprise pour réexaminer certaines questions reliées à la texture de surface des chaussées et à la résistance au dérapage et ainsi aider les ministères des transports dans ce domaine. Les aspects de texture de surface des chaussées et de la résistance au dérapage ont été examinés attentivement en utilisant les données colligées sur neuf surfaces de béton bitumineux. La texture de surface des chaussées a été mesurée en utilisant la méthode d’étalement de couches de sable et un laser pour mesurer la texture à haute vitesse. La résistance au dérapage a été mesurée en utilisant le pendule SRT (skid resistance tester) et une remorque de glissance. L’analyse a confirmé que la qualité des agrégats est le principal facteur de la résistance au dérapage des surfaces de bétons bitumineux. La profondeur de la texture et la résistance au dérapage des pneus nervurés ont augmenté avec l’augmentation du contenu en agrégats grossiers, prouvant ainsi leur interdépendance. Ni le pourcentage en vides dans les agrégats minéraux ni le pourcentage en vides d’air ne présentent une corrélation importante ou statistiquement significative avec la texture de la surface ou la résistance au dérapage. De relativement bonnes corrélations ont été découvertes entre le BPN (British Pendulum number), un indice de glissance des pneus nervurés (SN – skid number) et la profondeur moyenne de la texture rejetant l’hypothèse que le BPN ne soit qu’une mesure de la microtexture de la surface et que l’indice de glissance des pneus nervurés est indépendant de la texture de la surface. Mots‐clés : béton bitumineux, pendule SRT, profondeur moyenne du profilé, profondeur moyenne de la texture, composants mixtes, coefficient de dérapage, texture de surface. [Traduit par la Rédaction]

Received 15 October 2010. Revision accepted 27 September 2011. Published at www.nrcresearchpress.com/cjce on 14 December 2011. M.A. Ahammed. Manitoba Infrastructure and Transportation, Materials Engineering Branch, 920-215 Garry Street, Winnipeg, MB R3C 3P3, Canada. S.L. Tighe. Department of Civil and Environmental Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada. Corresponding author: M. Alauddin Ahammed (e-mail: [email protected]). Written discussion of this article is welcomed and will be received by the Editor until 31 May 2012. Can. J. Civ. Eng. 39: 1–9 (2012)

doi:10.1139/L11-109

Published by NRC Research Press

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Can. J. Civ. Eng. Downloaded from www.nrcresearchpress.com by Renmin University of China on 05/28/13 For personal use only.

Introduction The main purpose of a transportation system is to facilitate safe and efficient movement of people and goods. However, over one million people die and fifty million are injured annually from highway crashes around the world (Snyder 2006). Driver skill and behaviour, roadway geometry, traffic control features and measures, pavement condition, vehicle and tire conditions and loadings, vehicle speed and brake performance are primary factors that contribute to highway crashes. However, uncontrolled skidding due to inadequate surface friction and poor visibility due to splash and spray have been found to be the two primary causes of wet weather crashes with skidding alone contributing to 15% to 35% of all wet weather accidents (Hoerner and Smith 2002). A number of studies have indicated that skid related accidents can be reduced by an improvement in pavement surface friction. For example, Rizenbergs et al. (1976) found that the ratio of wet-weather accidents to dry-weather accidents decreased sharply (from 0.7 to 0.23) as skid number (SN) increased above 41 (a critical level). Hosking (1987) and Kennedy et al. (1990) found that an improvement of surface friction coefficient of 0.1 could reduce the wet-weather accident rate by 13%. The wet-weather accidents were shown to reduce by 35% with a net return of 540% after laying antiskid surfacing at more than 2000 sites in London, UK (Kennedy et al. 1990). Inadequate surface friction may also play a role in many crashes on dry roads, especially at intersections, work zones (frequent slow-stop-go operations), and curved sections (Swanlund 2005; Snyder 2006). The surface friction or resistance to skidding is available from different shapes of texture on pavement surfaces. According to Larson et al. (2004), 70% of the wet weather crashes are preventable with improved texture or friction on pavement surfaces. The splash and spray that contribute to 10% of wet weather accidents can also be minimized with deeper textures (Hoerner and Smith 2002). Alternatively, deeper textures may contribute to increased roughness, noise and vibration, vehicle wear and fuel consumption. Selection of appropriate asphalt concrete (AC) surface mix or Portland cement concrete (PCC) surface texturization therefore is important for achieving the optimal performance.

Desired surface texture The available skid resistance of pavement surfaces largely depends on surface microtexture (texture wavelength of