Polishing of asphalt pavements is an obstacle faced regularly on the roads of Lebanon. This behavior of the pavement causes its skid resistance to be reduced, knowing that the lower the skid resistance value, the higher the percentage of the traffic accidents especially during the winter season.
The following report presents a project carried out in the Highway materials and Construction course taken at AUB for a better understanding of the effect polishing and wet conditions have on skid resistance.
A concise literature review on skid-resistance, polishing causes and polishing experimentation is conducted followed by a detection of the main experimental concerns.
Following the literature review, laboratory experiments of which results are clearly presented are carried out in the Civil Engineering department soils and materials labs at AUB.
Finally, an analysis of the results and possible improvement methods and precautions to avoid polishing of asphalt pavements are proposed.
During the entire life cycle of a pavement, highway agencies are expected to monitor and maintain an adequate surface roughness to facilitate friction between car tires and pavement surface.
Polishing is a smooth slippery surface caused by repeated wear on the pavement due to traffic and even heavy pedestrian load on parking lot pavements. This behavior of the pavement will cause its skid resistance to be reduced. For high-speed pavements this can be a serious surface distress, while on most parking facilities, the distress is negligible.
Our transportation problems in Lebanon are not only caused by the huge demand for transportation services but also by the distresses or damages the pavements experience without any appropriate maintenance.
A better understanding of asphalt pavements polishing behavior helps in a better perceptive on how to avoid this problem or solve it.
Polishing Definition and Causes
Polishing of the aggregate is the reduction in microtexture, resulting in the smoothing and rounding of exposed aggregates. It is caused by repeated traffic applications. Generally, as a pavement ages the protruding rough, angular particles become polished. This can occur quicker if the aggregate is susceptible to abrasion or subject to excessive studded tire wear.
Susceptible to abrasion: Aggregates undergo substantial wear and tear throughout their life. In general, they should be hard and tough enough to resist crushing, degradation and disintegration from any associated activities including manufacturing, stockpiling, production, placing, and (Roberts et al., 1996). Furthermore, they must be able to adequately transmit loads from the pavement surface to the underlying layers. Aggregates not adequately resistant to abrasion and polishing will cause premature structural failure and/or a loss of skid resistance. Studded tire wear: Tire studs are small metal protrusions inserted into winter tires to improve tire-road friction in snow or ice conditions. In addition to this friction improvement, studded tires also have an unwanted and detrimental side effect: increased pavement wear. [pic]
Figure 1: Polished Aggregate
Skid-resistance of roads decreases due to the polishing of pavements, which seriously affects drivers’ and passengers’ safety. There is a need to dispose of a laboratory test to forecast variations on asphalt-mix specimens before road construction.
According to Do, Minh-Tan, Zhenzhong Tang, Malal Kane, Francois De Larrad (2007), skid-resistance of a roadway surface may decrease when it is worn due to traffic and climatic conditions. For highway engineers, it is important to order tools to forecast such variations before any construction, in order to predict maintenance and optimize mix formulation. Currently, long-term skid-resistance is assessed through the polishing resistance of coarse...