Original paper

A photogeomorphological study examining 50 years of pavement soiling in Toronto, Canada

Thornbush, Mary J.

Abstract

Sidewalks (pavements) are rarely considered as part of weathering science research even though concrete is comprised from limestone and validly constitutes a stone-derived weathering material. Importantly, because of their location in the built environment, pavements weather quickly due to use and represent a considerable calcareous subject in cities. This study examines pavements in central Toronto, Canada as part of a northern (cold) environment that is susceptible to physical weathering processes (abrasion, freeze-thaw, etc.). The emphasis here was on examining evidence of soiling on pavement slabs in place since 1965, which would be evident by a darkening of concrete, with a temporal extent of 50 years from the time that the fieldwork was executed. A digital camera was mounted on a tripod and used to capture images along eastern and western sides of street pavements located in a historical neighbourhood dating back to the founding years of the city. This residential neighbourhood was selected for the study because of its age as well as relatively low traffic, allowing for the appearance of older pavement concrete slabs. Images were captured using a colour chart in order to calibrate outdoor lighting conditions performed on an overcast morning, when the pavement was clear of any seasonal covering (leaves, snow, etc.). A total of 129 photographic pairs were acquired, and the images were analysed for comparisons of soiling across time affecting mean and median lightness values. The results convey brighter surfaces after calibration, denoting a faster (mean, median) decline in lightness since 1965 at a rate of 0.01 % per year. These strong positive linear correlations did not uphold for Std Dev L values, which showed a less positive (although still strong) linear decline over time. The findings indicate that this method could be employed as a technique to quantify the soiling of horizontal (pavement) surfaces in addition to previous work already performed on building walls.

Keywords

calcareous materialconcrete slabsdigital photographyo-idipphysical weatheringlightnesssurface roughness