Field and laboratory characterization of the albedo of asphalt and horizontal surfaces

Abstract

The rise in temperature in urban areas compared to surrounding rural zones is a major concern for modern cities. Part of this phenomenon is attributed to the widespread use of modern construction materials with low albedo, particularly for road pavements. While outdoor albedo measurement standards exist, there is currently no consensus on a standardized laboratory method. This article aims to develop a multi-material, laboratory-to-field scale law for predicting outdoor albedo using only laboratory tests. This predictive law is intended to facilitate the design of new light-colored pavements and surfaces, without the need for full-scale construction and testing. The American standard ASTM E1918 provides guidance for accurate and reliable albedo measurements on low-sloped surfaces; however, it presents several limitations, which are discussed in this paper, and it is demonstrated that albedo measurements can be reliably performed on-site under a broader range of conditions than those specified by the standard. Additionally, although some studies have explored laboratory-based albedo characterization, no agreement has been reached regarding the testing apparatus or conditions. In this work, a parametric study was conducted to develop a laboratory procedure. Special attention was given to the type of lighting and sensor sensitivity in order to accurately replicate solar illumination and ensure reliable measurements. Colorimetry was used to confirm material consistency across laboratory and field scales. The final transformation equation proposed is simple to apply and sufficiently accurate to provide reliable predictions of outdoor albedo.