Colorimetry of pavements for urban planning

In recent years, the use of light-coloured pavements has been encouraged internationally for urban design. In particular, colour is a lever that allows the designer to meet an objective of urban roads: the sharing of space, for uses and users. It is also a key factor for pavements in environmental and monumental contexts, where the aesthetics and appearance of the finished layer are essential characteristics.The Pavements and Lighting working group has established a large library of current and innovative urban pavements available on the French market. The colour of these surfaces is notably part of the assessed properties. The objective of this study is to have a tool and an analysis method to understand the development of a project and its evolution according to the effects of colour change.A set of 30 pairs of samples were characterised in their initial state and after 30 months of natural ageing in outdoor conditions, i.e. exposed to rain and sun. It included pavements of several categories: asphalt concrete (bituminous or synthetic binder), mastic asphalt, poured and precast cement concrete. The colour of each sample was measured using three different processes (devices and methods).The results provide a first overview of the colorimetric coordinates per pavement family and show a wide range of achievable colorimetric characteristics. The impact of natural ageing on the colour of the road surface is studied by the comparison of the original with the 30 months measurements. The obtained results highlighted that not all pavements evolve in the same way, depending on their mixture and their finishing stage. Usually, the asphaltic pavements (concrete and mastic) tend to evolve more than the cement concrete samples (poured and precast). The colour of a pavement without surface treatment changes more than a treated one, as well as when dark aggregates are used. The same is true when the binder is synthetic, but it seems that the use of TiO2 in synthetic asphalt pavements reduces the colour evolution.