As urban slow-moving systems, landscaped parks, and scenic highways continue to expand, colored asphalt pavements are increasingly becoming part of everyday scenery. From eye-catching red bike lanes to serene blue parking zones, vibrant green walkways to warm yellow intersections—the unsung heroes behind these colorful roadways are specialized pigments for colored asphalt.

Pigment Systems: The Inorganic-Based Technical Approach

In colored asphalt mixtures, pigments are typically added in powder form, achieving coloring by partially replacing mineral fillers. Based on chemical composition, inorganic pigment systems are currently the most widely used, with common varieties including iron oxide red, iron oxide yellow, chrome oxide green, and ultramarine blue. These pigments, fundamentally composed of metal oxides, exhibit excellent heat resistance, enabling them to withstand the high-temperature mixing conditions during asphalt mixture production. Research indicates that the optimal addition ratios for different colored inorganic pigments in colored asphalt binders vary. For instance, red, yellow, and green pigments each have their specific recommended addition ranges to achieve ideal color expression while ensuring road performance.

Coloring Mechanism: Synergy with Binder

The color presentation of colored asphalt is not solely attributable to pigments but results from a color system formed by pigments interacting with light-colored binders and aggregates. Within this system, pigments are physically dispersed and uniformly distributed throughout the binder while forming a coloring layer on aggregate surfaces. Tests indicate that pigment addition not only imparts color to the pavement but also positively influences the mixture's high-temperature performance and water stability, though its impact on low-temperature performance is relatively limited. Therefore, in designing colored asphalt mixtures, comprehensive consideration must be given to the binder's softening point, ductility, viscosity, and other indicators, as well as the selection of pigment series and particle size, to achieve overall optimization of both road performance and color effect.

Color Stability: Technological Breakthroughs in Interface Enhancement

Ensuring long-term color retention remains a critical technical challenge in colored asphalt applications. Research indicates that adding coupling agents—such as silane, titanate, or aluminate coupling agents—can improve the interface interaction between inorganic pigments and organic binders, significantly enhancing pigment color intensity and dispersion. This approach not only enhances compatibility among the binder, aggregate, and pigment but also boosts the pavement's lightfastness, weather resistance, and water damage resistance, effectively ensuring the color durability of colored asphalt pavements. The introduction of nanomaterials offers an alternative solution. Inorganic layered nanomaterials interact with the binder through intercalation effects, forming a “bridging” structure. This enhances high-temperature stability while inhibiting oxygen ingress, thereby helping to delay pigment aging and discoloration.