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In the road sector, biobased light colored binders, although marginal, are attracting attention because of their environmental, practical and aesthetic benefits. But what are they, what are their particularities and how to produce them?
Light colored binders
Light colored binders (or clear binders) are characterized by their lack of pigmentation and sometimes their transparency, unlike traditional bituminous road binders, which are dark, due to the presence of asphaltenes in bitumen. The family of light colored binders includes biobased binders, made from biosourced materials, and synthetic binders (“mineral” or “hydrocarbon”) mainly composed of petroleum products. This lack of dark pigmentation makes it easy to color them with a wide range of light and bright colors, or to bring out the natural coloring of aggregates for soft mobility infrastructures (cycle paths, car-parks), or urban development (parks, schoolyards, city centres). Combined with clear aggregates, they contribute, for example, to reducing the phenomenon of heat islands in cities by storing less energy from the sun’s radiation, or even to delimiting specific traffic areas, thus contributing to improving the safety of users.
Biobased light colored binders
Biobased (or plant-based) light colored binders are composed mainly of plant-based ingredients and therefore have a high renewable carbon rate. They are made by mixing several biosourced organic compounds, modified or not to improve their resistance to oxidation. These compounds are generally derived from the wood industry used by the paper industry, and extracted from by-products that now find new applications. Tall-oil pitch and wood resins, for example, are known for having a high aggregating power. Vegecol ® from COLAS, Biophalt® from EIFFAGE and Sequoia® from EUROVIA are made out of those ingredients.
Particularities of biobased light colored binders
Beyond their transparency (depending on the ingredients used), vegetable binders have a large number of advantages over hydrocarbon binders. Although they still tend to oxidize faster and exhibit lower softening points, these alternative binders are already stapples for aesthetic coatings, patching, maintenance and low traffic areas, all of this with very interesting performances.
The volume of Life Cycle Assessment (LCA) data available on biobased binders is still low because these solutions are still in their early ages. Nevertheless, the studies carried out to date clearly demonstrate their interest in reducing the environmental impact of infrastructures. This is due, among other things, to:
- the renewable nature of the raw materials;
- their lower manufacturing temperatures;
- their low ecotoxicity.
In addition to this, biobased binders are compatible with recycled asphalt pavement applications (RAP and RAS maining Recycled Asphalt Shingles) and uses in emulsion for the production of cold asphalt, to further reduce the carbon footprint of construction sites compared to traditional uses. For these different applications, the formulator has a lot of possibilities to adapt the rheological and mechanical properties of the biobased binder. Nature of the ingredients, origin, proportions, additives: there are many ways to specifically adapt the needle penetration, the softening point or even the viscoelastic properties of biobased light colored binders.
Production and process
Apart from the component mixing stage, the processes are the same as for bituminous binders. Therefore, the same methods can be used to process biobased binders. Nevertheless, to preserve the transparency of those binders and comply with the quality and safety standards in the field, companies that wish to produce and use biobased binder must have dedicated machines and equipment, preferably mobile and of sizes adapted to the usual production volumes. For this, VIALAB has developed a specific range of units for the production and emulsification of light colored binders, combined with a mobile cold asphalt mixing plant.
Biobased light colored binders are still evolving and are becoming more popular for aesthetic structures and pavements subjected to low traffic constraints. They contribute to reducing the environmental impact of the public works sector and limiting heat island phenomena. In addition, their composition can be customized for hot or emulsion applications. Finally, a dedicated, mobile and appropriately sized production tool is necessary for a company wishing to develop a biobased binder activity.
A. RICHARD, Chemical Engineer and Vincent HESRY, Ph.D.
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