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Stronger eco-friendly asphalt from forest waste

paved road through forest
To develop more environmentally friendly and durable asphalt mixtures, KTH researchers are combining chemical and mechanical tests with 3D imaging techniques from X-ray and neutron radiation sources. “The combination of testing methods allows us to understand the internal properties of the new biomaterial. We want to be able to ensure that the material maintains the right quality throughout the life of the road,” says KTH researcher Maria Chiara Cavalli. Photo: Mostphotos
Published Sep 06, 2024

KTH researchers aim to make paved roads more sustainable by using the natural material lignin, a by-product of the wood and paper industry.
“The new material will reduce the need for oil-based asphalt. We are working to make roads both more environmentally friendly and stronger,” says Maria Chiara Cavalli, Senior Lecturer in Civil Engineering at KTH Royal Institute of Technology.

A large part of the carbon dioxide emissions associated with Sweden's roads are related to the production of the road material.
“In order for society to become less dependent on petroleum-based asphalt, we are increasingly using the bio-based binder lignin. The goal is to make road construction more sustainable over time,” Chiara Cavalli  says.

Maria Chiara Cavalli in research lab
Maria Chiara Cavalli

Her research team is working to strengthen the internal structure of lignin.
“We use microscopy combined with chemical methods to find the ultimate recipe for the lignin mixture,” Chiara Cavalli says.

“Today, some companies mix lignin into asphalt without taking into account that the life expectancy of asphalt is only about 20 years, which makes road maintenance more expensive. We are investigating whether it is possible to make asphalt both more environmentally friendly and stronger, so it will last longer.”

The project is part of a three-year Formas project  on the use of natural and sustainable biomaterials in urban environments.
“We have two years left on this project. Formas chose to collaborate with us because of our scientific approach here at KTH,” Chiara Cavalli says.

Traditional asphalt production uses crude oil from countries such as Kuwait, and the filler material is extracted from mountains or river beds. Now the researchers want to replace as much of the oil and filler as possible with sustainable material.
“A bonus is that the lignin mixture gives the roads increased resistance to moisture damage. Moisture damage is one of the biggest road problems we see today.”

samples of asphalt with lignin
Samples of asphalt mix with lignin being tested for durability in the KTH laboratory

Lignin can be described as a rigid and waterproof ‘cement’ that contributes to the structural strength of plants. It is a by-product of the wood and paper industries and is usually burned.
“We aim to reuse large amounts of lignin for the new bio-based asphalt material, which we hope to make more environmentally friendly and more durable,” says Maria Chiara Cavalli.

Text: Katarina Ahlfort
Photo: Aleksandra Kuksova

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