Pulp and paper waste could help build roads of the future

The construction industry has long sought to use waste materials from the pulp and paper industry as possible fillers for building products such as cement, but for years these materials have ended up in landfills. Now, researchers at The University of British Columbia (UBC) Okanagan are developing guidelines to use this waste for road construction in an environmentally friendly manner.

To help create such guidelines, the researchers turned their attention to wood-based pulp mill fly ash (PFA), which is a non-hazardous commercial waste product, to investigate the potential of using a waste material from this industry in constructing roads.

The North American pulp and paper industry generates over one million tons of ash annually by burning wood in power boiler units for energy production. When sent to a landfill, the producer shoulders the cost of about $25 (£18) to $50 (£36) per ton, so mills are looking for alternative usages of these by-products.

“Anytime we can redirect waste to a sustainable alternative, we are heading in the right direction,” said Dr Sumi Siddiqua, associate professor at UBC Okanagan’s School of Engineering. Dr Siddiqua leads the university’s Advanced Geomaterials Testing Lab, where researchers uncover different reuse options for industry by-products.

The new research, co-published with postdoctoral research fellow Dr Chinchu Cherian, investigated using untreated PFA as an economically sustainable low-carbon binder for road construction.

“The porous nature of PFA acts like a gateway for the adhesiveness of the other materials in the cement that enables the overall structure to be stronger and more resilient than materials not made with PFA,” Dr Cherian explained. “Through our material characterisation and toxicology analysis, we found further environmental and societal benefits that producing this new material was more energy efficient and produced low carbon emissions.”

But Dr Siddiqua noted there are concerns in the construction industry that toxins used in pulp and paper mills may leach out of the reused material. “Our findings show that because the cementation bonds developed through the use of the untreated PFA are so strong, little to no release of chemicals is apparent. Therefore, it can be considered as a safe raw material for environmental applications.”

While Dr Cherian explains that further research is required to establish guidelines for PFA modifications to ensure its consistency, she is confident their research is on the right track.

“Overall, our research affirms the use of recycled wood ash from pulp mills for construction activities such as making sustainable roads and cost-neutral buildings can derive enormous environmental and economic benefits,” she said. “And not just benefits for the industry, but to society, by reducing waste going to landfills and reducing our ecological footprints.”

In the meantime, while cement producers can start incorporating PFA into their products, Dr Cherian said the team will be continually testing and evaluating the PFA properties to ensure overall quality for future use.