Recycled pulp mill waste adds strength and resilience to cement

Recycled pulp mill waste adds ...
Study author Chinchu Cherian with a sample of the cement incorporating recycled pulp mill fly ash
Study author Chinchu Cherian with a sample of the cement incorporating recycled pulp mill fly ash
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Study author Chinchu Cherian with a sample of the cement incorporating recycled pulp mill fly ash
Study author Chinchu Cherian with a sample of the cement incorporating recycled pulp mill fly ash

Pulp mills generate significant amounts of waste and we're seeing scientists get quite creative with how it might be put to use, with the possibilities including everything from foams, to batteries to stronger concrete. The latest example comes from researchers at the University of British Columbia (UBC), who have used a pulp mill waste product as a filler material for cement, which they report proved stronger and more resilient.

The waste product at the heart of the breakthrough is known as pulp mill fly ash (PFA), which the pulp and paper industry in North America generates more than a million tons of each year. Rather than consigning it all to landfill, the UBC team set out to investigate how it could be used as a sustainable binder material for road construction instead.

Through their experiments, they found that the structure of this recycled wood ash serves to form stronger bonds between the different materials making up cement. They were also able to produce this sustainable construction material in a more energy-efficient fashion than conventional cement.

“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,” says study author Dr. Chinchu Cherian. “Through our material characterization and toxicology analysis, we found further environmental and societal benefits that producing this new material was more energy efficient and produced low-carbon emissions.”

One of the issues around using recycled pulp mill products like PFA is the possibility that toxins used as part of the initial processes at these facilities might leach out of the material and into the environment. The team confirms that the bonds within the cement are so strong that little to no chemicals are able to leak out, and therefore describe it as safe for use.

“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,” Cherian says. “And not just benefits for the industry, but to society as a whole by reducing waste going to landfills and reducing our ecological footprints.”

The study was published in the Journal of Cleaner Production, while the video below offers an overview of the research.

School of Engineering keeping pulp mill waste out of the landfill

Source: University of British Columbia

A dozen years ago they used coal power plant fly ash to produce fiber-cement siding - there were concerns about leeching of heavy metals, toxins, out-gasing, and I've heard that contractors found it hard to handle and disliked using the product. I don't know if they are even marketed any longer - but our concern was for fire personnel if a structure caught fire. Would the water used cause the hot fiber cement-siding to shatter and wash away into yards and streams, could it contribute to silicosis type pulmonary issues for fire fighters? Fire is a lessor concern with Pulp wood waste locked into concrete - maybe this is a really good thing. Or maybe not - time will tell.
I also read an article that the the 'black liquor' waste product from just a few paper plants could be refined to power several major cities. I've been to paper plants, their throughput is amazing (a 30 foot wide roll of paper created at 3000 linear feet per minute).
This product should be investigated for printing buildings directly with clay, bypassing the production of cement. Mud brick houses often use paper or straw mixed in with the clay. 3D printing of houses from clay not from cement / concrete could be the best future carbon wise.