Concrete is made by combining a chemically inert mineral aggregate (gravel or crushed stone) with water and cement. Once the mixture has dried, the material hardens and bonds with the aggregate to form a solid cement block.
However, the production process of the cement used in concrete is a significant contributor to CO2 emissions. To remedy the issue, a team of scientists at the University of Tokyo looked at recycling existing concrete. In a study, the team added wood waste to discarded concrete, making it even stronger and more flexible than before.
The team, led by Asst. Prof. Yuya Sakai ground chunks of discarded concrete into a powder then added water and lignin extracted from wood waste. Lignin is a class of highly cross-linked organic polymers and is responsible for the structural strength of the wood and its rigid structure. It’s also a crucial element of the supporting tissue in vascularized plants.
This mixture was heated and placed under high pressure after perfecting variables like the concrete/lignin ratio, amount and duration of pressure, temperature, and water content. The lignin then formed into a highly effective adhesive, binding the concrete mix together.
The team tested the recycled concrete’s durability and found it to have more flexibility than the original concrete from which it was made. As a bonus, recycled concrete is likely to be biodegradable once discarded due to its lignin content.
Sakai concluded:
These findings can promote a move toward a greener, more economical construction industry that not only reduces the stores of waste concrete and wood but also helps address the issue of climate change.
Furthermore, the scientists are confident that lignin extracted from other discarded plant matter could be used instead of wood. It may also be possible to create virgin concrete, in which lignin replaces cement.
