Environment

Wood waste makes recycled concrete stronger than ever

Wood waste makes recycled conc...
To turn this into even stronger concrete ... just add lignin?
To turn this into even stronger concrete ... just add lignin?
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To turn this into even stronger concrete ... just add lignin?
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To turn this into even stronger concrete ... just add lignin?

Production of the cement used in concrete is a huge source of CO2 emissions, so the more that we can recycle existing concrete, the better. That's where a new study comes in, which indicates that discarded concrete becomes even stronger than it was before, when wood waste is added to it.

Concrete is made by mixing an aggregate such as gravel with water and cement. Once the mixture has cured, the cement hardens, and binds with the aggregate to form a solid block of material.

Led by Asst. Prof. Yuya Sakai, scientists at The University of Tokyo ground pieces of such concrete into a powder, then added water, along with lignin obtained from wood waste. Lignin is a highly crosslinked organic polymer, and is a key component of the support tissue in vascularized (water-conducting) plants – it's what gives wood its rigidity.

The mixture was then simultaneously heated and placed under high pressure. It was found that by precisely tweaking variables such as the concrete/lignin ratio, water content, temperature, plus the amount and duration of pressure, the lignin formed into a highly-effective adhesive, binding the pieces of concrete powder together.

When subsequently tested, the recycled concrete was found to have more bending strength than the original concrete from which it was made. As an added bonus, because of its lignin content, the material should likely biodegrade once discarded.

What's more, the scientists believe that lignin obtained from other plant sources (such as agricultural waste) could be used instead. It may even ultimately be possible to create new "virgin" concrete, in which lignin is utilized in place of cement.

"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," says Sakai.

As an interesting side note, a 2018 study conducted at the National University of Singapore concluded that adding wood waste to cement and mortar made them both stronger and more watertight.

Source: The University of Tokyo

9 comments
paul314
So do you have to use recycled concrete, or will any mineral powder do?
WONKY CLERKY
Congratulations, oh cutting edge, high tech, ultra thingy, hyper everything, and, for good luck I'll throw in the current must-have - hybrid, wondrous far eastern Yuya Sakai-san on the mixer.
NOW, see the Oggy's - They've been knocking out building blocks under the brand name of 'LIGNACITE'* since Jethro was first on ze zyder.
*There could be some kind of clue in the name.
Eric Rodz
It is nice that the lignin makes the material biodegrade after discarding it, but hat prevents the material from biodegrading BEFORE it is discarded?
piperTom
Most cements used in construction (e.g. Portland cement) don't actually dry, as suggested here. Instead, mineral hydrates form, incorporating the water into the mix. Good practice is to keep the concrete wet while it sets; evaporation of water can result in a weaker structure.
Curtis White
Under high heat and high pressure? How will you pour a roadway or bridge under those conditions? How will you pour a slab or tilt panels?
WMaxJeff
could this principle achieve the same flexible waterproof concrete by crushing old masonry onsite & using Joinery Shops & Timber Mills waste Re Wood waste makes recycled concrete stronger than ever
Cheers Jeff M. Weeks
WMaxJeff@gmail.com
Nigel Mckee
Well this sounds like total trash? You've made trash. Concrete has barely any bending strength. In fact I'm pretty sure when they're doing structural calculations, they set the flexural strength as zero it's so close to negligible. All that comes from the steel rebar. And as an added bonus, it biodegrades?? That renders it even more useless. I don't slate the scientists, it's important that this kind of work is done because this is how we end up with new technology, but this article takes that and makes it misleading. Concrete is a massive problem in the world. Both in terms of cement and aggregate, it's damaging the planet severely. I would argue however, that we need to address the problems of concrete, not find a brand new material altogether. It really is so perfect, and it's made the world we live in. First we need to find a way to lengthen the lifespan of reinforced concrete, as everything we build has an expiration date due to the rusting of the rebar, second we need to find a way to wean ourselves off the absolutely insane amounts of sand that our drawn from our environment. Things like high strength concrete are doing this. It means we can MASSIVELY reduce the amount we use at the outset, and produce concrete that should last practically indefinitely. Higher strength both compressive and flexural, higher erosion resistance and chemical resistance. We need to focus on making it commonplace, and really solve these problems.
Signguy
Again...HEMPCRETE surpasses all requirements for "concrete"...Better Than!
windykites
What happens if the new product starts to bio-degrade before it is discarded, i.e. whilst still in a building?
I suggest using ground up plastic as an inert filler, replacing some or all sand.