When I was in grad school the civil engineers would enter the annual concrete canoe contest where the teams would have to build a canoe entirely out of conrete and then race it against those of other teams. Most broke up or sank before the finish line, but the builders did use unusual fillers to reduce the density. One mix had a specific gravity of just 0.75, about equal to oak, and it had an amazing tensile strength, almost two percent that of oak.
You're absolutely right about "specific chemical requirements," which is what I said. But there's cellulosic and then there's cellulosic: they're by no means all the same. And the stuff we're writing about here is not leaf mold--which, BTW, can also vary widely in chemical content (for example, high tannin content in oak leaves). Depending on its chemical composition, some cellulosic material adds nitrogen and other nutrients to the soil, some takes those out, and some doesn't do anything nutritionally, but does add bulk and loft, which is not always needed or wanted, BTW. The stuff being recycled here doesn't add much in the way of nutrients and/or can leach it out. It can also cause rot problems. This is a complex subject, which we touched on in the DuPont article. Check it out.
All gardeners know what they buy in a store - the synthetic, or maybe not, fertilizers I mentioned - have specific chemical requirements. Good gardeners also swear by leaf mold: cellulosic material partly consumed by mold that they turn under in the spring to give the soil more tilth. Sounds like what we're taking away from the soil this way.
Elizabeth, the model of using waste plant material for making biofuel and bioplastics is already well underway, as we've covered in several posts in DN. One is the DuPont story about biofuel: http://www.designnews.com/author.asp?section_id=1392&doc_id=257126 Another is using cane trash to make bioplastics: http://www.designnews.com/document.asp?doc_id=237554
Not all farmers want to recycle this stuff, for several different reasons (one being that cellulosic material doesn't make very good fertilizer, which has very specific chemical requirements, as any gardener knows). Some of them are covered in the story we did on DuPont using corn stover for making biofuel--we gave the link in this story, but here it is again http://www.designnews.com/author.asp?section_id=1392&doc_id=257126
Excellent use for recycled materials. Concrete has been reinforced for eons to make it stronger or lighter. From adding straw to mud bricks in thy neighbors hut, steel rebar in just about everything cast concrete, to adding limestone or pumice (lavarock) in the concrete domed cielings of ancient structures such as the Parthenon. A building which has survived earthquakes and other factors for 1900+ years...
I would have thought it would be better to turn any such "waste" under to replenish the organic material in the soil. Since it is cellulosic, I would think this would also help keep the soil loose. This should make it a little less important to put synthetic fertilizers on the ground the next spring.
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