Concrete has been dubbed the “most destructive material on earth” and for good reason.
“By the time you are halfway through this article, the volume would fill the Albert Hall and spill out into Hyde Park. In a day it would be almost the size of China’s Three Gorges Dam. In a single year, there is enough to patio over every hill, dale, nook and cranny in England,” The Guardian newspaper explains.
“After water, concrete is the most widely used substance on Earth. If the cement industry were a country, it would be the third largest carbon dioxide emitter in the world with up to 2.8bn tonnes, surpassed only by China and the US,” the newspaper goes on.
It’s no surprise then that the race is on for sustainable alternatives to concrete. One team of international researchers, led by scientists at Flinders University in Australia, has come up with a novel solution by replacing synthetic reinforcement materials with natural fibres and materials from waste streams.
Their technique, they report, has yielded “geopolymers reinforced with renewable natural fibres and made with industrial by-products and waste-based sands from lead smelting or glass-making can match the strength, durability and drying shrinkage qualities of those containing natural sand, which in turn consumes more raw resources and generates extra emissions in its processing.”
The newly made alternative to conventional concrete shows great promise with the use of natural fibres in structural-grade construction materials. Test results show that geopolymers made with waste glass sand have superior strength and lower water absorption than geopolymers made with natural river sand.
At the same time, lead smelter slag-based geopolymers have lower drying shrinkage compared to geopolymers prepared with natural river sand. Natural fibres such as ramie, sisal, hemp, coir, jute and bamboo were also trialed in experiments.
“The geopolymers containing 1% ramie, hemp and bamboo fibre — and 2% ramie fibre — exhibit higher compressive and tensile strength and a lower drying shrinkage than unreinforced geopolymers, while those containing 1% ramie fibre have the highest strength and lowest drying shrinkage,” the researchers report.
Each year some 25 billion tons of concrete are used worldwide with the making of concrete consuming about 30% of non-renewable natural resources and emitting about 8% of greenhouse gases. However, the new concrete substitute, if scaled up sufficiently, could make the industry a lot more sustainable, the scientists say.
“[W]e can not only recycle huge volumes of industrial by-products and waste materials, including concrete aggregates, to improve the mechanical and durability properties of concrete, but also use alternative eco-friendly natural fibres which otherwise would not be used constructively,” says Aliakbar Gholampour, a researcher in structural engineering who was an author of a study on the findings.
“[We] will also look to design mixes of recycled coarse aggregates and other types of cellulosic fibres, including water paper, for different construction and building applications. We also plan to investigate their application in construction 3D printing for the future.”
