Taking the ‘con’ out of concrete

In an effort to make the construction industry more sustainable, alternative concrete materials are becoming much more frequent. Below, we discuss some noticeable ones.

Concrete consists of fine and coarse aggregate bonded together with cement powder and water. The cement industry produces about 10 per cent of global CO2 emissions, so by taking cement out of the equation or at least using less of it, concrete production can become more sustainable.

Hempcrete is a biocomposite alternative to concrete. It consist of a mixture of the woody inner fibres of the hemp plant and lime. The material is more lightweight than concrete and also lacks its brittleness. Additionally, the hemp acts like a thermal insulator, and because hemp absorbs CO2 from the atmosphere as it grow, hempcrete sequesters more carbon dioxide than it generates. However, hempcrete does not have the requisite strength for constructing foundation and has to be supported by a frame.

Fly ash are fine particles of fuel that are driven out of coal-fired boilers. In ashcrete of fly ash concrete, Portland cement is replaced by fly ash. Fly ash has great strength and durability, and is of course more sustainable because it is recycled. Ashcrete is more acid- and fire-resistant than concrete, and has also has higher compressive and tensile strength.

However, because fly ash comes from coal, a major contributor to air pollution, in an ideal, sustainable world, we wouldn’t have much of it.

Timbercrete is a blend of sawdust, cement, sand, binders, and a non-toxic deflocculating additive. The material is about 2.5 times lighter than concrete and can be screwed or nailed like wood. Like hempcrete, timbercrete is more insulating than concrete, and sequestrates carbon. The material is not waterproof and has to be sealed properly when used outside.

Sand is used in the production of concrete, but the supply of construction-grade sand is dwindling. A spin-off company of Imperial College London called Finite developed a concrete alternative made of desert sand, a type of sand usually too smooth to be used in concrete. The Finite material has a carbon footprint of less than half of that of concrete. Read more about the material here.

Rather than generating CO2, some researchers are working on using CO2 in concrete. Compared to steel, CO2 is four times lighter and has six times the bearing capacity. Read more about this type of concrete here.

Miracle material graphene has been added to all sorts of things, amongst them concrete. Graphene-reinforced concrete is twice as strong and fur times more water-resistant than the original materials. Additionally, by including graphene, the amount of materials required to make concrete can be reduced by 50 per cent. Read more about this material here.

Ferrock is made from waste steel dust, usually discarded from industrial processes, and silica from round up glass. The iron in within the steel reacts with CO2 and rusts to form iron carbonate, fusing into a hard material. The material is five times stronger than Portland cement concrete, and is more flexible. Rather than emitting CO2 as it dries, Ferrock actually absorbs and binds it.