Another brick in the wall
Low-carbon alternatives to traditional bricks15th Apr 2020
When we think of bricks, we tend to think of either baked clay bricks or cement bricks, both of which have a very high carbon footprint – conventional clay bricks are fired at temperatures of over 1,000°C, and cement requires temperatures in excess of 1,400°C, which requires the burning of coal with all its attendant environmental fallout.
But there are bricks – or brick-like things – that can be produced at much lower temperatures, thereby using much less carbon, and producing less pollution. Some are the result of amazing new technological breakthroughs, and are only in the trail phase, while some are so old as to have been virtually forgotten.
Bricks out of the box
Building technology evolves pretty rapidly, so you should always at least consider new approaches when planning developments, whether to be more sustainable, more profitable, more efficient – or all three. Of course, not all technologies will work for all developments but, as we start to think out of the box in terms of development types, we can consider replacing some or all of the traditional high-carbon-footprint building materials with some of these low-carbon options. Some may work particularly well for off-the-grid eco-estates, affordable housing projects, or other developments that may become feasible and/or desirable in the future.
Researchers from the Kalinga Institute of Industrial Technology (KIIT) School of Architecture have, in partnership with the Indian Institute of Technology (IIT), developed a low-cost, low-carbon brick from agricultural waste such as straw, rice husks and sugar-cane bagasse. It’s a relatively simple process; the waste is chopped into smallish pieces, mixed with a lime-based slurry, and then put into moulds, compressed and allowed to dry.
The biobrick is not as strong as a clay or cement brick, so it can only be used for relatively simple, single-storey structures, but the material can also be formed into structural and/or insulation panels.
Bricks from urine
Emulating the process by which sea creatures form shells from the chemicals in seawater, researchers at the University of Cape Town have successfully created bricks from human urine and some sand – a different type of biobrick. This innovative process upcycles a waste material that traditionally uses vast resources, including water, to dispose of, and creates two useful products – bricks and fertiliser. It’s a total win-win situation, saving water and energy, as well as producing a low-carbon building material. This process is still in the development phase, but it has enormous potential, particularly when we consider how much water we use to deal with urine waste.
Geopolymer-stabilised soil bricks
Geopolymer-stabilised soil materials (GSSM) are made by dissolving soil (not valuable topsoil) to create a slurry-like solution that is put into moulds and fired in order to reconstitute the dissolved minerals to form a strong geopolymer that holds the brick together. This is done at about 100°C – the sort of temperature easily reached by domestic stoves. It’s a great idea that has worked in trials, but it’s not yet commercially viable.
Fly-ash bricks are a type of geopolymer brick that utilises fly ash – the waste product from coal-fired power stations. Developed in India in 2008, the process is doubly clever. It has the same low-temperature advantage of GSSM, and it effectively recycles the waste from power stations. Brilliant! Even better, fly-ash bricks are stronger than clay bricks, so they can be used for a wide range of applications. While still not widely commercially available, fly-ash bricks may be commercially viable, especially considering that they utilise and neutralise an otherwise toxic waste product.
There’s nothing new about mud bricks. They are basically clay bricks that have not been fired and, as they are often made from clay found on site and so do not need to be transported, they have a much lower carbon footprint. They are, obviously, not as strong as fired bricks, but they are surprisingly resilient – some traditional buildings built from mud bricks are still standing after 300 years.
Sandbags are not really bricks, but that sort of depends on the definition you choose to use for the word ‘brick’. If you define a brick as a discrete component that can be used with others like it to construct a wall, then sandbags are bricks. They have many advantages – and some disadvantages – but, especially if you are building affordable housing, the benefits far outweigh the drawbacks.
Sandbags are very cheap to transport because most of the sand can be found on site from the foundation excavation, which also saves on the cost of transporting that away from the site. Construction is three times faster than laying conventional bricks, and sandbags offer great thermal insulation.
The biggest disadvantage is that sandbags don’t have sufficient structural stability to hold up on their own, but this problem is easily solved by using some kind of framework, in which case they can safely be used to create double-storey buildings. The bags are not held together with mortar, but the finished wall has to be plastered.
Straw bales, which could be considered giant bricks, have the advantages of speed of construction, superb thermal properties and the fact that they are a natural carbon sink, in that they store the carbon created through photosynthesis deep within the building.
Ecobricks are not really bricks, but they are a great way to divert plastic from landfill and from the oceans by incorporating it into permanent structures. It’s not practical to build large structures from ecobricks but, especially if you plan ahead and colour-code them, they can be used for decorative features such as retaining walls or steps.