Clay brick is a product of a brick dough, which consists of clayey soil and water. It is formed primitively, naturally dried, and fired in the kilns. Clay brick is the oldest and most used building material, has been manufactured at the waterfronts where suitable soil could be found. However, Clay brick production is associated with critical environmental problems in terms of CO2 emission and natural resources depletion.
Biosolids are a by-product of the wastewater treatment process that can be used as fertiliser, in land rehabilitation or as a construction material. Around 30% of the world’s biosolids are stockpiled or sent to landfill, using up valuable land and potentially emitting greenhouse gases, creating an environmental challenge.
Now a team at RMIT University in Melbourne, Australia, has demonstrated that fired-clay bricks incorporating biosolids could be a sustainable solution for both the wastewater treatment and brickmaking industries.
As well as being cheaper to produce, the biosolids bricks also had a lower thermal conductivity, transferring less heat to potentially give buildings higher environmental performance.
The EU produces over 9 million tonnes of biosolids a year, while the United States produces about 7.1 million tonnes. In Australia, 327,000 tonnes of biosolids are produced annually. The study found there was a significant opportunity to create a new beneficial reuse market – bricks.
About 5 million tonnes of the biosolids produced in Australia, New Zealand, the EU, US and Canada currently go to landfill or stockpiles each year. Using a minimum 15% biosolids content in 15% of bricks produced could use up these 5 million tonnes.
Lead investigator Associate Professor Abbas Mohajerani said the research sought to tackle two environmental issues – the stockpiles of biosolids and the excavation of soil required for brick production. He further said that more than 3 billion cubic meters of clay soil is dug up each year for the global brickmaking industry, to produce about 1.5 trillion bricks.
Using biosolids in bricks could be the solution to these big environmental challenges. It’s a practical and sustainable proposal for recycling the biosolids currently stockpiled or going to landfill around the globe.
The research examined the physical, chemical and mechanical properties of fired-clay bricks incorporating different proportions of biosolids, from 10 to 25%.
The biosolid-enhanced bricks passed compressive strength tests and analysis demonstrated heavy metals are largely trapped within the brick. Biosolids can have significantly different chemical characteristics, so the researchers recommend further testing before large-scale production.
The biosolids bricks are more porous than standard bricks, giving them lower thermal conductivity.
The research also showed brick firing energy demand was cut by up to 48.6% for bricks incorporating 25% biosolids. This is due to the organic content of the biosolids and could considerably reduce the carbon footprint of brick manufacturing companies.
The results of a comparative Life Cycle Assessment and an emissions study conducted as part of the research confirmed biosolids bricks offered a sustainable alternative approach to addressing the environmental impacts of biosolids management and brick manufacturing.
Trillions of cigarettes are produced every year worldwide, resulting in millions of tonnes of toxic waste being dumped into the environment in the form of cigarette butts. As butts have poor biodegradability, it can take many years for them to break down, while heavy metals such as arsenic, chromium, nickel and cadmium trapped in the filters leach into soil and waterways.
Now a team at RMIT University led by Dr Abbas Mohajerani has demonstrated that bricks with as little as 1 per cent cigarette butt content can cut brick production costs and save the environment.
About 6 trillion cigarettes are produced every year, leading to 1.2 million tonnes of cigarette butt waste. These figures are expected to increase by more than 50 per cent by 2025, mainly due to an increase in world population.
In Australia alone, people smoke about 25 to 30 billion filtered cigarettes a year and, of these, about 7 billion are littered.
This research shows that if just 2.5 per cent of the world’s annual brick production incorporated 1 per cent cigarette butts, we could completely offset annual worldwide cigarette production.
Mohajerani’s team discovered that adding butts can cut the energy needed to fire bricks by up to 58 per cent. Fired-clay bricks incorporated with cigarette butts were also lighter with better insulation properties – meaning reduced household heating and cooling costs.
In recent years as society has embraced environmental sustainability and moved towards a carbon neutral footprint there has been increased attention on the adaption of renewable resources within the construction industry. The production of Portland Cement has a significant impact on the CO2 emissions as it has been reported that for every 1 tonne of cement produced approx. 0.7 tonnes of CO2 is released into the atmosphere. The emissions contribute to the total from the construction industry and is is estimated to represent between 5-7% of CO2 emission worldwide. The emphasis in decreasing environmental pollution associated with cement production has brought attention towards alkali activated materials as sustainable alternative material, which can reduce CO2 emissions.
Fly ash can be principally divided into two categories: low calcium class F fly ash, which is produced from burning anthracite and bituminous coals and high calcium class C fly ash which comes from the burning of lignite and sub-bituminous coals, known as brown coal. Australia’s brown coal reserves are around 37 billion tonnes, corresponding to 25% of the worldwide resouces. The by-product brown coal fly ash in Australia was 25 million tonnes in 2013, with a forecast suggesting this will double by 2050. Due to the chemical composition, most notably high sulphur content, almost all the ash collected is directly disposed into ponds and has the added potential to leach out heavy metal to local aquifers and surface water.
RMIT University is currently undertaking a research program as part of the ARC NanocommHub, with industry partners, Energy Australia, AGL and Adbri bricks to assess the feasibility of producing brown coal fly ash geopolymer concrete bricks. The research developed bricks using fly ash from both Yallourn and Loy Yang power plants. Prototype bricks with a compressive strength satisfying both 5 MPa and 15 MPa requirements have been manufactured.
The research has used a range of advanced analytical techniques including thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, Nuclear magnetic resonance, Scanning election microscopy and Computer Tomography to assess the chemical and physical characteristics. It has then used this information to develop mix designs appropriate for each fly ash. The research is also investigating the methods of material recovery and preparation and optimising the commercial production process. The project is currently investigating long term performance and environmental costs/benefits.
