How do you turn poo into aggregate? No, it's not the start of a joke, but the subject of a BBC article last year about Thames Water's efforts to produce 2 million carbon-negative construction blocks a year. This is another example of the rise of manufactured secondary aggregates, reducing the need to dig up irreplaceable natural resources:
A flush deal signed this week could see Londoners’ waste used for building new homes. In a breakthrough development, Thames Water has found an inventive way to use sewage – which already generates renewable power – to help create a material for carbon negative heavy-duty bricks.
Every day, the waste of four million Londoners entering Europe’s largest sewage works in Beckton is drained of water, with the leftover solids roasted in the company’s waste-to-energy incinerator. The high temperatures sanitise the waste and release heat for producing electricity on site. The leftover ash has – until now – been binned.
The latest innovation announced today will see this dried residue ash reacted with carbon dioxide, water, sand and a small quantity of cement to form aggregate for individual breeze blocks – each weighing 17kg. Thames Water’s supply deal is expected to produce 18,000 tonnes of aggregate every year, enough for around 2.3 million construction blocks to be used in a range of property and business developments across the capital and beyond.
Using ash to produce synthetic aggregate locks in around 800 tonnes of CO2 and will replace 18,000 tonnes of natural resources being dug out of the ground annually – contributing to the UK’s circular economy. In addition, the synthetic aggregate is carbon beneficial as more CO2 is captured than is generated in the manufacturing process.
Another type of brick made from waste material was announced last week. The world’s first building brick made with 90% recycled content – using construction and demolition waste and no cement – has gone into production in Scotland. Developed at Heriot-Watt University,
The K-Briq is said to produce just 10% of the CO2 emissions of a traditional fired brick, uses less than a tenth of the energy in its manufacture and can be made in any colour.
