Alternative aggregates

Two UK companies are at the forefront of converting flyash - the waste material produced by coal-fired power stations - into valuable recycled construction materials.

Lytag is a lightweight aggregate manufactured by making pellets from fly ash (pictured right) through the controlled addition of water in special pans. The pellets are then heated on a sinter strand to a temperature of 1100⁰C where they form a hard, honeycomb structured round particle up to 14 mm in diameter.

Lytag is +50% lighter than natural aggregates and +25% lighter than natural aggregate concrete. Concrete made using Lytag features the same structural strength as conventional material yet also has improved durability and insulating properties.

Meanwhile, Rocktron has opened a new facility in Cheshire, UK, which will process 800000 tonnes of fly ash per year (pictured left is the carbon storage tank at the facility). The facility is designed to process both fresh and stockpiled flyash, a move the company believes is what differentiates its process.

Rocktron estimates that for every 500000 tonnes of Rocktron Alpha (An alumina-silicate) used as a substitute for ordinary portland cement, up to 450000 tonnes of CO₂ could be saved.

The eco-minerals that Rocktron generates from flyash include glass spheres in particle sizes of between 1 and 45 microns; carbon (with a purity exceeding +90%); cenospheres (lightweight, inert, hollow spheres filled with inert air or gas) and spherical magnetite (a ferrimagnetic mineral of the iron oxide family).

Through Rocktron's unique process, the company says a majority of unwanted materials are separated out from the flyash which allows its eco-minerals to be used in greater proportions in cement and concrete than was possible in the past.

"Our new 100% recycled eco-mineral products will increase our customer's margins, help cut their costs and reduce their carbon footprint," said Lord Wade, chairman of Rocktron.