Scientists test new recycled flyash building block

The concrete blocks made from 70% flyash weigh around one-fifth as much as conventional concrete blocks, and are being tested for one year at a Habitat for Humanity home to be built in northern Georgia. Walls made from the blocks will be tested for energy efficiency and air-tightness. The results will be compared to data obtained from insulation monitoring carried out at two other buildings constructed more than a year ago.

“One of the unique aspects of this particular research project is that it helps the supply of energy by utilising historic waste stream – being flyash from coal-fired power plants – and enhances the country’s efforts to improve energy efficiency by providing an energy efficient construction material,” said Jeff Christian, Director of ORNL’s Building Technology Centre.

Preliminary tests on the blocks have indicated that they can produce a thermal mass effect, absorbing the sun’s energy during the day and radiating it into a home at night, long after the sun has set. This allows a building to remain relatively cool during the day, but warm at night, Christian told edie. However, this characteristic is climate specific, applying to regions with sunshine during the day and that are cold at night.

“The thermal mass benefits of the autoclaved aerated concrete wall can result in a home as energy efficient as a typical home constructed of two-by-fours in the Knoxville area,” said Christian.

The lower weight of the blocks can be a drawback. “Their compressive strength is not as strong,” Christian told edie. “It generally means that there is some reinforcing that might be needed.” This is carried out by drilling a hole from the top to the bottom of a stack of the blocks in the corners of a new building into which the strengthening is inserted, and renders the system adequate for one to two storey buildings.

The project is designed to help the US Department of Energy achieve its goals of providing energy supply in an environmentally responsible manner and promote energy conservation, the researchers say. The blocks are already available commercially.