Recycled steel slag is being turned into a credible alternative to cement. 'Enviro-crete' promises to be cheaper, environmentally friendly and potentially superior to traditional concrete.

A new by-product from steel-making is set to be transformed into the basic construction material of buildings, bridges and pathways.

Researchers in Monash University's Department of Civil Engineering have used waste from steelworks to make Australia's first batch of concrete that is far more friendly to the environment and cheaper to produce than conventional methods of concrete manufacturing.

'Enviro-crete' is made from blast furnace slag waste, a waste product from the steel-making process that is similar to gravel. The slag is activated by alkalis and water to create cement.

Reduced emissions

According to researchers Dr Jay Sanjayan and Mr Frank Collins, by substituting ordinary concrete with enviro-crete, the construction industry will not only make good use of a waste product but also help reduce the emissions arising from the burning of fossil fuels during the making of ordinary concrete.

"Australia produces six million tonnes of ordinary portland cement each year, a process that uses a vast amount of fossil fuel energy. By using slag, we can save fossil fuels, reduce the carbon dioxide emissions and make a dent in the four million tonnes of slag waste material produced each year."

In addition to its environmental qualities, enviro-crete may be superior in other ways to traditional concrete made with portland cement.

"Current tests indicate that enviro-crete overcomes two shortcomings of ordinary cement -- namely a high rate of heat hydration and inferior durability," Dr Sanjayan said. "Hydration of cement normally releases heat shortly after the concrete is placed, which can lead to thermal cracking, especially in large concrete pours where the variation in temperature within thick sections causes uneven rates of cooling. Enviro-crete releases at a much lower temperature, so the risk of thermal cracking is minimal.

"Enviro-crete also appears to be more resistant to aggressive chemicals that normally cause concrete deterioration."

Commercial potential

After discovering that this process had been pioneered by Russian researchers in the 1960s, Dr Sanjayan and postgraduate student Mr Collins decided it was time Australia explored the potential commercial application of the process for contemporary building constructions. Another postgraduate student, Ms Tanya Bakhahrev, is also working with Dr Sanjayan on this project for her PhD.

At this stage, the researchers have already produced concrete with similar strength and slightly better durability than ordinary concrete, and are now testing longer-term properties such as shrinkage and strength retention.

"The Australian construction industry already has a good concrete product. It will not begin to use enviro-crete unless we can establish a convincing case that it is a credible alternative. It is simply not good enough to say it is cheaper and more environmentally friendly. The research currently under way must also show that it has properties that at least match those of traditional concrete," Dr Sanjayan said.