Fly ash can replace cement to develop eco- friendly concrete

Over 20 billion tonnes of concrete is produced every year

Washington, June 19: Scientists have developed a material using fly ash—a byproduct of coal- fired power plants — that can replace cement in concrete, paving the way for greener buildings and structures in the future.

Fly ash binder does not require the high- temperature processing of cement, yet tests showed it has the same compressive strength after seven days of curing.

It also requires only a small fraction of the sodiumbased activation chemicals used to harden cement.

The material is cementless and environment friendly, said Rouzbeh Shahsavari, an assistant professor at the Rice University in the US.

Over 20 billion tonnes of concrete are produced around the world every year in a manufacturing process that contributes 5 to 10 per cent of carbon dioxide to global emissions, surpassed only by transportation and energy as the largest producers of the greenhouse gas.

Manufacturers often use a small amount of siliconand aluminum- rich fly ash as a supplement to

Portland cement in concrete.

“The industry typically mixes 5 to 20 per cent fly ash into cement to make it green, but a significant portion of the mix is still cement,” said Shahsavari.

Previous attempts to entirely replace cement with a fly ash compound required large amounts of expensive sodium- based activators that negate the environmental benefits, he said.

“And in the end it was more expensive than cement,” he said.

“A majority of past works focused on so- called type F fly ash, which is derived from burning anthracite or bituminous coals in power plants and has low calcium content,” Shahsavari said.

“But globally, there are significant sources of lower grade coal such as lignite or sub- bituminous coals. Burning them results in high- calcium, or type C, fly ash, which has been more difficult to activate,” he said.

“The work on fly- ash provides a viable path for efficient and cost- effective activation of this type of high- calcium fly ash, paving the path for the environmentally responsible manufacture of concrete.

Future work will assess such properties as longterm behaviour, shrinkage and durability,” he added.

Shahsavari suggested the same strategy could be used to turn other industrial waste, such as blast furnace slag and rice hulls, into environmentally friendly cement- like materials without the use of cement.

Fly ash binder does not require the high- temperature processing of cement, yet tests showed it has the same compressive strength after seven days of curing

Currently, the manufacturing sector mixes 5 to 20 per cent fly ash into cement to make it green, but a significant portion is still cement. A shift to fly- ash can reduce pollution substantially.