Rice engineers use byproduct from coal-fired power plants to replace Portland cement
The material is cementless and environmentally friendly, according to Rice materials scientist Rouzbeh Shahsavari, who developed it with graduate student Sung Hoon Hwang.
Fly ash binder does not require the high-temperature processing of Portland cement, yet tests showed it has the same compressive strength after seven days of curing. It also requires only a small fraction of the sodium-based activation chemicals used to harden Portland cement.
The results are reported in the Journal of the American Ceramic Society.
More than 20 billion tons of concrete are produced around the world every year in a manufacturing process that contributes 5 to 10 percent 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 silicon- and aluminum-rich fly ash as a supplement to Portland cement in concrete. “The industry typically mixes 5 to 20 percent fly ash into cement to make it green, but a significant portion of the mix is still cement,” said Shahsavari, an assistant professor of civil and environmental engineering and of materials science and nanoengineering.
Previous attempts to entirely replace Portland 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.
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