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alkali activated concrete

Cementless concrete made from industrial waste could reduce global carbon emissions

Image credit: Kaunas University of Technology

Concrete made from fly ash and other industrial waste products could lower the carbon emissions associated with large construction projects, according to scientists at Kaunas University of Technology (KTU) in Lithuania.

The final product is as strong as traditional concrete, is more resilient to the damaging effects of acid and is more stable in cases of exposure to extreme heat and cold.

Current estimates find that the global cement industry is responsible for 7 per cent of yearly carbon dioxide emissions into the atmosphere.

To produce one metric ton of Portland cement - a basic ingredient of concrete and the most commonly used type of cement around the world - up to one ton of carbon dioxide is released.

“At first, the idea that concrete can be produced without using cement seemed radical. Now, after several years of intensive work we succeeded to develop alkali-activated concrete, which compressive strength is 55MPa (the same as in usual concrete). Instead of Portland cement we are using alkali-activated industrial waste products – fly ash, biofuel bottom ash, AlF3 production waste – silicagel etc,” said Vytautas Bocullo, a researcher who worked on the project.

Theoretically, any material containing silicon and aluminium compounds could be used, such as blast furnace slag or metakaolin or material derived from modifying the clay mineral kaolitine.

Treated with a special alkaline solution, these materials start melting and binding similarly to traditional cement.

Depending on the composition, the final product can be either geopolymer or alkali-activated material. Alkali-activated concrete is much more resilient to the effects of fire and acid. Also, due to its higher pH, this concrete is protecting armature against corrosion.

Bocullo said that alkali-activated concrete can be used instead of traditional concrete in many fields and is becoming a globally popular alternative to traditional concrete.

“We are trying to use waste materials from local industry, such as aluminium fluoride production waste – silica gel and biofuel ash. The preparation of the substance depends on the material itself. For example, fly ash of coal can be used instantly, but biofuel ash needs to be grinded up [sic] to the fineness of the cement.

“In order to improve the qualities of the final product, several substances can be mixed, but before that their chemical composition and additives need to be investigated for their impact on the environment and on the compressive strength of the concrete”, Bocullo said.

The research groups working in the KTU Faculty of Civil Engineering and Architecture are also experimenting and developing other types of concrete mixtures, such as ultra-high performance concrete, which is being used for safe production, self-renewing concrete and others.

Earlier this week, a study recommended that cities build future pavements out of travertine, a common form of limestone, to reduce urban flooding and remove heavy metal pollutants from local water. 

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