A team at Kaunas University of Technology (KTU) in Lithuania is developing a method of producing concrete without cement.
The product uses industrial waste such as fly ash instead of cement and the KTU scientists claim it is as strong as traditional concrete, more resilient to damaging effects of acid, and more stable in cases of exposure to extreme heat and cold.
Aiming to reduce the concrete industry’s negative impact on the environment, KTU researchers have been investigating methods of substituting other materials for Portland cement, which is currently a basic ingredient of concrete and most commonly used types of cement around the world.
Producing one tonne of Portland cement releases up to a tonne of carbon dioxide (CO2). KTU says that the global cement industry is estimated to be responsible for 7% of yearly carbon dioxide emissions into the atmosphere.
“At first, the idea that concrete can be produced without using cement seemed radical," said Vytautas Bocullo, researcher at the KTU faculty of civil engineering and architecture. "Now, after several years of intensive work we have succeeded in developing alkali-activated concrete, which has a compressive strength of 55 MPa (the same as in usual concrete). Instead of Portland cement we are using alkali-activated industrial waste products – fly ash, biofuel bottom ash, AIF3 production waste, silica gel etc."
Bocullo said that the biggest advantage of this type of binder is that a great amount of industrial waste, containing silicon and aluminium compounds, can be used in its production. Theoretically, any material containing silicon and aluminium compounds could be used, such as blast furnace slag or metakaolin (material derived from modification of clay mineral kaolinite).
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 protects the armature component of electric motors against corrosion.
Bocullo maintains 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," Bocullo added. "The preparation of the substance depends on the material itself. For example, fly ash of coal can be used instantly, but the biofuel ash needs to be ground up 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”, says Bocullo.
KTU says its research groups are also experimenting and developing other types of concrete mixtures, such as ultra-high performance concrete and self-renewing concrete.
