Development of new trends in green concrete technology by using secondary raw materials and waste materials

miscellaneous

English

Concrete is still the most commonly used building material in the world, so there is a need to look for possibilities to make its production less harmful to the environment. Nowadays, many secondary materials are used that can make this construction material more ecological. However, much of the waste material created in the production of green concrete continues to be produced in huge quantities. As these materials’ problematic incorporation into cement matrix is common, an example of problematic behaviour is their negative influence on the rheology of fresh concrete and on hardened composite. An example of this waste material is fluidised bed combustion fly ash, which, based on its pozzolanic properties, provides a good premise for its use in concrete as an active admixture. On the other hand, its chemical composition and morphology makes the use of this material more problematic. The use of fluidised bed combustion fly ash in cement composite production as an admixture is not currently common, but there are some real possibilities for its potential. The most striking negative aspect is its chemical composition which supports the development of new product formation, influencing the durability of the composite. Another disadvantage is the morphology of grains, which have a negative effect on consistency. This raises the question of how, what had been considered waste material, can be used in concrete production, emphasising its positive properties rather than negatives. This contribution deals with the possibility of its safe incorporation into cement matrix together with next commonly used secondary raw material, which is high-temperature fly ash. Both of these materials have very a high pozzolanic ability, and the right combination could bring important improvements in both the physico-mechanical properties and the better durability of a cement composite. This contribution tries to determine the correct methodology for designing green concrete by using modern methods measuring rheology of fresh concrete and following hydration processes. The pozzolanic properties of high-temperature fly ash are considered a significant advantage, and its stable chemical composition makes it a good admixture for a cement composite. In comparison, the chemical composition of fluidised bed combustion fly ash is variable. The biggest difference is the amount of free CaO together with sulfates, which are higher in fluidised bed combustion fly ash. This can be solved by mixing fluidised bed combustion fly ash with water before adding it to the cement composite. Free CaO reacts with water to create Ca(OH)2, and this, to some extent, is an activator for the beginning of the faster pozzolanic reaction. When high-temperature fly ash and fluidised bed combustion fly ash are used in the right ratio, they can accelerate the pozzolanic reaction of high-temperature fly ash in the same manner. The focal point of the experiment carried out on cement pastes was particularly on the progress of hydration processes, aiming for the possible acceleration of pozzolanic reactions of both types of fly ash.

high-temperature fly ash, fluidised bed combustion fly ash, pozzolanic, CaO (calcium oxide), rheology

ŤAŽKÝ, M.; HELA, R.; NOVOSAD, P.; OSUSKÁ, L.

26. 10. 2017

Waset

Bangkok, Thajsko

2522-3631

Waset - conference proceedings

United Arab Emirates

2111

2116

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