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Fly Ash: safe and durable for constructions

For airport runways, tunnels, bridges, dams and buildings there are strict requirements. They are extensively and intensively used and the construction must also be safe and durable. This requires high investments; the material used needs to provide the quality that manufacturers and users rely on. Fly ash is a reliable raw material that is widely used in these types of concrete structures. With fly ash, producers can namely assign the necessary specific properties to mass concrete.

"the Westerscheldetunnel concrete had to meet requirements for strength, density and plasticity, but also resist aggressive substances and salts in the groundwater, melt-water and salt water."

drilling Westerscheldetunnel

Fly ash is a very popular product in the international construction industry. It has been successfully applied for more than sixty years. And certainly not in the least projects: the Channel Tunnel, the Puylaurent dam in France, the Logport logistic centre in Germany, the Picasso Tower in Madrid and the runway of Eindhoven Airport are just some examples of projects that made a conscious choice to use fly ash.

Fly ash is obtained by electrostatic or mechanical separation of dust particles from the combustion gases of pulverized coal. In the draft standard EN 450, the standard for application of fly ash in concrete, fly ash is defined as a fine powder from the combustion of pulverized coal, with or without co-combustion of secondary fuels (clean biomass), with pozzolanic characteristics and mainly consisting of SiO2 and Al2O3. In the Netherlands all the power stations are equipped with electrostatic fly ash precipitators (also known as E-filters).

An important characteristic of fly ash is it’s pozzolanicity. This means that the material is able to react with calcium hydroxide, a reaction product released during the hydration of Portland cement, in addition to which calcium silicate hydrates are formed that are insoluble in water. The pozzolanic properties are due to the presence of glasslike phases in the fly ash. In the alkaline environment of the concrete, the glasslike structure is broken and the components are available to react with calcium hydroxide to form calcium silicate hydrates.

Naturally, fly ash and its applications comply with all relevant legislation in the fields of health, safety and environment. In accordance with EURAL (or EWC, European Waste Catalogue) fly ash is classified as non-hazardous waste (code 10 01 02 of 10 01 17).

For the safe use of fly ash, a safety information sheet has been written.