Suppliers of EN 450 Fly Ash
Fly Ash is captured in the electro-static precipitators or bag filters of pulverised coal fired power stations. Fly Ash can have very wide ranging fluctuations in chemical composition subject to the coal source though the predominant oxides are SiO2 (ideally >50%) Al2O3; Fe2O3 and CaO. In addition, carbon levels can range from less than 2% to in excess of 20% dependent on coal source and operating efficiency.
Fly Ash may be used as an addition to Portland cement in virtually any concrete application. It can either be pre-blended with the cement or sold separately for subsequent blending at the concrete batching plant. For general purpose applications, concrete containing 15%-35% ash is most widely used. In terms of concrete properties, Fly Ash is widely acknowledged to offer many benefits such as improved durability, lower heat of hydration and improved pumpability and flow characteristics - especially when vibration is applied.
Many factors may influence the suitability of Fly Ash for use in cementitous applications and these include:
- Carbon content - ideally less than 5% though some standards allow up to 7%.
- Carbon surface activity and fineness can also have a major influence on Fly Ash performance in concrete and mortars – particularly with respect to admixtures and air entrainers.
- Mercury removal using activated carbon can have a detrimental impact on the suitability of ash for use in concrete or mortars.
- BMI has access to carbon removal technology through Separation Technologies Inc.
- Fineness - often measured as the percentage retained on a 45 micron mesh.
- Finer ashes are often associated with improved reactivity and water demand.
- Ash can be classified to produce finer fractions if necessary.
- Chemistry – this can differ widely and is subject to the coal source (including any bio-mass burned) and any environmental abatement technologies used within the power station. With regards to the use of ammonia in nitrous oxide reduction, ammonia levels in the ash should ideally be less than 50ppm.
- Particle shape – the more spherical the better in terms of water demand, “pumpability” and flow characteristics – especially when vibration is applied to concrete
- Glass content and reactivity – a result of many factors including chemistry, performance of the coal mills, burning temperature.
For any new source of Fly Ash, there is no substitute for undertaking detailed chemical and physical analysis and understanding what may influence these over time. BMI has access to both the Lafarge scientific network and partners such as Dundee University (materials properties and concrete testing); Separation Technologies Inc (carbon and ammonia removal) and Clyde Bergemann (pneumatic handling and blending).
Apart from the use of Fly Ash in blended cements or as a direct addition in concrete manufacture, Fly Ash may also be used as a raw material ingredient in clinker production where the silica and alumina contents are of particular interest. Non cementitious uses for Fly Ash are wide ranging and include use in roads, asphalt, soil and waste stabilisation, lightweight aggregates etc.
Cementitious Solutions has access to Fly Ash in many parts of the world – either through related companies or through its contracts with power stations. Fly Ash can be supplied in bulk or jumbo bags.