We do need Fly Ash Grades
During the first mass utilization of fly ash in Europe it became evident that fly ash of a finer particle size provided increased strength. As the use of fly ash in concrete became technical as well as economic success, the construction industry had to develop standards to find an equilibrium between concrete production cost and concrete quality requirements. The fly ash providers (mainly electricity companies) could see that the quality (mainly fineness) of the so called run-off-station ash vacillates too much. On the other hand, the fly ash users needed a constant and stable quality. The only solution was to extract the particles of a defined size from the run-off station ash by classifiers which could be set to produce a specific particle size.
The following table shows a spectrum of DIRK PHOENIX products of a specific particle size in comparison to a set of international Standards for fly ash used in concrete.
|Grade||Application||Typical replacement levels||Market Segments||Confirmation to Standards|
|DP 100||HPC & > M60 concrete / No additional MIC required||5 – 10%||HPC / High rise towers||All standards|
|DP 83||> M60 concrete / grouts||20 -30%||Site mix with high grade concrete||All standards|
|DP 63||M50 – M70 concrete||25 – 35%||Captive RMX with high grade/durability/work ability||All standards|
|DP 60||M40 – M60 concrete||25 – 25%||Commercial RMX plus captive RMX||IS 3812 & ASTM C618|
|DP 40||Mass concrete (Dams) & plaster/ mortar||upto 70% (RCC dams)||RCC dams||ASTM C618|
|DP 30||< M40 concrete||20 – 30%||Commercial RMX/compete against low price fly ash suppliers||ASTM|
|DP 10||Fly ash bricks / paver blocks / partial sand replacement||20 – 50%||Bricks / Pavers||None|
Over the time DIRK developed various fine and ultrafine fly ash products to further improve the concrete quality for specific requirements. As can be seen from the requirements of the Standards, the second quality parameter for fly ash is the Pozzolanic reaction of fly ash. Run off station fly ash has a particle size varying from 1 µm to 150 µm. Typically, the size less than 10 µm contributes to the pozzolanic activities, the size above 45 µm hardly contributes to pozzolanic activities at all.
The specific surface area as tested by Blaine technique and as collected by the ESP of the power station is found to be about 400 to 700 m2/kg as compared to specific surface area of cement 260m2/kg (average). It means more surface = more reactivity.
The most important Fly Ash criteria of the Standards are:
1) PHYSICALLY: the particle size, water requirement and carbon content.
2) CHEMICALLY: the pozzolanic reactivity (reactive surfaces defined by fineness)
The result of this physical and chemical interaction with the cement or lime is concrete strength.
DIRK PHOENIX fly ash products are designed with this knowledge accumulated for the last 40 years.