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EN 450 Fly Ash

EN 450 Fly Ash (formerly known as Part 1 PFA) can be used as a replacement for Portland cement in virtually any concrete application. For general purpose applications, concrete containing 25%-40% PFA is most suitable.

ScotAsh's EN 450 fly ash is specially selected at Longannet Power Station. Real time carbon analysers measure the Loss-on-ignition (LOI) of the PFA as it is carried out in the flue gases to ensure that the material selected has an LOI of less than 7%.


Three categories of fly ash are permitted under BS EN 450:

  • Category A: LOI not more than 5.0%
  • Category B: LOI 2.0% to 7.0% and
  • Category C: LOI 4.0 to 9.0%

ScotAsh does not produce Category C fly ash, which is not permitted in UK concrete, as the LOI upper limit under BS 8500 is 7.0%.

There are two categories for fineness:

  • Category N: not more than 40% retained on the 45 microns sieve and a limit of +_ 10% on the supplier’s declared mean value permitted
  • Category S: not more than 12% retained on the 45 microns sieve

ScotAsh produces Category N fly ash only.

Flyash can also be used in concrete as inert filler or an aggregate - known as a Type I addition

Uses and Benefits

EN450 fly ash in concrete offers improved rheology, reduced bleeding and uses less water than Portland cement concretes. It also improves pumpability and gives an excellent finish.

Recommended Construction Uses of PFA-based Concretes


Potentially alkali-reactive aggregates
Mass concrete sections
Effluent treatment plants
Marine environments
Pumped concretes
For high quality finishes
Sulfate-bearing environments
Chloride-bearing environments
Water retaining structures


Air-entrained concrete
Thin sections
Cold weather

Use with care

In high early strength applications unless hydration is accelerated by increasing temperature


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