fly Ash Percentage in PPC Cements


Different Cement companies have maintain different % of Flyash in cement. what are the advantage and disadvantage of Higher / Lower % of flyash in cement.

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Answers ( 5 )

  1. Fly Ash concrete mix proportioning Methods

    1. Simple Replacement Method -substitute fly ash for cement. Thb substitution is generally made on a one for one basis either by weight or by volume (water-cement requirements)
    2. Modified replacement method -The amount of fly ash put into the mix is greater than the amount of cement removed, the difference being accommodated by a change in the aggregate proportions.
    3. Rational Methods – Recommended ACI 211.1


    The use of fly ash in portland cement concrete (PCC) has many benefits and improves concrete performance in both the fresh and hardened state. Fly ash use in concrete improves the workability of plastic concrete, and the strength and durability of hardened concrete. Fly ash use is also cost effective. When fly ash is added to concrete, the amount of portland cement may be reduced.


  2. I herd that, the un-burnt carbon present in fly-ash effects concrete adversely. can u explain the same?

  3. Fly as is a by product of power station furnaces fired by pulverized bituminous coal. It replaces portion of concrete and hence improve sustainability of structures. Any replacement percentage can be considered provided that project requirement and specifications are not compromised. For example, concrete strength shall be the same of nearly the same of concrete without replacement materials.

    Generally, fly ash reduce heat of hydration, improve sulfate resistance, reduce chloride diffusivity, minimize risk of alkali aggregate reactivity, environmentally friendly, and improve concrete economy.

    As the percentage of replacement is increased, these advantages would manifest themselves better. However, higher percentages may decline ultimate concrete strength, and concrete need strict curing regime since early strength development of concrete with fly ash is low.

    In contrary, low replacement percentage would provide more certainty regarding strength of concrete, but the replacement would not be effective.

    In summary, suitable replacement percentage is not the same for all structures. Each condition shall be investigated and suitable replacement quantity shall be determined.

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