Fly Ash Concrete

Mechanical Properties

Fly Ash

What is Fly Ash Historical Background Chemical Nature Classification
Chemical Composition Mechanical properties Benefits High Volume
Fly Ash
Need for extending Strength Specifications to beyond 28 days – Restraints on use of Fly Ash in Highway Constructions

Mechanical Properties of Fly Ash

Mechanically, fly ash also pays dividends for concrete production.

fly ash:ball bearing effectBecause fly ash particles are small, they effectively fill voids.

Because fly ash particles are hard and round, they have a “ball bearing” effect that allows concrete to be produced using less water.

Both characteristics contribute to enhanced concrete workability and durability.

IS 3812 (Part 1) :2003 (Pulverized Fuel Ash — Specification for for use as Pozzolana in Cement, Cement Mortar and Concrete) specifies Physical requirements for Fly ash as tabulated below:

Physical Requirements

S.No Characteristics Requirements
1 Fineness – Specific surface in m2/kg by Blaine’s permeability method, min 320
2 Particles retained on 45 micron IS sieve (wet sieving) in percent, Max 34
3 Lime reactivity – Average compressive in N/mm2, Min 4.5
4 Compressive strength at 28 days in N/mm2, Min Not less than 80 percent of the strength of corresponding Plain cement mortar cubes
5 Soundness by autoclave test expansion of specimens, percent, Max 0.8

Note: Fly ash of fineness 250 m2/kg (Min) is also permitted to be used in the manufacture of Portland pozzolana cement by intergrinding it with Portland cement clinker if the fly ash when ground to fineness of 320 m2/kg or to the fineness of the resultant Portland pozzolana cement whichever is lower, meets all the chemical & physical requirements specified in this standard.


Concrete-Techgroup thanks Headwaters Resources , USA for granting them permission to use their resources in developing this article.