According to ASTM D 653 – 03, “fly ash is the finely divided residue that results from the combustion of ground or powdered coal and that is transported by flue gasses”. According to Makusa (2012), fly ash belongs to secondary binders that contain only little amount of cementitious properties. With the existence of fly ash, the water content of soils can be lowered, thus reducing the shrink-swell potential. Other than that, fly ash helps in the increment of workability, stiffness and strength of soils through the chemical reaction. The fly ash particles possess the fineness at the range of 1micron to 1mm size measured by Blaine’s specific area technique. Dry and wet sieving is an alternative measure for particle area. The specific gravity …show more content…
The pozzolanas include Al2O3, SiO2, and Fe2O3. The cementitious material formed is known as calcium silicate hydrate, with a gel texture or calcium aluminate hydrate, with a fibrous texture. The pozzolanic reactions are illustrated as below in Figure 2.10. Figure 2.10: The pozzolanic reactions of fly ash
The chemical composition of the fly ash is dependent on the features and configuration of the coal burned at the electric power generation facilities. The standard chemical composition and physical requirement for fly ash as defined in ASTM C 618 - 03 (2008) are shown in Table 2.7 and Table 2.8 below.
Table 2.7: The chemical requirements in ASTM (ASTM C 618 – 03, 2008)
Chemical Requirements Class N Class C Class F
(SiO2 + Al2O3 + Fe2O3), minimum % 70.0 70.0 50.0
SO3, maximum % 4.0 5.0
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Moisture content, maximum % 3.0 3.0 3.0
Loss on Ignition, maximum % 10.0 6.0 6.0
Table 2.8: The physical requirements in ASTM (ASTM C 618 – 03, 2008) Physical Characteristics Class F and Class C fly ash
Fineness – amount retained when wet sieved on 45 micron; No.325 sieve, maximum % 34
Strength Activity Index ▪ With Portland Cement at 7 days and 28 days, minimum % of control 75C ▪ Water requirement, maximum % of control 105
Soundness – autoclave expansion or contraction, maximum % 0.8
Uniformity Requirements ▪ Density, maximum % 5 ▪ Percent retained on 45 micron; No.325 sieve, maximum % points from average