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| Last Updated:: 29/03/2016

Properties of Flyash

Fly ash is a good material for a wide range of applications viz. manufacture of cement, substitute of cement in concrete, manufacture of bricks, blocks, tiles, etc. It is highly useful as a geo-technical material for construction of embankment and reclamation of low lying areas, filling of underground, open mines, use in agriculture and reclamation of degraded / waste lands, etc. The pozzolanic property coupled with lime reactivity makes it very suitable for cementitious / binding applications. Its geo-technical property makes it a good substitute of soil and the presence of required percentage of silica, alumina and iron oxide etc. makes it suitable for sintered applications. The suitability of flyash for various applications is very safe due to very low levels of heavy metals, toxic elements and radio nuclides in flyash as well as its physical and chemical properties being very close to the range of common soils.  

The following tables provide general range of physical, chemical, geo-technical properties, available major, secondary, micro-nutrients and trace / heavy metals and radio-activity levels in flyash and soil (source: Fly Ash India 2005 - International Congress)

 

Table-I:  Physical properties of flyash

Parameters

Fly Ash

Bulk Density (gm/cc)

0.9-1.3

Specific Gravity

1.6-2.6

Plasticity

Lower or non-plastic

Shrinkage Limit (Vol stability)

Higher

Grain size

Major fine sand / silt and small per cent of clay size particles

Clay (per cen)

Negligible

Free Swell Index

Very low

Classification (Texture)

Sandy silt to silty loam

Water Holding Capacity (WHC) (per cent)

40-60

Porosity (per cent)

30-65

Surface Area (m2 / kg)

500-5000

Lime reactivity (MPa)

1-8

Above properties are just approximation values. Depending on the types of flyash these valyes may vary

Table-II: Chemical composition of fly ash and pond ash

Compounds (%)

Fly Ash

Pond Ash

SiO2

38-63

37-75

Al2 O3

27-44

11-53

TiO2

0.4-1.8

0-1

Fe2 O3

3.3-6.4

3-34

MnO

b.d-0.5

b.d-0.6

MgO

0.01-0.5

0.1-0.8

CaO

0.2-8

0.2-0.6

K2 O

0.04-0.9

0.1-0.7

Na2 O

0.07-0.43

0.05-0.31

LOI

0.2-5.0

0.01-20.0

pH

6-8

6-8

bd: below detection limit, LOI: Loss on Ignition Above properties are just an approximation value. Depending on the types of flyash these valyes may vary

 

Table-III: Available nutrients in pond ash


Nutrients (ppm)

Pond Ash

Available N

0-30

Available P

2-4

Available K

60-150

Available Ca

30-140

Available Mg

40-50

Available S

30-60

Available Cu

0.5-1.6

Available Zn

0.4-1.8

Available Mn

0.9-1.5

Available Fe

10-25

Available B

0.5-1.8

Available Mo

0.1-0.6

Above properties are just an approximation value. Depending on the types of flyash these valyes may vary

       Table-IV: Available metals in pond ash


Trace/Heavy metals (ppm)

Pond ash

Available Se

0.1-0.4

Available Cr

0.3-0.6

Available Pb

BDL-0.2

Available Co

0.05-0.15

Available Ni

0.15-0.25

Available Cd

0.03-0.07

Available As

BDL-0.03

Available Hg

BDL

 * BDL:- Below detectable limit Above properties are just an approximation value. Depending on the types of flyash these values may vary

 

         Table-V: Radioactivity levels in fly ash


Parameters (Bq/Kg)

Flyash

226 Ra

30-110

228Ac

30-110

40K

180-500

 

Table-VI: Geo-technical properties of fly ash


Parameter

Range

Specific Gravity

1.6-2.6

Plasticity (per cent)

Lower or Non-Plastic

Maximum Dry Density (gm/cc)

0.9-1.3

Optimum Moisture Content (per cent)

18.0-38.0

Cohesion (kN/m2)

Negligible

Angle of Internal Friction(degrees)

30-40

Coeff. Of consolidation Cv(cm2/Sec)

1.75X10-5-2.01X10-3

Compression index Cc

0.05-0.4

Permeability (cm/sec)

8X10-6-7X10-4

Particle size Distribution
(per cent of materials)
Clay size fraction
Silt size fraction
Sand size fraction
Gravel size fraction

 

   
1-10
 8-85
 7-90  
0-10

Coefficient of Uniformity

3.1-10.7

Above properties are just an approximaAbove properties are just an approximation value. Depending on the types of flyash these values may vary