TRANSFORMATION OF FLY ASH FROM THE
STATE OF INDUSTRIAL WASTE TO THAT OF
SOCIO-ECONOMIC WEALTH
Dr. Anjan K Chatterjee
Coal Ash Institute of India
&
CONMAT TECHNOLOGIES PRIVATE LIMITED
ICUFA 2013
KOLKATA
PAST INITIATIVES FOR PROMOTING FLY ASH
• National Housing Policy (1988) : Exemption
of
excise duty for fly ash bricks
• BMPTC (1990) : Fly ash bricks promotion with
CPWD, DDA, DESU and NTPC.
• HUDCO & NHB (1990) : Initiation of financing the fly
ash based projects.
 Department of Power (1990) : Setting up of a
Working Group for drafting policy / guidelines.
 Fly Ash Mission under Department of Science &
Technology (1993) : Thrust on application
promotion.
FLYASH UTILISATION BY CLASS OF APPLICATION
RISE OF FLY ASH IN APPLICATION HORIZONS
IN SIX DECADES
FLY ASH GENERATION AND UTILISATION
IN INDIA
Year
Generation,
Mt
Utilisation, Mt
(% of generation)
1987-88
30
Not known
Wet disposal and brick making.
1993-94
40
1.2 (3%)
Commencement of the National
Fly Ash Mission
2004-05
112
42 (38%)
Fly Ash Mission continuing as
Fly Ash Utilization Programme
2006-07
130
60 (46%)
Same as above
2010-11
200
100 (50%)
Total utilisation planned but not
achieved
2016-17
300
300 (100%)
Projection made
2021-22
450
450 (100%)
Projection made
2031-32
900
?
Yet to be planned
Source : FAUP
Remarks
PAST AND FUTURE POTENTIAL OF FLY ASH
UTILISATION (Mnt)
Sl.No. Areas
2011
2012
2017
2022
1.
PPC Production
50
85
130
200
2.
Concrete
8
15
20
25
3.
Road embankment
8
15
20
20
4
Low lying area filling
9
20
20
20
5.
Ash bund raising
8
5
5
10
6.
Mine fill
12
20
70
120
7.
Brick and blocks
4
10
15
25
8.
Agriculture & others
1
2
20
30
100
172
300
450
TOTAL :
Source : FAUP
BRIEF HISTORY OF FLY ASH USAGE AS
SUPPLEMENTARY CEMENTITIOUS MATERIAL
• First Anonymous report : An investigation of the
pozzolanic nature of coal ashes (Engineering News,
Vol.71, No.24, 1914, pp. 1334 – 35).
• Pioneering research at the University of California,
Berkeley (Davis R.E., Carlson R.W., Kelly J.W. and
Davis H.E., Properties of Cements and concretes
containing fly ash, Journal of the American Concrete
Institute, Vol.33, 1937, pp 577 – 611).
• Construction of Hungry Horse Dam in Montana : USBR
Report CH – 95, 1948.
• Proliferation of use in the next half century.
• The first standard in India published in 1966.
AMERICAN ROAD & TRANSPORTATION BUILDERS ASSOCIATION
TRANSPORTATION DEVELOPMENT FOUNDATION
• Fly ash is a key component of high performance
concrete pavement designed for a lifespan of
30 – 60 years for concrete roads compared to
the current average of 20 – 25 years.
• The cost to build roads, runways and bridges
would increase by an estimated $104.6 billion
over the next 20 years, if fly ash is no longer
available as a transportation construction
building material.
ARTBA FOUNDATION STUDY
ESTIMATE OF THE POTENTIAL BENEFITS IN ACORDANCE WITH
THE DESIGNED SERVICE LIFE OF ROADS
• $ 25 billion over 20 years if built to last 35 years
• $ 33.5 billion over 20 years if built to last 40 years
• $ 51.5 billion over 20 years if built to last 50 years
• $ 65.4 billion over 20 years if built to last 60 years
RELATIVE ECONOMIC ADVANTAGE OF CONCRETE
PAVEMENT WITH FLY ASH IN INDIA
•
•
•
•
An illustration for 1 km x 2 lane 7m wide pavement.
Soil CBR of 5.
A life span of 25 years (against 15 years for flexible pavement).
Maintenance every 5 years.
NPV of Whole Life Cycle Costs (Rs. Lakhs)
Costs
Flexible
Concrete
Without fly ash
With fly ash
Initial
Maintenance
172
47
165
3
156
3
Total
219
168
159
FLY ASH IN CEMENT MAKING
WITH THREE TO FIVE FOLD
VALUE ADDITION
TREND OF PRODUCTION OF BLENDED CEMENTS IN
INDIA IN THE LAST TWO DECADES
TRANSPORTATION OF FLY ASH FROM
POWER PLANT TO CEMENT PLANT
Fly Ash
conveying
pipe line
Overall view
Fly Ash conveying pipe rack
FLY ASH TRANSPORTATION
SOME ESSENTIAL FACILITIES
Ash Intake Vessel
Fly Ash Transport Compressor
Fly Ash Control Room
Fly Ash Silo Loading System
FLY ASH ATTRIBUTES AND GROUP CENTROIDS
PARTICLE MORPHOLOGY OF THE INDIAN FLY ASHES
(Magnification 200 X)
(a) Angular glass fragments
(b) Acicular mullites in a spherical glassy particle
(c) Darker glassy spherical particles
COMPOSITIONAL VARIABILITY AT THE PARTICULATE
LEVEL
Fly Ash 1
Canadian Fly Ash for reference
SPECIFIC SURFACE AREA
INDIAN FLY ASHES
SOURCE NO
COMPARATIVE CRYSTALLINITY OF THE INDIAN AND
FOREIGN FLY ASH SAMPLES
Indian Fly Ash 2
Indian Fly Ash 1
Canadian Fly Ash
PSEUDO – TERNARY COMPOSITIONAL DIAGRAM FOR ALKALI
ACTIVATION OF FLY ASHES
• • Typical Indian fly ashes
LIME REACTIVITY - INDIAN FLY ASHES
IMPEDIMENTS IN ENHANCING THE
APPLICATION POTENTIAL OF INDIAN FLY ASHES
• Inter-Source and Intra-Source variability
• Wide distribution of particle size
• High order of crystallinity
• Wide fluctuation of surface area
CURRENT TECHNOLOGY FOR QUALITY UPGRADATION OF
INDIAN FLY ASHES
FOR HIGHER REACTIVITY
ULTRAFINE GRINDING OF FLY ASH TO MAKE LARGE
CHANGE OF PROPERTIES
• Mechano - chemical activation – chemical
conversions in fly ash particles by milling.
• Possibilities of introducing elastic, plastic and shear
deformations leading to fracture and
amorphization.
• Options :
– Ball milling
– Use of high energy vibratory mills
– Application of tower mills
TYPICAL ULTRAFINE BALL MILLING OF
THE INDIAN FLY ASH
Grinding time, h
Blaine surface,
m2/kg
Density, g/cm3
Lime reactivity,
MPa
Raw
300
2.10
5.8
1
490
2.30
7.0
2
550
2.35
--
3
630
2.39
--
4
710
2.42
9.5
5
780
2.48
--
Interesting to note that the high-Blaine fly ash demonstrated d50 of 5 – 7 μm, while the
metals and Intermetallics in a ball mill can be ground to 200-5 nm in 4 – 12 h.
COMPARATIVE PARTICLE SIZE CHARACTERISTICS OBTAINED
FROM CLASSIFICATION & FINE GRINDING
Raw
D50 : 19.2 μm
Ground
D50 : 8.4 μm
Cycloned
D50 : 2.0 μm
Ground and
classified Fine
Fly Ash
THE MOST SIGNIFICANT TREND OF
DEVELOPMENT
OPC
Blended
(PPC / PSC / PLC)
Multi component Portland
Composite cement
Nano – Particulate Cement
NANO CEMENT TECHNOLOGY
Simoloyer Milling Device
HIGH ENERGY VIBRATORY MILLS FOR
INDIAN FLY ASHES
•
•
•
•
•
Vibratory Mill
A lab mill has shown the potential of
increasing the Blaine surface of fly
ash from 260 to 950 m2/kg in 1 hour.
The d50 value, however, remained 6-7
μm reduced from 30 μm.
The product behaviour resembles
that of a ball mill.
A pilot mill of 1.5 tph rated
throughput with twin tubes of 600 x
3500 mm length has been installed in
an Indian Cement plant.
The scaling-up problems of low
reduction ratio (<2.0) and high
specific power consumption are
noticed in preliminary operations.
UNSUITABILITY OF TOWER MILLS FOR FLY ASH
GRINDING
1.
The Indian attempts of trial runs
with fly ash in Tower mills have
not been very encouraging.
2. Although throughputs of upto 100
tph are claimed for Tower mills or
its improved version of vertimills
with product fineness of 1-100
μm, for Indian fly ashes achieving
a d50 of 10 μm became difficult
with very high specific power
consumption. Use of coarse
media (6 mm) and low tip velocity
of the stirrer (3 m/s) perhaps
were responsible.
Tower Mill
PARTICLE SIZE AND CRYSTALLINITY EFFECTS
OF SILICO – ALUMINATE MATERIALS
RESEMBLING FLY ASHES ON
THEIR PERFORMANCE
PERFORMANCE COMPARISON OF CLASSIFIED FINE FLY
ASH WITH SILICA FUME IN CONCRETE
Composition/Properties
Control
d50, μm
-Addition, %
0
W/C
0.40
Cement, Kg/m3
400
Slump, mm
100
Compressive Strength, MPa
7 day
56.2
28 day
67.9
Rapid Cl- permeability, coulomb
7 day
2922
28 day
2340
FA
3
10.0
0.40
357
80
SF
<0.1
10.0
0.40
356
80
54.5
68.7
71.0
80.7
1083
758
429
297
RELATIVE PERFORMANCE OF SILICA FUME AND SILICA COLLOID
IN POZZOLANIC REACTION
CH quantity based on XRD counts per second
Weight loss between 4000C to 5000C with
respect to time
[C : Reference; SF 4 : 4% addition; SF 8 : 8% addition; SF 16 : 16% addition;
KF : 4% Silica colloid; KF 8 : 8% Silica colloid addition]
XRD PATTERNS OF DIFFERENTLY MILLED FLY
ASHES AND SILICA GEL
2 – Theta - Scale
XRD pattern of differently milled fly ash
2 – Theta - Scale
XRD pattern of silica gel
DETERMINATION OF CALCIUM HYDROXIDE IN DIFFERENT PPC
BLENDS ON 3-DAY HYDRATION
IN PASTE BY TG – DSC AT 10000C
Seria Blend Compositions
l No.
Ca (OH)2 %
1.
OPC + 25%
as- received fly ash
10.90
2.
OPC + 25%
Ball Mill ground fly ash
11.60
3.
OPC + 25%
Vibratory Mill Ground fly ash
7.73
4.
OPC + 25%
Silica Gel
Nil
STATUS OF PRESENT-DAY COMMINUTION AND CLASSIFICATION
OF CRYSTALLINE FLY ASHES AND THEIR PERFORMANCE
• Mean particle size generally achieved 8-10 µm and
with special efforts and facilities 2-4 µm.
• Performance of pozzolanicity and reactivity
commensurate with increased surface created for
denser packing and higher nucleation.
• Performance of these fly ashes still far away from
that of silica fume, silica colloid or silica gel.
• New opportunities for high-tech applications.
FLY ASH UTILISATION CLASSIFICATION FOR HIGH VALUE
ADDED APPLICATIONS
BIOTREATMENT POTENTIAL OF
FLY ASH
• ADHESION OF MICROORGANISMS
MINERAL SURFACE
TO
• BIOCATALYSED OXIDATION/ REDUCTION
• ADSORPTION / CHEMICAL INTERACTION OF
METABILIC PRODUCTS
SOME MICROORGANISMS IMPLICATED
IN METAL ACCUMULATION
Types of Organisms
Possible Metal Ions
Thiobacillus ferroxidans
Cd2+. Co2+, Ci2+, Cr3+, Fe3+, Ni2+
Cyanobacteria
Au3+
Chlorella Pyrenoidosa
Chlorella regularis
Bacillus Subtilis
Cd2+, Co2+, Ni2+, Zn2+, Uo2+
Pseudomonas Sp.
Cd2+,CO2+,Ni2+,UO2+ radio nucleides
Yeasts
Cd2+,Co2+,Cu2+,Ni2+,Zn2+
Aspergillus niger
Radio nucleides, Co2+, Cu2+, Zn2+
*Rhodoceccus Sp.
TiO2
Cd2+,Co2+,Cu2+,Zn2+,Fe3+,Au3+,Uo2+
TREATMENT SCHEME
NEWER OPPORTUNITIES WITH FLY ASH
1.
RECOVERY / REMOVAL OF TRACE ELEMENTS
(BIOLOGICAL AND/OR HYDROMETALLURGICAL METHODS)
2.
PHOSPHATIC COMPOUNDS OF ALUMINIUM (AND SILICA ?)
3.
SYNTHESIS AND SEPARATION OF MULLITE
CONCLUDING REMARKS
• The scope of enhancing the potential use of Indian Fly Ashes
is phenomenally large and is expected to be magnified
further in decades to come.
• The chemico-physical properties of the Indian fly ashes
create impediments in improving their reactivity, which is
essential to achieve enhanced usage of this resource.
• To a large extent the adoption of efficient cyclone-based
classification technology has helped the industry to separate
the fine particles below 10 µm size with improved
interaction properties in cement and concrete.
CONCLUDING REMARKS (Cont’d)
• The industrially practised ultrafine grinding technology has
not shown any viable process so far to reduce the mean
particle size of Indian fly ashes to submicrocrystalline level.
• No clear indications of real mechano-chemical activation of
the fly ashes are visible in micron-sized grains.
• Perhaps the feasibility of particle size reduction to 300 – 100
nm needs to be explored for significantly large changes in
grain properties.
• While the cyclone classification coupled with micron-size
fine grinding may satisfy the immediate technology needs of
the industry, some of the emerging ultrafine grinding
technologies should receive careful attention.