Status of Availability, Utilization and Potential of Fly ash use in Construction

A.K. Jain, Technical Advisor, UltraTech Cement Ltd., anand.jain@adityabirla.com

Introduction:

Fly ash is a byproduct from coal based thermal power plants. It has been generally

considered a waste material in the past and disposal of which has posed numerous

ecological and environmental problems. However, recent researches have shown

that fly ash has potential to act as invaluable ingredient in cement and concrete if

used within the framework of prescribed specifications and quality systems. The fly

ash is now considered as a resource material rather than a waste in civil engineering

and material science. In addition fly ash can be gainfully used for various other

applications.

In developing countries like India power generation is most important requirement

for economic and social development. At the time of independence in 1947, the

installed capacity was 1,361 MW, which has increased to 1, 87, 732 MW on 31 March,

2012. Out of it, 1, 10, 232 MW is thermal (Coal/Lignite) based and is responsible to

co-generate nearly 200 million tons of fly ash per year. In 12th Five Year Plan, the

Planning Commission has set up target to enhance power capacity by 89,000MW,

out of which 53,400 MW will come from Coal/Lignite based thermal power plants.

By the end of 12th Plan (2017), the fly ash generation is expected to reach 300 million

tons per year and likely to continue to grow with same pace at least for next two to

three decades.

The disposal of such large quantity of fly ash is indeed a challenge before all

stakeholders. In this paper an effort has been made to outline the present status of

generation, utilization and future strategy to increase effective use of this wonderful

material.

Key Words: Fly ash, Construction, Concrete, Cement, Energy, Bricks, Sand

Availability of Fly ash:

The average ash content in Indian Coal used in thermal power plants is about 35%.

The generation of 1 MW power with Indian coal results in co-generation of nearly

1800t of fly ash. Out of this quantity, nearly 20% is coarser bottom ash and about

80% (1500t) is fly ash which is collected through Electro Static Precipitators (ESPs).

At the end of 11th Five Year Plan (31 March’ 2012), the Coal /Lignite based thermal

plants capacity was 1,10,232 MW. The breakdown of this capacity State wise and

approximate fly ash generation is shown in Table- 1.

State

Installed Capacity (MW) Approx Fly ash

Generation usable for

Cement /RMC per Year (in tons)

Sector

Central State Private Total Total Andhra Pradesh 4600.00 5.092.50 450.00 10142.50 14244300.00

Bihar 2340.00 440.00 0.00 2780.00 3906000.00

Chattisgarh 4920.00 1780.00 1483.00 8183.00 11970000.00

Delhi 705.00 382.50 0.00 1087.50 1575000

Gujarat 0.00 3970.00 632.00 10290.00 11346300

Haryana 1000.00 3270.00 660.00 4930.00 7408800

Jharkhand 2020.00 1260.00 1410.00 4690.00 5537700

Karnataka 0.00 2720.00 2060.00 4780.00 7056000

Madhya Pradesh 3260.00 2982.00 0.00 6242.50 7812000

Maharashtra 0.00 8742.50 2486.00 11228.50 16695000

Odisha 3460.00 420.00 1800.00 5680.00 8379000

Punjab 0.00 2620.00 0.00 2620.00 3906000

Rajasthan 250.00 3490.00 540.00 4280.00 4851000

Tamil Nadu 3240.00 2970.00 250.00 6460.00 5481000

Uttar Pradesh 731.00 4642.00 2805.00 14757.00 22465800

West Bengal 5790.00 5031.00 1260.00 12081.00 17917200

Total 38895.00 49813.00 21524.00 110232.00 150,551,100

Note:

1. In useable fly ash availability, the bottom ash is not taken into account,

which is about 20% of the total ash generated.

2. Fly ash from coal based plants is only considered in available quantity.

Lignite based plants on 31 March’ 2012 had installed capacity of 4650 MW.

The location of major thermal power plants in India is shown on attached map.

Quality of Indian Fly ash:

There are two types of fly ash available, siliceous and calcareous depending upon

the fuel used, coal or lignite respectively. The specifications of both are given in

Indian standard IS: 3812 (Part 1) 2013 and they generally conforms to class ‘F’ and

class ‘C’ fly ash respectively as per ASTM C618-12a. The typical chemical and

physical characteristics of siliceous fly ash collected from few major thermal power

plants in India is given in Table 2 to 5.

Table: 2 Chemical characteristics of fly ash from some major thermal power plants

TPP Chemical Characteristics (%)

SiO2 Al2O3 Fe2O3 Sx CaO MgO Na2O (eq)

P2O5 SO3 C LOI

Chandrapur 66 23 4 93 2 0.4 0.85 0.5 0.2 0.1 0.4

Badarpur 60 25 6 91 1 0.5 1.3 1.0 0.4 0.9 2

Tuticorin 65 20 5 90 1 0.5 1.2 0.5 0.4 0.9 2

Simhadri 63 25 6 94 1 0.7 1.2 0.7 0.2 0.2 3

Singrauli 66 22 6 94 1 0.6 1.3 0.3 0.2 2.2 0.5

IS 3812 – Part I (Specifications of Pulverized Fuel Ash) requirement Siliceous FA 35

(min) NS NS 70

(min) NS 5

(max) 1.5

(max) NS 3

(max) NS 5

(max)

Calcareous FA 25 (min)

NS NS 50 (min)

NS 5 (max)

1.5 (max)

NS 3 (max)

NS 5 (max)

Sx : SiO2 + Al2O3 + Fe2O3

Na2O(eq): Total alkalies Na2O (equivalent)

NS: Not Specified

Table: 3 Other chemical characteristics of fly ash from some major thermal power plants

Chemical Characteristics TPP pH Moisture content

(%) Acid insoluble residue

(%) Chloride

(%) Reactive silica

(%)

Chandrapur 10 1 64 0.09 38

Badarpur 7 1 57 0.09 35

Tuticorin 8 1 61 0.003 28

Simhadri 10 1 65 0.023 34

Singrauli 10 1 66 ND 30

IS 3812 Part I (Specification of pulverized fuel ash) requirement

Siliceous FA NS NS NS 0.05 20

Calcareous FA

NS NS NS 0.05 20

ND: Not Detected

NS: Not Specified

Table: 4 Trace metal /Heavy metal analysis of fly ash samples

TPP Trace Metal (mg/kg)

As Zn Cd Co Mn Pb Cr Mo V Be Cu Hg

Chandrapur 5 66 29 39 139 27 144 105 113 10 49 0.009

Badarpur 3 100 32 44 79 26 112 105 144 9 59 0.07

Simhadri 4 92 - 34 69 7 140 27 66 - 55 0.003

Singrauli 4 36 - 41 87 11 128 89 21 - 56 0.007

Note:

1. Data for Tuticorin TPP are not available

2. No limits are prescribed in IS 3812 (Part I) - 2013

Table: 5 Physical Properties of Fly ash samples

TPP Specific gravity g/cc

Specific surface area (cm2/g)

Lime reactivity

(MPa)

Soundness Lechatelier’s Method

(mm)

Chandrapur 2.1 3065 5.7 4

Badarpur 2.0 3675 6.5 4

Tuticorin 2.0 3270 6.0 4

Simhadri 2.1 3449 7.4 3

Singrauli 2.0 3334 7.2 3

IS 3812 (Part – I ) requirement

NS 3200 4.5 NS

Note:

1. IS: 3812 (Part -1) 2013 Specifies soundness measured by Autoclave test (0.8% max).

2. The code specifies fineness 3200 cm2/g (min) if fly ash is directly used as cementitious

material in concrete or mixed with OPC to produce PPC. However, if fly ash is inter

ground with clinker to produce PPC, the fineness of fly ash 2500 cm2/g (min) is

permitted.

3. NS: Not Specified

Discussion on Quality of Fly Ash:

The thermal plants for testing of fly ash were selected from North, South Central and

East India covering large geographical area. It is seen that chemical properties like

oxide composition, LOI, insoluble residue, chloride content and reactive silica are in

close proximity. The carbon content has shown variability. In modern thermal power

plant new units like in Chandrapur, Simhadri and Singrauli, the carbon contant is

about 0.2% while in older plant units Badarpur and Tuticorin, it is about 0.9%. this

may be due to change in technology of burining coal in boilers. However, the total

carbon content in various fly ash samples is below 1%. The variation in Trace/ heavy

metals is alslo not too large though sources of coal for these power plants are quite

different. In all the chemical parameters, the quality of fly ash conforms to Indian

Standard IS: 3812 (Part 1) -2013 with reasonable margin.

The physical properties like specific gravity, lime reactivity and soundness are also

within very close range and within acceptable limits of IS: 3812 (part 1) – 2013. The

fineness of fly ash varies depending upon the field of ESP from which it is drawn or

a composite sample representing all the fields of ESP. IS 3812 (Part 1) – 2013 specifies

minimum fineness of fly ash 3200 cm2/g if it is directly mixed with OPC or used in

concrete mix as cementitious material, and 2500 cm2/g if it is inter-ground with

clinker to produce PPC. The fineness of fly ash can be increased to required level

either through grinding or through classification method. Both these methods are

now widely used in India to obtain requisite fineness of fly ash.

Present Utilization of fly ash:

The present utilization of fly ash in various sectors is shown in table – 6 and Fig 2.

Nearly 100 million tons of fly ash is reported being utilized out of 200 million tons

generated during 2012 by Ministry of Science and Technology. Though percentage

utilization has gone to nearly 50% but in absolute terms, very large quantity of fly

ash still remains unutilized.

Table – 6 Present Utilization of Fly ash Sector Mnt % of utilization In production of Portland Pozzolana Cement 40 40

Cement Replacement at Concrete batching Plants (RMC)

10 10

Filling in low lying areas 17 17

Roads and Embankments 16 16

Dyke Raising 4 4

Brick Manufacturing 4 4

Agriculture Sector 4 4

Other miscellaneous uses. 5 5

Total 100 100

(Source – Fly ash utilization Unit – DST Govt. of India)

Fig – 2 Present Utilization of Fly ash in Different Segments

Potential of Fly ash Utilization

Cement:

The utilization of fly ash in cement in future will be driven by the following factors;

Environmental Issues:

o Cement industry globally account for nearly 6.5% of CO2 emissions. Use of

fly-ash would reduce clinker consumption and bring down emission of green

house gases in the atmosphere. The increasing awareness and legislation on

environmental issues would enable cement industry to use fly ash not only in

production of cement but as a constituent in raw-meal in production of

clinker wherever possible. The durability of construction especially in

aggressive and marine environment will also help in utilization of more fly

ash as cementitious material.

Economic Issues:

o . Reduction in cost of production

o . Increase in throughput of cement plant

The continuous increase in production and distribution cost of cement is putting

great pressure on the financial viability of the cement business. The utilization of fly

ash would help in reducing the cost of production and providing technically

superior product to consumers at more competitive rate. In addition the production

40%

10%17%

16%

4%

5%

4%4%

Cement

Concrete

Filing

Roads/Embankments

Dyke raising

Brick Manufacturing

Agriculture

Miscellaneous

capacity of the manufacturing units will also increase to meet the increasing demand

of cement.

Conservation of Minerals:

o Limestone reserves are limited in the country and due to increasing demand

of cement, it is essential that cement grade lime-stone is conserved by using

fly ash and ggbs to the maximum possible extent. In addition, availability of

good quality coal is also becoming scarce and nearly 150-200kg coal is used

for production of 1 ton of clinker. There would be increasing pressure on the

industry to conserve these minerals in future and to utilize more of fly ash for

increasing share of PPC.

Energy Saving:

o Shortage and high cost of energy is proving bottleneck for the industrial

development of the country. Use of fly ash in the cement production saves

approximately 8% to 10% electric energy. However, the percentage

production of PPC in overall cement production in the country has reached a

plateau. The percentage of PPC which has already reached to 67% of total

cement production in India is likely to remain within the range of 65% to 70%

in future years. In future the only increase in production of PPC can be

expected due to overall growth of cement consumption. Utilization of fly ash

in cement and concrete has therefore limitations due to mismatch between

growth in consumption of cement and co-generation of fly ash. Based on the

this premise, the utilization of fly ash upto the end of 12th Five Year Plan is

given in Table -7

Table – 7 Likely utilization of fly ash in cement production up to 2017

Year Total Cement

Production PPC % of total

Cement Production PPC

Production Fly ash

Utilization

2009-2010 202.74 67.21 136.26 32.00

2010-2011 214.90 66.5 142.9 35.72

2011-2012 226.70 65.5 148.48 37.12

2012-2013 239.20 66.0 157.87 39.46

2013-2014 254.00 65.5 166.37 41.59

2014-2015 269.24 66 177.69 44.42

2015-2016 285.39 66 188.38 47.09

2016-2017 302.52 67 202.68 50.67

Note:

1. All figures are in Mnt except %

2. Fly ash utilization in PPC is considered 25% (average).

3. The figures for 2013-2014 to 2016-2017 are based on average expected growth of 6%

per annum CAGR.

Utilization of Fly Ash in Concrete (RMC)

The mechanization in concrete production through batching plants is continuously

increasing. This mode of production of concrete is promoting addition of fly ash at batching

plants with OPC.

The, consumption of fly ash can be increased as cementitious material if the use of following

types of products/ concretes is increased.

a. High Volume Fly Ash Concrete (HVFAC):

Presently cement can be replaced upto 35% by fly ash as per Indian Standard in

concrete but research from CANMET and similar institutions has shown that fly

ash up to 50% can be used in structural grade concrete without affecting its

mechanical and durability characteristics. Rather the long term strength,

impermeability, impact resistance, resistance to acids is better of HVFAC. The

appropriate promotional strategies and proper codal support can help to increase

volume of HVFAC especially for heavy foundations, retaining walls, mass

concreting works in irrigation and marine structures.

b. Self Compacting Concrete:

Self Compacting Concrete (SCC) has many applications and is emerging as a

preferred construction material. Apart from cement, large quantity of fly ash to

the extent of 200 to 300 kg/m3 of concrete can be used in SCC. The promotion of

SCC would also increase utilization of fly ash.

Recently IS 456: 2000 Indian Standard on Plain and Reinforced Concrete through

amendment No.3 in 2007 has added new annex ‘J’ prescribing the specifications of

SCC. Though SCC is very useful in numerous structural applications like

columns, monolithic structures, locations of congested reinforcement, etc. but its

present use is very low (below 3%).

c. Geo-Polymer Concrete:

Fly ash can be activated with alkalies at suitable temperature for producton of

geo-polymer concrete. This type of concrete can utilize up to 90% to 95% fly ash as

cementitious material and is reported to be in use in countries like Australia and

Newzealand. In certain applications like precast elements use of geo-polymer

concrete can not only increase utilization of fly ash but will result in long term

durability and appreciable economy. The technology of geo-polymer concrete is

required to be studied and adopted in India if found economically viable vis-à-vis

conventional cement based concrete.

d. Controlled Low Strength Material (CLSM):

CLSM is a low strength cementitious material which is widely used in USA,

Canada and other countries as back fill material in utility trenches, bedding under

pavements and filling abandoned underground structures. CLSM has

compressive strength typically in the range of 1.2 to 2 MPa with cement content

varying 25 kg to 75 kg/m3. The low strength of CLSM allows its re-excavation by

normal means whenever needed in future. CLSM is composed of water, cement,

fly ash and in some cases 10mm down aggregates. CLSM may utilize large

quantity of fly ash varying from 800 to 1000kg/m3.

In India even the utility trenches are backfilled by soil, which is not properly

compacted and settles down under load resulting in uneven road shoulders. It is

very inconvenient to the pedestrians and road traffic and poses serious traffic

hazard. The use of CLSM on large scale will help in increasing the use of fly ash

and to create more durable and safe road infrastructure.

e. Roller Compacted Concrete (RCC):

ACI 207.5R-89 defines Roller compacted concrete as concrete compacted by roller

compaction. The concrete mixture in its unhardened state must support a roller

while being compacted. In RCC cement consumption is lower because much

leaner mix can be used. Mineral admixture like fly ash is used widely in RCC in

large quantity as part replacement of cement and part replacement of fine

aggregate.

RCC can be used for construction of dams, spillways, sub-base for highways and

other mass concrete works. Recently large quantity of RCC has been used 6,50,000

m3 in 12 months at Ghatghar dam in Maharashtra which was placed with belt

conveyor delivering 400m3/hr. RCC is also being used for construction of sub-

base on National Highway. However, there is large scope for use of RCC in

various Civil Engineering works.

Other Potential avenues for utilization of fly ash

a) Fly ash Bricks:

It is estimated by BMTPC (Building Materials and Technology Promotion Council)

that nearly 320 billion bricks are used in India every year. The share of fly ash

based bricks /blocks are estimated about 12%. The balance is either clay bricks or

cement concrete blocks. Govt. of India vide Gazette Notification of 16th November,

2009 has made it mandatory that within 100 km radius of thermal power plant, in

all types of construction works fly ash bricks (fly ash content 25% min) will be

used. If the above notification is implemented by all State Govts rigidly, there is

potential of utilizing fly ash in bricks to the extent of 50 to 60 million ton per year.

In this application, the accumulated pond ash at TPPs can also be effectively

utilized.

There is immediate need to set up fly ash brick production units in public and

private sector to replace clay bricks and other conventional walling materials.

Govt., Thermal Power plants and other stake holders can consider to provide

incentives to popularize the use of fly ash bricks in coming years to the

manufacturers and the consumers.

b) Use of Fly ash as part replacement of sand:

IS 456: 2000 has recently allowed vide amendment no 4 that fly ash beyond 35%

can be used in concrete but such additions will be considered as part replacement

of sand.

In view of shortage of good quality sand and environment concerns on its

extracting from rivers, fly ash offers a viable alternative to part replace sand to the

extent that grading remains within the provisions of IS 383: 1970, Code of practice

for coarse and fine aggregates for concrete. Fly ash can replace 15% to 25% sand

depending upon fineness modulus of sand for majority of concrete works. This

concept is required to be promoted especially amongst the RMC producers and at

major project sites.

c) Construction of embankments:

Fly ash can be effectively used in construction of embankments for Highways,

flood control works, dykes and for other similar works. Large quantity of fly ash

was used in construction of embankment for Noida-Greater Noida Express Way

and its performance is reported quite satisfactory.

National Highways and other road projects have started using large quantity of

fly ash for this purpose. Eastern parts of India are prone to floods and fly ash can

be effectively used for construction of barriers against flood water and prevention

of coastal erosion works.

d) Filling in low lying areas and Reclamation of Sea:

The buildability of land can be improved by leveling the low lying areas. Govt. of

India vide notification of 27th August, 2003 has permitted use of fly ash for

reclamation of sea. Clause 2 ‘A’ states “Subject to the rules made under the

Environment (protection) Act (1986) reclamation of sea shall be a permissible

method of utilization of fly ash”. If this provisions is implemented judiciously at

suitable locations, then large quantity of fly ash can be used to reclame land from

sea especially in coastal urban cities. Many Indian cities are suffering due to

shortage of land and reclamation from sea will provide great relief to these cities.

Singapore has recently done such reclamation on appreciable scale.

e) Light Weight aggregates(LWA):

Another potential utilization of fly ash can be made in producing light weight

aggregates. LWA is used in many European countries as part replacement of

natural coarse aggregate to produce concrete of structural grade in density range of

1800-2000 kg/m3. LWA is also used in manufacture of bricks/blocks for wall

construction. It is also used for insulation purposes.

In India it has not yet become popular due to lack of appropriate production

technology and project financial viability. However, more research and field work

may help in developing appropriate technology to reduce cost of plant and LWA.

However, LWA holds very promising future for use in various applications and to

utilize appreciable quantity of pond and fly ash.

Conclusion:

The fly ash generation has already crossed 200 million tons per year and likely to increase to

more than 300 million tons by the year 2017. The utilization and disposal of such large

quantity of fly ash is a herculean task which has to be performed within various

environment protection laws. The effective utilization of this resource material would not

only minimize the disposal problem but help in conservation of scarce minerals, reduce

emission of green house gases and enhance performance and durability of structure.

During the last decade starting from the year 1999, cement and construction industry have

appreciably increased the utilization of fly ash. The PPC share in total cement production

was only 21.8% during 1999, which has increased to about 67% during 2014. However, the

PPC share has already reached a plateau in total cement production in India and new

initiatives are required to increase the utilization of fly ash especially in different types of

concrete as discussed in the paper. The scope of utilization of fly ash in cement in future is

limited only to the extent of rate of increase in cement consumption.

It may however, be realized that cement and concrete alone would not be able to utilize

increased volumes of fly ash in future and new avenues have to be found and promoted.

The other potential areas are fly ash bricks, filling in embankments, reclamation of sea,

improving the agricultural soil quality and light weight aggregates. The use of fly ash in all

these areas has been tried in many countries but to suit the Indian conditions, extensive

laboratory and field work is required to achieve desired results.

Reference:

1. Cement - Data book 2011-2012 published by CMA, New Delhi.

2. Fly ash Utilization and generation published by NTPC.

3. Corporate Sustainability Report prepared by Ernst and Young in June 2008.

4. Inputs provided by Fly ash utilization Cell, DST, Govt. of India.

5. IS 1489-1991

6. IS 3812 (Part – 1) 2003

7. IS 456: 2000

8. IS 383: 1970

9. ACI 207.SR – 89

10. ASIM C618-12a