Fly Ash - An Innovative Building Material

FLY ASH: A RESOURCE MATERIAL FOR INNOVATIVE BUILDING MATERIAL


- INDIAN PERSPECTIVE

C. N. Jha* & J. K. Prasad**

1.0 INTRODUCTION

India’s present housing shortage is estimated to be as high as 31.1 million units as per 2001 Census and out of this shortage 24 million units are in rural area and 7.1 million unit in urban areas. The Govt. of India has targeted the year 2010 for providing Housing for All. In 1998, Government of India announced a National Housing and Habitat Policy which aims at providing “Housing for All” and facilitating the construction of 20 lakh additional housing units (13 lakh in Rural Areas and 7 lakh in Urban Areas) annually, with emphasis on extending benefits to the poor and the deprived. Apart from the above housing needs, nearly 1% of the housing stock in the country is destroyed every year due to natural hazards.

Such large scale housing construction activities require huge amount of money running into thousands of crores of rupees. Out of the total cost of house construction, building materials contribute to about 70 percent cost in developing countries like India. Therefore, the need of the hour is replacement of costly and scarce conventional building materials by innovative, cost effective and environment friendly alternate building materials. The new material should be environment friendly and preferably utilize industrial/agro wastes because as a result of rapid industrialization, the generation of wastes has increased several fold during the last few years, which needs to be utilized/disposed safely on priority. Large number of innovative alternate building materials and low cost construction techniques developed through intensive research efforts during last three to four decades satisfies functional as well as specification requirements of conventional materials/techniques and provide an avenue for bringing down the construction

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cost. Fly Ash, a industrial by-product from Thermal Power Plants (TPPs), with current annual generation of approximately 108 million tonnes and its proven suitability for variety of applications as admixture in cement/concrete/mortar, lime pozzolana mixture (bricks/blocks) etc. is such an ideal material which attracts the attention of everybody. Cement and Concrete Industry accounts for 50% Fly Ash utilization, the total utilization of which at present stands at 30MT (28%). The other areas of application are Low lying area fill(17%), Roads & Embankments(15%), Dyke Raising(4%), Brick manufacturing(2%) etc. The life cycle cost of Fly Ash based building materials/constructions is much lower taking into account the environmental benefits and durability aspects.

2.0 FLY ASH CHARACTERISTICS AND UTILISATION POTENTIAL Ash is a residue resulting from combustion of pulverised coal or lignite in Thermal Power Plants. About 80% of total ash is in finely divided form which is carried away with flue gases and is collected by Electrostatic precipitator or other suitable technology. This Ash is called (dry) Fly Ash or chimney Ash or Hopper Ash. The balance 20% of the Ash gets collected at the bottom of the boiler and is referred as Bottom Ash. When Fly Ash and Bottom Ash is carried to storage pond in the form of water slurry and deposited, it is termed as Pond Ash. Fly Ash consists of inorganic materials mainly silica and alumina with some amount of organic material in the form of unburnt carbon. Its fineness is comparable to cement, however, some particles have size less than 1 micron in equivalent diameter. It possess pozzolanic characteristics. However, all kind of Ashes are sometimes referred as Fly Ash by common people. The different kind of Ashes are suitable for different applications as given below:

Fly Ash - For use as pozzolana and admixture in cement, mortar, concrete (/Cellular light weight concrete) Fly Ash - Lime pozzolana Mixture Applications (Bricks, Blocks etc.) (The quality parameters are not as stringent as in above application)

Bottom Ash / Pond Ash - Sintered Applications, Geotechnical Applications, Structural Fills, Clay- Fly Ash bricks (burnt type),Agricultural Applications, etc.



2.1 Fly Ash as Pozzolana

Pozzolans are defined as silicious and aluminous materials which in themselves possess little or no cementitious value but, will in finally divided form and in the presence of moisture chemically react with calcium hydrauxide at ordinary temperature to form compounds possessing cementitious properties.

The properties of pozzolananic materials which are to be used for the manufacture of pozzolana Cements, Concrete, Lime/Cement based bricks/blocks are governed by stipulated standards which differ from country to country. The requirement of Fly Ash for these applications in terms of pozzolanic properties is as follows:

S. No. Component/

Characteristics

Unit British Standard BS:3892

American Standard

ASTM :C618

Indian Standard:

3812 (Part 1) : 2003

Fly Ash^

Indian Standard:

3812 (Par 2): 2003

Fly Ash^SPFA CPFA SPFA CPFA

Chemical Requirements1. SiO2 + Al2O3 + Fe2O3 % - 70 70 50 70 50

2. Sio2 Min % - - 35 25 35 25

3. Reactive SiO2 Min (Optional)

% - - 20 20 - -

4. CaO, Max % - - - - - -5. MgO, Max % 4 - 5 5 5 56. Total S as SO3, Max % 2.5 5 3 5 5 5

7. Alkali as Na2O, Max % - 1.5 1.5 1.5 1.5 1.5

8. Total CI, Max % - - 0.05 0.05 0.05 0.059. Loss on Ignition, Max % 7 12 5 5 5 510. Moisture content, Max % 1.5 3 2 - - -

Physical Requirements1. Specific surface

(Blaine), MinM2/kg Variable 325 320# 200

2. Sieve residue on 45 um sieve, Max

% - 32 34 (Optional) 50 (Optional)



3. Control figure (Product of loss and sieve residue on 45 µm sieve), Max

% - 255 - -

4. Lime reactivity** (Average compressive strength), Min

N/mm2 - - 4.5 -

5. Compressive strength at 28 days, Min

N/mm2 - - Not less than 80% of the strength of

corresponding plain cement mortar cubes

-

6. Drying shrinkage, Max % - - - -7. Soundness

(Autoclave), Max% - - 0.8 0.8

^Part I : For use as pozzolana in cement, cement mortar and concrete

^Part II : For use as admixture in cement, cement mortar and concrete

SPFA : Silicious Pulverised Fuel Ash

CPFA : Calcareous Pulverised Fuel Ash

#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 and physical requirements.

** The method of test covers the procedure for determining the reactivity of the pozzolanic material with hydrated lime, as represented by compressive strength of standard mortar test cubes prepared and tested under specific conditions as per IS 1727:1967.

2.2 Fly Ash collection and storage in the Thermal Power Plant

The fly ash is collected in most of the old power plants in India through wet system, since it is cheaper than any other mode of transport. In the wet system, fly ash is mixed with water and sluiced to the settling ponds or dumping areas near the plant. However, due to limited disposal area many of the TPPs are in the process of converting to dry collection system (through ESP’s) particularly the NTPC Power Plants.

ESP’s are most popular equipment and widely used for emission control today which enables the



collection of dry fly ash. In the dry collection system, after arresting the fly ash in the ESP, it is taken to the silos for storage by pressurized or vacuum pneumatic system. When required, this can be obtained in a container for further transportation directly from the silos or conveyed further to the delivery point by pneumatic pressurized system. All new plants commissioned recently/being commissioned have provision for dry fly ash collection system.

Fly ash collected through dry collection system is preferred for pozzolanic applications (i.e. in Building Industry).

2.3 Need for “Processing of as received Fly Ash

The chemical composition and physical characteristics of a fly ash from a coal fired furnace are controlled by the type pf coal and processing conditions of the furnace. These vary not only from one plant to another but also within the same plant. Large variation in the chemical composition of fly ashes is, therefore, natural. Fortunately, however, the pozzolanic properties of a fly ash are not governed so much by the chemistry but by the mineralogy and the particle size of the fly ash. It may be noted that modern coal fired thermal power plant generally produce good quality fly ash that is characterized by low carbon and high glass content with 75% or more particles finer than 45 microns. For coarse fly ashes or those with high carbon content, a number of beneficiation technologies are available to improve their suitability for use by the cement and concrete industries.

Another road block to the increased use of fly ash as a component of cement and concrete is the uniformity of ash from a single source of supply. With industrial by-products, the variability in physical and chemical characteristics are unavoidable. However, this need not be an un-surmoutable task to make the product suitable for its desired use. As for years, the cement and concrete plants have practiced the art of blending inhomogeneous batches of material to obtain end-products of acceptable and uniform quality.

As can be seen from the above there is a need to provide the fly ahs in graded form so that the needs of the individual industries can be catered to. The fly ash is available from different fields of ESP (also varies from plant to plant) from 1000 blaines to 6000 blaines. It will not be economical to collect the ash from different fields and moreover is required to classify the fly ash after dry collection in the plant and also to grind the surplus amount of coarse ash.



Hence, to increase the market of the fly ash it is required to grade and grind the fly ash to meet the requirement of wide spectrum of market.

3.0 FLY ASH BASED INNOVATIVE & COMMONLY PRODUCED BUILDING PRODUCTS IN INDIA

Some of the innovative and commonly manufactured environmental friendly building materials utilizing Fly Ash are covered below;

3.1 Cellular Light Weight Concrete (CLC) Blocks

Cellular Light Weight Concrete (CLC) blocks are substitute to bricks and conventional concrete blocks in building with density varying from 800 kg/m3 to 1800 kg/m3. The normal constituents of this Foaming Agent based technology from Germany are cement, Fly Ash (to the extent 1/4th to 1/3rd of total materials constituent), sand, water and foam (generated from biodegradable foaming agent). Using CLC walling & roofing panels can also be produced. Foaming agent and the Foam generator, if used for production of CLC with over 25% fly ash content invites concession on import duty by Govt. of India.

Advantages of Cellular Light Weight Concrete;

● Better strength to weight ratio

● Reduction of dead load resulting in saving of steel & cement and reduction in foundation size

● Better Acoustics and thermal insulation (Air conditioning requirement is considerably reduced)

● Saving in consumption of mortar and Higher Fire Rating

3.2 Development of Fly Ash Based Polymer Composites as Wood Substitute



Fly ash based composites have been developed using fly ash as filler and jute cloth as reinforcement. After treatment, the jute cloth is passed into the matrix for lamination. The laminates are cured at specific temperature and pressure. Number of laminates are used for required thickness. The technology on fly ash Polymer Composite using Jute cloth as reinforcement for wood substitute material can be applied in many applications like door shutters, partition panels, flooring tiles, wall paneling, ceiling, etc.

With regard to wood substitute products, it may be noted that the developed components / materials are stronger, more durable, resistant to corrosion and above all cost effective as compared to the conventional material i.e. wood.

This technology has been developed by Regional Research Laboratory, Bhopal in collaboration with Building Materials & Technology Promotion Council (BMTPC) and TIFAC. One commercial plant has also been set up based on this technology near Chennai.

3.3 Portland Pozzolana Cement (Fly Ash based)

Upto 35% of suitable fly ash can directly be substituted for cement as blending material. Addition of fly ash significantly improves the quality & durability characteristics of resulting concrete. In India, present cement production per annum is comparable to the production of Fly Ash. Hence even without enhancing the production capacity of cement; availability of the cement (fly ash based PPC) can be significantly increased.

3.4 Ready mixed Fly Ash concrete

Though Ready Mix concrete is quite popular in developed countries but in India it consumes less than 5 percent of total cement consumption. Only recently its application has started growing at a fast rate. On an average 20% Fly ash (of cementitious material) in the country is being used which can easily go very high. In ready mix concrete various ingredients and quality parameters are strictly maintained/controlled which is not possible in the concrete produced at site and hence it can accommodate still higher quantity of fly ash.

3.5 Fly Ash- Sand-Lime-Gypsum (/Cement) Bricks /Blocks



Fly Ash can be used in the range of 40-70%. The other ingredients are lime, gypsum (/cement), sand, stone dust/chips etc. Minimum compressive strength (28 days) of 70 kg/cm2 can easily be achieved and this can go upto 250 Kg/cm2 (in autoclaved type).

Advantage of these bricks over burnt clay bricks:

● Lower requirement of mortar in construction

● Plastering over brick can be avoided

● Controlled dimensions, edges, smooth and fine finish & can be in different colours using pigments

● Cost effective, energy-efficient & environment friendly (as avoids the use of fertile clay)

3.6 Clay-Fly Ash Bricks

Fly Ash content can be 20 to 60% depending on the quality of clay. Process of manufacturing is same as for the burnt clay bricks.

Advantages:

● Fuel requirement is considerably reduced as fly ash contains some percentage of unburnt carbon

● Better thermal insulation

● Cost effective and environment friendly

4.0 DURABILITY OF FLY ASH BASED PRODUCTS 4.1 Blended Cement (Fly Ash based)/Concrete using Fly AshUse of blended cement has now become quite popular world over from durability and environmental benefits point of view. For example, blended cement constitutes 91% of the total



cement production in Italy. In India also 45% of total cement manufactured is fly ash based blended cement. Now the advantages achieved with the use of blended cement in concrete quite well documented;

● Reduced heat of hydration

● Improved workability & Ease of pumping

● Superior microstructure leading to lower permeability

● Higher long term strength

● Better performance in aggressive environment (Sulphates, Chlorides etc.)

● Reduced risk of alkali silica reaction

● Higher Electrical Resistively leading to lesser chances of reinforcement corrosion

4.2 Fly ash bricks viz-a-viz clay bricks A lot of studies have been conducted on durability aspects of Fly Ash bricks in many CSIR Labs, IITs, etc. Recently a study was sponsored by Fly Ash Mission, TIFAC and implemented by four CSIR Labs namely: CBRI - Roorkee, RRL-Bhopal, ERADA-Vadodara and CFRI-Dhanbad to assess the durability of Fly Ash brick viz-a-viz clay brick. In this study all kind of aggressive environment as acidic, saline etc. were quantified (in terms of its concentration and exposure duration) to conduct accelerated tests on Fly Ash bricks and clay bricks both. The study has been completed and it has concluded that Fly Ash bricks are as durable as clay bricks and in fact in certain aggressive environments perform better than clay bricks. 5.0 ENERGY SAVINGS AND ENVIRONMENTAL BENEFITS Most of the developing countries face energy scarcity and huge housing and other infrastructure shortage. Ideally in these countries materials for habitat and other construction activities should be energy efficient (having low energy demand). The following table shows some examples of energy savings achieved through the use of Fly Ash in the manufacture of conventional building materials. It should be noted that use of Fly Ash also improves the properties of building material,



as mentioned above:

Energy Savings in the Manufacture of Building Materials through Use of Fly AshBuilding Material Composition Material Compared Energy savings (%)

Portland pozzolana cement 75% Ordinary Portland cement

25% Fly Ash

100% Ordinary Portland Cement

20

Lime-pozzolana mixture 25% Acetylene gas lime

75% Fly Ash

25% Lime

75% Calcined brick

75

Calcium silicate brick 90% Fly Ash tailings

10% lime

(waste source)

Burnt Clay brick 40

Burnt brick 75% Clay

25% Fly Ash

Burnt Clay brick 15

Source: Building Materials in India: 50 Years – A Commemorative Volume, Building Materials & Technology Promotion Council, New Delhi, India, 1998

Studies show that one tonne of Portland cement production discharges 0.87 tonne of CO2 into the atmosphere. One Japanese study indicates that every year barren land area approximately 1.5 times of Indian territory need to be afforested to compensate for the total global accumulation of carbon dioxide discharged into the atmosphere because of total global cement production. Utilisation of fly ash in cement/concrete minimises the Co2 emission problem to the extent of its proportion in cement. Use of Fly Ash – Sand-lime-gypsum bricks also brings similar environmental benefits if used in place of burnt clay bricks.

6.0 SOME OF THE INITIATIVES TAKEN BY VARIOUS GOVT. DEPARTMENTS IN INDIA

6.1 Initiatives by Ministry of Environment and Forest, Govt. of India

(This Ministry is primarily responsible for preserving environment and forest in the country)

MOEF recently issued notifications containing directive for greater Fly Ash utilization, some of which are as follows;



i. Within a radius of 100 kms from coal or lignite based thermal power plants, manufacturers of bricks/blocks/tiles would use at least 25% of ash in their product.

ii. Every construction agency engaged in the construction of buildings within a radius of 50 to 100 kms of TPP have to use 100% fly ash based bricks/blocks in their construction project by the end of August 2007. Within 50 kms of radius of TPP the deadline for use of 100% fly ash based bricks/blocks is end of August 2005. It is pertinent to mention here that any brick/block containing more than 25% fly ash is designated as fly ash brick/block.

6.2 Status of Standardisation in the country

Several initiatives taken by country’s standardization body (BIS) regarding higher utilization of fly ash are as follows:

i. Updation of Indian Standard on “Portland Pozzolana Cement – Specification Part 1 Fly Ash based”( IS 1489 (Part 1): 1991)

In the amended form, the Fly Ash constituent to be used shall not be less than 15% (from earlier 10%) and not more than 35% (from earlier 25%) by mass of Portland Pozzolana Cement.

ii. Revision of basic Indian Standard Design Code for Plain and Reinforced Concrete (IS 456:2000)

This revised Code lays emphasis on the use of PPC/Fly Ash in concrete in aggressive environmental conditions.

iii. Revision of Indian Standard on “Specification for Fly Ash for use as Pozzolana and Admixture” (IS 3812-1981)

Updation of standard has been done keeping in view the change in technologies leading to generation of better quality of Fly Ashes and wider applications of Fly Ashes. In the revised standard, the concept of improvement of Fly Ash properties through beneficiation/segregation/processing has also been introduced.



6.3 Circular by Country’s Premier Govt. Construction Agency (CPWD)

CPWD has taken a decision for use of fly ash as part replacement of cement where concrete is obtained from RMC manufacturers for large projects in concrete grade M30 and above:

7.0 ROLE OF BMTPC IN PROMOTING FLY ASH BASED BUILDING MATERIALS In order to bridge the gap between research and development and large scale application of new building material technologies, the erstwhile Ministry of Urban Development, Government of India, had established the Building Materials & Technology Promotion Council in July 1990. The Council strives to undertake identification of potential technologies with emphasis on utilisation of agricultural and industrial wastes. For promoting fly ash based products, BMTPC has taken several initiatives some of which are as follows:

7.1 Machines developed by BMTPC

BMTPC has developed more than 30 machines for cost-effective building products through its associated agencies. This has been done to popularize the cost-effective building materials at grass root level. Some of these can be used for manufacturing fly ash based products.

• Alternate station hydraulic brick making machine:

This machine has capacity of 10,000 bricks per day and can produce Fly Ash – sand lime (/cement) bricks and clay/clay Fly Ash bricks.

• Bi-Directional Vibro Presses of different capacities (AS 1824, AS 1818, AS B 189, etc.)

The same vibro press can be used for manufacturing fly ash based solid blocks, hollow blocks and pavers by just changing the moulds. These presses are available for different capacities.

• Pan Mixer

As normal concrete mixer is not suitable for mixing raw materials used for fly ash based products,



Pan Mixer has been developed which ensures kneading action also.

7.2 Role of Advisory Body to Govt. of India and in conducting training and Entrepreneurship Development Programme

BMTPC is represented in various Govt. Committees responsible for issuing notification related to utilization of industrial and agricultural wastes. It is also represented in various standardisation committees. Regular training and entrepreneurship development programmes are conducted to popularize the waste based and cost-effective building materials and technologies at grass root level from time to time.

7.3 Initiatives taken in the direction of creating Fly Ash Grading facility at Thermal Power Plant

As circular by CPWD, IS 456:2000 etc. specifies certain grade of fly ash (conforming to IS 3812) for cement/concrete applications which is not easily available at Thermal Power Plants. Even products like fly ash based bricks, blocks, tiles, pavers, etc. require fly ash of graded quality. Therefore, it was felt necessary to create some fly ash processing facility at TPP so that graded fly ash can be made available to end user. In this regard, letters have been issued to many Thermal Power Stations detailed presentation has been made to Central Electricity Authority and discussions are in progress with some of the TPPs.

7.4 Publications by BMTPC particularly the “Standard and Specification of certain Cost-effective, and Environment-friendly Building materials / Techniques

BMTPC has published over 30 publications covering a wide spectrum of housing sector. Despite a number of innovative cost-effective building materials, components and construction techniques developed through extensive research, the housing and building agencies have not adopted them in their construction practices because of number of reasons. Lack of standardization and non-listing of the above techniques in Indian Standard Codes is quoted as one of the foremost reasons by construction agencies for non-adoption of these techniques in their practices. Realising this Building Materials and Technology Promotion Council (BMTPC) has published “Standards & Specifications for Cost effective Building Materials and Techniques” which outlines detailed specifications for the cost effective building materials, components and construction



techniques including Fly Ash based. The detailed specifications have been so formatted that these can be readily inducted in the schedules and specifications by public and private construction agencies.

7.5 Performance Appraisal Certification Scheme (PACS)

Under a notification issued by Ministry of Urban Development & Poverty Alleviation, Govt. of India, BMTPC has also been entrusted with the responsibility of running an innovative scheme called ‘Performance Appraisal Certification Scheme (PACS)’. Under this scheme any new product, system or technique related to housing/building not covered so far by Bureau of Indian Standards in the form of any IS Code may be certified after detailed evaluation. Such certification will develop confidence among the users of the new product/system/technique and provide marketing tool to the manufacturers. The evaluation parameters and their results may later form the basis for the formulation of new IS Code on the specific product/system/technique.

REFERENCES

● Census of India 2001.

● MOEF Notification dated September 14, 1999 regarding Utilisation of Fly Ash and Amendments to this dated August 27, 2003.

● “Building Materials in India: 50 Years” A commemorative volume published by BMTPC.

● Circular by CPWD No. CDO/SE (RR)/Fly Ash (Main)/387 dated May 13, 2004.

● Proceedings of the International Symposium on “Concrete Technology for Sustainable Development in the Twenty First Century” edited by P. Kumar Mehta, Hyderabad, India, February, 1999.

● Singh G. B. “Cellular Light Weight Concrete”, The Construction Journal of India, September-October 1998, Vol. 1 issue 4.

● Saxena Mohini and Prabhakar J. “Emerging Technologies for Third Millennium on Wood



Substitute and Paint from coal ash” 2nd International conference on “Fly Ash Disposal & Utilization”, New Delhi, India, February 2000.

* Development Officer (BM & PE), Building Materials and Technology Promotion Council (BMTPC), Ministry of Urban Employment & Poverty Alleviation, Govt. of India** Chief (BM), Building Materials and Technology Promotion Council (BMTPC), Ministry of Urban Employment & Poverty Alleviation, Govt. of India

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Fly Ash - An Innovative Building Material

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