Use of Fly Ash in Construction

8/13/2019 Use of Fly Ash in Construction

1/5

Use of fly ash in construction

India produces about 70 million tons of coal ash per year from burning about 200 million tons of coal

per year for electric power generation. Coal-ash management poses a serious environmental

problem for India and requires a mission-mode approach. Considerable research and development

work have been undertaken across the country towards confidence building and developing suitable

technologies fordisposal and utilization of fly ashin construction industries. At present about 10%

ash is utilized in ash dyke construction and land filling and only about 3% of ash is utilized in other

construction industries. This is very much in contrast with 80% or more fly ash used in developed

countries for the manufacture of bricks, cellular concrete blocks, road construction, land fill

application, ceramics, agriculture, insulating bricks, recovery of metals and cenospheres and dam

constructions. Currently, about one acre per MW of land is needed for ash disposal.

Several pilot projects were undertaken in recent years to demonstrate the bulk utilization of fly ash

specifically for Indian conditions. Also, it has been successfully demonstrated that fly ash can be

utilized in major construction projects such as dams, ash dyke, landfills, roads and pavements, soil

stabilization and for other purposes such as brick manufacture, cement industry, tiles, and paint

industry. Realizing the large scale generation of flyash and its very low utilization, the Government of

India set up theFlyash Mission under the Department of Science & Technology at New Delhi for

coordinating all such efforts. A law has also been enacted in 1999 projecting 100 per cent utilization

of flyash within a stipulated period and making it mandatory to use flyash for the purpose of road

construction, bricks etc. within a radius of 50 km from coal based thermal power plants. In spite of

an all-out effort, the flyash utilization in the country is still very low. There are several factorsresponsible for this namely, lack of awareness and confidence, higher production cost, non

availability of dry ash, and most important of all, easy availability of land with top soil at cheap rates.

Here Im going to discuss about the Methodologies for low cost housing by highlighting the different

prefabrication components and techniques, and the economical advantages achieved by adoption

Physical Properties

Fly ash particles are typically spherical ranging in diameter from 1 to 150 microns. Fly ash consists of the large part of solid or hollow spherical particles of siliceous and

aluminous gas with small proportions of thin walled, multifaceted polyhedrousiron content

and are irregularly shaped, relatively porous carbon or carbon coated particles.

The fineness of fly ash in many a case is to the same extent as that of Portland cement.Thecolor varies from light to dark grey depending upon its carbon contents

Chemical Properties

Indian fly ashes, contents of SiO2, Al2O3 are relatively higher than Fe2O3,SO3. Thecrystalline phases were identified as mullite, magnetite, hematite and quartz.

The chemical composition of fly ash and its particle size differ widely for different powerplants. This is due to different types of coal used, their various treatment and different types
http://www.iitk.ac.in/infocell/Archive/dirjuly2/techno_flyash.htmlhttp://www.iitk.ac.in/infocell/Archive/dirjuly2/techno_flyash.htmlhttp://www.iitk.ac.in/infocell/Archive/dirjuly2/techno_flyash.htmlhttp://www.tifac.org.in/do/fly/fly.htmhttp://www.tifac.org.in/do/fly/fly.htmhttp://www.iitk.ac.in/infocell/Archive/dirjuly2/techno_flyash.html


2/5


3/5

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 considerablyreduced)

Saving in consumption of mortar and Higher Fire RatingFAL-G (fly ash-lime-gypsum)

Fal-G bricks and blocks are manufactured without using thermal energy, in contrast to thesintering involved in the production of clay bricks.

Fal-G bricks are made of a mixture of fly ash-limegypsum or fly ash-cement-gypsum.In either combination, Fal-G is a hydraulic cement, which means it sets and hardens in the presence

of moisture, on the lines of ordinary portland cement,gaining strength progressively over ageing

FlexCrete

FlexCrete block is suitable for load bearing and non-load bearing walls in all types ofcommercial, industrial and residential applications

In contrast with other forms of aerated concrete, because of the unique physical propertiesof fly ash, FlexCrete is cured at low temperatures and ambient pressure, thus eliminating the

use of energy intensive autoclaves

FlexCrete fiber-reinforced aerated concrete is a product of FlexCrete Building Systems, LC. Building with FlexCrete provides many advantages over other traditional concrete

construction alternatives. All FlexCrete materials are formulated using high volumes of flyash,

. FlexCrete is typically provided in rectangular blocks or as Thin Cladding Boards (TCBs). . Flexural strengths can be enhanced with the addition of polypropylene fibers, making

FlexCrete an excellent choice of building materials for areas that are prone to earthquakes

and hurricanes or other extreme winds.

Durability. Because FlexCrete contains no organic material, it is not susceptible to pestsUses of Fly Ash Concrete in Pre-cast


4/5

Fly ash may be used to advantage in both architectural

and structural Pre-cast concrete.

Fly Ash is ideal in applications where the concrete will

be exposed to sulphates. Concrete which will be buried in sulphate soils or be in contact with

sulphate bearing liquids are ideal applications for Pre-cast Fly Ash concrete.

Power utility products, such as street light bases, utility vaults, barriers, etc. are also ideal Pre-cast

applications as they are typically inventoried products. Fly Ash in machine extruded concrete

products, such as hollow core, is advantageous because it improves the lubricity of the concrete,

allowing for easier extrusion.

Benefits of Fly Ash in Pre-cast Concrete

When used in correct proportions and under the right technical conditions, the use of Fly Ash offers

significant benefits:

Sulphate resistance without the use of Type 50, (sulphate resistant cement)

Improved resistance to chloride ion penetration

Reduced instances and severity of AAR

Reduced thermal cracking

Improved long term abrasion resistance

Improved resistance to aggressive chemicals

Improved form surface finishes

Ease of concrete placement

Reduced concrete water bleed

Technical Considerations

Fly Ash reduces the heat of hydration as concrete sets, resulting in delayed set times, low early

strengths and prolonged form cycle times. Accelerating the curing cycle offsets the prolonged

form cycle times when Fly Ash is used in a concrete mix. Accelerated curing is achieved through

one, or a combination of the following:

Heating

Lower water cement ratios

Increased cement content

Cost and Environmental Factors

Concrete utilizing Fly Ash produces a superior final product. Life cycle costs are lower, the concrete

lasts longer, has greater strength and may have an initial lower cost than concrete using only

Portland Cement. As Fly Ash use in concrete increases, it leads to greater environmental

sustainability through both the avoidance of landfill and the reduction of natural resource

consumption, saving precious resources for future use. Incorporating Fly Ash in a concrete mix

design also enables cement and concrete producers to reduce GHG emissions.

The methodology for low cost housing has to be of intermediate type less sophisticatedinvolving less capital investment. The Govt. of India has to popularize these components and

the implement them at least for low cost Govt. houses. People should be more aware about

these products and save the environment by using the thermal waste in a better manner.

Use the Thermal Waste in proper way and gets the Economical Construction


5/5

Use of Fly Ash in Construction

Documents

Transcript of Use of Fly Ash in Construction