Explore utilisation of fly ash in cement plant: NGT

The National Green Tribunal (NGT) has directed a Faridabad based thermal power plant to explore utilisation of fly ash in cement plants and also directed the Central Pollution Control Board (CPCB) to monitor whether covering of the ash dump meets scientific environmental norms.

• Taking note of a report furnished by the Haryana Pollution Control Board, a Bench headed by NGT chairperson Justice Adarsh Kumar Goel said: “It appears that the exposed surface has been covered and the pond ash is not being allowed to be lifted. 
• The question whether covering of the ash dump meets the scientific environmental norms needs to be cross checked to prevent the potential of any damage by such exercise.”
• “This may be done by the CPCB within two months. The power plant in question may explore utilisation of the fly ash in cement plants, taking precautions and ensuring that no air pollution is caused during transportation and handling. 
• This aspect may also be monitored by the CPCB,” the Bench said.

Recommendation

In its report, the state pollution control board had recommended that installation work of solar power plant “must be expedited to avoid any possibility of air pollution.”

Fly Ash

• Fly ash is a fine powder that is a byproduct of burning pulverized coal in electric generation power plants.
• Fly ash is a pozzolan, a substance containing aluminous and siliceous material that forms cement in the presence of water.
• When mixed with lime and water, fly ash forms a compound similar to Portland cement. 
• This makes fly ash suitable as a prime material in blended cement, mosaic tiles, and hollow blocks, among other building materials. 
• When used in concrete mixes, fly ash improves the strength and segregation of the concrete and makes it easier to pump.

Benefits

Fly ash requires less water than Portland cement and is easier to use in cold weather.

• Produces various set times
• Cold weather resistance
• High strength gains, depending on use
• Can be used as an admixture
• Considered a non-shrink material
• Produces dense concrete with a smooth surface and sharp detail
• Great workability
• Reduces crack problems, permeability, and bleeding
• Reduces heat of hydration
• Allows for a lower water-cement ratio for similar slumps when compared to no-fly-ash mixes
• Reduces CO2 emissions

Disadvantages

Smaller builders and housing contractors may not be familiar with fly ash products, which can have different properties depending on where and how it was obtained.

 Additionally, fly ash applications may face resistance from traditional builders due to its tendency to effloresce along with concerns about freeze/thaw performance. Other concerns about using fly ash in concrete include:

• Slower strength gain
• Seasonal limitation
• Increased need for air-entraining admixtures
• Increase of salt scaling produced by higher proportions of fly ash

Applications for Fly Ash 

• Fly ash can be used as prime material in many cement-based products, such as poured concrete, concrete block, and brick. 
• One of the most common uses of fly ash is in Portland cement concrete pavement or PCC pavement. Road construction projects using PCC can use a great deal of concrete, and substituting fly ash provides significant economic benefits.
• Fly ash has also been used as embankment and mine fill, and it has increasingly gained acceptance by the Federal Highway Administration.
• The rate of substitution—of fly ash for Portland cement—typically specified is 1 to 1 1/2 pounds of fly ash for 1 pound of cement. 
• Accordingly, the amount of fine aggregate in the concrete mix must be reduced to accommodate the additional volume of the fly ash.