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fly ash

What is Fly Ash?

Two people died as a result of a breach in the fly ash dyke of  Sasan Ultra Mega Power Project in Singrauli, Madhya Pradesh on April 10, 2020.The toxic slurry spread to an area of six kilometres and also destroyed agricultural fields.

Fly ash is a fine powder that is a byproduct of burning pulverized coal in electric generation power plants.Fly ash is a byproduct of power generation with coal. Sustainable ash utilisation is one of the key concerns

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.Fly ash includes substantial amounts of oxides of silica, aluminum and calcium. Element like Arsenic, Boron, Chromium, lead etc. are also found in trace concentrations.

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.

The fly ash is utilised mostly in the cement and building industries including road construction, concrete and bricks manufacturing and filling of low-lying areas. Together, these activities account for around 60 per cent of the  ash utilisation.

  • For  Soil Stabilistion-

Soil stabilization is the alteration of soil properties to improve the engineering performance of soils.

Modification of soil properties is the temporary enhancement of sub-grade stability to speedup construction.

Stabilization can increase the shear strength of a soil and/or control the shrink-swell properties of a soil, thus improving the load-bearing capacity of a sub-grade to support pavements and foundations.

Stabilization can be used to treat a wide range of sub- grade materials from expansive clays to granular material

However, all these activities have come to a halt due to the ongoing lockdown, leading to accumulation of  ash, according to experts.

  •  In Agriculture

1.Improve permeability status of soil.

2.Improve fertility status of soil/agriculture yield.

3.Improve soil textural properties and soil aeration.

4.Reduces soil bulk density and crust and compact formation.

5.Improves water-holding capacity/porosity.

6.Provides several micronutrients such as Mo, B, Fe, Zn, Cu. Etc.

7.Alternative for gypsum for reclamation of sodic soils and lime for reclamation of acidic soils.

8.Improves soil microbial activities in combination with other organic amendments

In Mining:

Cave backfill grouting implies grouting of the caving rock mass prior to it being compacted. The filling materials strengthen the caving rock and support the overlying strata to achieve the purpose of slowing down the surface subsidence. The broken roof will fail and collapse during mining operations performed without appropriate supporting measures being taken. It is difficult to perform continuous backfill mining on the working face of such roofs using the existing mining technology. In order to solve the above problems, fly ash and mine water are considered as filling materials, and flow characteristics of fly-ash slurry are investigated through laboratory experiments and theoretical analyses.

  • In Waste Treatment:

In view of its alkalinity and water absorption capacity, may be used in combination with other alkaline materials to transform sewage sludge into organic fertilizer or biofuel

  •  In Portland Cement:

Fly ash, being primarily pozzolanic, can actually replace a percentage of the Portland cement, to produce an even stronger, more durable and more environment friendly concrete.

The initial compressive strength is low but as days pass, fly ash concrete gains more strength and eventually has a lot more strength as compared to normal Portland cement.

Significantly reduces the release of CO2 into the atmosphere.

Can be used for construction of structures on/under water.

  • Raw Materials for Ash based bricks

Fly Ash, Sand and Cement (Ordinary Portland Cement). Or

Fly Ash, Sand, Lime and Gypsum.

Consumption of Fly Ash to produce a single fly ash based brick is 1.250gm

  • Ash Dyke Raising

In a coal based Thermal Power Station, the Ash disposal pond or lagoon should not be a source of pollution on the land and water. This can be ensured by providing liner in the base area that prevent the seepage of the dykes where the ash water comes in contact. … Ash pond Lining is a basic necessity

Ash pond was constructed by raising the dykeover the previously deposited ash. The upper pond was constructed by using bottom ashexcavated from ash complex. Geogrid is provided to add stability for the new embankments. Toe drain system is installed.

What went Wrong?

The cement factories are now in lockout due to pandemics since March 25. This means power plants are required to pump more ash into ash ponds,

This sudden accumulation of load and water creates a burden on the ponds. Ash ponds are designed to withstand stress owing to ash retention, they are not designed to withhold hydraulic stress due to excess water in the slurry

Under normal circumstances, TPSs dispose of the fly ash on a daily basis, according to the official.

Power stations would need to build methods for safely handling and storage of this waste with less water use, and periodically removing water from the ponds, he further added.

To add to the problem is the fact that ash dispersion is the maximum in summer months, before going down during the monsoon.

Important Topics Prelims 2020

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