Use of fly ash cuts down the use of cement proportionately and reduces emission of carbon dioxide in the production of cement,writes G.V. Prasada Sarma

Use of flyash in structures including hydroelectric and water projects has increased over a period of time but still a lot of fly ash remains to be utilised or effectively disposed.

Use of flyash cuts down the use of cement proportionately and reduces emission of carbon dioxide in the production of cement. On the other hand, fly ash is produced in abundance by thermal power plants burning coal.

Use of concrete aggregate in hydroelectric projects in the Himalayan region has led to alkaline aggregate reaction. The reaction manifests itself in cracks in cement concrete structures, according to Murari Ratnam, Director of Central Soil and Materials Research Station under the Ministry of Water Resources of the Union Government. It was evident in Rihand dam in Uttar Pradesh and Hirakud in Odisha. Cement concrete aggregate has minerals like sodium and potassium causing the reaction while flyash almost all protects construction in the Himalayan region against such reactions.

Gazette notification

To increase use of fly ash, the Ministry of Environment and Forests has made a gazette notification that fly ash be used in infrastructure projects within 100 km. radius of thermal power plants. The biggest use of the material is in making fly ash bricks. It saves quality clay, again an environmental-friendly move, increases quality of buildings and reduces cost of construction. Flyash can also be used to replace up to 35 per cent of Portland cement in concrete, contributing considerably to conservation of environment, agriculture-related studies, structural fills and backfilling. Part of the ash can also be used for ash dyke construction in power plants, he says. The use of fly ash and cutting down on cement will also result in accrual of carbon credits.

It still leaves a massive problem of fly ash disposal behind which requires lot of space. Quoting statistics of the Department of Science and Technology, Mr. Ratnam told The Hindu recently that the utilisation of fly ash was a mere 20 per cent in 1994. Now it has increased to more than 50 per cent. India produces 200 million tonnes of fly ash.

He points out that though the utilisation has gone up considerably, owing to increase in thermal and super thermal plants the country is producing more and more fly ash and is left with massive quantities that can not be used.

“Thermal plants are running out of space as they are storing ash in the open. Since Indian coal is low grade with high ash content the more coal is burnt the more ash is produced,” says Mr. Ratnam.

One of the options that are talked about is sending the ash back to coal mines from where the coal was dug out. There is lot of space in the coal mines. Care must be taken by providing a layer before dumping so that any scope for pollution of groundwater is ruled out, suggests Mr. Ratnam.

However, he points out that flyash does not pollute water but any possibility must be dealt with.

Thermal plants are running out of space as they are storing ash in the open. Since Indian coal is low grade with high ash content the more coal is burnt the more ash is produced