Blending fly ash in cement is the most environmentally sustainable and financially attractive method of its utilisation.
Fly Ash is a fine powder, which is the by-product of burning coal in thermal power plants. Its Composition:- 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.
Fly ash or flue ash, also known as pulverised fuel ash in the United Kingdom, is a coal combustion product that is composed of the particulates (fine particles of burned fuel) that are driven out of coal-fired boilers together with the flue gases. Ash that falls to the bottom of the boiler is called bottom ash.
In the past, fly ash was generally released into the atmosphere, but air pollution control standards now require that it be captured prior to release by fitting pollution control equipment. In the United States, fly ash is generally stored at coal power plants or placed in landfills.
About 43% is recycled, often used as a pozzolan to produce hydraulic cement or hydraulic plaster and a replacement or partial replacement for Portland cement in concrete production. Pozzolans ensure the setting of concrete and plaster and provide concrete with more protection from wet conditions and chemical attack.
At present, 63% of the fly ash is being utilised in India but the target is for 100% utilization of the fly ash.
Fly Ash Utilisation Policy in India
The Ministry of Environment, Forest and Climate Change (MoEF&CC) had issued the first Fly Ash notification on September 14, 1999. It was subsequently amended in 2003, 2009 and 2016 in order to enhance fly ash utilisation in the various infrastructure development projects.
- Maharashtra has become the first state to adopt Fly Ash Utilization Policy, paving way for prosperity by generating “wealth from waste”, and environment protection.
- The policy will create new employment opportunities in the power plant areas and also make available raw material for construction at low cost to help ‘Housing for All’ projects.
- The policy seeks 100% use of fly ash generated from thermal power plants and biogas plants for construction activities.
- The policy extends use of fly ash to 300 kms radius of power plant from earlier 100 kms radius of power plant.
- It will help in environment protection and save soil excavation.
The utilisation of fly ash has increased from 66.6 million ton (MT) in 2008-09 to 132 MT in 2017-18, marking an improvement of 50 percent in a decade. On the other hand, the percentage of fly ash utilisation has increased from 57.11 percent in 2008-09 to 67 percent in 2017-18.
Fly Ash Utilization – Merits
- Prevent Contamination of Water Resources– by preventing contamination of surface water through erosion, runoff, air-borne particles landing on the water surface; of ground water moving into surface waters, flooding drainage, or discharge from a coal ash pond.
- Prevents Soil Erosion– Helps restrict usage of topsoil for manufacturing of bricks.
- Used in variety of construction works– Fly ash is a proven resource material for many applications of construction industries and currently is being utilized in manufacturing of portland cement, bricks/blocks/tiles manufacturing, road embankment construction and low-lying area development, etc. Flyash bricks have been found to show better strength.
- Used in Agriculture– as an agent for acidic soils, as soil conditioner – improving upon some important physicochemical properties of the soil such as hydraulic conductivity, bulk density, porosity, water holding capacity, etc.
- Using fly ash in concrete is environmentally beneficial because it reduces the Portland cement (a major contributor of CO2) required in concrete.
Government Initiatives for Optimum Utilization of Fly Ash:
- GST rates on fly ash and its products have been reduced to 5%.
- ASH TRACK Mobile App has been launched by the Ministry of Power for better management of fly ash produced by thermal power plants.
- Ash-park, for promoting fly ash-based product manufacturing units, has been developed and awareness programme for utilisation of fly ash and its products have been conducted.
- “ASHTRACK” is a mobile-based application and a web portal for monitoring of fly ash generation and utilization data of Thermal Power Plants.
- It provides an interface between fly ash producers (Thermal Power Plants) and potential ash users such as – road contractors, cement plants etc.
Fly Ash Utilization – DeMerits
- Slower Strength Gain – Concrete changes from a liquid to a solid a few hours after pouring, but the curing process may take much longer. It continues to gain strength for weeks after its initial setting period. This can cause problems when slow strength gain means delays in construction.
- Longer Setting Times – Fly ash admixtures can lengthen the time it takes for concrete to set. Sometimes this is desirable, particularly in hot weather which speeds up concrete set times, but at other times it is an inconvenience and can cause delays in construction. Other admixtures may be necessary to adjust the set time of the concrete, depending on the percent fly ash in the mixture and the outside temperature.
- Air Content Control – Concrete is susceptible to damage from freeze/thaw cycles if it does not contain air. Fly ash reduces the amount of air entrainment, and concrete mixtures high in fly ash often require more air-entraining admixture.
- Seasonal Limitations – The winter season is problematic for concrete pouring, and mixtures high in fly ash are even more susceptible to low temperatures.
- Color Variability – The structural effects of fly ash may be more critical, but cosmetic concerns also affect its use in concrete. It is more difficult to control the color of concrete containing fly ash than mixtures with Portland cement only.