With reference to 'fly ash' produced by the power plants using coal as fuel, which of the following statements is/are correct? 1. Fly ash can be used in the production of bricks for building construction. 2. Fly ash can be used as a replacement for some of the Portland cement contents of concrete. 3. Fly ash is made up of silicon dioxide and calcium oxide only, and does not contain any toxic elements. Select the correct answer using the code given below Correct Answer 1 and 2 The correct answer is 1 and 2. Fly ash is the finely divided residue that results from the combustion of pulverised coal and is transported from the combustion chamber by exhaust gases. Fly ash is produced by coal-fired electric and steam generating plants. Fly ash is used annually in a variety of engineering applications that includes: portland cement concrete (PCC), soil and road base stabilization, flowable fills, grouts, structural fill and asphalt filler. Portland cement, Embankment, Soil stabilization, Flowable fill, Asphalt concrete, Geopolymers, Roller compacted concrete, Bricks, Metal matrix composites, Waste treatment and stabilization, Catalyst Environmental benefits increasing the life of concrete roads and structures by improving concrete durability, net reduction in energy use and greenhouse gas and other adverse air emissions when fly ash is used to replace or displace manufactured cement, reduction in amount of coal combustion products that must be disposed in landfills, and conservation of other natural resources and materials. Characteristics Size and Shape Fly ash is typically finer than portland cement and lime. Fly ash consists of silt-sized particles which are generally spherical, typically ranging in size between 10 and 100 micron. Chemistry - Fly ash consists primarily of oxides of silicon, aluminum iron and calcium. Magnesium, potassium, sodium, titanium, and sulfur are also present to a lesser degree. Color - Fly ash can be tan to dark gray, depending on its chemical and mineral constituents. Tan and light colors are typically associated with high lime content. A brownish color is typically associated with the iron content. A dark gray to black color is typically attributed to an elevated unburned carbon content.