A new alternative for energy production has been introduced in recent times to save the environment from greenhouse gases emission. However, despite all the new resources available, the consumption of coal is never reduced. Various Industries like Construction, Oil & Gas, Paints & Coating utilize the residue of coal like fly ash, cenosphere, and hollow microspheres in an appropriate manner. In one of the recent market surveys conducted by a leading company, it is revealed that the annual production of fly ash is around 500 million tonnes.
When a lump of coal goes through the combustion process at a certain temperature around 0.2 to 2 wt% fly ash remains entrapped in the air. When these fly ashes are combined with various gases used in the coal combustion process they form spherical-shaped particles known as Cenospheres. Cenospheres are aluminosilicates, having low thermal density and conductivity ranging from 400 to 900 kg · m-3. In a coal combustion power plant, the average formation of the cenosphere is estimated to be approximately 0.20 ±0.02 wt% (0.6 vol%). The particles of the cenosphere are finer than the sand, show monodisperse distribution, and when combined with cement it can change the rheological properties of concrete. Cenospheres exhibit remarkable thermal stability when a high amount of mullite is present. It further shows resistance to shock, high creep resistance, and low thermal expansion in the presence of mullite. The forecast report of the market in the US exhibit the increased use of the Cenosphere at a compound annual growth rate from 388.3 million in 2017 to USD 689.2 million by 2022. The cenosphere plays an important role in structural appliances due to its lightweight concrete and aggregates. Cenospheres form a compatible bond with cement. Due to its high strength, low water absorption, and low weight concrete, cenospheres can reduce the construction and transportation costs when combined with cement matrix. Cenospheres produce different results when mixed with different types of cement. For example, when cenospheres mixed with Portland cement it behaves as a pollozan, enhancing the interfacial bond between the aggregate and cement matrix. The alkali-silica reaction does not allow cenospheres to exhibit potential deleterious action when Cenosphere goes under an alkali environment with Portland cement.
Cenospheres are widely used with cementitious material due to their reduction of weight, increase in thermal conductivity, cost-effective and eco-friendly nature. It further provides resistance to shrinkage, impermeability, workability, and improves the flow of electricity. With the use of cementitious material, compressive strength greater than 60 MPa can be achieved. The physical properties of the cenosphere play an important role when combined with cementitious material for fillers. Cenospheres are spherical in shape thus they possess a lower surface area to volume ratio. The cenosphere shell has about 3–11% thickness and a lower bulk density ranging from 200 kg/m3 to 1000 kg/m3. The water absorption capacity of the cenosphere is approximately 66% and the porosity is 1% depending upon the type of cement mixed to be used as filler. The crush strength of the Cenosphere range from 1.6–3.2 MPa and its Moh's hardness is approximately 5 which builds strength in the product made from the cementitious material. When combine with cement, the cenosphere reports thermal conductivity of about 0.07–0.11 W/mK and a melting point of about 1600 °C.
The chemical composition of the Cenosphere also plays an important role in their overall performance when merged with cementitious material. As cenospheres are exposed to high temperature and alkali environments, their chemical composition must have proper composition. An ideal cenosphere-cement mixture must have the 62% SiO2, 29.7% Al2O3, 0.90 % CaO, and 3.5%Fe2O3. At present times, Cenospheres are 70% replacements of the other materials used in construction with cement. The reason is they can reduce the density of the substance up to 42% and volume up to 50%. Compared to the natural aggregates, the density of cenosphere is comparatively low i.e., 618 – 908 kg/m3). It further decreases the air content with a diameter of 106 μm and 160 μm which increases the workability of the product. PETRA FILLIT produces one of the fine qualities of the Cenosphere. They use high-quality coal for the combustion process and it is widely used by the leading construction companies. PETRA BUILDCARE PRODUCTS is also a leading exporter of Cenosphere to other countries such as the USA, Africa, East Europe, and East Asia.