Cenosphere (Litefil) - Manufacturing and Construction Aspects
The cenosphere is also known as Litefil, a naturally occurring byproduct of the coal burning process mainly in power plants. When compared to the fly ash, the cenosphere is inert, light weight hollow spheres made up of largely silica, iron and alumina. It is a unique and free flowing powder with hard shelled hollow and minute spheres. The particle size ranges from 1-500 microns and they have been found to have an average compressive strength of over 3000 psi. The color of the product ranges from white to dark grey, and they are essentially thin walled glass spheres. They are also referred to as microspheres, micro balloons or glass beads. Continued research has led to the discovery that the cenosphere (litefil) can be used to replace some of the concrete components in construction.
Important Properties of the Litefil (Cenosphere)
- Low bulk density, hence a light weight aggregate.
- High thermal resistance
- High workability and high strength characteristics
- Thermal reflectivity, important in heat dissipation
- Flame retardant properties make it useful in foundries and high temperature coatings.
- Noise attenuation properties hence can be a good material for sound proofing.
Advantage of Cenosphere over Other Materials in Concrete
In construction, good concrete mix design employs a variety of aggregate sizes for best performance. This variety of particle sizes allows for good packing of particles and more saving on cement usage. The very small sizes of cenosphere particles create greater surface area for coating with cement as compared to an equivalent volume of the larger sand particles. This factor also improves the workability of the aggregate.
The fine texture and light color of the cenosphere particles makes them also very ideal for bulk filling in the making of the cement grout slurry. The added particles help increase the volume of the grout without having to add more cement. The particles also prevent too much shrinkage.
Packing of particles inside pin holes becomes easier and more effective due to scrubbing action provided by the cenosphere. The smooth and spherical shape easily moves into the small holes as compared to the jagged and angular crushed particles.
The litefil cenosphere can also be graded into various categories based quality. The main parameters used in classification are the crush strength, specific gravity and the particle size distribution. Through this, the processors are able to develop standard grade cenosphere and specialty grades as well. Other parameters that are used in determining the quality of the material include the true density, sinker’s, particle size distribution and the moisture level of the material. These parameters are ascertained through laboratory tests and analysis.
In oil fields the product is used in oilfield cementing, whereby during the cementing process, it serves to decrease the slurry density without having to increase the water content. This enhances the compressive strength of the cement as well.
- In plastic manufacturing, they act as good light weight filler, reducing the cost of the composite while at the same time enhancing the performance of the plastic product.
- In paints and coatings, the litefil / cenospheres act as special additive that enhance product performance. The sphere has low surface area and when these microspheres are incorporated, they help reduce the resin demand and enhance the volume loading capacity.