Asbestos is a naturally occurring thin crystalline long which when used for the preparation of concrete improves the fresh and hardened properties of concrete such as compressive and flexural strength. In the construction industry, it finds its application in heat and acoustic insulation, fireproofing, roofing and flooring jobs.
In this article, we discuss the characteristics, effect on concrete properties, advantages, disadvantages and uses of asbestos.
Characteristics of Asbestos
Asbestos was first discovered by the Greeks and Romans in the 18th century where they referred to it as a Miracle Mineral.
Asbestos is obtained by extraction of asbestos-containing rock which is crushed and milled to produce a thread like fibrous material known as asbestos. The asbestos thus obtained contains thousand of which can be further divided into microscopic fibrils.
Asbestos is majorly divided into two types based on the crystalline structure :
- Serpentine - Sheet or a layered structure.
- Amphibole - Chain like crystal structure.
Chrysotile, the only mineral in the serpentine group, is the most commonly used type of asbestos and accounts for approximately 95% of the asbestos that finds in different purposes. Chrysotile is commonly known as "white asbestos".
Asbestos in Concrete
Asbestos is added to the concrete in two ways :
- Addition of asbestos fiber in cement
- Addition of asbestos fiber in concrete.
1. Asbestos in Cement
Most of the asbestos concrete components are made up of using asbestos cement due to the high risk of consumption of asbestos through inhalation. Generally, 10-15% of the cementitious material is replaced with asbestos in the production process of cement.
The long asbestos fibers or higher percentages of fibers produce higher strength properties. With the help of high curing pressure or forming pressures, increased density can be achieved which in turn produces higher strength properties. The higher density products are less porous and sometimes give the effect of improving chemical resistance properties.
2. Asbestos in Concrete
As asbestos is a very hazardous material, use of raw asbestos for the concrete mix at the site is not recommended. But under a controlled environment, the of asbestos in concrete is permissible.
Effect of Asbestos on Concrete's properties
1. Compressive Strength
Tests conducted on concrete with varying percentage of asbestos fiber show that the compressive strength of the concrete is most when 0.75% of cement is replaced with asbestos fibers. The strength of 0.75% fiber reinforced concrete is 40.89MPa whereas that of conventional concrete is 30 MPa.
From the results, it can be clearly seen that there is an increase of 33% in compressive strength with the introduction of asbestos fiber in concrete to that of conventional concrete.
2. Flexural Strength
Test conducted on concrete with varying percentage of asbestos fiber also show that the flexural strength of the concrete is most when 0.75% of cement is replaced with asbestos fibers. The strength of 0.75% fiber reinforced concrete is 6.27 MPa whereas that of conventional concrete is 5.13 MPa.
By comparing the two, it can be clearly seen that there is an increase of 23% of flexural strength with the introduction of asbestos fiber in concrete to that of conventional concrete.
Advantages of Asbestos Concrete
- Asbestos is a very good thermal insulator and increases the energy efficiency of the building.
- It is highly resistant to fire and does not burn easily.
- It forms a very strong material when mixed with cement and used as an additive to form a composite material called asbestos cement.
- It is a very inexpensive and a very cost effective material, hence widely used.
- It is extensively used as a protective roofing material in corrugated form.
- It is highly durable and weatherproof.
- It is resistant to damage from termites.
- Asbestos is very easy to clean and maintain but difficult to repair.
Disadvantages of Asbestos Concrete
- The major disadvantage of using asbestos is that it is seriously hazardous to health. Asbestos comprises of invisible microparticles which when released in the air can cause life-threatening diseases if inhaled for a continuous span of time.
- Due to this major disadvantage, new materials are being manufactured as a replacement for asbestos.
Uses of Asbestos Concrete
- Pipe and duct insulation.
- Wall and ceiling panels.
- Roofing materials.
- Artificial fireplaces and materials.
- Concrete Floor Tiles.
- Asbestos concrete pipes.