Heat insulation of any material is the resistance provided to the transfer of heat from the higher temp. to the lower temp.
Heat Resistance (R) is defined as: Number of hrs for 1 watt of energy to transfer heat from 1sqm of area with a temp difference of 1*C.
The heat resistance of any material is denoted by R. But for combination of materials it is U-value, which is the reciprocal of the R value.
Need of Heat insulation
The excessive use of artificial mechanisms for achieving the comfort level, has led to high emissions of chlorofluorocarbons & other poisonous gases.
Government of India has passed an Environment act, which will be applied in 2007.
According to this act the external envelop of any structure must have a U-value of min 0.5 W/m2K.
What is Asbestos cement?
Asbestos is a naturally occurring mineral found in underground rock formations.
Asbestos is also called as a magic mineral because no other substitute can match its properties.
Asbestos fiber is a major reinforcing component of Asbestos cement.
AC products consist of a mix of chrysotile fibers, cement & silicates of calcium & magnesium.
Heat Insulating properties of AC sheets
In general any material having open or closed pores is a good insulating material.
Asbestos cement has more of open pores therefore it is not as good as hair felt or straw boards.
If the AC sheets are waxed or coated with waterproofing material, it will seal the open pores & therefore the resistance to heat may increase.
The Thermal resistivity of AC sheets is 0.95 which is more compared to plastering, therefore they can be used as cladding on walls.
-The AC sheets also can be used for roofing, since rest of the materials do not meet the demand of U value=0.5
-Asbestos cement is also used for drainage pipes.
Longer life if properly fitted
Less noise from heavy rain and thermal movements
Better thermal insulating properties
Rigid & Durable
Non corrosive, fire proof
They are heavier ,thus it is more expensive to transport and requires a stronger roof structure.
Brittleness causes a high rate of waste due to breakage during transport and installation..
Labour intensive due to weight and brittleness.
The corners of the sheets must be mitred prior to fitting and holes for the fixing screws must be drilled.
Easily discolors with dust and algae.
The manufacture, processing & discarding of asbestos products presents hazards to health.
Standard lengths-3, 2.75, 2.5, 2.25, 2, 1.75, 1.5 m
Overall width-1050 mm
Effective depth-1010 mm