Thermal Properties
Thermal properties of concrete to understand the behavior of concrete to heating and cooling.The study of thermal properties of concrete is an important aspect while dealing with the durability of concrete.
Concrete is a material used in all climatic regions for all kinds of structures.The important properties that will be discussed are:
· Thermal conductivity
· Thermal diffusivity
· Specific heat
· Coefficient of thermal expansion
Thermal Conductivity
This measures the ability of material to conduct heat. Thermal conductivity is measured in joules per second per square meter of are conductivity of concrete depends on type of aggregate a of body when the temperature difference is 1degree C per meter thickness of the body.
The conductivity of concrete depends on type of aggregate moisture content, density and temperature of concrete. When the concrete is saturated, the conductivity ranges generally between about 1.4 to 3.4 J/S/m2
Thermal Diffusivity
Diffusivity represents the rate at which temperature changes within the concrete mass. Diffusivity is simply related to the conductivity by the following equation:
Diffusivity=Conductivity/CP
Where C is the specific heat, and P is the density of Concrete. The range of diffusivity of concrete is between 0.002 to 0.006m2/h
Specific heat
It is defined as the quantity of heat, required to raise the temperature of a unit mass of a material by one degree centigrade. The common range of values for concrete is between 840 to 1170 j/kg3/C
Coefficient Thermal Expansion
It is defined as the change in unit length per degree change of temperature. In concrete, it depends upon the mix proportions. The coefficient of thermal expansion of hydrated cement paste varies between 11x10^-6 and 20x10^-6 per degree C. The coefficient of thermal expansion of aggregates varies between 5x10^6 and 12x10^-6 per degree C Limestone and Gabbros will have low values and gravel and Quartzite will have high values of coefficient of thermal expansion.