The Thermal Properties Of Concrete
Thermal properties of concrete are of special concern is structures where thermal differentials may occur from environmental or for any other reason. Knowledge of thermal expansion of concrete is required in the design of mass concrete structures such as the dam, mass repairs, airport runways, port-pavements, expansion, and contraction joints, in the provision of bridge support movement both horizontally and vertically, and in the design of statically indeterminate structures subject to temperature variation.
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The thermal properties of concrete are based on the parameters.
- Specific Heat
- Thermal Conductivity
- Thermal Diffusivity
- The Linear Coefficient Of Thermal Expansion
Specific Heat
The heat capacity per unit mass of a substance. Specific heat represents the heat capacity of concrete and is little affected by the mineralogical character of the aggregate. Specific heat increase considerably by an increase in the moisture content of concrete. Specific heat increase with an increase in temperature and with a decrease in the density of concrete. Specific heat of concrete is usually in the range of 0.20 to 0.30 kcal/kg/C.
Thermal Conductivity
Thermal Conductivity is the rate at which heat is transmitted through a material of unit area and thickness when there is a unit difference in temperature between the two faces.
The thermal conductivity of normal conventional concrete depends on its composition and when the concrete is saturated the conductivity ranges generally between about 1.4 and 0.5 kcal/m/hr/C. The degree of saturation of concrete is a major factor because the conductivity of water is about 24 to 26 times that of air.
Thermal diffusivity
Thermal diffusivity is a measure of the rate at which temperature changes within the mass place. Diffusivity () is related to the thermal conductivity (k) by the following relationship.
δ⅔
Where e= Specific heat (kcal/kg/C)
P= Density of concrete (kg/m3)
K+=thermal condiucitivity
Diffusivity is affected by the moisture content of concrete and the rock type used in the concrete.
Diffusivity of Concrete with Different types of Rack type on the value of the coefficient of expansion of cement paste and aggregate, for ordinary cured concrete the coefficient of decreases slightly with age but this is not the case in the concrete curved under high-pressure steam, for ordinary concrete the value of coefficient of thermal expansion varies from 9*10-6 per C to 12*10-6per C.
Coefficient Of Expansion Of 1:6 Concrete made with Different Aggregate
δ⅔
Where e= Specific heat (kcal/kg/C)
P= Density of concrete (kg/m3)
K+=thermal condiucitivity
Diffusivity is affected by the moisture content of concrete and the rock type used in the concrete.
Diffusivity of Concrete with Different types of Rack type on the value of the coefficient of expansion of cement paste and aggregate, for ordinary cured concrete the coefficient of decreases slightly with age but this is not the case in the concrete curved under high-pressure steam, for ordinary concrete the value of coefficient of thermal expansion varies from 9*10-6 per C to 12*10-6per C.
Coefficient Of Expansion Of 1:6 Concrete made with Different Aggregate
| TYPE OF AGGREGATE | Air-cured concrete 10±6 per °C |
Water-cured concrete 10±6 per °C |
Air cured and wetted concrete 10±6 per °C |
|---|---|---|---|
| 13.1 | 12.2 | 11.7 | |
| Granite | 9.5 | 8.6 | 7.7 |
| Quartizite | 12.8 | 12.2 | 11.7 |
| Dolerite | 9.5 | 8.5 | 7.9 |
| Sandstone | 11.7 | 10.1 | 8.6 |
| Lime Stone | 7.4 | 6.1 | 5.9 |
| Portland Stone | 7.4 | 6.1 | 6.5 |
| Blast furnace Slag | 10.6 | 9.2 | 8.8 |
| Formed Slag | 12.1 | 9.2 | 8.5 |