# Thermal Diffusivity | Definition | Relation With Conductivity

Thermal diffusivity is used for the calculation of thermal conductivity. It represents the rate at which temperature changes within a defined mass. It is represented by δ and it is measured in meter square per hour. Thermal diffusivity is like an index that facilitates you in temperature changes of concrete.

Diffusivity is related to conductivity by an equation;
$large delta = frac{k}{crho }$

Where;

δ= thermal diffusivity

K= thermal conductivity

C= specific heat

Ρ= density of concrete

The equation is representing a direct relation between thermal diffusivity and thermal conductivity. As the concrete density is inversely proportional to the thermal diffusivity therefore, moisture content of the concrete affects the diffusivity.

For a normal concrete value of diffusivity lies in between 0.002 to 0.006 m2h and this value depends on the type of aggregates used in concrete.

Diffusivity can be measured by finding the relation between the time and temperature differential of the concrete specimen at interior and on the surface. Complete procedure of diffusivity measurement is mentioned in U.S Bureau of Reclamation (procedure 4909-92). During calculation of diffusivity, make sure that the same moisture content exists on the specimen as that in the actual structure.