Coefficient of thermal expansion 
    The coefficient of thermal expansion describes how the size of an object changes with change in temperature. Specifically, it measures the fractional change in size per degree change in temperature at constant pressure, such that lower coefficients describe a lower propensity for change in size.

α - Coefficient of linear expansion. 
As per IS Code 
The coefficient of thermal expansion of cement concrete- 3 × 10-6 per°C 
The coefficient of thermal expansion of steel - 12 × 10-6 per°C