In countries where a concrete floor will experience a large range of temperature fluctuations on a regular basis, for example in the Middle East or Australia, where large swings in temperature can be experienced between day and night, it is essential for the floor’s designer to consider the concrete’s behaviour in these conditions. This is also true to a lesser extent in the UK, where seasonal cycles should be considered.
Concrete’s thermal movement, Δj, is given in mm. In Technical Report 34, the change in width of joints due to thermal movement can be found using the following equation: , where:
α = coefficient of thermal expansion of the concrete (mm/mm/oC).
T = change in temperature (oC).
L = distance between free-movement joints (m).
The thermal expansion coefficient holds true for both expansion and contraction, and can vary between different concrete mixes. It usually falls in the range of 7-12 x10-6/oC (microstrain/oC) and is largely dependent on the type of aggregate used in the mix.
Thermal contraction can cause a lot of problems to a floor slab if any part of the slab is restrained. Because the restraints impede contraction, they cause a tensile stress throughout the slab. As concrete is very weak in tension, especially if it hasn’t yet matured, this may cause cracking.