Answer
5.0 mm
Work Step by Step
There’s no problem in the winter as the concrete shrinks. When the concrete heats up in the summer, it expands. A expansion joint must be created between the slabs, equal to the increase in length of the concrete slab as its temperature rises by 50 – 15 = 35 Celsius degrees.
$$\Delta \mathcal{l}=\alpha \mathcal{l}_o \Delta T=(12\times 10^{-6}/C^{\circ})(12m)(35 C^{\circ})=0.0050m$$
