The specific heat capacity of concrete is small this means that

That means that the concrete will increase it temperatures quicly compared with other substances whose specific heat is higher.

Explanation:

Specific heat is the amounf of heat to raise the temperature of 1 gram of substance (or kg depending on the unis used) 1 Celsius degree.

The water, for example, has a high specific heat. That means that you need to add a great amount of heat to raise its temperature, compared with, for exampple the concrete, which is told to have a smaller heat capacity.

You can see that mathematically form the formula for heat released or absorbed from/by a substance:

Q = mass × Specific heat × ΔT

⇒ ΔT = Q / (mass × Specific heat).

So, for the same mass, a certain amount of heat (Q) will result in a bigger ΔT when the specifif heat is smaller.

The mass has escaped into a gas which you can not see so the law stays true.