The volume of a cylinder is given by the formula V = πr^2h, where r is the radius and h is the height (or length) of the cylinder.
In this case, the radius of the cylindrical construction pipe is 2.5 ft and the length is 20 ft. So, the volume can be calculated as:
V = π(2.5)^2(20)
= 125π cubic feet
Therefore, the volume of the cylindrical construction pipe is 125π cubic feet.