In the first week, the construction worker bought 40 pounds of nails.
In the second week, he bought 2 times as many nails as the first week. To find out how many pounds of nails he bought the second week, we multiply the amount from the first week by 2:
\[ 40 \text{ pounds} \times 2 = 80 \text{ pounds} \]
Thus, the construction worker bought 80 pounds of nails in the second week.