Q.: Someone drove a pickup truck over a concrete driveway my crew had just placed 18 hours earlier. Immediately after the truck was driven off the driveway, a crack appeared in the contraction joint the truck had crossed. What is the possible unseen damage to the driveway?

A.: It's possible the truck loading could have caused a midpanel flexural crack at the bottom of the slab that might not yet be visible at the top. Depending on temperature conditions, an engineer could estimate the concrete's flexural strength, consider the weight of the truck, make a rough calculation of the stress and determine whether the calculated stress exceeded the estimated flexural strength. However, because of several unknown variables, including subgrade support and pavement thickness, the accuracy of this determination could be challenged.

Contraction joints are intended to induce a crack, which may be caused by thermal contraction rather than an applied load. So the presence of that crack doesn't necessarily indicate the truck caused additional damage. Wait and see if any other random cracks appear in the area over which the truck passed. If none appear within a few weeks after the driveway is in use, you may have dodged a bullet.