A contractor had been trying to place a driveway for days. However, the pour kept being delayed due to rain. Finally, a sunny day occurred and the concrete was placed. Unfortunately something went wrong. Several soft spots occurred throughout the driveway. Some of the soft spots were so soft that a screwdriver could easily be pushed through. What went wrong?
The first clue is the rainy weather for days before the pour. The sub-grade became wet and mucky. As the finishers screeded the concrete, their boots pulled up muck from the sub-grade and contaminated the concrete as the finishers walked around. The contamination consisted of blobs of muck in the concrete forming weak spots. Finally, the driveway had to be removed and replaced.