When it comes to outdoor flatwork problems, prevention is better than trying to correct the problem later. Several common problems and some guidelines are as follows:

  • Shrinkage cracks: Minimize cracking by reducing concrete shrinkage and by jointing the slab. Reduce shrinkage by using the largest possible maximum-size aggregate. Control shrinkage cracking by forming or sawcutting joints to a depth of at least one-fourth of the slab thickness.
  • Craze cracking: Craze cracks are caused by shrinkage of the paste-rich top surface of a slab. Prevent this problem by starting to cure the concrete as soon as possible.
  • Settlement: Inadequate soil compaction is the most usual cause for settlement. Compact cohesive subgrade soil by ramming, and compact granular subgrade soil by vibrating.
  • Surface scaling: Caused by freezing and thawing cycles and deicing salts, scaling is most likely to occur during the first or second winter after the concrete has been placed. Scaling can be prevented by using only air-entrained concrete. Required air content is 5 percent to 8 percent.
  • Popouts: Popouts are pock marks in the concrete surface caused by internal pressure from particles near the surface. Most are caused by absorptive particles and can be minimized by using a jitterbug on the surface.