When a new slab is added and bleeds during placement, and it is joined to an older slab, what is the predicted surface outcome?

• A. The surface will become smoother
• B. The surface will gain a dusty finish
• C. The surface will cure with no cracks
• D. The surface will develop cracks

Answer: (D)

When fresh concrete bleeds, water rises to the surface and carries some cement paste with it, creating a weaker, laitance-rich top layer if finishing isn’t timed properly. If that new slab is then bonded to an older slab, the two pours can’t move freely relative to each other. The old slab restrains the shrinkage of the new one during curing, so tensile stresses develop at the interface and across the surface. That restrained shrinkage leads to cracking, often at or near the joint between the slabs. So the predicted surface outcome is cracks.