Most of the problems introduced at the design and construction stages don't show up until the concrete is hard. Questions answered are how to prevent blow ups, loss of bond between a topping and the floor, the meaning of cold joints and how to prevent them, the corrosion of reinforcement, cracking from drying shrinkage, crazing, curling, damp floor slabs discoloration, dusting, popouts and piting, scaling and spalling, slippery surfaces, strength variations, loss of subgrade support, to thin slabs, and low wear resistance. Blow ups (also known as buckling or tenting) are caused by upward buckling or pavement on both sides of a joint. Karl H. Renner, Chief Engineer, Chicago, reported that blow-ups are a problem inherent in pavements that contain joints and that the most positive solution is to build a continuously reinforced concrete (CRC) pavement initially. There is an alternative solution where a jointed pavement has already been built. If this shows deterioration and significant amounts of infiltration of material into the joints so that a blow up may be anticipated, a CRC overlay may be placed to strengthen the original pavement structurally and prevent blow ups from occurring. Most CRC overlays have been 6 inches thick. A cold joint is a plane of weakness in concrete caused by an interruption or delay in the concreting operations. It occurs when the first batch of concrete has begun to set before the next batch is added, so that the two batches do not intermix. To prevent cold joints when slabs are placed, the concrete should be placed against the preceding batch and not dumped in an individual pile. On sloping grades the work should proceed uphill. Vacuum dewatering of concrete slabs can be used to reduce significantly the amount of free water in the concrete. This free water is usually responsible for the uneven shrinkage from top to bottom of the slab that causes the curling at joints and edges. Ti si claimed that if the subbase is properly prepared, joints properly located, concrete thoroughly consolidated and the slab vacuum precessed, curling can be eliminated.