Occasionally the word "problem" is associated with structural lightweight concrete. As a general rule, the so-called problems encountered in structural lightweight concrete are not inherent in the aggregate, per se, but rather are created by non-adherence to fundamental knowledge of the properties of both the aggregate and the concrete. Some examples are as follows. The first is the flat plate floors of a multi-story building were deflecting because they were constructed of structural lightweight concrete. The problem was that the shoring for a typical floor was removed at 7 days and curing during this period was casual. The green floor was used for supporting the forms of the floors above. In addition, materials in concentrated stacks in excess of the design live load were stored on the green slab. The net effect of this excessive loading of the floor at an early age was a large deflection held in the slab as it continued to gain strength, in effect, a built-in deflection. The second is a floor of a building was disintegrating under normal foot traffic. The problem was that lightweight and normal weight concretes were being batched in trucks operating from the same plant and different air-entraining agents were specified for the two concretes. Inadvertently, both agents were introduced into the lightweight mix. Ninety cubic yards of concrete completed a 115 cubic yard floor slab. The concrete weight was approximately 15 pcf low, strength was 50 percent below design strength, and air content was in excess of 20 percent. Obviously, this error would have been noted during placement if unit weight determinations had been taken of the plastic concrete for control purposes. The examples are all from case histories. Further examples can be found in the article.