The concept is actually quite old. By using forming systems, engineers have decreased the weight of floor slabs by creating voids through a variety of techniques for a very long time. But newer systems now make it possible to increase the efficiency of cast-in-place (CIP) concrete construction and reduce overall cost.
Traditional voided-slab forming systems that have been used include waffle slabs, single-direction and double-direction span forming systems, and hollow-core precast slabs. The guiding principle, is that building owners and designers can get the advantages of a thin two-way-spanning flat-plate structure while the structural engineer can lighten the floor by more efficiently using the concrete.