16 are then covered with a layer of the previously described flowable settable concrete to form the slab 11 which is then allowed to set in the conventional manner it will be apparent that when the concrete of the slab 11 is set it forms a rigid pavement slab which is cellular in the sense that hemispherical voids 19 are formed beneath its surface by the shells 15 traffic load imposed downwardly on the upper surface of the concrete slab 11 is distributed triaxially around each dome shaped void with close to the same load bearing capacity as a solid concrete slab yet substantially less concrete is required for the cellular slab 11 of the invention because of the voids for example a pavement slab of eight inch thickness may have dome form shells 15 of six and one half inches in radius with those dimensions a reduction in pavement material volume of more than thirty percent is achieved the shell thickness in that example would be approximately one sixteenth of an inch in addition to the hemispherical voids 19 the set concrete slab 11 also includes drainage passages 20 formed by the weeps 16 as shown in fig3 these passages 20 interconnect through the hemispherical voids 19 and from one panel 12 to the next across the border 18 to allow any water percolating upwardly from the subgrade or seeping downwardly from road surface to drain away easily in addition to minimizing the volume of concrete necessary for a given slab 11 without measurably impairing load bearing ability a further advantage of a rigid pavement slab formed in accordance with the invention is.