Tests Of Concrete Pavements On Crushed Stone

Static load tests were performed on 8-in. thick concrete slabs on densegraded and open-graded stone subbases in 5-in., 10-in., and 15-in. thicknesses. Both types of crushed stone subbases and all thicknesses contributed to the load capacity of the slabs by reducing slab strains and deflections and subgrade pressures. The first 5 in. of subbases were more effective in reducing strains and deflections than the next 10 in. In areas without frost or soil swell problems, a subbase of 5 in. of 6 in, is ordinarily optimum, and it was shown that thin additions to the slab thickness will meet load capacity requirements as readily as thick subbases. Agreement between experiment and theory was good with respect to deflections, but measured strains were more sensitive to foundation bearing value than theory. For each 5-in. thickness of stone subbase beneath the slab, the subgrade pressures were reduced approximately 1 psi at free corners, ½ psi at edges, and ¼ psi at interiors. Incidental studies were made to observe response for many load positions, to study the effect of plate size, and to evaluate joint effectiveness.