Tests to Evaluate Concrete Pavement Subbases

The contribution of subbases under concrete pavements to the strength of the roadway structure was evaluated by load-testing concrete panels built on five different foundations. Plain concrete slabs were cast and instrumented on the foundations to register the strains in the concrete, the panel deflections, and the vertical pressures at the slab-subbase interface and subbase-subgrade interface. Static loads were applied to the panels at the corners, edges, and interiors. The data obtained from tests made when the panels were fully in contact with the supporting soil showed the extent to which the granular subbases contributed to the strength of the pavement structure. An analysis was made, based on measured load-strain relationships and load-deflection relationships under edge loadings and on close-fitting theoretical curves. Measured strains and deflections generally exhibited reasonable agreement with theoretical values that were computed using the Westergaard theory. However, in many cases, measured values were more sensitive to changes in subgrade support than is indicated by the theory.