Comparative analysis of deflection bowl forward calculations for rigid pavements

Back calculation programs developed to interpret FWD deflection measurements include a group of forward calculation procedures based on the AREA parameter. This group of procedures has been suggested by AASHTO and the FAA for concrete-pavement evaluations. The USCOE has a somewhat similar procedure based on the characteristics of the defection bowl. In light of these procedures, the paper presents a comparative study of their outputs carried out on simulated deflection basins as calculated for interior loading in a theoretical, two-layered, elastic model. These simulated deflection basins enabled the development of an additional forward calculation procedure, titled REVALIV, based again on the AREA parameter. Through this procedure, both the subgrade resilient modulus, in contrast to the subgrade reaction modulus obtained in the previous procedures, and the concrete modulus of elasticity can be directly obtained. A comparative study of these different procedures indicates the following: 1. the modulus of subgrade reaction and the concrete modulus of elasticity are dependent on the option chosen for calculation, with the minimum values obtained amounting to less than half the maximum values obtained; b. the relationship between the modulus of subgrade reaction values and their comparative subgrade resilient modulus values differs, even substantially, from one procedure to another. These findings suggest that all the discussed procedures should be used with care, with preference to AASHTO and REVALIV ones. (a) For the covering record of this conference, please refer to ITRD abstract no E220164.