Research efforts at the Waterways Experiment Station have resulted in the development of a pavement evaluation methodology based upon a multilayered elastic model and limiting stress/strain criteria which use deflection basin measurements obtained by applying a load to the pavement surface with a nondestructive testing (NDT) device.
Growing acceptance of the NDT methodology has led to the formulation of a comprehensive nondestructive testing and evaluation procedure for airfield pavements which has been used by and is under consideration for adoption by the Army and is also being used by the Air Force and Navy (there is presently no official DA published manual or standard for NDT, but one is currently being drafted). A testing scheme is presented for airfield pavements that includes recommendations for the number of tests, location of tests, magnitude of NDT loadings, and sensor spacings. In addition to NDT data, other information such as layer thicknesses, surface and five-day mean air temperatures, and portland cement concrete flexural strengths are required for an accurate evaluation. The computer program BASIN has been developed to graphically and statistically analyze NDT deflection data and to select a representative deflection basin to be used for the evaluation of a pavement section. A description of the modulus backcalculation process using the computer program BISDEF is provided. The final evaluation is based upon a projection of the total number of passes of each aircraft type that a pavement will be expected to support over its design life. A method is described for determining the critical aircraft and design pass level for a given projected aircraft mixture. Allowable aircraft loads, strengthening overlay requirements, etc. are then obtained using the moduli from BISDEF and the program AIRPAVE, which compares stresses and strains within a layered system to appropriate limiting criteria. Limiting stress/strain criteria included in AIRPAVE have been calibrated with performance data to ensure consistency with current Corps of Engineers design criteria.
The use and significance of the pavement classification number (PCN) determined from the allowable load rating for expressing the load-carrying capacity of a pavement by a single unique number without specifying a particular aircraft is discussed. Sample data have been used to demonstrate evaluation techniques and the presentation of results.
The NDT procedure presented here provides a rapid and versatile method for determining the structural capacity of a pavement system. Rigid, flexible, and composite pavements consisting of stabilized or unstabilized layers can be evaluated by using data from a variety of commercially available NDT equipment. While developed to meet specific military requirements, the procedures are equally applicable to the evaluation of civil airports and could be modified to include the evaluation of roads and streets.