Aftercare

An assessment of structural condition might be needed during the life of a pavement, for monitoring its rate of deterioration, calculating residual life and planning future maintenance requirements, or as part of the design of strengthening measures for use by heavier aircraft or an increase in the number of aircraft.

Pavement evaluation is often complex because of the diverse constructions that have developed. Some of these forms of construction cannot be properly dealt with by analytical design methods.

An assessment will comprise:

• A structural investigation to determine the properties required for a pavement evaluation and overlay design.
• An evaluation of the pavement strength and residual life.

Detailed guidance on structural investigations for airfield pavements is given in Guidance Notes on Structural Investigations of Airfield
Pavements (Ministry of Defence, Defence Estates. 2002), and on nondestructive testing in Use of Nondestructive Testing in the Evaluation of Airport Pavements (Advisory Circular No. 150/5370-11B, FAA). Both A Guide to Airfield Pavement Design and Evaluation and Airport Pavement Design and Evaluation describe evaluation methods by Reverse Design.

The pavement investigation might comprise:

• A visual inspection, possibly including a Pavement Condition Index (PCI) survey to determine the pavement rating and its distress mechanisms.
• Non-destructive testing by Falling Weight Deflectometer (FWD) to survey pavement variability, measure load transfer at joints and provide data for the back-calculation of layer elastic stiffnesses.
• A Ground Penetrating Radar (GPR) survey to determine pavement thickness.
• Coring to obtain layer thicknesses and material condition, and recover samples for concrete strength testing.
• Dynamic Cone Penetrometer (DCP) (Figure 10) testing and to assess the subgrade strength.
• Unbound Material Sampler (UMS) through the core hole to obtain unbound material for testing in the laboratory.
• A material testing programme; in particular concrete strength tests on samples recovered from cores.

The Pavement Condition Index (PCI) method presented in the ASTM standard D5340-98 can be used to monitor pavement visual condition.
The PCI was developed to provide engineers with a numerical indication of overall pavement condition. Once the whole pavement area has been
divided into sections, each with similar construction and traffic level, the distress type, severity, and extent are all identified and recorded. The calculated PCI for a section is a number from 0 to 100, with 100 representing a pavement in excellent condition.