Concrete Pavement Strength Investigations at the FAA National Airport Pavement Test Facility

Abstract

The Federal Aviation Administration (FAA) conducted airplane gear load tests on three new concrete pavement test items at the National Airport Pavement Test Facility (NAPTF) to determine the in-situ concrete slab strength and estimate the actual stress ratios to be expected under full-scale traffic loads. Full-scale static loads were applied incrementally to designated slabs within the test items to identify the cracking loads for both bottom-up and top-down cracks. Crack initiation was determined by monitoring real-time strain gage measurements. Some of the strength tests were supplemented by rolling-wheel traffic loads to try to propagate the already initiated cracks to full depth. A limited set of beam fatigue tests on standard lab-cured beams cast at the time of construction provided laboratory data for comparison. The immediate practical result of the strength tests was to allow the FAA to set the wheel loads for the CC6 full-scale trafficking phase at approximately 80 percent of the slab cracking strength measured for the low-strength test item. The long-term goal of these investigations is to relate pavement cracking strength to flexural beam strength from standard ASTM C 78 tests, and to relate the pavement stress ratio to the stress ratio in laboratory fatigue tests performed on standard concrete specimens. Both tests are needed to satisfy the requirements of fatigue theory.