A full-scale rigid pavement experiment, designated CC8 Fatigue Strength (F/S) test, is undergoing simulated aircraft loading at the Federal Aviation Administration (FAA) National Airport Pavement Test Facility (NAPTF). The objective of this test was to isolate and estimate fatigue life of two phases of bottom-up cracks, crack initiation and propagation. The test pavement consisted of eight groups of four slabs (15’ x 15’) each. These slabs were designed with different combinations of flexural strength (650 vs. 900 psi), thickness (9 vs. 12 in), and subgrade strength (CBR 3-4 vs. 7-8). Heavy Weight Deflectometer (HWD) was conducted at weekly basis to evaluate the structural integrity of the test pavement.
Static load tests were first performed to initiate bottom-up cracks using Single Wheel Load (SWL) and Dual (D) configuration. For most cases, the in-situ cracking strength was about 50 - 60% of the flexural strength from ASTM C78 on field cured concrete beams. Then, traffic test was carried out to develop full-length and full-depth crack. During this crack propagation stage, 80% of the bottom-up cracking load were used. It was observed that the thin PCC slabs with higher strength required more load repetitions to initiate bottom-up cracks but less repetitions to propagate the cracks to pavement surface.
An analytical method was developed to compute cumulative strain energy during both crack initiation and propagation using the strain gage responses under dynamic loading.