Abstract
To obtain fatigue crack propagation properties of ordinary concrete commonly employed in bridge construction, 48 replicate single-edge notched beam specimens were fabricated using C50 plain concrete. Twelve of these were subjected to monotonic loading to determine their static capacity; the remaining 36 were fatigue-loaded with various combinations of maximum stress level and stress ratio under three-point bending. Visual observation, strain gauges, and the compliance method were used to determine the evolution of crack length during fatigue loading. The fatigue crack growth rates were then evaluated for each specimen using linear regression. This study shows that the fracture surface under fatigue loading exhibits greater zigzagging than under monotonic loading, with multiple microcracks coalescing. The elastic compliance method captures the three-stage development of fatigue crack well, and the derived equivalent crack size is consistently smaller than surface measurements. Significant scatter exists in the test data; however, the crack growth rate and stress intensity factor range follow a straight line on logarithmic scales, indicating that the Paris Law applies to plain concrete. The slope and intercept of C50 concrete, based on 27 fatigue-failed specimens, follow a Normal distribution, with means of 16.46 and -24.81 (in N-mm units), and coefficients of variation of 0.38 and -0.38, respectively. The corresponding mean and coefficient of variation for slope and intercept by the Forman Equation are 14.80 and 0.42 and -21.18 and -0.44, respectively. The fatigue crack in C50 concrete of this study shows a faster growth rate (46.7% larger slope) than that in lower-strength concrete in the literature. With further research needs identified, this study contributes to a better understanding of the fatigue crack growth properties of ordinary structural concrete, providing valuable information for fatigue assessment and service-life extension of existing concrete bridges.