2020 Volume 76 Issue 1 Pages 18-35
The size effect on the flexural fatigue failure of pavement concrete specimens was investigated experimentally using specimens measuring 150 mm, 300 mm, and 450 mm in height. The set ratios of stress/strength in flexure were 0.7, 0.8, and 0.9, respectively.
At the stress/strength ratio of 0.7, the number of repetitive stress cycles until fatigue failure was observed to increase with increasing specimen height, and the increase was dependent on fatigue failure probabilities. At the stress/strength ratio of 0.8, the size effect was almost negligible, and at 0.9, the numbers of repetitive stress cycles until fatigue failure of the 300 mm and 450 mm specimens were roughly the same, but greater than that of the 150 mm specimens.
Based on the results, a flexural fatigue curve consisting of three parameters, i.e. concrete slab thickness, fatigue failure probabilities, and stress/strength ratio S, was proposed in the case of 0.7≤S≤0.8, along with a flexural fatigue curve consisting of two parameters, i.e. fatigue failure probabilities and stress/strength ratio S, in the case of 0.8≤S≤ 0.9.
The usefulness of these fatigue curves was demonstrated through comparison of the fatigue cracking ratio obtained from the survey of cracks in unreinforced concrete pavement of a national highway in long use, with the fatigue failure probability at the fatigue degree of 1.0 calculated based on the proposed fatigue curves and the fatigue curve of the JSCE Standard Specifications for Pavements–2007.
By integrating these two curves, a new design flexural fatigue curve incorporating the size effect in order to contribute to practical works is proposed.
