Effect of specimen size on mode I fracture performance of hot mix asphalt at the low temperature

Abstract

The size of test specimens plays a significant role in determining the fracture characteristics of asphalt mixtures. Nonetheless, current research exploring how specimen dimensions affect the fracture behavior of asphalt concrete remains somewhat scant. This investigation employed a sequence of laboratory-based semi-circular bending (SCB) tests to examine the effect of specimen diameter on the fracture characteristics of two distinct asphalt mixtures at −10 °C. The study assessed specimens across four varying diameters − 76 mm, 100 mm, 125 mm, and 150 mm - paired with two notch-to-radius ratios of α = 0.2 and 0.4. To assess the fracture resistance, key parameters including the stress intensity factor (KIC), stiffness, and various energy metrics – fracture energy (GF), elastic storage energy (Ue), dissipated energy (Ud), and post-peak energy (Up) - were meticulously measured. Results indicated that for both AC10 and AC16 mixtures, there was a consistent increase in KIC corresponding with larger diameters for all examined notch-to-radius ratios. Additionally, this progressive rise in KIC with increasing diameter demonstrated a decreasing rate of growth, particularly noticeable as diameters approached the 150 mm mark. Maintaining a constant notch-to-radius ratio (α), the fracture energy was observed to increase in step with specimen size. With α fixed at 0.2, enlarging the diameter from 76 mm to 150 mm resulted in considerable gains in fracture energy – 53.7 % for the AC10 mixture and an even more striking 70.5 % for the AC16 mixture. With the increase in specimen size, an initial uptick followed by a subsequent decrease in stiffness was observed. This pattern is attributed to the interplay between the fracture process zone and variations in porosity distribution. The increase in α led to a discernible reduction in the magnitudes of Ue as well as its relative contribution for specimens of equivalent size. Simultaneously, as specimen sizes expanded, there was a consistent climb in the proportion of Ue, usually culminating at a specimen diameter of 125 mm, and then decreased when the specimen diameter continuously increased to 150 mm. Besides, the evolutions of Gf, Ue, and Ud were analyzed to acquire the effects of specimen size and notch-to-radius ratio (α). Statistical analysis showed that specimen size, and notch-to-radius ratio were both significant factors affecting KIC and GF, while mixture type did not emerge as a substantial factor influencing these properties within the scope of this study.