Experimental and numerical investigations of non-standardised semi-circular bending test for asphalt concrete mixtures
Fracture due to mechanical loads is one of the main distresses of asphalt concrete (AC) pavement. Characterisation of fracture properties of AC is thus vital. The semi-circular bending (SCB) test is recognised as a simple but robust test to evaluate the fracture resistance of AC. Current SCB test standards adopt a fixed sample geometry of 150 mm diameter, while the 100 mm diameter sample has not standardised yet. However, in specifications for AC design and quality control purposes, such as indirect tensile test and resilient modulus, cylindrical samples with either 100 or 150 mm diameter obtained from existing pavements or fabricated in laboratories are used in parallel. This raises the question of whether the 100 mm diameter SCB sample is applicable. The literature review shows the limited investigation into the applicability of SCB test on 100 mm diameter. It also shows no clear justification for why standardised geometry is preferred compared to 100 mm one. For these reasons, this study attempts to investigate the applicability of the SCB test with a non-standardised 100 mm diameter samples using a combined experimental and numerical approach. The numerical approach is based on the discrete element method combining with an enriched cohesive damage-plasticity contact model suitable for AC. The predictive capability of the numerical model is first assessed against the experimental data. Subsequently, the validated numerical model is applied to investigate the effects of notch length and sample thickness on the fracture properties of AC. The study demonstrated that the proposed non-standardised sample geometry of SCB test can provide reliable results with high repeatability. Furthermore, with an appropriate notch length and sample thickness, the non-standardised test can produce a similar value of fracture toughness as the standardised test. These results suggest that the non-standardised test can be used to characterise the fracture properties of AC mixes.
Keywords: Asphalt concrete, semi-circular bending test, discrete element method, cohesive contact model, fracture properties