1. Scope

This test method covers the procedures for preparation and testing cracking resistance of asphalt mixture at intermediate temperatures using semi-circular bending (SCB) geometry using monotonic loading scheme. Samples are 100 mm diameter samples fabricated with a Marshall Hammer. The SCB sample is a half-disk with a notch parallel to the loading and vertical axis. The test is for asphalt mixtures with the nominal maximum aggregate size of 19 mm or smaller. The thickness of samples prepared in laboratories should be 50 1 mm, and cores can be applied for asphalt pavement layer with the thickness of minimum 38 mm. This thickness requirement is similar to ASTM D8044 16 for the SCB test with 150 mm diameter. The suitable notch length ranges from 5 15 mm. The notch length for standard test should be 10 1 mm. The loading rate is recommended from 0.5 1.0 mm/min.

Keywords

SCB, Marshall Hammer fabrication, Cracking Resistance Index, intermediate temperature

Rationale

Cracking at intermediate temperatures is one of the main distresses in asphalt concrete pavements. Therefore, it is critical to have a reliable test method to evaluate the cracking resistance performance of asphalt mixtures for quality assurance and quality control. The Semi-circular bending (SCB) geometry is a practical, simple, and truly describe the cracking behaviour of asphalt concrete. The SCB test is accepted and used by many researchers and agencies. Currently, the available standard SCB test protocols are only for 150 mm diameter samples, including EN12697-44:2010, AASHTO TP 105-13, ASTM D8044 16, AASHTO TP 124-18. So far, there is no SCB standard test protocols developed for 100 mm diameter. The SCB standard for 100 mm diameter is important because it allows the use of Marshall Hammer Compacted samples to be tested using the SCB. Furthermore, the SCB test on 100 mm diameter can also be used for gyratory compactor samples and cores from asphalt pavement layers. The new SCB test protocol for 100 mm diameter provides more choices for agencies around the world to use the SCB test flexibly with their own available equipment. The research works conducted by the authors (Lu et al. 2019) showed that 100 mm diameter SCB samples produced acceptable and comparable repeatability with the SCB 150 mm diameter. The research work found that fracture stiffness in mode I (KI), fracture energy (Gf), and Cracking Resistance Index (CRI) of both diameters are equal or convertible, depending on the mechanical parameters used. This proposed ASTM standard is designed to standardize a new test protocol to test 100 mm diameter SCB samples. The new test standard can be used as part of the asphalt mixture design, quality control and quality assurance purposes. The users of this test method will be asphalt concrete mix contractors, Departments of Transport, and asphalt pavement consultants. Reference: Lu, D.X., Nguyen, N.H., Saleh, M. and Bui, H.H., 2019. Experimental and numerical investigations of non-standardised semi-circular bending test for asphalt concrete mixtures. International Journal of Pavement Engineering, pp.1-13.

The title and scope are in draft form and are under development within this ASTM Committee.