Brush testing of bitumen stabilised materials

Various investigations into durability brush testing of Bitumen Stabilised Materials (BSM) have been carried out in the recent past. The aim of these studies has been to determine whether the brush test can confidently be used as an indicator of a BSM’s susceptibility to premature moisture related durability problems, with the ultimate goal of potentially including brush testing to supplement the current information used for BSM classification in terms of Asphalt Academy, Technical Guideline: Bitumen Stabilised Materials, Technical Guideline 2, May 2009. The studies have experimented with various conditioning, brushing and drying regimens to find a regimen that is suitable for BSM’s. Some of the studies have also tried to relate the percentage material loss of through brush testing to the Retained Cohesion, as determined through Monotonic triaxial testing of dry and Moisture Induction Simulation Testing (MIST) conditioned samples. This was in order to suggest parameters for percentage material loss from brushing for BSM 1, 2 and 3 material classification. There appears to be a significant difference in the percentage material loss from brush between BSM foam and BSM emulsions, with BSM emulsions yielding very low losses. A strong relationship between the percentage passing the 4.75 mm sieve and the percentage material loss from brushing is apparent. A relationship between the Retained Cohesion at 100 kPa on the monotonic triaxial test and percentage material loss from brushing was also established. This paper report on these finding in more detail and offers recommendations on how to proceed with further studies to determine whether brush testing is viable on BSM’s.