IMPROVED HMAC PLANT BINDER AGING SIMULATION REPORT OF PRELIMINARY FINDINGS AND INTENDED PROJECT DIRECTION

Two procedures to simulate hot mix asphalt concrete (HMAC) plant aging are currently used. These are the rolling thin film oven test (RTFOT) and the thin film oven test (TFOT). When used for unmodified asphalts these methods are essentially identical in simulating asphalt short-term aging. However, when applied to modified binders, practitioners have encountered a number of problems with both RTFOT and TFOT procedures. Modified asphalts tend to form surface films that reduce oxygen diffusion and cause uneven aging. Many modified materials are too viscous to form good films in RTFOT bottles and are also difficult to remove after the test is completed. The objective of this research is to develop an improved test procedure and a new apparatus to address the shortcomings of the existing aging techniques. The procedure should meet the following requirements: non-prohibitive cost, similar testing time and aging effect to the RTFOT, capable of producing up to 200 g of aged material per test, no prolonged handling of hot equipment or materials, and simplified cleanup. Preliminary results show that an air blowing technique in an agitated vessel allows duplication of the RTFOT aging effect and therefore can serve as a procedure to simulate HMAC aging. Constant agitation of material by the mixer prevents film formation and enhances air diffusion through the bulk of the asphalt. The time required to achieve the same aging is the same or even shorter than specified by the RTFOT. In addition to these advantages, the ability to control sample temperature, to collect volatile compounds and to use a single, easy to clean reusable container, as well as potentially lower equipment costs and decreased handling of hot equipment should be noted.

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