Highlights of AAPT 2016 Conference:
The Leading Edge Workshop kicked off the conference with group discussions on each performance test. A panel of experts then discussed the common questions for each test. Minnesota is currently beginning to implement the Disk-Shaped Compact Tension Test (DCT). This test is performed at low temperatures to test for the cracking performance of the mixture. Some debate was on the baseline for the appropriate fracture energy (J/m^2) . It was recommended that each state decide on the baseline for their region.
Andrew Hanz with MTE Services Inc presented on the field performance of high RAP mixtures on 4 projects in 2014 & 2015. These projects used performance tests to evaluate cracking and rutting performance. The DCT, SCB and Hamburg were used. Some of the logistical challenges were agency approval of mix design and test strip results. The minimum lag time between test strip and construction was ~10 days. The approach to the project was:
1) Characterize the RAP by extracting the binder to determine PG grade
2) Determine the binder properties by applying blending charts
3) Volumetric mix design
4) Verify binder properties
5) Evaluate the hamburg for rutting potential
6) Evaluate cracking resistance with performance tests
Observations after 1 year in service appear to be performing well. There are very few transverse cracks on the sections.
Balance mix design was presented with various perspectives. The contractor perspective was presented by Shane Buchanan with Oldcastle Materials. Overall, the goal of balanced mix design is to optimize the field performance of rutting vs cracking. Performance test need to utilize practical approaches to find solutions to problems. In general, performance tests could be a way to allow contractors to innovate mix designs.
Other states presented on their implementation on balanced mix design. Various states use different performance tests on their pilot projects. The objective is to have a simple, affordable and meaningful set up test to predict flexibility and stiffness of the mix.
AAPT sends out all the papers to members each year. For more information visit http://www.asphalttechnology.org/