Mix design of bituminous base courses and variation assessment of indirect tensile strength for specimens compacted under gyratory compaction

The research focuses on the comparison of Indirect Tensile strength (UN EN 12697-23) and air voids content of bituminous specimens (UNI EN 12697-8) when the mix design is carried out by adopting the Marshall method (UNI EN 12697-34) and additional tests are carried out according to Italian Local Technical Specifications on road maintenance that require specimens prepared using Gyratory Compactor (UNI EN 12697-31). A total of 90 specimens were prepared of which 20 in first phase of mix design and the remaining to validate the solution. Different 4 HMA mixtures were prepared at different bitumen contents between 3.5% and 4.25% by total aggregate weight at 0.25% increments for bituminous mixture design solutions to define the optimum percentage of bitumen and Marshall Stability, Marshall Flow, Percentage of voids were in the first phase assessed. To validate the results, as discussed before, another set, outside the first one but reflecting its characteristics, was prepared and compacted under gyratory compaction. It was observed how the air voids content and Indirect Tensile Strength can change with the number of revolutions and the height of the specimen. This research may help to better understand that some Italian Technical Standard require for the acceptance of the mixture in situ