Full-Scale Experiment on Foam Bitumen Pavements in an Accelerated Testing Facility

Foam bitumen stabilization is a viable alternative for reducing aggregate consumption in New Zealand. An accelerated full-scale experiment on foam bitumen pavements was conducted in the Canterbury Accelerated Pavement Testing Indoor Facility as part of a Transit New Zealand research project to study the effects of foam bitumen on unbound granular materials. Six pavement sections were tested. Three were constructed with foam bitumen contents of 1.2%, 1.4%, and 2.8% and with a common active filler content of 1.0% cement. Two more pavements were constructed with adding cement only (1.0%) and foam bitumen only (2.2%). In addition, one control section with the untreated unbound material was tested. Strains were collected with a three-dimension Emu soil strain system installed in each pavement section. Results showed that surface deflections decreased at sections with higher bitumen contents. After the application of 5,710,000 equivalent standard axles, the control section and all sections that had been stabilized with cement only and bitumen only showed large amounts of rutting. Conversely, little rutting was observed in the three sections stabilized with 2.2% foam bitumen and 1.0% cement. Water was introduced into these three pavements with additional accelerated loading; this caused the section with the lowest foam bitumen content to fail. These results showed that foam bitumen and cement had a significant effect on improving the performance of the materials studied. Material samples taken for indirect tensile strength (ITS) and repeat load triaxial (RLT) for laboratory tests showed that the ITS test was a good predictor of the pavement performance and produced a clear trend, although RLT results were not conclusive.