Sustainable foundations through in situ recycling with foamed bitumen technology (FOAM)

In Flanders, more and more attention is being paid to sustainable road structures, but rather to the pavement. In the next decades, we will also have to renew the foundations and sub-foundations of existing roads in the most sustainable way possible. Only this will allow us to perpetuate our road infrastructure, which is of primary economic and social importance, for generations to come. Abroad, we see more and more innovative use of materials for foundations: new material types (e.g geopolymers) and production technologies (e.g. emulsions, foamed bitumen). In this project, one of the promising innovative technologies was deployed: recycling old asphalt pavements into bonded foundations with foamed bitumen technology. With this technology, the existing asphalt is first milled off and crushed into an aggregate. The aggregate is then processed with a hydraulic binder and foamed bitumen to form a semi-bound mixture (FOAM). FOAM is then transported to the site and compacted (cold), just like unbound foundation material. Optionally, the process can even be done in situ, with emulsion and the foundation present. In this project, the asphalt was crushed and reduced to granules near the job site and mixed in ambient temperature to form a bitumen-bonded mixture. Being able to mill, mix and process on site mainly saves transport, leading to a lower environmental impact and economic balance. This project included a market study, an elaborated lab methodology to design quality mixtures with an alternative compaction that is more applicable to contractors, process control guidelines, an elaborated road design methodology with standard structures, the construction of two trial sections with different sections and a comprehensive LCA-LCCA calculation showing that this road structure is a favourable alternative to bonded and unbonded foundations. The use of FOAM allows more road construction materials to be economically recycled on site, with equivalent mechanical quality and less environmental impact.

Keywords:ASPHALT, BITUMEN, GEOPOLYMER, RECYCLING

Disciplines:Construction materials technology, Life cycle analysis of construction materials, Infrastructure engineering and asset management, Materials recycling and valorisation

Project type:Collaboration project

Results:This project employed one of the promising innovative technologies for use of old asphalt layers: recycling asphalt pavements into bonded foundations with foam bitumen technology. With this technology, the existing asphalt is first milled off and crushed into an aggregate. The aggregate is then processed with a hydraulic binder and foamed bitumen to form a semi-bound mixture (FOAM). FOAM is then transported to the job site and compacted (cold) just like unbound foundation material. Optionally, the process can even be done in situ, with emulsion and the foundation present. In this project, the asphalt was crushed and reduced to FOAM near the job site, mainly saving transportation. This project included a market study, an elaborated lab methodology to design quality mixtures with an alternative compaction that is more applicable to contractors, process control guidelines, an elaborated roadway design methodology with standard structures, the construction of two trial sections with different sections, and a comprehensive LCA-LCCA calculation showing that this roadway structure is a favorable alternative to bonded and unbonded foundations. The use of FOAM allows more materials to be recycled on site, with equivalent mechanical quality and less environmental impact. From the post-project survey, it is stated that most of the partners can continue to innovate FOAM independantly, but the technology should be included in the flemish standards SB250. Reports are available at https://www.uantwerpen.be/en/research-groups/emib/rers/projects/highlighted/foam/