Results of surface hot-in place recycling (remix) of modified and alternative asphalt mixtures in Finland. Part I: mixture scale

Abstract

Surface hot-in place recycling of asphalt mixtures has been conducted on Finnish roads for several years. The procedure is performed either in full-lane ('remix') or shorter widths ('rut-remix'). In a 2020–2021 project, different mixture types were subjected to both kinds of recycling; reference mixtures, and mixtures modified with aramid fibres, FEP elastomer pellets, polymer, Storelastic rubber additive, recycled asphalt shingles, steel slag, and soft bitumen. This paper (Part I) presents the results of an extensive laboratory test plan at the mixture scale. Asphalt mixture cores were recovered from four roads. Various tests were performed on the mixtures in original state (aged, before recycling) and after recycling (remix or rut-remix), including strength (ITSR), stiffness, Prall abrasion, creep permanent deformation, as well as bulk, air voids, and thickness measurements. The effect of remix/rut-remix is assessed using scores calculated from mixture-scale test results. The results show that remix and rut-remix are highly heterogeneous processes, affecting every material differently and sometimes erratically. Adequate air void contents and evenness in compaction are critical for good performance. The results provide a reference performance database for an extended group of materials. Data appendices are accessible from the link at the bottom of the page.