Cold recycling is a road rehabilitation procedure/technique, where the reclaimed road material from rehabilitated pavements is recycled completely and used in the new structure with only small contents of new road materials. This is done preferably in-situ to save time, costs and environment. However, internationally various mix design procedures were developed since decades resulting in diverse contents of bituminous binders (emulsion or foamed bitumen) and/or mineral binders (cement or hydraulic road binder). The different material compositions result in diverse mechanical material properties and demand for different pavement designs. Based on an international comparison of cold recycling experience, commons and differences were elaborated during European CoRePaSol project funded by the CEDR. The existing definitions of various cold recycled materials were assessed and supplemented in order to introduce clear material definitions in future European specification documents. Based on intensive test campaigns suitable assessment procedures are proposed to address these materials. At the same time based on local traffic and weather conditions as well as availability of source materials, a decision model is proposed for choosing the optimum cold recycling material for the given rehabilitation project.
Cold recycling technique is a road construction method for producing a new base layer from existing road material. For in-situ cold recycling, a recycler mills the existing road structure in a depth up to 30 cm by mixing these materials with bituminous emulsion or foamed bitumen and/or hydraulic binder (e.g. cement). The composition of the mix granulates results from the structure of the recovered pavement and may contain different proportions of reclaimed asphalt, reclaimed cement concrete and reclaimed unbound material. The mix design of the new cold-recycling material is optimised for the site-specific mix granulate composition. Though, pavement structures may show inhomogeneities due to partly conducted road maintenance, road widening or former excavation works. In this study it is evaluated, in what extend inhomogeneities in pavement structure will influence the mechanical properties of cold recycling materials. Therefore, cold recycling mixtures are produced with constant binder content by varying the mix granulate composition (reclaimed asphalt, reclaimed cement concrete and reclaimed unbound material) to evaluate the sensitivity of the material performance on differing pavement structures. As a bias, it is evaluated if the binder of the reclaimed asphalt materials affects the properties of the new cold recycled material. In total eight different cold recycling mixes were produced in laboratory by varying the composition of the mix granulate material. All mixtures were produced with the same grading, a constant residual virgin bitumen content of 4% and cement content of 2%. After static compaction, indirect tensile strength after 7 and 28 days of conditioning, water susceptibility and CBR properties were tested. Limits of pavement inhomogeneity could be evaluated which may be tolerated during cold recycling mix application. Further the test results indicate a significant effect of old RA bitumen on the performance of the cold recycled material.
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