There are continuing pressures on DTLR to increase the usage of recycled materials and industrial by-products in road construction. One such area is in capping layers, where previous studies at TRL have led to the introduction of Class 6F3 covering the use of recycled bituminous planings and granulated asphalt into the Specification for Highway Works. This project has extended the previous studies to look at mixtures of planings with other recycled roadbase layers and granular materials. The project was carried out in two phases. Phase 1 covered the literature review into published works on the use of recycled bituminous planings. In Phase 2, laboratory trials were carried out on a range of bituminous planings and granular material mixes, designed to study the effects of varying the bitumen content on compaction and settlement. Following the laboratory testing, limited pilot-scale trials were carried out on large samples compacted to representative densities, to enable the stiffness of typical mixtures to be measured in situ with a number of performance testing devices. This is the final report of the project and makes recommendations for the inclusion of a new Class 6F4 material into the current Specification for Highway Works. This would allow mixtures of bituminous planings and granular materials having the same grading as Class 6F3, but with maximum bitumen contents of 2% to be compacted using the same method as for Class 6F3, but in layers up to 250mm thickness, rather than the 200m limit imposed for Class 6F3. An outline of the proposed amendment is given in the report. (A)

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