Volumetric properties and influence of water content on the compactability of cold recycled mixtures

Volumetric characteristics significantly influence the mechanical performance and the durability of bituminous mixtures. Indeed, they are important parameters to be considered in both mix design and quality control phases. Nowadays, among compaction methods, the gyratory compactor (GC) is worldwide used for bituminous mixtures. Even if there is not a universally accepted compaction procedure for cold recycling, numerous universities and road administration agencies have employed the GC especially for bituminous emulsion treated materials. However, the presence of recycled aggregate, cement, bituminous emulsion and water requires adapting the traditional volumetric parameters to these recycled materials. This paper describes the volumetric characteristics of cold recycled mixtures based on the traditional principles used for hot bituminous mixtures. In particular, the compactability and the influence of water content on a mixture containing 50 % of reclaimed asphalt stabilized with 3 % of emulsion and 2 % of cement were investigated. Moreover, closed and slotted moulds were used to study in depth the saturation process. Results showed that specimens compacted in a closed mould, at high water contents, have a bi-linear evolution of the voids content, which defines two compaction phases. In addition, laboratory compaction using a closed mould seems to simulate better the full-scale compaction procedure. Finally, the water content that allowed the saturation state to be reached at the end of the compaction process corresponded to the optimum water content of the mixture.