Mechanical properties of polypropylene fibre reinforced recycled concrete aggregate for sustainable road base and subbase applications

There is limited research on the dynamic behaviour of soils reinforced with polypropylene (PP) fibres and a scarcity of literature on using PP fibres to improve the mechanical properties of recycled construction and demolition (C&D) waste subjected to dynamic wheel loads. To fill these research gaps, this study introduces varying proportions of PP fibres (0%, 0.1%, 0.2%, and 0.3% by dry weight of recycled concrete aggregate (RCA)) to enhance unbound granular RCA for pavement base/subbase applications. Incorporating PP fibres resulted in increased unconfined compressive strength, primarily attributed to the reinforcement effect of the fibres, which improved the tensile strength and resistance to stretching between aggregates and hindered the development of tension cracks through a bridging mechanism. Moreover, the enhanced stretching resistance between RCA particles, achieved by incorporating PP fibres, led to a 7% increase in Mr when the PP content was increased from 0 to 0.1%. Incorporating PP fibres into RCA also reduced permanent deformation and permanent strain rates. Notably, adding 0.1% PP fibres yielded the most favourable outcome in terms of permanent deformation response, transforming the behaviour of RCA from “Incremental Collapse” to “Plastic Creep.” This distinctive characteristic makes the blend of RCA with 0.1% PP fibres suitable for application as base and subbase layers.