Hybrid fibre reinforced recycled aggregate concrete: dynamic mechanical properties and durability

Research into recycled aggregate concrete (RAC) has been on the rise as there is a need to preserve natural resources and promote sustainable infrastructure practices. In our previous study, a new hybrid-fibre reinforced recycled aggregate concrete (FRRAC) with micro basalt fibre (BF) and recycled macro polypropylene fibre (PF) was developed and its physical and mechanical properties were investigated. As a continuous work, this study investigated the dynamic mechanical properties and durability of the developed FRRAC. Dynamic compressive and splitting tensile strength tests were undertaken using a Ø 100 mm split Hopkinson pressure bar (SHPB) system. The failure processes and failure modes of RAC and FRRAC specimens under different strain rates were recorded using a high-speed camera. For dynamic compressive strength, the stress-strain curves, dynamic increase factor for compressive strength (DIFf'c) and energy absorption capacities of RAC and FRRAC were evaluated and compared in the strain rate range from around 27.9 s-1 to 138.0 s-1. The stress-time histories, crack-opening displacement values and dynamic increase factor for splitting tensile strength (DIFfst) at the strain rates of around 3.03 s-1 to 8.17 s-1 of the two materials were obtained and compared. The test results indicated that RAC specimens were slightly more strain rate sensitive than natural aggregate concrete (NAC) under dynamic compression and splitting tension. On the other hand, FRRAC specimens showed similar strain rate sensitivity as their counterparts with no fibres under dynamic compression but showed lower DIFfst values with increasing strain rate under splitting tension. Empirical formulae for DIFf'c, DIFfst and energy absorption capacities against strain rates were proposed. In addition, the durability performance was assessed by examining the water absorption, volume of permeable voids (VPV), water sorptivity and chloride ion penetration resistance. Durability test results indicated that RAC and FRRAC in this study are suitable for structural applications.