Exploring the use of recycled rubber aggregate in seismically resilient concrete structures

Abstract

This dissertation investigates the structural performance of rubberised concrete with a focus on its behaviour under static and cyclic loading. Building upon previous research conducted at the Faculty for the Built Environment at the University of Malta, an experimental programme was undertaken to compare a conventional control concrete mix with a rubberised concrete mix incorporating 25% crumb rubber replacement of fine aggregate (CR25). The experimental investigation comprised concrete cube compressive strength tests, static and cyclic reinforced concrete short column compressive strength tests, and static and cyclic reinforced concrete beam flexural tests. The experimental results confirmed that the inclusion of crumb rubber as partial fine aggregate replacement in reinforced concrete structural members leads to 56.39% and 16.16% reductions in compressive and flexural strength respectively when compared to conventional reinforced concrete structural members. However, under cyclic loading, rubberised reinforced concrete specimens exhibited enhanced deformation capacity, improved crack closure during unloading, and more ductile modes of failure. In contrast, conventional reinforced concrete specimens exhibited stiffer responses at the cost of brittle failure with reduced energy dissipation. Cyclic testing highlighted that rubberised concrete experiences accelerated stiffness degradation at higher stress levels relative to lower and moderate stress levels, where they retain superior shape recovery and damage tolerance. Overall, the experimental results obtained indicate that rubberised concrete may not be suitable for strength-critical structural elements, rather excelling in applications where characteristics such as ductility, energy dissipation, and seismic resilience are preferred. This research study demonstrates that rubberised concrete has potential as a specialised structural material in tailored cyclic and seismic environments, provided its use is appropriately supported by further research work.