Experimental And Numerical Investigation of the Impact Behaviour of Geopolymer Crumb Rubber Concrete

End-of-life tyres, depletion of natural sand, and the high CO₂ footprint of Portland cement motivates the development of concretes that are both structurally capable and environmentally responsible. Geopolymer crumb-rubber concrete (GCRC) combines an alkali-activated binder with waste-tyre rubber as a partial sand replacement and is a promising candidate. However, its behaviour under localised, low-velocity impact, and its reliable numerical representation, are not yet well established. This thesis investigates the impact behaviour of GCRC through an integrated experimental and numerical programme across material and member scales, and develops a calibrated modelling route for design. At the material scale, 100-mm cubes are loaded by a hemispherical indenter in quasi-static and drop-weight regimes across two geopolymer binders and multiple rubber contents (untreated and NaOH-pre-treated). Responses are reported in three layers: absolute force–deformation and energy; strength-normalised metrics to remove the bias introduced by rubber-induced strength loss; and a strength-matched comparison between a rubberised mix and a non-rubber control to isolate composition effects from strength. This framework establishes how rubber content and pre-treatment influence localised impact response and energy dissipation while separating intrinsic rubber effects from the confounding influence of compressive strength. At the member scale, under-reinforced beams (1.6 m × 150 mm × 150 mm) cast from six representative mixes are subjected to low velocity, mid-span drop-weight impacts. Instrumentation combines an impact load cell with high-speed imaging and digital image correlation. Analysis again proceeds in absolute and strength-normalised terms, and culminating in a strength-matched pair (25% pre-treated rubber versus non-rubber control at similar strength) to quantify the intrinsic role of rubber at the structural level. This design removes compressive strength as a confounder and provides a strength-controlled picture of how rubber and its pre-treatment alter flexural impact response. A finite-element framework in LS-DYNA is developed and calibrated using the Karagozian & Case concrete model (MAT_072R3) for the six mixes, with single-element simulations informed by measured stiffness, strengths, and tensile softening. The calibrated cards are validated against the beam tests under matched geometry, supports, and impact conditions, with comparisons performed in the same three layers: absolute, strength-normalised, and strength-matched. Findings show that many perceived gains in rubberised concretes arise from differences in strength rather than from rubber alone. In the strength-matched pair, peak force, deflection history, and absorbed energy are essentially coincident, indicating that once compressive strength and softening are controlled, global low-velocity impact performance is primarily governed primarily by strength. The calibrated K&C parameters reproduce experimental force–time pulses and mid-span deflections with close fidelity and preserve the observed rankings. Therefore, within the bounds of the mixes and impact regimes tested, these results support the recycling of waste tyres in geopolymer concretes, provided that the target compressive strength is maintained through mix design or pre-treatment. This offers a defensible pathway to impact-resistant elements that are both performance-focused and more sustainable.