Paper Title
Mechanism-Guided Design of Rubber–Fiber Hybrid Concrete for Structural Resilience

Abstract
Addition of recycled rubber and fibers to concrete conventionally leads to lower compressive strength, which limits the structural usage and leads to the perception of inferiority of the material. The paper presents a stress-modifying mesoscale phase of composite materials in the form of a pre-mixed rubber-fiber hybrid (CRH) composite that is essentially a network of mesoscale-scale stress modifiers, which radically changes the stress transfer and crack propagation and damage evolution in M30 and M40 concretes. The interfacial transition zone (ITZ) at CRH inclusions is rethought as a graded energy-dissipation zone, which helps in deflection of the crack and redistribution of stress. A mix design strategy that is guided by mechanisms replaces the traditional percentage replacement with volumetric optimization allowing the establishment of including densities that maximize functional performance. Non-monotonic strength recovery, energy absorption, and stress redistribution trends are quantitatively measured in terms of novel dimensionless indices; Flexural Strength Recovery Index (FSRI), Stress Redistribution Efficiency (SRE), and Energy Dissipation Potential Index (EDPI). Experimental results indicate that the moderate denser transfer of stress is optimized by moderate to high inclusions of concrete, whereas the high inclusion is more effective in the dissipation of energy and decay-prone fatigue-sensitive structural components as CRH. Such limitations are the absence of full-scale seismic tests or fatigue tests and the use of mechanisms based interpretations. Such results present a new model of function-based design of rubber-fiber hybrid concrete, which does not depend on the seemingly lost apparent strength on the structural performance. Keywords - Rubber–fiber Hybrid Concrete, Mesoscale Composite Inclusions, Energy Dissipation, Stress redistribution, Functional Performance Indices, Sustainable Structural Materials