Finite Element Analysis of Inclusion Stiffness and Interfacial Debonding on the Elastic Modulus and Strength of Rubberized Mortar

Rubberized concrete is one of the most studied applications of discarded tires and offers a promising approach to developing materials with enhanced properties. The rubberized concrete mixture results in a reduced modulus of elasticity and a reduced compressive and tensile strength compared to traditional concrete. This study employs finite element simulations to investigate the elastic properties of rubberized mortar (RuM), considering the influence of inclusion stiffness and interfacial debonding. Different homogenization schemes, including Voigt, Reuss, and mean-field approaches, are implemented using DIGIMAT and ANSYS. Furthermore, the influence of the interfacial transition zone (ITZ) between mortar and rubber is analyzed by periodic homogenization. Subsequently, the influence of the ITZ is examined through a linear fracture analysis with the stress intensity factor as a key parameter, using the ANSYS SMART crack growth tool. Finally, a non-linear study in FEniCS is carried out to predict the strength of the composite material through a compression test. Comparisons with high density polyethylene (HDPE) and gravel inclusions show that increasing inclusion stiffness enhances compressive strength far more effectively than simply improving the mortar/rubber bond. Indeed, when the inclusions are much softer than the surrounding matrix, any benefit gained on the elastic modulus or strength from stronger interfacial adhesion becomes almost negligible. This study provide numerical evidence that tailoring the rubber’s intrinsic stiffness—not merely strengthening the rubber/mortar interface—is a decisive factor for improving the mechanical performance of RuM.