Study of recycled aggregate concrete mechanical behavior using multiscale modeling by MEF

Author(s)

Marcela Gimenes

• Document type: Master's Dissertation
• Press: Bauru. 2020-05-28.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Engenharia. Bauru
• Defense date: 2020-04-27
• Advisor: Osvaldo Luís Manzoli; Eduardo Alexandre Rodrigues

Abstract

This research presents a numerical analysis proposal for recycled aggregate concrete (RAC), whose recycled aggregates are obtained from the crushing of concrete waste. The developed tool facilitates the mechanical behavior evaluation of the RAC, verifying the feasibility of its use for structural purposes. Considering that in Brazil the current use of the material is still quite limited in comparison with other countries, the RAC could be used more widely and properly, bringing structural, economic and mainly environmental advantages. Due to the occurrence of mesoscopic specificities, the RAC modeling requires a more refined scale model to represent the altered properties of recycled aggregate, so that a recycled aggregate generator was developed to represent its variable composition. The failure mechanisms that occur at the several interfaces of the recycled aggregate (RA) and concrete matrix introduce nonlinearity to the mechanical problem. In order to represent this nonlinearity, the proposed modeling strategy uses the finite element mesh fragmentation technique together with robust and stable damage constitutive model. This fragmentation technique is based on the use of finite elements with high aspect ratio, which can be used to represent the additional phases of this composite material, corresponding to the different mesoscale RAC intrinsic interfacial transition zones (ITZs), as well as potential pathways for the propagation of fractures. A constitutive model based on the Continuum damage mechanics is used to represent the non-linear behavior of these different RAC phases, which together with the cited fragmentation technique are valuable tools for the study of the influence of recycled aggregate on the mechanical behavior of concrete. The validation of the methodology occurred through preliminary tests for calibration of parameters and later through simulations of more advanced cases carried out in experiments in which the qualitative and quantitative numerical results obtained are compared with the respective experimental results from the literature. A great correspondence between the results was obtained in most of the simulated cases, indicating that the model is capable of representing the RAC in the 2D distribution of aggregates, simulation of ITZs and in the propagation of cracks due to tension damage. The influence of RA was greater in concretes with higher matrix strength and, in addition, a partial substitution of up to 25% of natural aggregate (NA) by RA did not produce a great loss in resistant capacity. (AU)

• FAPESP's process: 18/05784-3 - Study of recycled aggregate concrete mechanical behavior by FEM multiscale modeling
• Grantee: Marcela Gimenes
• Support Opportunities: Scholarships in Brazil - Master