Análise da interface bioagregado-matriz cimentícia: efeito de recobrimentos poliméricos e matriz pozolânica

Abstract

The macauba endocarp (Acrocomia aculeata) is a promising bio-aggregate because it enhances ductility and exhibits good mechanical anchorage in bioconcrete. However, its limited interaction with the cementitious matrix leads to the formation of weak Interfacial Transition Zones (ITZs), which compromise the mechanical strength of the material. This study evaluates strategies to improve the quality of the bio-aggregate-matrix interface through surface treatments using carboxylated styrene-butadiene polymer (XSBR), either pure or combined with cellulose nanofibrils (CNF), and by employing a pozzolanic cementitious matrix with partial replacement of cement by fly ash and metakaolin. These approaches aim to improve interfacial compatibility and strengthen chemical interactions, thereby promoting microstructural refinement and enhancing interface quality. The physical properties of the bioaggregates before and after treatment were assessed by water absorption and contact angle tests, while ITZ characterization was performed using Scanning Electron Microscopy (SEM), X-ray Micro-Computed Tomography (MicroCT), and semi-adiabatic calorimetry. The mechanical performance of interfacial adhesion was investigated through pull-out and single-particle flexural tests. The polymer coatings rendered the bio-aggregate surface more hydrophobic and reduced the initial water absorption from 6.9% to 3.7% (XSBR) and 2.8% (XSBR+CNF). Semiadiabatic calorimetry showed that the XSBR coating may act either as an accelerator or a retarder depending on the matrix composition, while CNFs modulate this effect by acting as water micro-reservoirs and nucleation sites. Microstructural analysis indicated that the XSBR+CNF treatment promoted the highest ITZ densification, reducing its porosity to approximately 7.8-10.7%. Regarding mechanical performance, the treatments improved load transfer capacity, with an increase of about 32% in the maximum pull-out load for the XSBR+CNF treatment in the reference matrix. The results indicate that interface quality is controlled by the balance between moisture control, hydration kinetics, and matrix composition, rather than by the coating alone. Although the pozzolanic matrix shows potential for microstructural refinement, its effect did not result in direct improvements in interfacial adhesion at the ages evaluated. The XSBR+CNF coating stood out as the most promising strategy for achieving a denser and mechanically more efficient ITZ.