The influence of elevated temperatures on mechanical behavior was studied for curaua, hemp, and sisal natural fibers. Tensile tests were performed on fibers heated at 100 °C, 150 °C, and 200 °C for 24 h, and reference samples were maintained without thermal treatment for comparisons. The cross sectional area of the fibers was measured using a scanning electron microscope (SEM), and the image analysis was performed using the open source software Fiji/ImageJ. These data allowed the computation of the tensile stresses and the correlation of the fiber morphology with its macro-mechanical behavior. The thermal degradation behavior of the natural fibers was measured via thermo-gravimetric analysis (TGA) and X-ray diffraction (XRD). The morphological and mechanical characteristics were described and discussed on a microstructural basis. The results showed that the loss of moisture leads to a significant increase in tensile strength before reaching the limits of the degradation range.

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The measurement of cross-sectional area of natural fibers is fundamental in the determination of their mechanical properties. Several authors investigated the mechanical behavior of natural fibers and reported, for samples of same species, different values for tensile strength and elastic modulus. This variability can be due to many factors, such as plant variability, damage during processing or cutting, testing conditions and accuracy. This work presents a method for the measurement of cross-sectional area natural fibers that guarantees the dimensional integrity of the fiber and in which the measurement is performed on a plane perpendicular to its longitudinal axis. It comprises sample preparation, image acquisition on a reflected light microscope, and image analysis using the open source software Fiji/ImageJ. The method was applied to curaua, hemp, and sisal samples.

Besides the strength enhancement and strain improvement (strain-hardening behavior), the use of natural fibers as reinforcement in cement-based matrices can also be highlighted as an economical and eco-friendly alternative for the future of the construction industry. In the present work, cement-based composites reinforced by natural sisal fibers were produced and tested under direct tensile loading. The Portland cement was partially replaced by pozzolans (metakaolin -MK and fly ash -FA), aiming to produce a calcium hydroxide-free matrix to ensure the durability of the fibers. The natural sisal fibers were used in a 5% volume fraction (in mass), divided into three layers. The mechanical properties of composite plates were compared to other literature results and demonstrated to be compatible with recent research. The crack pattern was analyzed by Digital Image Correlation (DIC) for a better understanding of their failure mechanisms. The material presented a tensile strength increase after the first crack formation, marked by multiple cracking partners from this point. Finally, a comparison between direct (LVDTs) and indirect (DIC) methods of strain measurement was done and demonstrated minor results for the DIC, approximately 84% of those obtained from the LVDTs.

Today's demand for environmentally friendly and energy-efficient solutions to the construction industry has driven researchers to match natural resources with traditional technics to develop new building technologies. However, there are literature limitations about the correlation of fiber-matrix interface with the failure of natural fibers in mortar plates, which hinders the advances in understanding the mechanical properties of these composites on a structural scale. The present work investigated the mechanical behavior and fractography of cement-based composites reinforced by natural piassava and jute fibers. The experimental program included flexural tests and scanning electron microscopy analyzes. The developed composite material under flexural tests demonstrated a flexuralsoftening behavior, reaching up to 5.7 MPa, with a considerable residual strength ruled by toughness. The fractography analyses presented the fibers' structure after mechanical tests and how effective its interaction with the matrix was. The piassava fibers demonstrated significant adherence when favorably oriented, while jute fibers (used as twisted yarn) provided voids in the composite by its partial matrix-covered filaments.

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Civil construction is an industry sector that has been used as an outlet for the reuse of industrial waste. The present work aims to use the residue of Ethylene Vinyl Acetate (EVA) from the footwear industry as a partial substitute for a granulometric range of aggregates, aiming at the production of structural concrete and application to industrial floors. The proposed mixing ratios were evaluated from uniaxial compression, three-point bending, and drying shrinkage tests. The results of the uniaxial compression tests showed that the concrete with EVA addition still has enough strength to be considered structural concrete. In addition, the EVA and polypropylene fiber particles act as stress transfer bridges in the cracked zone, resulting in an increase in residual stresses and, consequently, in the toughness of the concrete in the three-point bending test. Finally, Technical Report 34 was used as a procedure to design an industrial floor based on the compressive strength, Young's modulus, and flexural behavior of the tested composites. The final result showed that even with lower compressive strength, fiber-reinforced concrete with EVA achieves greater structural efficiency for an industrial floor with the same cross-sectional height as ordinary fiber-reinforced concrete.