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Abstract This paper presents the results of a study about the mechanical behaviour, before and after aging, of two cement-based composites reinforced with long sisal fibres cured at early age in a CO 2 environment. After curing, samples of both composite systems were submitted to wetting and drying cycles to accelerate the aging of the materials allowing the evaluating of the efficiency of the CO 2 treatment. Besides promoting CO 2 capture, the used cure also allowed the increase in the durability of the sisal fibre-cement based composites by the Calcium Hydroxide (CH) consumption and pH decrease promoted by the carbonation reactions. The lime-pozzolanic material composite was also treated with CO 2 at early stages of formation, with the carbonation and pozzolanic reactions acting simultaneously to deplete the Ca(OH) 2 thus improving its durability. Four-point bending test, thermogravimetry analysis of the matrix and SEM analysis of the fibres were done before and after aging to study the durability mechanisms of the composites. The obtained results showed that the CH free cement-based composite containing metakaolin and fly ash presented the best mechanical behaviour before and after accelerated aging. The early age carbonation of the lime-pozolan composites improved its mechanical response, before and after accelerated aging, when compared with the non-carbonated samples. The thermogravimetry test showed that the increase of the carbonation time of the reference Portland cement-based composite consumed the C S H, compromising the ductility and strain capacity of this composite family after aging. The SEM pictures showed petrified fibre effect by the migration of hydrated products after 10 and 20 cycles of ageing for this composite system. [ABSTRACT FROM AUTHOR]

The use of Natural Fibers in cementitious composites is an innovative technical solution but, they are characterized by a complex microstructure and significant heterogeneity, which influence their interaction with cementitious matrices, whose identification requires further advances in the current state of knowledge. The present study summarizes the results of a wide series of pull-out tests carried out on sisal, curaua and jute fibers. Then, the experimental results are employed in an inverse identification procedure aimed at unveiling the key features of the aforementioned bond-slip laws. Morphological, chemical, physical and mechanical characterization of the natural fibers were correlated with the resulting bond properties within the embedding matrix. The obtained results in terms of relevant parameters, such as bond strength and fracture energy (under pull-out stresses) of the fiber-matrix interface, pave the way for future studies intended for a better understanding of the structural response of Natural Fiber Reinforced Cementitious Composites. [ABSTRACT FROM AUTHOR]

This paper analyzes the bond behavior of natural fibers in cement-based matrix. First, it presents the results of pull-out tests carried out on jute fibers embedded in a cementitious mortar. Then, the experimental results are employed in identifying the bond-slip relationship which describes the interaction between fiber and matrix. A theoretical model, capable of simulating the various stages of a pull-out test, is formulated and applied for an inverse identification of the bond-slip law. Finally, the obtained results demonstrate the soundness of the proposed theoretical interpretation for the bond behavior of jute fibers embedded in a cementitious matrix. [ABSTRACT FROM AUTHOR]

This experimental research investigation aims to explain the influence of several treatments on the sisal fiber properties and bonding strength with a cement based matrix free of calcium hydroxide. Four different treatments were studied: hornification, alkali treatment with calcium hydroxide, polymer impregnation with styrene butadiene and a combination of hornification and polymer impregnation. Modifications in the sisal fiber structure were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infra-red spectroscopy (FTIR) and scanning electron microscopy (SEM). Water absorption and direct tensile tests were performed on the fibers to determine the influence of the treatments on their physical and mechanical properties. In order to study the sisal fiber–matrix bond, pullout tests were performed in fiber embedment lengths of 5, 10, 25 and 50 mm. All applied treatments resulted in a reduction of the water absorption capacity and increase in tensile strength and stiffness. Significant improvements in the fiber–matrix interface were verified through the pullout test for the several used treatments. The hornification treatment increased the elastic and frictional bond, whereas the polymer and hybrid treatments resulted in a fiber slip-hardening behavior. [ABSTRACT FROM AUTHOR]

• Humidity variations barely altered the mechanical properties of jute fiber. • Sisal fiber presented better adhesion under the proposed humidity levels. • Humidity effect on fibers can be assessed by their cellulose crystallinity index. • Sisal fiber presented better adhesion under the proposed humidity levels. The aim of this study is to determine how the mechanical behavior of natural fibers is affected by the environmental and internal relative humidity, especially on the fiber-matrix interface. For that, curauá, jute and sisal fibers were selected. The experimental program commenced determining the fibers' mechanical properties under tensile stresses, followed by X-ray diffraction measurement, thermogravimetric analysis, infra-red spectroscopy and dynamic water vapor sorption analysis, as well as a microscopic examination of fibers' rupture under tensile stresses. In addition, a 2D finite element analysis was carried out to assist the interpretation of the mechanical behavior of the pull-out tests. The results indicate that the absorption capacity of each fiber can be correlated to the amount of hemicellulose and cellulose cristalinity, and the fibers' swelling process was influenced by each microstructure and hemicellulose content. Results from the mechanical tests showed a strength enhancement when the fibers were submitted to low levels of relative humidity, while a drastic decrease in strength was observed along with higher levels. The development of finite element models helped understanding the geometric particularities of each fibers. From the results it is possible to state a unique correlation between each fiber and its respective moisture content. It is believed that this data can help the use of such fibers as reinforcement of cement-based systems and their durability under a wider range of relative humidity levels. [ABSTRACT FROM AUTHOR]

• Temperatures until 100 °C promote an improvement on tensile strength. • Temperature does not promote substantial modification on fiber cross-section. • Temperatures over 300 °C promote a breakage on microfibrils bonding. • Sisal fiber present a good adhesion to cement until 100 °C. This experimental investigation aims to study the influence of temperature on natural fibers mechanical performance and on its interface to cement based systems. Natural sisal fiber was used on this study. Temperatures of 20, 100, 150, 200, 250 and 300 °C were used as conditions for this research. The influence of temperature on this fiber was evaluated by scanning electron microscopy (SEM), x-ray diffraction patterns (XRD), thermogravimetric analysis (TGA). The mechanical properties were evaluated by tensile test. Pullout test were performed in order to evaluate bonding on cement-based matrix after exposition to higher temperatures. The results indicate a minor modification on sisal morphology after temperature exposition until 200 °C. At 250 °C a few microcracks were observed on fiber surface, indicating a debonding of sisal fibercells and microfibrils. Sisal mechanical behavior was improved until 150 °C. This may happen due the water evaporation and shrinkage, promoting a closed and densified fiber structure. Cement main component degradation was observed before degradation of the natural fiber (around 250 °C). Bonding to cement matrix decreased after 100 °C and was maintained stable until 150 °C, and resulted in pullout forces reduction of 75% in comparison to fiber tested at 20 °C. [ABSTRACT FROM AUTHOR]

This paper proposes a study of the macauba endocarp (Acrocomia aculeata (Jacq.) Lodd. ex Mart.), to evaluate its behavior as a coarse aggregate in bio-concretes. The endocarps were characterized as to its chemical composition, anatomical characteristics, physical properties. The chemical compatibility between untreated and hot water-treated endocarp and the cement matrix was assessed using semi-adiabatic calorimetry, with a 10% endocarp-to-cement mass ratio. Bio-concretes were produced with Portland cement (CP-V ARI), substituting 25%, 50%, and 100% of the coarse aggregate volume with macauba endocarp. Mechanical characterization included axial compression and splitting tensile strength tests. The results showed that the endocarp has a bulk density of 1.23 g/cm 3 , absorption capacity of 9% and low extractive content (3.10%). Hot water treatment effectively removed extractives and improved chemical compatibility. The addition of 25% macauba endocarp resulted in a bio-concrete with a compressive strength of approximately 30 MPa. The presence of bio-aggregate enhanced concrete ductility and anchorage between bio-aggregate and matrix, suggesting its potential use in structures where energy absorption and flexibility are crucial, making macauba endocarp a viable alternative for the construction industry. • The macauba endocarp thrives as a sustainable bio-aggregate for bio-concretes. • The hot water treatment effectively reduces extractives with minimal impact in hydration. • The endocarp replaces up to 100% of aggregate, increasing fracture energy by 182%. • The bio-concrete with macauba endocarp showed improved ductility and crack control. • Bio-concrete with 25% endocarp replacement achieved structural strength (≈ 30 MPa). [ABSTRACT FROM AUTHOR]