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This work aims to describe a facile approach for sisal fiber surface functionalization based on polyphenol chemistry, and to study fiber-matrix bonding as well as durability behavior in highly alkaline conditions. The modification process was accomplished through a two-step procedure including immersion in tannic acid (TA) solution (5 and 10 g/L) followed by treatment with octadecylamine (ODA) solution (1, 2.5, 3.75, and 5 g/L). Analytical techniques were employed to examine the effect of the treatment, including Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). SEM images along with mapping analyses were obtained to evaluate the formation, chemical composition and distribution of TA-ODA layer on modified fibers. Changes in the water uptake ability were studied by water absorption and contact angle measurements. Fiber-matrix interactions were also evaluated throughout single fiber pullout tests from a cement-based matrix. To characterize the mechanical properties of the fibers before and after the modification, single fiber direct tensile tests were applied. Moreover, the stability in alkaline environments (NaOH and Pore solutions) was investigated in terms of mechanical properties degradation after fiber exposure for 28 days. The results showed that modification with a low concentration of TA and ODA solutions was efficient to reduce the hydrophilic tendency of these fibers while enhancing roughness and interlock with the cement-based matrix. Also, the modified fiber presented improved stability in aggressive alkaline environment. This work demonstrates that polyphenol chemistry could be a simple and effective sisal fiber modification alternative to enhance fiber stability and interfacial bond with cement-based matrices. [ABSTRACT FROM AUTHOR]

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 thermogravimetric 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. [ABSTRACT FROM AUTHOR]

The impact response of unidirectional continuous sisal fiber-reinforced cement composites was investigated. An impact test setup based on a free-fall drop of an instrumented hammer on a three-point bending configuration test was used. The effect of impact energy on the composite response was investigated by using three different drop heights. Mechanical properties obtained under impact loading were compared with static three-point bending tests. A comparison with the impact behavior of glass fabricreinforced composites was addressed. Furthermore, damage mechanisms were investigated by characterizing the cracking patterns during the impact event using a high-speed digital camera. It was observed that while the maximum flexural stress values were in the same range for static and impact tests, the absorbed energy increased up to a maximum level of 0.0090 kJ/in.2 (14.0 kJ/m2) for the impact energy of 20 J. The damage process was initiated by tensile and shear cracks. Delamination of the plies within the continuous fiber composites was observed only when the impact energy was 27 J. [ABSTRACT FROM AUTHOR]

Abstract: The tensile fatigue behavior of long aligned sisal fiber reinforced cement composites was investigated. The fatigue behavior was examined in terms of the stress versus cycles and stress–strain hysteresis behavior of the composites. Composites were tested at stress levels ranging between 4 and 9.8MPa which represent approximately 30–80% of the monotonic ultimate tensile strength. The composites did not fail in fatigue below a maximum fatigue level of 6MPa up to 106 cycles. Monotonic tensile testing was performed for composites that survived 106 tests to determine the residual strength. Crack spacing was measured by image analysis technique. There was no observed loss in strength, but a decrease in Young''s modulus and an increase in first crack strength was observed with increasing fatigue stress. Fluorescent optical microscopy was used to investigate the micro-crack formation in composites subject to fatigue loading. [Copyright &y& Elsevier]

Highlights • The behavior of concretes with polypropylene and sisal fibers was investigated. • Both fibers could provide similar residual strength, if at equivalent dosages. • Evaluation of fiber-matrix interface showed a similar behavior for both fibers. • The use of low alkaline matrix resulted in no degradation after ageing tests. Abstract This investigation aims to compare the mechanical behavior of concretes reinforced with polypropylene and sisal fibers. Both fibers were 51 mm long and were incorporated in fractions of 3, 6 and 10 kg/m3 into the matrices. The composites were tested under three-point monotonic and cyclic flexural loads. Pullout tests were performed to study the fiber-matrix interaction. It was observed that the sisal fiber could provide the same level of residual strength as the polypropylene fiber, as long as the equivalence of the dosages of the fibers is taken into account. The composites were classified according to fib Model Code 2010 based on parameters obtained from flexural tests. The durability of the composites was studied by assessing the flexural behavior after wetting and drying cycles. Concrete reinforced with both fibers did not present mechanical losses after the cycles. [ABSTRACT FROM AUTHOR]

The present work reports the results of an experimental program on the mechanical characterization of Reinforced Concrete (RC) beams externally strengthened/repaired by natural sisal Fabric-Reinforced Cementitious Matrix (FRCM) composite. For such, undamaged and pre-cracked RC beams were U-wrapped with a sisal FRCM composite and then tested under bending load. The results showed significant increases in shear strength, up to 25 % for beams with stirrups and 75 % for beams without them. The strengthened/repaired beams also presented stirrups yielding delay during the tests. When compared with other synthetic FRCM strengthening systems from the literature, the enhanced mechanical results of the present work were mechanically equivalent. The cracking pattern and debonding of the sisal FRCM wrap system were measured by the Digital Image Correlation (DIC) technique. The wrap application reduced the crack propagation and debonding behavior was not detected. Finally, the experimental results were confronted with an analytical approach guided by ACI 549.4R-20 and considered sufficiently accurate. • Sisal FRCM composite provided significant shear strengthening for the RC beams. • The sisal FRCM strengthening gains were comparable with the synthetic FRCM. • Experimental results and the analytical approach were sufficiently accurate. [ABSTRACT FROM AUTHOR]

• Composites reinforced with saturated sisal fibers resulted in a denser interface with smaller crack width. • The fiber–matrix interface plays a major role during creep tests in pre-cracked specimens. • During creep tests composites reinforced with saturated sisal fibers showed lower crack widths. • Composites reinforced with natural humidity fibers presented higher first crack strength but larger crack widths in static and long term tests. In the present paper, the creep behavior of sisal fiber cement based composites was investigated. The composites were manufactured using a matrix with low calcium hydroxide content, obtained by partially replacing the cement by fly ash and metakaolin. Two types of composites were developed, each with three layers of long and unidirectional sisal fibers, varying the condition of the fibers in saturated with water and with natural humidity. The mechanical behavior was evaluated through direct tension and four-point flexural tests. The composites reinforced with saturated fibers showed higher strain capacity in tension due to the properties of the fiber–matrix interface and lower ultimate bending strength. Cracking mechanisms were studied through photographs obtained during the tests, as well as analyzes by a stereoscopic microscope. All composites presented strain/deflection hardening behavior with the formation of multiple cracks. Tensile and flexural creep tests were performed on pre-cracked composites in order to study time-dependent responses. The evolution of cracks was monitored throughout the creep test with a stereoscopic microscope. The composites showed a reduction in strength and strain capacity after the creep tensile and flexural test, which resulted in a decrease in toughness of 36.9% and 48.5% for the composites with saturated fibers and natural humidity, respectively. In addition, for the flexural creep test, the composites with saturated fibers showed a decrease in toughness of 48.2% while the composite with natural humidity had a decrease of 35.3% for the load equivalent to 50% of their strength. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effective modification of sisal fibers using XSBR emulsion was developed. • The polymeric layer in sisal fiber reduces water absorption by 80%, and also minimizes fiber alkaline degradation. • Effective polymeric coating transforms sisal structure, leading to substantial changes in the fiber's mechanical properties. • Polymer-coated sisal fibers presented enhanced adhesion and stability in cement-based matrices. The performance of sisal fibers in cement-based matrices is highly dependent on the interface efficiency between the fiber and the matrix. This behavior in turn is directly related to two main factors: the sisal fiber swelling tendency and fiber alkaline degradation. To enhance these properties and consequently the fiber–matrix adhesion, this study proposed the use of carboxylate styrene-butadiene rubber latex (XSBR) as a coating for sisal fibers. Different XSBR polymers and emulsions concentrations were adopted. The effects of this treatment on various properties of the fibers such as physical, chemical, and mechanical properties were studied. The physical properties of the modified fibers were investigated by means of scanning electron microscopy (SEM) and atomic force microscope (AFM) analyses. Also, changes in the moisture absorption capacity of the coated fibers were evaluated. To study the chemical influence of the polymer coating in the modified fibers, thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) techniques were adopted. Direct tensile and pullout tests were also assessed in natural and coated sisal fibers, to mechanically evaluate the modification in terms of fiber strength and adherence, respectively. The results evidenced the formation of a new polymeric layer around the fiber, responsible to reduce the water absorption tendency of the natural fiber. The increase in the fiber–matrix adhesion obtained in the pullout evaluation was attributed to the rougher superficial aspect of the modified fibers and increased chemical interaction between the polymer and the cementitious matrix. Moreover, it was proven that the polymeric layer reduced the fiber's alkaline degradation susceptibility resulting in a more stable sisal fiber. [ABSTRACT FROM AUTHOR]

• Alkali treatment improves the mechanical performance of sisal fibers. • Stretch of the fibers during treatment procedure results in enhanced fiber strength. • Treated sisal fibers present an improved bond with cement-based matrix. • Alkali-treated sisal fibers are more stable in alkaline aggressive conditions. This work aims to evaluate the effect of alkali treatment on sisal fibers to improve the fiber properties and the effectiveness of their use as reinforcement in cement-based matrices. Alkaline solution concentration (1, 5 and 10 wt% NaOH) and post-treatment protocol (use of distilled water or acetic acid) influence were evaluated. The physical, chemical, thermal, wettability and surface characteristics were analyzed. Also, single-fiber direct tensile and pullout tests were performed. Results showed an increase in cellulose proportion with a reduction in hemicellulose and lignin content upon alkali treatment. Consequently, enhanced thermal stability and a decrease on the water uptake tendency were reached. Additionally, improved tensile properties, as well as an enhanced bond with the cementitious matrix, were found for alkali-treated fibers. Also, fibers became more stable when subjected to alkaline aggressive conditions. Thus, the alkali-treated sisal fiber seems to be an adequate and sustainable alternative as reinforcement for cement-based matrices. [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]

[Display omitted] • Post-cracking tensile strength, toughness and pull-out resistance were improved using treated fabrics. • SEM-EDS analysis suggests pozzolanic reaction of NS along the treated sisal yarns. • The peeling of yarns promoted a strain hardening response in the composites. • The combination P + NS resulted in superior pull-out and toughness performance. This work presents an experimental investigation focused on the mechanical properties of a Textile Reinforced Concrete fabricated with bi-directional sisal fabrics treated with three different procedures. The treatments consisted of immersion in a suspension of nano-silica, mechanical peeling and mechanical peeling followed by immersion in a suspension of nano-silica. Results indicated that the treatments on the fabric influenced the cracking process of the composites and were capable to improve their post-cracking tensile strength and the yarn-matrix bonding. The combination of nano-silica and peeling treatments proved to be more effective than the treatments applied independently. [ABSTRACT FROM AUTHOR]