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In the present work, textile-reinforced concrete (TRC) specimens were produced using high-performance natural curauá unidirectional fabrics as reinforcement. Portland cement was partially replaced by pozzolanic materials to produce a matrix with low calcium hydroxide content. Composites with different numbers of layers and thicknesses were produced. Their mechanical behaviour was evaluated through tensile testing. Crack formation was investigated using an image capture procedure and a digital image correlation (DIC) methodology. From the DIC analysis, it was possible to provide an estimate of the number of cracks, the mean crack spacing and width during the tensile tests. The curauá textile was shown to be a promising reinforcement, resulting in a composite with multiple cracking formation and strain-hardening behaviour. This newly developed composite showed similar mechanical behaviour to that of man-made fibre-reinforced composites. Combined with its low cost and sustainability characteristics, the curauá TRC may represent a good alternative to conventional construction materials. [ABSTRACT FROM AUTHOR]

The work in hand presents results of an experimental and numerical research on the post-heating residual strength of a basalt textile refractory composite submitted to tensile loading. The tensile tests were performed after a preheating process at temperatures ranging from 25 to 1000 °C. The mechanical performance and cracking mechanisms were discussed and compared to that obtained at room temperature. Image analysis by means of digital image correlation method was used to obtain the evolution of crack width which was subsequently correlated with the stress response for all target temperatures. Scanning electron microscopy was used to investigate the damage processes in the fiber–matrix interfaces after exposure to high temperatures. A finite difference model was used to simulate the tension stiffening behavior of TRC (Textile Reinforced Concrete) systems predicting their crack spacing and stress vs. strain responses. The obtained results indicated that due to the coating decomposition the reliability of basalt TRC can only be guaranteed from room temperature to 150 °C. [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]

• Sustainable composites reinforced with natural fibers can be used as shear reinforcement in R/C structures. • The reinforcement with natural fibers for shear strength is comparable to conventional reinforcement materials. • The used composite did not show any signs of delamination during shear loading. • A new shear model is proposed using experimental data from Iosipescu tests. The use of fabric reinforced cementitious matrix for shear strengthening of concrete structures has been widely investigated and its field of application is not an uncommon practice. However, the majority of previous works has been limited to synthetic or metallic fabrics. Thus, the present study seeks to investigate the shear mechanical behavior of a cementitious composite reinforced with natural curauá fabrics and its application as a shear structural reinforcement. The experimental program includes Iosipescu tests and the use of Digital Image Correlation technique for material characterization and flexural tests for strengthened structural beams. The developed composite material under shear tests demonstrated a shear strain-hardening behavior with well-defined stages. The beam externally reinforced with the composite presented an improved ultimate strength of 28%. Analytical model predictions were compared to experimental results and a good agreement was achieved. [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]

Strain-hardening geopolymer composites (SHGC) exhibit remarkable ductility, crack control and high energy dissipation capacity when subject to quasi-static tensile loading. However, their mechanical performance under dynamic loading has not yet been explored. A comprehensive assessment of possible rate effects is required to facilitate a targeted material design for various practical applications. The article presents the results of an experimental investigation on the mechanical behavior of two types of SHGC under both quasi-static and impact tensile loading. The composites were reinforced with 2% of either short polyvinyl alcohol (PVA) fiber or ultra-high molecular-weight polyethylene (UHMWPE) fiber. The experiments were performed both at the composite scale and at the fiber level. The impact tests on the plain geopolymer matrix and SHGC were performed in a gravity-driven split-Hopkinson tension bar (SHTB) at strain rates of up to 300 s−1. The tests were accompanied by optical measurements to assess specimen deformation and multiple cracking by means of Digital Image Correlation (DIC). The dynamic fiber-matrix bond properties were investigated in a miniature split Hopkinson bar. Both under quasi-static tensile loading and impact tensile loading, the SHGC made with UHMWPE fibers exhibited superior mechanical performance compared to the composite made with PVA fibers. When comparing the impact tensile performance of SHGC with normal-strength SHCC from previous studies, SHGC demonstrated higher dynamic tensile strength and energy dissipation capacity, making SHGC promising for strengthening/prospective applications against highly dynamic actions. [ABSTRACT FROM AUTHOR]

• Both K- and Na-based formulations are used for SHGC manufacturing. • Na-based SHGC achieves improved mechanical responses, with an enhanced strain capacity. • K-based SHGC do not present a typical strain-hardening curve when in presence of fine-grained sand. • When compared to typical SHCC, the developed SHGC shows a mechanically improved cracking behavior. • SHGC is expected to be used in a wide range of applications. Strain-hardening cementitious composites (SHCC) are known by their high deformation capacity due to a multiple cracking tolerance under increasing tensile loading. While SHCC have been well investigated, the design of geopolymer (GP) composites in the same context is not sufficiently understood, mainly due to varying precursor materials used in previous studies. In this work, two metakaolin-based GP mixtures were produced, using K and Na as alkali sources. The incorporation of fine-grained sand was extensively investigated to evaluate its compatibility with both strain-hardening geopolymer composites (SHGC) reinforced with short polyvinyl-alcohol (PVA) fibers. Their mechanical properties were analyzed by means of compression, bending, and tension tests. Digital Image Correlation (DIC) was used to evaluate the fracture mechanisms under uniaxial tension. Particle size distribution (PSD), X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and mercury intrusion porosimetry (MIP) were conducted. Additionally, single-fiber pullout tests with subsequent Environmental Scanning Electron Microscopy (ESEM) were carried out. NaGP composites, reinforced with fine-grained sand, yielded improved mechanical responses, reaching a strain capacity of approximately 4.5%, with enhanced multiple cracking, as opposed to the lower performance observed for KGP composites, that did not present a typical strain-hardening curve when in presence of fine-grained sand, but a strain-softening one. When compared to typical SHCC responses, Na-based SHGC showed a mechanically improved multiple cracking behavior, indicating the potential of this material for a wide range of applications, such as dynamic loading and requirements of long-term durability. [ABSTRACT FROM AUTHOR]