The hybridisation of fibre-reinforced polymers (FRPs), particularly with the combination of natural and synthetic fibres, is a prominent option for their development. In the context of the construction industry, there is a notable gap in research on the use of jute and glass fibres for the strengthening of concrete structures. This paper presents comprehensive experimental results from tests on seven reinforced concrete (RC) beams strengthened for shear using synthetic, natural, and hybrid jute–glass FRP composites. The beams were reinforced using the externally bonded reinforcement (EBR) technique with U-wrap bonding. A beam without any strengthening was tested and set as a reference for the other beams. Two beams were tested with synthetic FRP shear strengthenings, one with carbon fibre-reinforced polymer (CFRP) and another with glass fibre-reinforced polymer (GFRP). The remaining tests were on RC beams strengthened with natural jute fibre-reinforced polymer (JFRP) and hybrid jute–glass FRP. The paper discusses the experimental behaviour of the tested beams in terms of vertical displacements, crack widths, and strains on steel bars, concrete, and FRP. The experimental strengths are also compared with theoretical estimates obtained using ACI 440.2R and fib Bulletin 90. The tests confirm the effectiveness of natural jute FRP and jute–glass hybrid FRP as an option for the shear strengthening of reinforced concrete beams.

Structural accidents due to punching shear failures have been reported in flat slab buildings. Design recommendations presented by codes can lead to entirely different punching shear resistance estimates for similar situations. Furthermore, design codes do not present guidelines for the design of punching shear strengthening of existing slabs. This paper uses a database with 118 experimental results to discuss the performance of theoretical estimates of punching shear resistance using ACI 318, Eurocode 2 and ABNT NBR 6118 in the case of slabs without shear reinforcement. Another database with results of 62 tests on slabs strengthened with post-installed steel and CFRP dowels is used to evaluate the performance of these strengthening techniques and to propose adaptations in codes to allow their use in punching shear strengthening situations of existing slab-column connections.

Recycled concrete aggregates are potentially interesting for the precast concrete industry as they provide a new use for high-quality waste from its products’ life cycle. In precast concrete structures, it is common to use headed bars in several connection types between structural members. This paper presents the results of experimental tests to investigate the impact of replacing coarse natural aggregates with coarse recycled concrete aggregates in the concrete breakout strength of cast-in headed bars embedded in slender structural elements. Results of 12 tests on 16 mm headed bars embedded in 500 × 200 × 900 mm concrete members with an effective embedment depth of 110 mm are presented. The percentage of replacement of natural aggregates by recycled concrete aggregates was 0%, 30%, and 100%, and the flexural reinforcement ratio of the structural elements varied from 0.5% to 3.5%. The behavior and strength of the tested specimens are discussed, and comparisons with theoretical strength estimates are presented. The results showed that the concrete breakout strength of the headed bars was not affected by the use of recycled concrete aggregates and that the flexural reinforcement ratio significantly impacts the load-carrying capacity of the headed bars as they control the crack widths before failure.

This paper examines the impacts of the total replacement of Natural Coarse Aggregates (NCA) by Recycled Concrete Coarse Aggregates (RCA) on the mechanical properties in concrete's fresh and hardened state. It also investigates the impact of RCA on the response and resistance of slab-column connections with and without shear reinforcement. The total replacement of NCA by RCA reduced by 21.8% and 37.1% the compressive and tensile strength of concrete for the concrete mix investigation. Variations in mechanical properties were observed in the concrete used for slab-column connections, but due to material heterogeneity, they could not solely be attributed to the use of RCA. Using concrete with 100% RCA reduced in 5.6% and 12.6% the punching strength of slabs without and with shear reinforcement. The load-displacement response and the cracking pattern of the slab-column connections were not affected by the use of 100% RCA.

This article presents a parametric numerical study of the pullout behavior of headed bars embedded in concrete elements. The finite element model was developed using Abaqus software and validated to simulate the behavior of four pullout tests. The numerical results were validated against the experimental results and showed excellent agreement with the load-slip response and failure modes. Furthermore, a parametric numerical study with 23 simulations was planned to explore the influence of several variables on concrete cone failure, including concrete strength, flexural reinforcement ratio, geometry and head size, shaft diameter, and edge and group effects. The ultimate load results, failure modes, and influence on ultimate load are discussed.

Este trabalho apresenta uma revisão bibliográfica abrangente sobre as aplicações da fibra de juta em Polímeros Reforçados com Fibras (PRF) como reforço estrutural em vigas de concreto armado. A fibra de juta, amplamente disponível e de baixo impacto ambiental, tem sido estudada como alternativa sustentável às fibras sintéticas, destacando-se por sua resistência mecânica, viabilidade econômica e relevância para comunidades ribeirinhas da Amazônia, onde seu cultivo é uma importante atividade econômica. A revisão aborda estudos que demonstram o potencial da fibra de juta em PRF, com resultados experimentais indicando incrementos significativos no desempenho mecânico de vigas de concreto. Em ensaios à flexão, observaram-se aumentos de resistência de até 70%, enquanto, para força cortante, os ganhos atingiram 176%, comparados a vigas sem reforço. Além disso, a utilização da fibra de juta promove alterações no modo de ruptura, redução na propagação de fissuras e aumento da ductilidade das estruturas, características essenciais para aplicações em engenharia civil. A revisão também discute os desafios associados ao uso da fibra de juta, como sua durabilidade em condições ambientais adversas e a necessidade de tratamentos superficiais para melhorar a adesão à matriz polimérica. Por fim, o capítulo sintetiza as principais tendências e perspectivas futuras, destacando o papel da fibra de juta como material sustentável e eficiente para reforço estrutural, alinhado às demandas por soluções ecoeficientes na construção civil.