Mortar-based reinforcements are an innovative solution for retrofitting existing structures that combine effectiveness, compatibility, and sustainability. Despite the recent spreading of field ...applications, there is still insufficient knowledge on their fundamental mechanical properties, and a regulatory gap for experimental procedures and design criteria. A Round Robin Test initiative was organized by the Rilem TC 250-CSM (Composites for the Sustainable strengthening of Masonry) to investigate the tensile and bond behaviour of mortar-based composites with basalt, carbon, glass, polyparaphenylene benzobisoxazole (PBO), aramid and steel textiles. This paper presents the tests carried out on Steel Reinforced Grout (SRG) systems, comprising three textile and four mortar types, supplied by three producers. Ten laboratories from Italy, Poland and Portugal were involved for a total of 150 tests, including direct tensile tests on textiles and composites, and single-lap bond tests on masonry substrate. The influence of the layout of the textile, the mechanical properties of the mortar matrix, the manufacturing and curing conditions, as well as the testing setup and instrumentation, is discussed to contribute to the optimization of the reinforcement systems and to the development of recommendations for laboratory testing. Finally, results are combined to derive engineering parameters for qualification and design purposes.
•Fabric-to-matrix bond behavior in carbon FRCM with added short fibers was investigated by 75 pull-out tests.•The pullout force and toughness increased with the embedded length increased.•The ...characteristic parameter values were dependent on the type and volume content of short fibers.•The contribution of weft yarn was equivalent to the elastic response of a cantilever beam.•The trilinear bond-slip relationship considering the contribution of weft yarn can be obtained.
Fabric reinforced cementitious matrix (FRCM) composites are promising composite materials with useful properties, such as non-toxicity, fire resistance, corrosion resistance, and vapor permeability. However, the brittle failure mode, fabric efficiency, and tensile strength of FRCM composites require further improvement. Accordingly, the addition of short fibers to the matrix is proposed to improve the mechanical properties of FRCM composites, which are highly influenced by the fabric-to-cementitious matrix bond behavior. The objective of this study is to investigate the fabric-to-cementitious matrix bond behavior in carbon FRCM composites with added short fibers and to propose a method to evaluate the bond parameters. In total, 75 pullout specimens were designed to investigate the effects of short fiber type, short fiber volume content, and embedded length on the fabric-to-cementitious matrix bond behavior using double-sided pullout tests. The experimental results were evaluated in terms of the peak pullout force, displacement at peak pullout force, toughness, average bond strength, and initial stiffness. A closed-form solution was presented for the pullout force-displacement relationship based on a trilinear bond-slip model that accounted for the contribution of weft yarn. Furthermore, a method for the analytical extraction of bond parameters was proposed using the main characteristics of the experimental pullout force-displacement responses.
•Non-linear FE analysis of FRCM coupons in tension.•Experimental data characterized by a tri-linear behavior with large experimental scatter.•Utilization of elasto-plastic and elasto damaging 2D FE ...approaches.•Analysis of 3D FE models with geometric and mechanic imperfections to explain data scatter.•Sensitivity analysis conducted varying the parameters characterizing the imperfections.
Existing masonry structures often need to be strengthened or repaired. In many cases, the intervention is realized using composite materials bonded to the surface of the structural element.
In many masonry structures the use of fabric reinforced cementitious matrices (FRCM) is preferred to the fiber reinforced polymers (FRP).
The typical experimental stress–strain behavior exhibited by a FRCM composite under a direct tensile test is a tri-linear curve with a first phase that increases linearly according to mortar Young’s modulus, a second phase where the cracks in the mortar start to grow, and a last phase in which the mortar is fully cracked and the curve assumes the same slope of the stiffness of the fabric. According to a wide experimental campaign conducted on the subject at the Politecnico di Milano, the curves exhibit a relatively wide scatter, especially in the second phase, making the standardization of the direct tensile test a rather difficult task.
With the aim of having an insight into the observed experimental variability, a comprehensive FE numerical analysis was conducted and is presented in this paper. Two different FE codes were utilized. One with less sophisticated material models, the second with the possibility to deal with softening and damage in the post peak range. The use of commercial codes instead of home-made models was voluntary, with the precise final aim of enabling other researchers the reproduction of results with similar models and for analogous experiments. Three different variables that can affect the mechanical behavior in tension were examined (non-planarity of the composite grid, bending of the specimen and pre-existing micro-cracks), leading to three different sets of simulations.
A final objective of the numerical simulation was to study and compare possible constitutive models for the cementitious matrix to simulate the experiments. At this aim, three different material models were used for mortar belonging to FRCM specimens in tension.
The numerical results obtained satisfactory reproduce experimental evidences and provide a justification of the relative large scatter of the data.
This paper reports an experimental programme on masonry walls composed of handmade solid clay brick and hydraulic lime mortar. Reversed cyclic shear compression tests were carried out on the walls in ...three different configurations: unreinforced, repaired and retrofitted, and just retrofitted. Damaged walls were repaired and retrofitted with Basalt Textile Reinforced Mortar (B-TRM) and tested again to investigate the recovery of strength, stiffness and the improvement in drift capacity. The repair consisted in filling the open cracks and replacing the damaged bricks by following the so-called “scuci-cuci” technique. The just retrofitted configuration consisted of externally bonded B-TRM on undamaged walls. The B-TRM system comprised continuous bidirectional grids of basalt fibre embedded in hydraulic lime mortar on both surfaces of the walls. The experimental results showed the suitability of the proposed solutions for seismic retrofit and post-earthquake repair of existing masonry buildings. The research results highlighted the capacity of the proposed repair technique to reinforce damaged walls and the effectiveness of the investigated B-TRM system in increasing the resistance, the ductility, and the energy dissipation of unreinforced clay brick masonry. In addition, the results allowed a better understanding of the behaviour of masonry walls subjected to cyclic horizontal displacement in terms of failure mechanism and displacement capacities.
•Debonding occurred at the matrix–fiber interface.•A global width effect was not observed.•After the onset of debonding friction contributed to the increase of the load.•The effective bond length ...leff due to bond was estimated to be 255mm.•Cohesive material law and fracture energy were obtained from strain profiles.
The results of single-lap shear tests, conducted on specimens with fiber reinforced cementitious matrix (FRCM) composite strips bonded to concrete blocks, are presented in this paper. The FRCM composite was comprised of polyparaphenylene benzobisoxazole (PBO) fibers and polymer-modified cement-based mortar. This study indicates that in PBO FRCM–concrete joints debonding mainly occurs at the matrix–fiber interface. Friction between fiber filaments and between fibers and matrix is observed after the debonding process initiates. The experimental data suggest that a width effect does not exist among the fiber bundles, and an effective bond length can be defined and is approximately 260mm. Axial strain profiles along the bonded length are analyzed to investigate the stress-transfer mechanism at the matrix–fiber interface.
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•Fiber and matrix treatments tend to improve the mechanical behavior of cementitious matrix composites.•The use of treatments in cementitious composites increases the fiber–matrix ...interaction, improving the mechanical behavior of the composites.•Short vegetable fibers used as internal reinforcement improve the flexural and tensile strength and the toughness of cement-based composites.•Long vegetable fibers used as external reinforcement increase the strength and ductility of cementitious matrix composites under compression.•Vegetable fibers are mostly used in non-structural applications such as roof tiles, tiles, and masonry elements.
The need for sustainable building materials has progressively increased the interest in the use of vegetable fibers as reinforcements in cementitious matrix composites. These fibers are renewable, inexpensive, and offer other advantages, such as lightness, stiffness, biodegradability, and high impact resistance. This review presents research conducted in this field over the last 20 years. For this purpose, the most commonly used fibers and the treatments used to improve the mechanical properties of composites were identified. Moreover, the effect of fiber length on the mechanical properties of the reinforced composites was discussed. Some applications of vegetable-fiber-reinforced composites in structural and nonstructural elements have been highlighted. Based on the results, the treatment used the most was highlighted, which was matrix modifications that reduce the cementitious paste alkalinity by improving the fiber interactions within the composite. Furthermore, short fibers significantly increased the flexural and tensile strengths, and toughness of fiber-reinforced cementitious composites (FRCC), whereas long fibers, used as external reinforcement, increased the compressive strength of textile-reinforced cementitious composites (TRCC) by limiting lateral concrete expansion and abrupt failure. Despite the enhanced mechanical properties of fiber-reinforced composites, information related to fiber durability in cementitious matrices is limited thus far, which has restricted their application in primary structural elements that have high force demands.
Fabric Reinforced Cementitious Matrix (FRCM) materials are composed of a dry fiber grid embedded in an inorganic matrix, which may contain short fibers.
These materials are particularly well-suited ...for the reinforcement of masonry structures due to their high compatibility with the substrate, vapor permeability and durability against environmental agents.
The most important information needed for the characterization of these composite systems, for use as strengthening materials of masonry structures, are the tensile behaviour and the shear bond properties. A Round-Robin Test was organized by the RILEM Technical Committee 250-CSM and the Italian association Assocompositi in order to experimentally characterize different FRCM systems composed of PBO, carbon, glass, basalt, aramid and steel textiles embedded in cementitious or lime-based mortars. The systems were tested at different universities and research centers in Europe in order to investigate the influence of samples preparation, test set-up and instrumentation.
In this paper, the experimental tests performed on Carbon-FRCM systems are described and discussed. Important aspects are analyzed herein: differences in the testing procedure and instrumentation, influence of textile geometry and mechanical properties of the constituent materials, importance of specimen preparation and curing conditions. Moreover, a comparison between tensile and shear tests is reported in order to determine a reliable procedure towards the complete characterization of an FRCM material.
This paper reports on the flexural behavior of corrosion-damaged reinforced concrete (RC) beams strengthened with different fabric-reinforced cementitious matrix (FRCM) composites. Three groups of ...beams were subjected to accelerated corrosion for 70, 140, and 210days to obtain theoretical mass loss in their tensile steel bars of 10%, 20%, and 30%, respectively. The test parameters included the fabric type (PBO and carbon), the number of FRCM layers (two, three, and four), and the strengthening Scheme (end-anchored and continuously wrapped). Test results showed that FRCM composites governed the failure of the strengthened beams rather than the damage level to which the beam was subjected due to corrosion. The reported load-carrying capacities of the corrosion-damaged beams confirmed that the contribution of FRCM composites significantly offset the impact of corrosion damage on strength. FRCM-strengthened beams exhibited an increase in strength that ranged between 7 and 55% of that of the virgin beam based on the type, the axial stiffness, and the Scheme of the FRCM used. The strengthened beams showed energy absorption indices that ranged between 111 and 153% of that of the virgin beam. The theoretical formulations of ACI-549.4R-13 reasonably predicted the ultimate strengths of the end-anchored strengthened beams but underestimated those continuously anchored beams.
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