Fabric Reinforced Cementitious Matrix Research Articles

Tensile and bond properties at elevated temperatures of a PBO-FRCM composite system for strengthening concrete elements: Experimental and analytical investigations

This paper presents experimental and analytical investigations on the tensile and bond behaviour at elevated temperature of a polypara-phenylene-benzo-bisthiazole (PBO) fabric reinforced cementitious matrix (FRCM) system for strengthening concrete elements. Direct tensile (DT) and single lap direct shear tests (DS) were performed under steady-state conditions at the following temperatures: 20 °C, 85 °C, 150 °C, 230 °C and 300 °C. The results obtained were evaluated in terms of strength, stiffness, ultimate strain, load vs. slip response at the interface PBO FRCM/concrete and failure modes. Overall, the tensile and bond properties were significantly affected by the temperature increase. These results are mainly associated with the reductions of mechanical properties of the FRCM constituent materials as well as the degradation of the interaction between the fibres and the inorganic matrix at elevated temperatures. The experimental results were then used (i) to evaluate the suitability of the Aveston–Cooper–Kelly (ACK) model in describing the tensile response of FRCM at elevated temperatures and (ii) to calibrate temperature-dependent local shear bond stress vs. slip laws for the FRCM-concrete interaction.

Effect of anchorages on C-FRCM/concrete interfacial shear performance

In this study, single-lap shear tests were performed on 42 concrete specimens that were reinforced with Carbon Fabric Reinforced Cementitious Matrix (C-FRCM). The interfacial properties were enhanced through the use of fabric end-bending anchorage, a U-shaped hoop, and multiple U-shaped hoops. The bond performance of the C-FRCM/concrete interface was analyzed by examining the failure mode, ultimate stress, and interface slip of the specimens, considering four parameters: bond length of C-FRCM, number of fabric layers, fabric end-bending anchorage, and U-shaped hoop anchorage, as well as their respective mechanisms. The bond-slip constitutive parameters were calculated based on the trilinear cohesive material law and load-displacement simulation curves were obtained for each specimen through numerical simulation, which were in agreement with the test results, verifying the law's validity. Finally, the positive effect of anchorages on the constitutive parameters was analyzed.

FIRE RESPONSE OF CIRCULAR RC COLUMNS STRENGTHENED WITH PBO FRCM

The use of externally bonded fiber-reinforced system, specifically fiber-reinforced polymer (FRP) system, has increased over the past decades due to their demonstrated efficacy in enhancing the structural integrity of various RC members. However, the vulnerability of FRP systems to elevated temperatures has raised a major concern and led researchers to explore different strengthening systems. This paper investigates the fire performance of circular RC columns strengthened with poly-paraphenylene-ben-zobisoxazole (PBO) fabric-reinforced cementitious matrix (FRCM) system. Four identical columns were cast, three of which were strengthened with varying number of layers of PBO-FRCM. The fire exposure followed ASTM E119 standards. The temperature response curves were analyzed, and post-fire conditions were assessed. Initially, columns with a greater number of PBO-FRCM layers exhibited significantly lower temperatures. As the fire exposure time increased, FRCM strengthened columns experienced more significant spalling than the control column, where the reinforcement was visible from all sides. This excessive concrete spalling resulted in matching temperature readings in both the strengthened and non-strengthened columns.

Restoration of two-span RC beams with severely corroded reinforcement using C-FRCM composites

The feasibility and viability of using carbon fabric-reinforced cementitious matrix (C-FRCM) composites for restoration of continuous reinforced concrete (RC) beams with severely corroded reinforcement were examined. Five large-scale dual-span RC beams were fabricated and tested. One beam was not corroded to serve as a control. Four beams were subjected to accelerated corrosion that corresponded to a tensile steel cross-sectional loss of 40% in either the sagging or the hogging region. Such a steel cross-sectional loss would cause a comparable reduction in the yield load of bare steel reinforcing bars. Two of the corroded beams were repaired with C-FRCM composites. An analytical model was formulated and utilized to design the number of C-FRCM layers required to fully restore the original load capacity. Experimental results verified the redistribution of moments between the sagging and hogging regions due to yielding of the tensile steel at critical sections. Both sagging and hogging sections contributed to the load-bearing capacity, and hence, the reduction in the load capacity caused by corrosion in one of the critical sections was smaller than the tension steel cross-sectional loss caused by corrosion. It was possible to predict the load capacity of the tested beams with reasonable accuracy considering the residual cross-sectional area of the corroded tension steel bars while keeping their yield strength and Young’s modulus unaltered in addition to implementing other conventional assumptions adopted by international codes and guidelines. As predicted analytically and verified experimentally, rehabilitation of corroded continuous beams with appropriate number of C-FRCM composite layers fully restored their original load capacity. Research findings would assist practitioners in conducting a proper analysis of continuous RC beams with corroded reinforcement before and after repair with C-FRCM composites.

Fatigue and post-fatigue behavior of FRCM-concrete specimens under direct shear and bending conditions

The combined effect of cyclic loading and steel rebar corrosion can determine the premature deterioration of reinforced concrete (RC) structures subjected to dynamic and environmental actions. The use of fabric-reinforced cementitious matrix composites (FRCM) is a promising solution to extend the fatigue life of RC structures. Externally bonded FRCMs are applied to the tension side of structural members to reduce the rebar stress level, thus delaying fatigue crack nucleation and/or propagation. A key aspect for the design of FRCM strengthening of these structures is the matrix-fiber bond behavior under fatigue loading. In this paper, a critical review of currently available studies on the fatigue behavior of FRCM-strengthened RC beams is presented. Then, the results of 25 bond tests on PBO FRCM-concrete specimens are provided and discussed. These tests include both single-lap direct shear and modified beam tests performed in quasi-static and cyclic mode. The results obtained show that the cyclic load may induce progressive debonding at the matrix-fiber interface with rupture of fiber filaments. Modified beam tests are more affected by these phenomena than direct shear tests. The rupture of fiber filaments is confirmed by the results of post-fatigue tests that show capacities lower than those of corresponding quasi-static tests.

FRCM Confinement of Masonry: Strain Model Assessment and New Proposals.

One of the main limitations to the use of fabric-reinforced cementitious matrix (FRCM) composites for the external confinement of masonry is the lack of accurate formulas for estimating the compressive strength and ultimate strain of confined members. With the aim of providing a contribution on the topic, the authors have been carrying out studies on the FRCM-confined masonry for some time and, in a recent study, they proposed some formulations for the prediction of compressive strength. In continuity to that work, an analytical study on the ultimate strain of FRCM-confined masonry is presented in this paper, and preliminary models were derived by considering a wide experimental database compiled from the technical literature. The accuracy of the found relationships was examined based on a comparison with the few formulas published in the literature or reported in international guidelines. To this purpose, it is worth highlighting that the current Italian Guidelines CNR-DT 215/2018 do not provide indications about the estimation of the ultimate strain of FRCM-confined masonry, and the study proposed here attempts to provide a contribution to the mentioned document.

Shear Performance of the Interface of Sandwich Specimens with Fabric-Reinforced Cementitious Matrix Vegetal Fabric Skins

The utilization of the vegetal fabric-reinforced cementitious matrix (FRCM) represents an innovative approach to composite materials, offering distinct sustainable advantages when compared to traditional steel-reinforced concrete and conventional FRCM composites employing synthetic fibers. This article introduces a design for sandwich solutions based on a core of extruded polystyrene and composite skins combining mortar as a matrix and diverse vegetal fabrics as fabrics such as hemp and sisal. The structural behavior of the resulting sandwich panel is predominantly driven by the interaction between materials (mortar and polyurethane) and the influence of shear connectors penetrating the insulation layer. This study encompasses an experimental campaign involving double-shear tests, accompanied by heuristic bond-slip models for the potential design of sandwich solutions. The analysis extends to the examination of various connector types, including hemp, sisal, and steel, and their impact on the shear performance of the sandwich specimens. The results obtained emphasize the competitiveness of vegetal fabrics in achieving an effective composite strength comparable to other synthetic fabrics like glass fiber. Nevertheless, this study reveals that the stiffness of steel connectors outperforms vegetal connectors, contributing to an enhanced improvement in both stiffness and shear strength of the sandwich solutions.

Confinement of masonry with FRCM composites: Strength predictive models

Fabric reinforced cementitious matrix (FRCM) composites have emerged as an appealing alternative to fiber reinforced polymer (FRP) for the external confinement of masonry members; nevertheless, their use in practice is limited due to the lack of reliable formulas to estimate the compressive strength and ultimate strain of confined members.By following a recently published study, new formulas for the prediction of the compressive strength of the FRCM confined masonry are proposed here, which were obtained by considering an updated experimental database compiled from the literature.These formulas were developed by applying error minimization techniques to the collected experimental results; test data were treated in different ways, such as: (a) separating the members made of natural stones from those built with artificial blocks, and (b) treating separately the fiber types (basalt, carbon, glass, PBO and steel) of the FRCM system, or (c) considering the experimental data all together.Finally, to evaluate the reliability of the developed relationships, the strength predictions provided by the new proposals were compared with those obtained using the expressions reported in some international guidelines.

A state of art of review on strengthening of concrete structures using fabric reinforced cementitious matrix

Renovation, refurbishment, restoration, and retrofitting of existing structures have grown more challenging issues for the construction profession. Construction buildings are susceptible to damage at the time of the earthquake and need strengthening to enhance their strength, stiffness, and ductility. Fabric-reinforced cementitious matrix (FRCM) techniques have been recently introduced to the construction sector as a feasible solution for fiber-reinforced polymers (FRP) in strengthening application. FRCM composed of high strength fabric grids with cement-based material serve as a binder for FRCM matrices. The binder employed for FRCM composed of cement-based mortar along with polymers are added to improve the bond strength properties. The cementitious matrix utilized in FRCM has superior thermal resistance and better compatibility with the concrete surface. The utilization of FRCM matrix for upgrading and restoring the concrete members is gaining more prominence as a replacement to FRP. This work conducts a thorough analysis of the application of FRCM techniques to concrete structural members like beams, columns, slabs, and beam-column joints. This paper primarily aims to present the FRCM process on structural members and to discuss the flexural, shear, and load carrying FRCM materials that are used in the field.

Effect of reinforcement ratio and textile pre-impregnation on the mechanical properties of flax textile reinforced sulfoaluminate matrix

This study evaluates the effect of reinforcement ratio and textile pre-impregnation on the tensile behavior of flax textile, embedded in an inorganic CSA matrix (sulfoaluminate cementitious matrix), known as Fabric Reinforced Cementitious Matrix (FRCM). Two reinforcement ratios of (3 and 6%) and two impregnation techniques (polymeric and mineral) are applied. Direct tensile tests are conducted on FRCM specimens as well as on bare flax textiles featuring three configurations: NP (non-impregnated), PP (polymeric-impregnated), and PM (mineral-impregnated), between 1L (one layer) and 2L (two layers) of flax textile. The results show a direct correlation between the reinforcement ratio and the enhancement of mechanical properties, with a notable 44% increase in mechanical strength observed for NP FRCM specimens between 1L and 2L of flax textile. Mineral pre-impregnation enhances yarn-cement matrix bonding inside FRCM, while FRCM specimens with polymeric-impregnated textiles have limited influence on the mechanical properties due to premature failure. Polymeric impregnation has a pronounced effect when applied to bare flax textiles, with PP flax textiles demonstrating exceptional mechanical strength and rigidity, reaching up to 480 MPa and 37 GPa, respectively. In contrast, this effect was mitigated when employing PP textiles in FRCM specimens, where the lowest fabric efficiency reached 12% for the 2L.PP configuration suggests significant chemical incompatibility between epoxy resin and CSA matrix. Mineral-impregnated specimens display consistent efficiency regardless of reinforcement ratio, suggesting a novel and homogeneous distribution of cement matrix particles within the yarns of textiles. Two distinct failure modes of FRCM are observed in this study, a delamination for PP configurations and a fiber pullout for NP and PM configurations. No effect of reinforcement ratio is remarked on the failure mode. The cracking mode in PM FRCM configurations showcased improved aesthetics, durability, and elongation after rupture (6.28%). As a result, 2L.PM FRCM is the best configuration in terms of mechanical strength, rigidity, ductility, and durability.

Bond behavior between carbon fabric reinforced cementitious matrix (FRCM) composites with added short fibers and concrete substrates

Fabric reinforced cementitious matrix (FRCM) composites show an innovative solution for strengthening existing concrete structural elements to solve the drawbacks of organic resins in fiber-reinforced polymers (FRP) system. However, the brittle fracture of the cementitious matrix significantly reduces the efficiency of the fabric. Hence, the incorporation of short fibers into the matrix is proposed to increase the fabric efficiency. For externally bonded FRCM composites to structural element surfaces, it is a crucial issue to investigate the bond behavior at the fabric-matrix and matrix-substrate interfaces, where the effect of short fibers is non-negligible and requires further investigation. In this study, a single-lap direct shear test was used to investigate the bond behavior between carbon FRCM composites with added short fibers and concrete substrates. 36 specimens were tested and discussed by considering the effects of bond length, volume content of short fibers, type of short fibers, and bond width. The experimental results were discussed in terms of failure mode, load-slip curve, and characteristic parameters. Subsequently, the contribution of weft yarns was studied and accounted for in the developed bond-slip model, which additionally takes into account the effects of the volume content of the short fibers, the type of short fibers, and the bond width.

Influence of severe thermal preconditioning on the bond between carbon FRCM and masonry substrate: Effect of textile pre-impregnation

Fabric-reinforced cementitious matrix (FRCM) composites often include polymer-impregnated bundles to improve the exploitation of the textile mechanical properties. However, organic components may degrade when exposed to elevated temperature. In this paper, the bond behavior of a carbon FRCM applied to a masonry substrate and exposed to a thermal preconditioning up to 300 °C for 250 min is investigated. Tensile tests on the textile and flexural and compression tests on the mortar matrix, as well as single-lap direct shear tests of FRCM-masonry joints with bare and impregnated textiles, are performed. Results show that the polymeric impregnation improves the mechanical properties of the FRCM even after thermal preconditioning.

An investigation of bond behavior between composite materials (CFRP, GWMM, KPGC) and substrates (Brick and Concrete) for strengthening existing masonry structures

The use of novel composite materials to repair and upgrade existing masonry structures is a major research topic. The Rilem Technical Committee 250-CSM (Composites for the Sustainable Strengthening of Masonry) and Assocompositi (Italian Industry Association for Composite Materials) conducted a round robin test to study the properties of up to 25 types of composite materials in terms of direct tension and bonding behavior. These research results provide a more comprehensive understanding of the mechanical properties of fabric reinforced cementitious matrix (FRCM) reinforcement systems and further improve the standardization of testing procedures. However, owing to the diversity of composite materials and substrates, these results cannot be directly applied to strengthening existing masonry structures in China.In this study, we aimed to comprehensively investigate the bonding behavior between various commonly used composite materials and substrates. Three brick types commonly used in rural areas of China were selected as substrates, namely clay solid brick, shale perforated brick, and concrete hollow block, and three mainstream composite materials were selected as reinforcement materials, namely carbon fiber-reinforced polymer (CFRP), galvanized wire mesh mortar matrix (GWMM), and knitted polyester geogrid cementitious matrix (KPGC). It should be noted that both GWMM and KPGC can be viewed as FRCMs, because they comprise both a fabric and matrix. First, the mechanical properties of the composites were determined by unidirectional tensile tests. Second, single- and double-lap tests were conducted using a specially designed test setup. A comprehensive analysis of the experimental results was conducted, including failure modes, load-global slip curves, failure loads, peak stresses, and exploitation ratios. Finally, the prediction formula for the bonding load capacity of the composite materials mentioned above was explored using the experimental results recorded in this study and relevant literature. The results not only explain the bonding behavior among CFRP, GWMM, PGCM and different substrates, but also broaden the material selection scopes in the repair process of existing masonry structures in a large number of villages and towns in China.

Potential utilization of sugarcane bagasse ash in cementitious composites for developing inorganic binder

The sugar industry uses raw bagasse to generate electricity and subsequently produces tonnes of bagasse ash annually. This bagasse ash is dumped into a landfill, causing an adverse effect on the ecosystem. Sugarcane Bagasse Ash (SCBA) has gained widespread acclaim due to its sustainability and ease of use as a Supplementary Cementitious Material (SCM). SCM has been successfully used in concrete structures, but they are rarely used for the rehabilitation of concrete structures. This investigation's primary goal is to evaluate the mechanical strength of cement mortar which contains Sugarcane Bagasse Ash and Silica Fume (SF), to serve as an inorganic binder for the fabric-reinforced cementitious matrix (FRCM). Analysis using X-ray diffraction (XRD) and X-ray fluorescence (XRF) revealed the existence of amorphous and crystalline phases with silicon dioxide, which was identified as making up more than 70% of the sample. The scanning Electron microscopic (SEM) examination divulges the appearance of fibrous and tetrahedral shape in SCBA, which signify the presence of quartz mineral. The cement mortar was prepared by partially substituting cement with SCBA in a ratio ranging from 0% to 30% by weight and silica fume (SF) at a rate of 5% and 10%. Mechanical strength tests results exhibit that after 28 days of curing, the strength of cement mortar containing 10% SCBA and 10% SF was increased by 2.65% and 5.73%, respectively. A regression analysis was performed to derive a mathematical expression for the prediction of mechanical properties of mortar. This expression provides a high correlation to predict the strength with different mix proportion ratio.

Confinement of masonry columns with FRCM: A new confined strength formulation and experimental validation

In this work, a wide experimental dataset about the axial behavior of masonry columns confined with Fabric Reinforced Cementitious Matrix (FRCM) jackets (also refered to as TRM - Textile Reinforced Mortar or TRCC - Textile Reinforced Cementitious Composites), that contains the results from 226 confined specimens, was collected. Data were critically analyzed with the aim of identifying the influence of the most important parameters considered within the dataset (i.e., fibers type and number of layers, masonry type and unconfined strength, mortar type and mechanical strength, the effective lateral pressure, etc.). Further, a review of the main models proposed in different Codes and in literature was carried out, which were then applied to the dataset, highlighting some discrepancies in their predictions. Thus, a new formulation for the confined strength of masonry columns was proposed, aiming to consider also some other influencing variables such as the compressive strength of the masonry blocks and that of the mortar joint. Lastly, the validity of the proposal was verified on a new set of experimental results, which were obtained by the authors testing three unconfined and confined clay brick masonry columns. Specimens were subject to monotonic axial loading under displacement control until failure, and stress and strains were monitored continuously during the test. The jacketing system was realized with one layer of glass-based FRCM (GFRCM).

Enhancing slender reinforced concrete columns with G-FRCM jackets: Experimental and numerical analysis of confinement effects and cross-sectional shape impact

This research investigates the use of Glass Fabric Reinforced Cementitious Matrix (G-FRCM) as a confinement material for slender reinforced concrete (RC) columns with slenderness ratios greater than the slenderness criterion for isolated members. An experimental program was conducted on six slender RC columns, including two control and four G-FRCM-confined specimens. The results demonstrated that the G-FRCM strengthening strategy was highly effective, with the compression resistance of the columns increasing by 22.1% and 55.5% for one and two layers of G-FRCM, respectively, compared to the control samples. The experimental results were used to implement and validate the non-linear behaviour of G-FRCM-confined RC columns, employing the Finite Element Method (FEM) through the ABAQUS software. The results, in terms of compression strength, were consistent compared to the experiments, with a difference of less than 5%. Additionally, a parametric investigation has also been conducted to analyse the influence of the slenderness ratio on the response of confined columns. The findings of this study contribute to the understanding of the use of G-FRCM as a highly effective confinement material for RC columns.

Experimental Investigation of Concrete Cylinders Confined with PBO FRCM Exposed to Elevated Temperatures

Externally bonded fiber-reinforced polymers (FRPs) have been widely used for strengthening and retrofitting applications. However, their efficacy is hindered by the poor resistance of their epoxy resins to elevated temperatures and their limited compatibility with concrete substrates. To address these limitations, fabric-reinforced cementitious matrix (FRCM), also known as textile reinforced mortar (TRM), systems have emerged as an alternative solution. In this study, experimental tests were performed on concrete cylinders confined with FRCM systems that consisted of mineral mortar and poliparafenilenbenzobisoxazole fabric (PBO). The cylinders with concrete strengths of 30, 45, and 70 MPa, were confined with one or two FRCM layers, and were subjected to different target temperatures (100, 400, and 800 °C). The experimental results highlighted the confinement effect of FRCMs on the compressive strength of the tested cylinders. Cylinders exposed to 100 °C exhibited a slight increase in their compressive strength, while no specific trend was observed in the compressive strength of cylinders heated to 400 °C. Specimens heated up to 800 °C experienced a significant reduction in strength, reaching up to 82%.

Shear Mechanisms in Fabric-Reinforced Cementitious Matrix Overlays: Experimental and Numerical Investigation

Shear Mechanisms in Fabric-Reinforced Cementitious Matrix Overlays: Experimental and Numerical Investigation

Study on flexural behavior of BFRCM-autoclaved aerated concrete composite slabs: Effects of slab and strengthening thickness

Using basalt fabric-reinforced cementitious matrix (BFRCM) to strengthen existing masonry or concrete structures has become increasingly popular in recent years. To address the structural problems (e.g., easy cracking) caused by low tensile and flexural strength in autoclaved aerated concrete (AAC) slabs, this study demonstrates the results of an experimental and analytical investigation on the flexural behavior of BFRCM-AAC composite slabs. A group of unreinforced and five groups of composite specimens were prepared and subjected to four-point bending loads. The variables considered in the study were the thickness of BFRCM layer and slab thickness (cross-sectional height). Failure pattern, load–midspan deflection curves, and flexural performance indices of AAC slabs were compared and discussed. In general, the external BFRCM layer can significantly improve the first cracking load and peak load of AAC slabs. With the increase of BFRCM overlay thickness (reinforcement ratio), the ultimate deflections of composite slabs decreased. Finally, the results obtained from the present investigation, such as the approximately linearly distributed strain on the cross section, allowed the use of plane cross section hypothesis to predict the flexural strength of BFRCM-AAC composite slabs.

Effects of Defects on Masonry Confinement with Inorganic Matrix Composites

Fabric-reinforced cementitious matrix (FRCM) composites are currently considered a suitable solution for strengthening existing structures. Confinement applications are still being investigated, since experimental programs showed significant scatter in the results and theoretical models are struggling to become established as a consequence. The main aim of this study is the identification of potential sources of scatter in the confinement efficiency of FRCM wrappings, in defects such as fiber slip within the matrix or imperfect straightening of fibers, or premature failure of fibers once exposed after complete matrix cracking. A theoretical incremental approach is proposed to simulate such effects. The approach is incremental, but not iterative, so that no convergence is required and the incremental step size has an impact only on the smoothness of the nonlinear theoretical stress vs. strain curves of the FRCM confined material, among other simulation results. Theoretical results are compared to experimental outcomes of previous tests. The main source of variability can be identified in the cited defects, and the approach can be considered satisfactory to simulate the effects of defects and the high scatter found in experimental results; however, further uncertainties in the behavior of materials can be included in future refinements of this study.