Textile Reinforced Mortar Systems Research Articles

A multi-performance comparison between lime, cementitious and alkali-activated TRM systems: Mechanical, environmental and energy perspectives

The combined need to propose new solutions for the structural reinforcement of existing buildings and for the reduction of CO2 emissions is leading to the development of more sustainable composite materials, such as those based on alkali-activated mortars (AAM). In this study, different formulations of AAM, based on metakaolin or fly ash, have been evaluated as possible matrices for Textile Reinforced Mortar (TRM) systems. Two different bidirectional textiles, made of AR glass or basalt fibers, were used as internal reinforcement. The physical-mechanical properties of TRM systems based on AAM were evaluated and compared with those of commercial systems with cementitious or lime-based matrices. Direct tensile tests on TRM coupons and shear bond tests on clay brick substrates were carried out. Then, their energy and environmental-related performance have been compared. Results showed that alkali-activated matrices can be very promising and eco-friendly alternative solutions to traditional mortars in TRM systems.

Enhancing Load-Carrying Capacity of Reinforced Concrete Columns with High Aspect Ratio Using Textile-Reinforced Mortar Systems

Enhancing Load-Carrying Capacity of Reinforced Concrete Columns with High Aspect Ratio Using Textile-Reinforced Mortar Systems

Bond of textile-reinforced belite calcium sulfoaluminate cement mortar to concrete substrate

The fast aging of existing building stock requires effective and sustainable strengthening solutions. Textile-reinforced mortars (TRM) have already proved to be very effective as well as versatile retrofitting solutions for reinforced concrete and masonry structures. TRMs can enhance the load bearing capacity of reinforced concrete structures; however, current TRM systems are based on standard Portland cement-based binders, which largely contribute to global human-induced CO2 emissions. This work, for the first time, explores the use of belite calcium sulfoaluminate (BCSA) binder for carbon textile reinforcement through a cross-disciplinary study combining structural engineering and materials science. An experimental study was carried out on concrete block members with externally bonded strips of carbon textile-reinforced mortars, similar to a typical TRM retrofitting system for concrete beams. The textiles were embedded in an ordinary Portland cement-based (OPC) binder or in a BCSA-based binder to compare the bond behaviour to the concrete substrate. The tests revealed a superior bond between the BCSA mortar and the concrete, as well as outstanding adhesion to the textiles achieved using the BCSA binder, with performance levels largely surpassing those measured in their counterparts that used the OPC-based binder. Scanning Electron Microscopy, X-ray diffraction, and thermogravimetric analyses were used to understand this behaviour difference and it was concluded that the ettringite phase is responsible for the enhanced performance in the studied system. The results of this study suggest that BCSA binders have the potential to be a more effective and “greener” alternative to the standard binders based on Portland cement in TRM strengthening applications.

Development and performance evaluation of a novel high-ductility fiber-reinforced lime-pozzolana matrix for textile reinforced mortar (TRM) masonry strengthening applications

This paper discusses the development of a high ductility fiber reinforced lime mortar with deflection hardening behavior. In this study, polypropylene fibers have been incorporated in a cementless reference matrix comprising of Natural Hydraulic Lime, silica fume, siliceous aggregates and workability aid admixtures. The properties of the reference and fiber reinforced mortar compositions were assessed by means of standardized laboratory tests and scanning electron microscopy. The reference composition gave an average compressive strength of 12 MPa, rendering it suitable for structural applications. Fiber addition at a dosage of 0.76% by wt. of solids led to a reduction of the compressive strength; however, sufficient load bearing capacity was still achieved (8 MPa). More importantly, the fibers enabled the mortar to sustain useful load after damage initiation, improving post-peak ductility under compression and allowing the material to reach bending stresses up to 20% higher than the first-crack strength. To evaluate the practical application of the proposed materials, their use as matrices in textile reinforced mortar (TRM) strengthening systems was investigated through pilot applications on stone masonry. Diagonal compression tests were performed on 9 ashlar masonry wallettes, including both un-retrofitted and TRM-retrofitted specimens. Single-sided TRMs consisting of alkali resistant glass textiles embedded in either the reference or the fiber reinforced mortar were considered. Specimens retrofitted with TRM constructed using the fiber reinforced mortar, exhibited a remarkable ~ 270% increase in shear strength and > 50% higher deformation capacity, compared to un-retrofitted ones. The strength increment achieved with the reference mortar as the TRM matrix was 80%, with minimal impact on ductility. The TRM comprising the fiber reinforced mortar also showed superior performance in terms of ability to retain integrity at high levels of shear deformation. Overall, the results indicate that the use of fiber reinforced lime matrices in TRM systems applied to masonry substrates has the potential to substantially enhance mechanical performance under in-plane loading, even in cases where only single-sided retrofitting can be realized.

Out-of-plane performance of structurally and energy retrofitted masonry walls: geopolymer versus cement-based textile-reinforced mortar combined with thermal insulation.

This paper examines the out-of-plane performance of masonry walls (representative of infills in reinforced concrete frames) which have been upgraded with an outer skin of integrated structural and an energy retrofitting system. The benefits of such an integrated system are mainly cost-related. Nevertheless, before moving to full-scale applications, additional benefits to the structural performance need to be investigated. In this study, the examined configurations of this composite system comprised either thermal insulation boards bonded directly to the wall followed by layers of textile-reinforced mortar (TRM), or thermal insulation boards bonded in-between two TRM layers. Other than the retrofitting layers configuration, the following parameters were also investigated: a) the binder type (cement-based versus geopolymer-based mortars), and b) the textile type (open mesh glass fibre textile versus basalt fibre textile). The results of this experimental study are discussed in terms of failure modes, post-cracking stiffness and ultimate capacities. Overall, this study highlights the mechanical benefits of the TRM plus thermal insulation system while providing insights on the bond performance between the different materials selected. An important finding is that the integrated system is even more effective than a standard TRM application. Finally, the geopolymer mortar seems to be equivalent in terms of performance to the commercially available cement-based mortars.

Tensile behavior of textile-reinforced mortar: Influence of test setup and layer arrangement

Textile-reinforced mortar (TRM) systems are a popular solution for strengthening existing masonry structures these days. The vast application of these materials requires a thorough study of their properties and performance. The tensile behavior of TRMs has a significant role in their mechanical properties and requires a reliable setup to record their performance. Studies in the past focused on different gripping systems and setups for characterizing tensile behavior, but harmonization is still lacking. The present study aims at presenting a suitable setup for tensile testing. To this aim, two different TRM systems were utilized. Four different setups for the clamping of coupons were used: three of them were based on gripping textiles directly, while the other one was based on gripping the mortar. Also, the effect of the textile-to-mortar strength ratio variation was studied for different setups, and using a different number of plies and different mortar thicknesses. Furthermore, digital image correlation was used for all specimens to track cracking patterns and failure modes. Finally, a comprehensive discussion of the results is presented, and the most suitable testing setup is recommended.

Failure Mode Prediction of Unreinforced Masonry (URM) Walls Retrofitted with Cementitious Textile Reinforced Mortar (TRM)

The brittle failure of unreinforced masonry (URM) walls when subjected to in-plane loads present low shear strength remains a critical issue. The investigation presented in this paper touches on the retrofitting of URM structures with textile-reinforced mortar (TRM), which enables shifting the shear failure mode from a brittle to a pseudo-ductile mode. Despite many guidelines for applying composite materials for retrofitting and predicting the performance of strengthened structures, the application of TRM systems in masonry walls is not extensively described. A thorough retrospect of the literature is presented, containing research results relating to different masonry walls, e.g., bricks, cement, and stone blocks strengthened with TRM jackets and subjected to diagonal compression loads. The critical issue of this study is the failure mode of the retrofitted masonry walls. Available prediction models are presented, and their predictions are compared to the experimental results based on their failure modes. The novelty of this study is the more accurate failure mode prediction of reinforced masonry with TRM and also of the shear strength with the proposed model, Thomoglou et al., 2020, at an optimal level compared to existing regulations and models. The novel prediction model estimates the shear failure mode of the strengthened wall while considering the contribution of all components, e.g., block, render mortar, strengthening textile, and cementitious matrix, by modifying the expressions of the Eurocode 8 provisions. The results have shown that the proposed model presents an optimum accuracy in predicting the failure mode of all different masonry walls strengthened with various TRM jackets and could be taken into account in the regulations for reliable forecasting.

Seismic behaviour of RC columns retrofitted with textile-reinforced mortar (TRM) optimized by short PVA fibres

Textile-reinforced mortar (TRM) optimized by short polyvinyl alcohol (PVA) fibres was used as a strengthening material for seismically deficient reinforced concrete (RC) columns. Seven RC columns, including a reference column, a column strengthened with the inorganic matrix added short PVA fibres, and five columns strengthened with the optimized TRM, were subjected to low-frequency cyclic loading. The influences of the reinforcing ratio of carbon textile and axial load ratio on the seismic performance of the jacketed columns were studied. The results showed that the shear capacity and deformability of RC column respectively increased by 54.3 ∼ 55.2 % and 40.34 ∼ 78.62 % after strengthening with the optimized TRM system. Increasing the reinforcing ratio of carbon textiles in the strengthening layer, the displacement ductility and energy dissipation of the jacketed column were further enhanced. As the axial load ratio increased, the shear capacity of the jacketed column increased; however, the corresponding ductility and energy-dissipation ability decreased. The relationship between the shear contribution and material configuration of the TRM was established. The shear capacity of the TRM-strengthened columns can be estimated by a modified shear model considering the reinforcement ratio of textile and the volume content of PVA fibres.

Experimental Characterisation of Lime-Based Textile-Reinforced Mortar Systems Made of Either Jute or Flax Fabrics.

Existing buildings are often in need of strengthening interventions, and several technical solutions have been recently developed for this purpose. Among them, the use of textile-reinforced mortar (TRM) composites has gained consensus as a technically viable and economically convenient option. Moreover, TRM has the potential to be employed as a reversible and sustainable strengthening technique for masonry buildings. In this context, the present paper aims to investigate the mechanical properties of TRM systems consisting of sustainable phases, such as lime-based matrices and natural fabrics produced by waiving fibers obtained from plants, such as Jute or Flax. This class composite system can be referred to as natural TRM and is denoted by the acronym NTRM. The present study moves from the geometric and mechanical characterisation of fibres and fabrics and, after having also investigated the properties of the mortar, it reports the results of tensile tests carried out on specimens of the NTRM systems under consideration, with the main aim of providing the empirical bases of the relationships between the geometric and physical properties of the constituents and the resulting mechanical response of the composite system. The obtained results show that the considered Flax-TRM system has an apparent composite behavior, as its response to tension is clearly characterised by the well-known three stages corresponding to the elastic response, the formation of cracks, and the reinforcement response up to rupture. Conversely, the Jute-TRM system needs to be further improved in terms of balance between the properties of the matrix and the internal reinforcement. Further studies will be devoted to this specific aspect and, more generally, to investigating the relationships between constituents' properties and the NTRM behavior.

Out-of-plane strengthening of URM walls using different fiber-reinforced materials

Fiber-reinforced polymers (FRPs), textile-reinforced mortars (TRMs), and engineered cementitious composites (ECCs) have been extensively employed to address the insufficient load-carrying capacity and low deformation capability of unreinforced masonry buildings. In this study, eight groups of unreinforced masonry walls were built to test the efficiencies of various reinforcing methods under out-of-plane four-point loading. A high-strength mortar reinforcement were employed as benchmarks. Four types of ECCs—low-cost, high-strength, lightweight insulation, and high-toughness ECCs—were compared with carbon FRP (CFRP) sheet and TRM systems. The failure modes, midspan load–displacement actions, energy absorption capabilities, initial bending stiffness values, and ductility of the different reinforcement systems were obtained and analyzed. The results revealed that the TRM-reinforced specimens experienced the maximum midspan deformation. The best ductility and maximum bearing capacity were obtained respectively after reinforcements with high-strength and high-toughness ECCs. However, the exploitation of the CFRP sheet was limited owing to excessive reinforcement. Finally, the moment capacity was evaluated using a flexural model. For the specimens that failed in the shear mode, a shear model based on the equilibrium condition was established to predict their load-carrying capacities.

Effect of early curing and substrate preparation conditions on the physical and mechanical properties of TRM-masonry composites

• The effect of different curing conditions on TRM composites performance is investigated. • The influence of moisture content bricks on TRM-to-substrate bond behavior is investigated. • The development of the fiber-to-mortar bond behavior is influenced by the curing conditions. • The substrate initial water content affects the TRM-to-substrate bond behavior. Textile reinforced mortars (TRMs) are innovative sustainable composite materials that recently received extensive attention for strengthening of masonry structures. Understanding the mechanical performance of these composites has therefore been the subject of many recent studies. However, most of these investigations have focused on the mechanical properties of these composites under controlled laboratory conditions, and their performance under field conditions is still unknown. The critical role of substrate preparation and curing conditions on the performance of these repair systems have never been addressed before. To address this gap, this paper presents an experimental investigation on the role of these factors on the performance of two different TRM systems (a steel-based TRM and a glass-based TRM) commonly used for strengthening masonry structures. The results show the importance of these factors and the need for the identification of standard procedures for the application of these systems aiming the optimization of their performance in the field.

Experimental Investigation of the TRM-to-Masonry Bond after Exposure to Elevated Temperatures: Cementitious and Alkali-Activated Matrices of Various Densities.

Limited research has focused on the effect of high temperatures on the textile-reinforced mortar (TRM)-to-masonry bond. In this study, masonry prisms that were furnished with double-layered TRM strips were tested under shear bond conditions after their exposure to 200 °C and 400 °C for 1 h using the single-lap/single-prism setup. A total of four TRM systems were applied sharing the same type of textile –a dry AR glass fiber one– and different matrices: two cementitious matrices, namely a normal-weight (TRCNM) and a lightweight (TRCLM) one, and two counterpart alkali-activated matrices (TRAANM and TRAALM) based on metakaolin and fly ash. Specimens’ exposure to elevated temperatures did not alter their failure mode which was due to the sleeve fibers’ rupture along with core fibers’ slippage from the mortar. The residual bond capacity of the TRM systems decreases almost linearly with increasing exposure temperature. The alkali-activated textile reinforced mortars outperformed their cement-based counterparts in terms of bond strength at every temperature. All systems retained close to 50% of their original shear bond strength after heating at 400 °C. Per the type of binder, lightweight matrices resulted in either comparable (cement-based systems) or better (alkali-activated systems) heat protection at the TRM/masonry interface.

Diagonal Tensile Test on Masonry Panels Strengthened with Textile-Reinforced Mortar

This study presents the results of an experimental and numerical program carried out on unreinforced masonry panels strengthened by textile-reinforced mortar (TRM) plastering. For this purpose, five panels were constructed, instrumented and tested in diagonal shear mode. Two panels were tested as reference. The first reference panel was left unstrengthened, while the second one was strengthened by a traditional self-supporting cement mortar matrix reinforced with steel meshes. The remaining three panels were strengthened by TRM plastering applied on one or both faces and connected with transversal composite anchors. The numerical and the experimental results evidenced a good effectiveness of the TRM systems, especially when applied on both panel facings.

In-plane shear behaviour of adobe masonry wallets strengthened with textile reinforced mortar

Many people live in adobe masonry (AM) constructions in earthquake areas even if most of the existing constructions are not engineered, thus prone to seismic damage. Therefore, seismic retrofitting of existing AM structures is a critical issue. In this study, experimental results of diagonal compression tests on 21 adobe masonry wallets, before and after the installation of textile reinforced mortar (TRM) with either hemp or glass fibres, are presented. Hemp-TRM is found to be more effective than glass-TRM in improving the shear capacity of AM, showing a mean increase in shear strength and ductility of 25% and 260% in hemp-TRM-strengthened wallets and 12% and 100% in glass-TRM-strengthened wallets. The hemp textile allowed compatibility of the TRM to the masonry substrate, preventing premature debonding and local failure. Experimental results are compared to existing data on TRM systems made of vegetable fibres, evidencing a significant capacity enhancement through flax- and hemp-TRM systems.

Experimental analysis on tensile and bond properties of basalt-ettringite TRM for strengthening masonry structures

In recent years, a new generation of inorganic matrix-based reinforcement systems is under study worldwide known generically as textile-reinforced mortar (TRM). It is considered one of the most innovative and effective techniques for masonry rehabilitation. This paper focuses on a TRM system made of basalt fibers imbedded in an ettringitic mortar. The aim of this study is to identify the effectiveness of this kind of composite in the domain of masonry structures strengthening. The basalt-TRM performance had been investigated through direct tensile tests and single lap shear tests. Two series of direct tensile tests had been carried out on specimens characterized by two different basalt textile reinforcing ratios. The experimental results allowed to evaluate the tensile behavior of the TRM and to obtain useful information on the reinforcement concept. The use of digital image correlation facilitated a detailed description of the displacement fields and the evolution of the cracks during the tests. Two series of single lap shear tests had been carried out on brick masonry walls, reinforced with the same TRM’s systems tested in tension. The experimental results show a good adhesion between the matrix and the masonry substrate as well as between the matrix and the basalt textile.

Tensile behavior of flax textile reinforced lime-mortar: Influence of reinforcement amount and textile impregnation

Companies and practitioners working in the civil construction sector are more and more aware and motivated to develop and adopt sustainable building materials, possibly obtained from renewable and locally available resources. As part of this common effort, special attention is being paid to an emerging class of materials generally referred to as bio-based composite systems.In this context, this paper investigates the mechanical properties of a Textile-Reinforced Mortar (TRM) system produced with Flax textile embedded within a hydraulic lime-based mortar. The research aims at revealing the influence of either the reinforcement amount and the applied pre-treatment of the textile on the resulting tensile response and the cracking patterns exhibited by these TRM systems. The analysis of the results presented herein allows to have a comprehensive overview of the feasibility of using flax textiles for strengthening and retrofitting of existing structures.

Experimental and numerical investigations of the tensile behaviour of steel-TRM prepared with recycled glass sands and lime

Due to the decline in the material strength and increase in natural loading, the need to strengthen historical masonry buildings is vital, and different techniques have been used to enhance the structural performance of those buildings. Textile reinforced mortar (TRM) composite systems are one of the newly developed techniques that has attracted increasing interest from researchers. To investigate the feasibility of the use of more eco-friendly materials in mortars, recycled glass sand (RGS) is substituted for natural river sand in the preparation of mortar used in the TRM system, as well as lime as a partial cement replacement. RGS was substituted for river sand at 50% and 100%, and lime was substituted for cement at 50%. A total of ten mix proportions were prepared. The mechanical properties of the mortar were analysed in terms of the flexural strength and compressive strength at 7 and 28 days. The results showed that the strengths tend to decrease as the lime and RGS proportion increases. There are the maximum average reductions of 40.3% in flexural strength and 60.4% in compressive strength for the samples with 50% lime replacement, and 38.3% in flexural strength and 33.8% in compressive strength for the samples with 100% RGS replacement. The discrepancies in the strength increase rate from 7 to 28 days were observed in some samples which may due to the different surface area and grading of RGS particles change the rate of hydration and porous in mortar.Then, the tensile behaviour of steel-TRM prepared with recycled glass sand with four different mix proportions were experimentally studied. The tensile behaviours of the tested coupons agreed well with the three-phase tensile behaviour. The TRM composite coupons prepared with 100% RGS and 50% lime replacement showed the maximum reductions (73.4%) of average tensile strength compare to the TRM coupons with 50% RGS replacement, which follow the trend of the mechanical behaviour of mortar. Finally, analytical and numerical models considering varying parameters related to the material properties were developed to understand the stress–strain responses and crack patterns of different TRM coupons in tension. Both analytical and macromodelling approaches are able to capture the key global tensile behaviour of TRM as a reasonable fitting was observed with regard to predicting the change in the stiffness in the three stages. The results obtained by micromodelling approach show that TRM coupons with 100% RGS show a larger reduction in the mortar tensile strength and bond fracture energy of the mortar-textile interface. The reason for these reductions might be that higher RGS replacement can be more porous in mortar and the angular edges and rough texture of the RGS, respectively.

TRM reinforced tuff and fired clay brick masonry: Experimental and analytical investigation on their in-plane and out-of-plane behavior

The paper presents the results of an experimental campaign aimed at investigating the in-plane and out-of-plane behavior of tuff and fired clay brick masonry panels reinforced by a commercial, not yet tested, Textile Reinforced Mortar (TRM) system. The TRM, consisting of hydraulic lime mortar coupled with a bidirectional glass fabric (total thickness of 30 mm), was applied on both sides of the panels and connected through stainless-steel helical bars. First, a mechanical characterization of the TRM system was carried out, according to recent guidelines (AC434 and CNR-DT215) by means of tensile tests and single-shear bond tests on the two different substrates. Then, the effectiveness of the reinforcement was investigated through uniaxial compression, diagonal compression and three-point bending tests on masonry panels. After that, experimental results were compared to the predictions of recent guidelines and analytical models available in the literature, by using the mechanical parameters obtained from the TRM mechanical characterization. TRM showed to be very effective in increasing the in-plane shear strength of tuff panels, of about 170%, whereas in the case of fired clay brick ones the increase was limited to 33%. Besides, the diagonal compression strength of reinforced specimens seemed to be strongly influenced by the mortar matrix, instead of by the fabric reinforcement, as it usually happens i.e. for Fabric Reinforced Cementitious Matrix (FRCM) systems. Thus, novel simplified analytical formulations to predict the shear strength of reinforced panels by only considering the contribution of the TRM matrix were provided, discussed and compared to current analytical approaches for FRCM systems. As regards the out-of-plane behavior, the TRM system significantly increased the out-of-plane bending strength and ductility of both tuff and fired clay brick panels. The applicability of current analytical approaches, as well as possible amendments, was also investigated. Finally, the compressive behavior of the walls was not substantially modified by the reinforcement, reasonably due to the low axial stiffness of the connectors and, to a minor extent, because they were dry inserted within the masonry and simply folded over the glass fabric.

Multiscale Numerical Analysis of TRM-Reinforced Masonry under Diagonal Compression Tests

The present paper reports an experimental study coupled with a numerical modelling approach to simulate masonry walls strengthened with textile-reinforced mortar (TRM). This innovative reinforcing technique is based on high-strength fibre grids embedded into inorganic matrices, and it has recently been promoted for the seismic retrofitting of historical masonry buildings. In the experimental campaign presented here, two different commercial TRM systems are applied to single-leaf clay masonry panels. The specimens are then subjected to diagonal compression tests in order to evaluate the effects of TRM on the structural performance. The proposed finite element (FE) model, based on an original multiscale approach, is employed to simulate the diagonal compression tests. The numerical results show a very good agreement with the experimental data, including in terms of failure mode. In particular, the approach reproduces the macroscopic behaviour of the masonry panels as regards the force-displacement response, and it allows for the possibility of simulating bed joint sliding and TRM layer debonding.

A detailed micro-modelling approach for the diagonal compression test of strengthened stone masonry walls

The aim to retrofit and preserve the monumental stone masonry buildings due to their historical and cultural relevance is accompanied by the necessity of understanding the behaviour of the unstrengthen structure, as well as its behaviour after the strengthening systems are applied. There is scarce information related to the mechanical properties of stone masonry buildings and even less regarding the assessment of these characteristics in numerical models. Therefore, simulating the force displacement variation and the stress-strain distribution of stone masonry loaded in diagonal compression is a challenging issue. This work contributes to this topic by developing two detailed micro non-linear 3D models. The first model was designed for an unreinforced masonry (URM) wall and the second one was developed for a strengthened URM wall. For this purpose, a commonly used seismic strengthening system, referred to as reinforced plastering mortar (RPM) or textile reinforced mortar (TRM) was applied on the wall. All the components of the TRM strengthening system and the interfaces between the system and the stone masonry wall were considered in the numerical model. The structural responses of the models were analysed and compared and the TRM system effectiveness in increasing the in-plane load resistance and ductility of stone masonry walls was highlighted.