Reinforced Mortar Research Articles

Targeting functionalised carbon nanotubes at the interphase of Textile Reinforced Mortar (TRM) composites

Tensile performance of textile reinforced inorganic matrix composites strongly depends on the matrix-to-fabric bond strength, that is the weak chain in the system. In this work, we investigate the role of multi-walled carbon nanotubes (MWCNT) dispersion in an amorphous silica nano-coating for AR-glass and carbon fabric Textile Reinforced Mortar (TRM) composites. Two lime mortars are considered at 56-day curing. Comparative mechanical testing in uni-axial tension show remarkable enhancements in terms of mean ductility, strength and energy dissipation capabilities. Besides, coating successfully hinders telescopic failure and delamination, which significantly narrows data scattering and benefits design limits. Crack pattern analysis reveals that coating promotes diffuse cracking in the specimen, with gradual and progressive damage buildup. Indeed, mean crack width and mean crack spacing are consistently reduced. BET, optical and E-SEM microscopy supports the action mechanism of the coating, that promotes wettability, surface roughening and imparts a remarkable increase in the specific surface area of the reinforcement.

Constitutive Models for the Tensile Behaviour of TRM Materials: Literature Review and Experimental Verification.

In recent years, the scientific community has focused its interest on innovative inorganic matrix composite materials, namely TRM (Textile Reinforced Mortar). This class of materials satisfies the need of retrofitting existing masonry buildings, by keeping the compatibility with the substrate. Different recent studies were addressed to improve the knowledge on their mechanical behaviour and some theoretical models were proposed for predicting the tensile response of TRM strips. However, this task is complex due to the heterogeneity of the constituent materials and the stress transfer mechanism developed between matrix and fabric through the interface in the cracked stage. This paper presents a state-of-the-art review on the existing constitutive models for the tensile behavior of TRM composites. Literature experimental results of tensile tests on TRM coupons are presented and compared with the most relevant analytical models proposed until now. Finally, a new experimental study is presented and its results are used to further verify the reliability of the literature expressions.

Artificial Neural Network–Based Numerical Model to Predict Flexural Capacity of Masonry Panels Strengthened with Textile Reinforced Mortar

Abstract Widespread acceptance of textile-reinforced mortar (TRM) systems for various applications would require a universally accepted procedure for the qualification, characterization, and design...

Ultimate shear strength prediction model for unreinforced masonryretrofitted externally with textile reinforced mortar

Unreinforced masonry (URM) walls present low shear strength and are prone to brittle failure when subjected to in-plane seismic overloads. This paper discusses the shear strengthening of URM walls with Textile Reinforced Mortar (TRM) jackets. The available literature is thoroughly reviewed and an extended database is developed including available brick, concrete and stone URM walls retrofitted and subjected to shear tests to assess their strength. Further, the experimental results of the database are compared against the available shear strength design models from ACI 549.4R-13, CNR DT 215 2018, CNR DT 200 R1/2013, Eurocode 6 and Eurocode 8 guidelines as well as Triantafillou and Antonopoulos 2000, Triantafillou 1998, Triantafillou 2016. The performance of the available models is investigated and the prediction average absolute error (AAE) is as high as 40%. A new model is proposed that takes into account the additional contribution of the reinforcing mortar layer of the TRM jacket that is usually neglected. Further, the approach identifies the plethora of different block materials, joint mortars and TRM mortars and grids and introduces rational calibration of their variable contributions on the shear strength. The proposed model provides more accurate shear strength predictions than the existing models for all different types of the URM substrates, with a low AAE equal to 22.95%.

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.

Long-Term Bonding and Tensile Strengths of Carbon Textile Reinforced Mortar

This paper deals with the long-term bonding and tensile strengths of textile reinforced mortar (TRM) exposed to harsh environments. The objective of this study was to investigate the long-term bonding and tensile strengths of carbon TRM by an accelerated aging method. Moisture, high temperature, and freezing–thaw cycles were considered to simulate harsh environmental conditions. Grid-type textiles were surface coated to improve the bond strength with the mortar matrix. A total of 130 TRM specimens for the bonding test were fabricated and conditioned for a prolonged time up to 180 days at varying moisture conditions and temperatures. The long-term bonding strength of TRM was evaluated by a series of bonding tests. On the other hand, a total of 96 TRM specimens were fabricated and conditioned at freezing–thaw conditions and elevated temperature. The long-term tensile strength of TRM was evaluated by a series of direct tensile tests. The results of the bonding test indicated that TRM was significantly degraded by moisture. On the other hand, the influence of the freezing–thaw conditions and high temperature on the tensile strength of the TRM was insignificant.

In-plane shear cyclic behavior of windowed masonry walls reinforced with textile reinforced mortars

The current experimental study is focused on the mechanical performance of masonry walls under in-plane cyclic shear forces. All specimens were fabricated with a central window, in which the geometry considered the recommendations of the Spanish structural seismic design code. Windows represent a weak area in the masonry structure, in which there are stress concentrations responsible for crack initiation. In order to improve the mechanical strength and ductility, a reinforcement with a Textile Reinforced Mortar (TRM) was used on both sides of the wall. The performance of the unreinforced and reinforced masonry has been discussed in terms of strength and ductility gain, stiffness degradation and energy dissipation capacity. The experimental tests comprised an initial vertical preload, and shear cycles with increasing amplitude. All tests were monitored by means of traditional displacement transducers, and digital image correlation. The analysis of the images showed the time evolution of the overall crack distribution. The TRM effect could be observed as an increase of the mechanical strength (maximum shear from 120 kN to more than 300 kN), higher displacements (drift from 9 to 35 mm), and more energy dissipation (the cumulative energy loss from 2.7 to 12.7 kN·m). In addition, the TRM reinforcements were capable of controlling the crack initiation and growth. The widespread crack along mortar joints observed in the unreinforced masonry became localized cracks (from the window’s corners mainly), in which crack growth direction was not determined by masonry joints.

Shear capacity of masonry walls externally strengthened using Flax-TRM composite systems: experimental tests and comparative assessment

A growing environmental awareness is gradually changing the entire economic system and consequently, the building materials sector is increasingly interested in innovative sustainable solutions. The use of plant fibres as reinforcement in inorganic composite systems, generally referred to as Textile Reinforced Mortar (TRM), represents an innovative alternative to the use of more traditional high-strength inorganic fibres, which reduces the environmental impact of the composite. However, there are several unsolved issues regarding the correct mechanical behaviour of such innovative systems. Various studies have been conducted to assess the fibre-to-mortar bond properties and to investigate the tensile behaviour of TRMs based on plant textiles, such as flax, hemp, coir, sisal, and jute. Moreover, there is still a lack of experimental evidence concerning the efficiency of the composite material once applied to structural elements. Therefore, this paper reports on an experimental study on the shear capacity of walls strengthened by two TRMs characterised by a different amount of textile reinforcement. The experimental results are discussed and compared with the results of theoretical models derived from formulations proposed by the standards in this field. This study shows that Flax-TRM reinforcement enhances the strength and ductility of a masonry assemblage, confirming the potential utility of such materials. Furthermore, it points out some limitations of this reinforcement technique and paves the way for future studies aimed at improving the efficiency of the entire system.

Analytical model for textile reinforced mortar under monotonic loading

The recent evolution of using Textile Reinforced Mortar (TRM) as a sustainable and compatible solution for retrofitting masonry and heritage structures, requires the development of simplified models able to predict the behavior of this composite material in order to facilitate the implementation of numerical models of retrofitted structures using this technique, and further to create design guidelines for etrofitting structures using TRM. This paper presents a simple and easy to-implement tri-linear analytical model that correlates the mechanical properties and the geometric characteristics of the cement-based matrix and that of the textile reinforcement to define the stress–strain relationship of TRM under tensile load. The proposed nonlinear approach is based on the well-established Aveston–Cooper–Kelly (ACK) theory, which applies to fiber-brittle matrix, and extends it to textile cement-based matrix (TRM) using recommendations proposed by Eurocode 2 and by fib Model code 2010 for estimating the crack spacing, and the fracture energy of the composite material, respectively. TRM shows complex behavior in tension derived from the heterogeneity of its constituent materials (inorganic matrix and the fiber-textile). The proposed tri-linear analytical model proved accurate for predicting the stress–strain relationship of TRM under tensile loading, since the analytical curves properly fit the experimental results in almost any of the experimental case-studies that have been taken into consideration in the present study. A parametric study is also performed to examine the parameters that can influence the tensile behavior of TRM according to the proposed model.

Diagonal compression testing of masonry panels with irregular texture strengthened with inorganic composites

Inorganic composites for enhancing the in-plane shear capacity of masonry walls with irregular texture were investigated on twenty-one panels under diagonal compression tests. Three specimens were used as control and twelve specimens were strengthened with two Fibre Reinforced Mortars (FRM-A and FRM-B), characterized by a different content of fibres embedded in the lime-based matrix. The remaining six specimens were strengthened with Fabric Reinforced Cementitious Mortars (FRCM), consisting in a GFRP grid embedded in a fibre reinforced matrix (the same used for FRM-A). The influence of single-side and double-side strengthening configurations on the capacity of strengthened panels was also investigated, to point out the reduction in strengthening effectiveness in case of single-sided applications. The results showed that all the inorganic composites adopted for the strengthening techniques provided a substantial increase of shear capacity. The grid in FRCM strengthened panels played an important role in both strength and deformation capacity at peak. The different fibres content (lower than 50% in weight) in FRM systems slightly affected the overall performance of panels. Finally, analytical predictions of experimental results were reported and discussed and a preliminary analytical model for estimating the FRM shear contribution was proposed, obtaining a good agreement with test results.

Effect of corner over-reinforcing strips on the compressive behaviour of TRM confined masonry columns

Several recent works studied the efficiency of inorganic matrix composites, namely Textile Reinforced Mortar (TRM) or Fabric Reinforced Cementitious Matrix, for enhancing the strength and shortening capacity of masonry columns subjected to axial load. Literature studies were addressed to study the great number of variables involved in the problem, such as the nature and the grade of mortar, the strength of the fabric, the number of reinforcing layers, the type, the arrangement and the strength of the masonry, and helped to draw the first technical guidelines for practitioners and designers. All the experimental works highlighted that the actual performance of TRM confinement in masonry members was limited by the premature failure of the external layer in correspondence of the corners of sharp-edged sections, due to the stress concentration, limiting the confinement pressure achievable from the external wrap. This paper presents the result of an experimental investigation which aims to study the effect of a corner strengthening detail on the compressive behaviour of calcarenite masonry columns wrapped with glass TRM. The study was performed by varying the number of textile layers and the grade of the mortar adopted for the composite. The results show that the introduction of a fabric strip in correspondence of the corners can limit the stress concentration at the edges, allowing to exploit the confinement pressure of the TRM and achieving greater strength increases.

Experimental Study on Clay Brick Masonry Assemblies Strengthened with Basalt Textile Reinforced Mortar

Abstract This research proposes the use of a basalt textile-reinforced mortar (TRM) system as an overlay to strengthen brick masonry. A comparison of the strength performances, namely, the compressive strength, flexural bond strength, and shear bond strength, between unreinforced brick assembly and basalt TRM–reinforced brick assembly was made. The reinforced specimens exhibited improved strength performance, in particular, the flexural bond and shear bond strengths whereby more than a two-fold increase was observed. Additionally, the coefficient of variations in the compressive and flexural bond strength of brick assemblies was reduced when reinforced with the basalt TRM.

Effectiveness of Textile Reinforced Mortar (TRM) materials for the repair of full-scale timbrel masonry cross vaults

This paper presents the experimental results obtained from tests on two masonry vaults reinforced by Textile Reinforced Mortar (TRM) materials subjected to monotonic and cyclic vertical settlements in one of their supports. Two full-scale square masonry timbrel vaults were built in one of ICITECH’s laboratories at the Universitat Politecnica de Valencia (Valencia, Spain) using the traditional Catalan layered-construction technique, with various layers of clay tiles arranged in two perpendicular masonry textures joined by lime and cement mortar joints. Due to their peculiar geometric and mechanical features, i.e. their high slenderness ratio, low tensile strength and high material heterogeneity, these structures are especially prone to damage from high-risk events such as soil settlement or seismic excitation. To evaluate their response to vertical support displacements, both vaults were pre-damaged by either vertical monotonic or cyclic settlements. They were then strengthened by a radial TRM strengthening configuration and re-tested until failure. A complex network of traditional and optical sensors was used to monitor displacements, deformation and the development of the cracking mechanism under both settlement conditions. The results obtained show that TRM materials can be used to effectively repair severely damaged masonry timbrel vaults, helping to partially restore the initial elastic stiffness, as well as doubling the vaults’ elastic phase and ultimate displacements. In addition, TRM materials did not alter the stiffness degradation trend, although they had a strong effect on peak reaction degradation and failure modes. This investigation represents a valuable and unique source of information about the efficacy of TRM materials to repair full-scale pre-damaged masonry timbrel vaults.

Behaviour of Circular RC Column Confined with Textile Reinforced Mortar under Compression Load

The effectiveness of a new structural material, namely textile-reinforced mortar (TRM), was investigated experimentally in this study as a means of confining circular RC columns with two layers at different wrapping design. Four circular columns with size 600 mm height and 150 mm diameter were wrapped with glass fibre mesh at different types of wrapping design was prepared and tested under compression load. This study aims to establish an in- depth understanding on the effect of wrapping material and the design as a contributing factor in increment of load capacity. This research come into conclusion that wrapping the circular columns with TRM has increased the load capacity for the columns as compared to unwrapped columns, the best design is 100% wrapping with 14% increment in strength. Moreover, multiple researches have proven the efficacy of TRM wrapping design with different type of materials used in their studies. Based on the contemporaneity researches, this study was the first in term of studying the behaviour of circular RC column confined with various types of glass fibre design.

Tensile Characteristics of Carbon Fiber-Textile Reinforced Mortar with Aluminum Oxide Treated Anchorage Surfaces

The present study investigated the tensile characteristics of carbon fiber textile-reinforced mortar (TRM) with aluminum oxide treated anchorage surfaces. The main test parameters of this study include the thickness of TRM, the volume fraction of carbon fiber mesh, and the content of impregnated epoxy resin adopted in anchorage zones. The experimental results indicated that the tensile characteristics of TRM specimens in the pre-cracking stage are dominated by the mechanism of the mortar matrix; meanwhile, the tensile characteristics of TRM specimens in the cracked stage are governed by the volume fraction of carbon fiber mesh, and the amount of epoxy resin used in the anchorage zones. Based on the test results and material properties, an idealized bilinear model for predicting the tensile force–strain curve of TRM test specimens with aluminum oxide treated anchorage surfaces was developed based on ACI 549.4 R-13, and its prediction showed reasonable agreement with the test results.

Retrofitting of RC Beams Using Coir Textile Reinforced Mortar

Textile Reinforced Mortars (TRM) has been broadly concentrated during the most recent two out of this world across as a promising option in contrast to Fibre Strengthened Polymers (FRP) retro-fitting solution for strengthening of reinforced. The effectiveness of using TRM over FRP has been researched previously but research proving the effectiveness of use of natural fibres textiles with TRM is lacking, which is studied with the comparison of strength parameters of the Reinforced concrete structures jacketed with natural textile and commonly used synthetic textiles viz. glass fibre textiles. Also the effectiveness of chemical treatment subjected to natural fibres textiles in terms of strength increase is studied. Coir fibres being the most widely available natural fibres with favourable strength are selected for this study. The results obtained show us an increase in flexural strength in beam specimens retro-fitted with TRM. And coir textile wrapped specimens gave comparable results in comparison to glass textile wrapped counterpart. Chemical treatment of coir fibres also proved to be effective with increased strength over untreated coir fibres. The use of natural fibres is hence proved to be feasible at a fraction of the cost of the synthetic fibre textiles used.

Effectiveness of textile reinforced mortar (TRM) materials in preventing seismic-induced damage in a U-shaped masonry structure submitted to pseudo-dynamic excitations

This paper presents the experimental results obtained from tests on a 2/3 scale U-shaped masonry building constructed in one of the ICITECH laboratories at the Universitat Politècnica de València (Spain). The prototype measured 3.31 × 4.19 m2 by 2.15 m high and had a wall thickness of 230 mm. The masonry was composed of 230 × 110 × 50 mm3 solid clay bricks with approximately 10 mm-thick mortar joints arranged in English bond. The tests were aimed at evaluating the effectiveness of cement-based reinforcing materials (Textile Reinforced Mortar) applied to weak masonry substrates severely damaged by horizontal loads such as those induced by a seismic event. The tests were carried out in three phases: (i) testing of the as-built structure, (ii) application of one external layer of TRM to restore the masonry’s original load-bearing capacity and then (iii) testing the TRM-strengthened structure. Dynamic behaviour was monitored by both traditional and fibre optic sensors (FO), including 28 Linear Variable Displacement Transducers (LVDTs) and 3 long-gauge optical sensors. Strengthening effectiveness was evaluated by several parameters: hysteretic curves, strength degradation, computed cumulative energy dissipation and cracking mechanisms. TRM reinforcement was shown to significantly extend the load-bearing and displacement capacity of the masonry prototype, reducing seismic-induced damage applied by pseudo-dynamic excitation, although it had a limited effect on cumulative energy dissipation.

Experimental analysis of strengthening solutions for the out-of-plane collapse of masonry infills in RC structures through textile reinforced mortars

Seismic events worldwide clearly showed that a crucial issue for life-safety and reduction of losses due to earthquakes for reinforced concrete (RC) buildings is related to the out-of-plane (OOP) collapse of infill masonry walls. In the literature, few studies addressed this paramount topic. This paper presents an experimental work about the assessment of possible strengthening solutions to prevent the out-of-plane collapse of masonry infills in RC buildings. Four nominally identical full-scale one-bay-one-story RC frames were built and infilled with a thin masonry wall made up of horizontal hollow clay bricks. The first specimen was representative of the as-built condition. The other specimens were strengthened against the out-of-plane collapse by means of Textile Reinforced Mortar (TRM) strengthening techniques based on the application of high-ductility or common mortar plaster and fiberglass reinforcing bidirectional nets, varying the TRM-to-RC frame connection’s effectiveness. Tests consisted of a semi-cyclic history of imposed displacements in the OOP direction through small uniformly distributed pneumatic jacks. Experimental results are shown and compared to assess the effectiveness of the selected strengthening techniques and to provide a support towards the choice of the best strategies for future further investigations and applications.

In-plane shear behaviour by diagonal compression testing of brick masonry walls strengthened with basalt and steel textile reinforced mortars

This paper presents an experimental study of the structural behaviour of masonry walls retrofitted with Textile Reinforced Mortar (TRM) to improve their in-plane shear strength and deformation capacity. The experimental programme consists in diagonal compression testing of ten specimens of clay brick and lime mortar masonry retrofitted with three different TRM systems: i) continuous bidirectional grids of basalt TRM, ii) discrete bands of unidirectional steel TRM and iii) continuous basalt TRM on the wall’s inner face and bed joints structural repointing with near surface mounted helical stainless steel bars on the wall’s outer face. Two of the specimens were tested two times, i.e. in the unreinforced condition and subsequently in the repaired configuration including basalt TRM retrofitting. The experimental results show that the adopted TRM solutions produce a beneficial increase of shear resistance and ductility, making them suitable for seismic retrofitting and post-earthquake repair.

Experimental Study on the Adhesion of Basalt Textile Reinforced Mortars (TRM) to Clay Brick Masonry: The Influence of Textile Density

Textile Reinforced Mortar (TRM) composite systems are gaining consensus within the scientific and technical communities as a viable and advantageous alternative to the most conventional Fibre-Reinforced Polymer (FRP) composites. Due to the good compatibility both in terms of stiffness and vapor permeability between the inorganic matrix and the substrate, the TRMs appear to be particularly well suited for strengthening masonry members and enhancing their capacity to withstand tensile and shear stresses, such as those induced by seismic shakings. This paper aims to investigate the mechanical response of a TRM system featuring an internal reinforcement made of basalt fiber textile. Therefore, the paper reports the results of an experimental campaign carried out by single-lap shear bond tests on masonry substrate reinforced by TRM strips. Three different kinds of TRM have been taken into account, each one characterized by a variable number of fabric plies. The results show that, in all cases, TRMs fail prematurely due to debonding between fabric and matrix. However, the aforementioned premature failure is the main concern emerging from these test results, and further work is requested in reformulating the matrix composition towards enhancing their tensile strength and, hence, restraining the occurrence of fabric-to-matrix debonding.