Search Results (93)

This study investigates the bond behavior of fabric-reinforced cementitious matrix (FRCM) composites with three common masonry substrates—solid clay bricks (SBs), perforated bricks (PBs), and concrete hollow blocks (HBs)—using knitted polyester grille (KPG) fabric. Through uniaxial tensile tests of the KPG fabric and FRCM system, along with single-lap and double-lap shear tests, the interfacial debonding modes, load-slip responses, and composite utilization ratio were evaluated. Key findings reveal that (i) SB and HB substrates predominantly exhibited fabric slippage (FS) or matrix–fabric (MF) debonding, while PB substrates consistently failed at the matrix–substrate (MS) interface, due to their smooth surface texture. (ii) Prism specimens with mortar joints showed enhanced interfacial friction, leading to higher load fluctuations compared to brick units. PB substrates demonstrated the lowest peak stress (69.64–74.33 MPa), while SB and HB achieved comparable peak stresses (133.91–155.95 MPa). (iii) The FRCM system only achieved a utilization rate of 12–30% in fabric and reinforcement systems. The debonding failure at the matrix–substrate interface is one of the reasons that cannot be ignored, and exploring methods to improve the bonding performance between the matrix–substrate interface is the next research direction. HB bricks have excellent bonding properties, and it is recommended to prioritize their use in retrofit applications, followed by SB bricks. These findings provide insights into optimizing the application of FRCM reinforcement systems in masonry structures. Full article

This study investigates the in-plane shear behavior of solid brick masonry walls, both unreinforced and retrofitted using Reinforced Khorasan Jacketing (RHJ), a traditional pozzolanic mortar technique rooted in Iranian and Ottoman architecture. Six one-block-thick English bond masonry walls were tested in three configurations: unreinforced with Horasan plaster (Group I), reinforced with steel mesh aligned to wall edges (Group II), and reinforced with mesh aligned diagonally (Group III). All the walls were plastered with 3.5 cm of Horasan mortar and tested after 18 months using diagonal compression, with load-displacement data recorded. A detailed 3D micro-modeling approach was employed in finite element simulations, with bricks and mortar modeled separately. The Horasan mortar was represented using an elastoplastic Mohr-Coulomb model with a custom softening law (parabolic-to-exponential), calibrated via inverse parameter fitting using the Nelder-Mead algorithm. The numerical predictions closely matched the experimental data. Reinforcement improved the shear strength significantly: Group II showed a 1.8 times increase, and Group III up to 2.7 times. Ductility, measured as post-peak deformation capacity, increased by factors of two (parallel) and three (diagonal). These enhancements transformed the brittle failure mode into a more ductile, energy-absorbing behavior. RHJ is shown to be a compatible, effective retrofit solution for historic masonry structures. Full article

This paper presents a study on the uniaxial compressive behavior of fully grouted concrete bond beam block masonry prisms. A total of 45 (i.e., 9 hollow and 36 fully grouted) specimens were tested, and the failure modes and initial crack were reported. The effects of block strength, grout strength, and loading scheme on the compressive strength of the fully grouted prism were discussed. The results show that the compressive strength of bond beam block prisms increased with an increase in grouting, while they were less affected by the block strength; the peak strength of the grouted block masonry was, on average, 35.1% higher than the hollow masonry prism. In addition, although the specimens’ strength was lower under cyclic compression than under monotonic compression loading, the difference in their specified compressive strength was statistically insignificant. The stress–strain curve of block masonry under uniaxial compression was also obtained. Through nonlinear fitting, the compressive stress–strain relationship of grouted masonry, considering masonry strength parameters, was established, which demonstrated alignment with prior experimental studies. This study not only provides a strength calculation method for grouted masonry structures using high-strength blocks in the code for the design of masonry structures in China but also offers a dedicated stress–strain curve for precise finite element analysis and the design of masonry structures. Full article

Fiber-reinforced polymers (FRPs) are effective for strengthening masonry walls. Debonding at the polymer–masonry interface is a major concern, requiring further investigation into interface behavior. This study utilizes detailed micro-modeling finite element (FE) analysis to predict failure mechanisms and analyze the behavior of brick masonry walls strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) under in-plane loading. The research investigates three CFRP strengthening configurations (X, I, and H). The FE model incorporates the nonlinear behavior of brick masonry components using the Concrete Damage Plasticity (CDP) model and uses a cohesive interface approach to model unit–mortar interfaces and the bond joints between masonry and CFRPs. The results demonstrate that diagonal CFRP reinforcement enhances the ductility and capacity of masonry wall systems. The FE model accurately captures the crack propagation, fracture mechanisms, and shear strength of both unreinforced and reinforced walls. The study confirms that the model can reliably predict the structural behavior of these composite systems. Furthermore, the study compares predicted shear strengths with established design equations, highlighting the ACI 440.7R-10 and CNR-DT 200/2013 models as providing the most accurate predictions when compared to experimental results. Full article

Textile-reinforced alkali-activated mortar (TRAAM) is a composite material that is characterized by a strain- or deflection-hardening response under tension or flexure, respectively, as well as by a good bond with concrete and masonry substrates. Owing to comparable or even superior mechanical performance compared to “conventional” cement- or lime-based textile-reinforced mortar (TRM) systems and its potentially eco-friendly energy and environmental performance, TRAAM has been incorporated to retrofitting schemes. The current article reviews the studies that investigate TRAAM as a strengthening overlay for masonry and concrete members. This article focuses on the mechanical performance of the strengthened members, which, where possible, is also compared with that of members strengthened with conventional TRM systems. It is concluded that TRAAM can enhance the flexural and shear capacity of masonry and concrete members, while it can also upgrade the compression strength and seismic response of concrete members. In addition, it is concluded that the effectiveness of TRAAM can be comparable with that of “conventional” TRM systems. The combination of TRAAM with thermal insulation boards has also been proposed for structural and energy upgrading of masonry walls. Furthermore, TRAAM can be a promising solution for increasing the fire resistance of strengthened masonry members. However, research on the long-term performance of TRAAM, including durability, creep, and shrinkage, is still limited. Finally, the lack of established standards for TRM retrofitting is more evident for TRAAM applications. Full article

This study investigates the interfacial bond behavior of clay brick masonry strengthened with carbon fiber-reinforced polymer (CFRP) through single-side shear tests. Two specimen types (single bricks and masonry prisms) were tested under varying parameters, including bond length, bond width, mortar joints, and end anchorage. Experimental results revealed cohesive failure within the masonry substrate as the dominant failure mode. Mortar joints reduced bond strength by 12.1–24.6% and disrupted stress distribution, leading to discontinuous load–displacement curves and multiple strain peaks in CFRP sheets. Increasing bond width enhanced bond capacity by 16.3–75.4%, with greater improvements observed in single bricks compared with prisms. Bond capacity initially increased with bond length but plateaued (≤10% increase) beyond the effective bond length threshold. End anchorage provided limited enhancement (<14%). A semi-theoretical model incorporating a brick–mortar area proportion coefficient (χ) and energy release rate was proposed, demonstrating close alignment with experimental results. The findings highlight the critical influence of mortar joints and provide a refined framework for predicting interfacial bond strength in CFRP-reinforced masonry systems. Full article

In this study, unreinforced masonry (URM) walls constructed from concrete blocks and clay bricks were strengthened using horizontally and vertically oriented glass fiber-reinforced polymer (GFRP) grid strips bonded with sprayed polyurea. The walls were subjected to diagonal compression loading until failure. The results demonstrated a significant improvement in both the shear capacity and pseudo-ductility of the strengthened URM walls compared to their unstrengthened counterparts. The primary conclusions drawn from this research are as follows: (1) the maximum strain in the vertical GFRP strips increased with the higher axial stiffness of the strips; (2) the discrete vertical strips contributed substantially to enhancing the shear capacity and pseudo-ductility of the URM walls; (3) increasing the axial stiffness of the vertical strips can alter the failure mode of the walls, shifting it from joint failure to tension or compression failure of the blocks or bricks; (4) a reduction factor is necessary to account for the potential asymmetrical performance of double-sided strengthening schemes applied to URM walls. The experimental program was reported in a previous publication and additional information is presented in this paper. Full article

The seismic response of confined masonry (CM) walls, built from innovative hollow clay blocks featuring large thermal insulation cavities and bonded with polyurethane glue instead of thin-layer mortar, was investigated. A 3D micro-model was subsequently developed in Abaqus and validated against results from cyclic shear tests on full-scale CM wall specimens. Once validated, the model was utilized in an extensive parametric study to investigate the effects of openings on the walls. This parametric study considered the size of the opening, its position, the aspect ratio of the walls, and different sizes of tie-columns. The results showed that the size and placement of openings substantially and negatively affected seismic response, and that the detrimental effects can be alleviated by placing strong tie-columns next to the openings. Full article

This paper presents the results of an experimental investigation on a steel-reinforced polyurethane (SRPU) composite system with a mineral interlayer, designed for the protection of existing structures. The composite SRPU was reinforced with unidirectional steel textile embedded in polyurethane matrix PS. In the study, SRPU was applied to a brick substrate via a layer of lime- or cement-based mortar of a thickness of 3 mm, 6 mm, or 10 mm. Single-lap shear tests (SLSTs) were carried out on specimens with and without a mortar interlayer. The reference specimens without a mineral interlayer carried higher loads than the specimens with an interlayer. An increase in the interlayer thickness reduced the shear bond strength. The stiffness of the bond under shear of the tested systems was unaffected by the presence of the mineral interlayer. The mechanical properties of the applied mortars influenced the observed failure modes. The tested SRPU system demonstrated notable efficiency in monotonic testing, outperforming previously reported results. Full article

This research presents an experimental analysis of the mechanical behavior of masonry mortars incorporating disposable face masks (FMs) cut into two different sizes. The objective is to provide experimental data contributing to the consolidation of recycling FMs in mortar mixtures. To achieve this, two types of mixtures were prepared: one with strips of 3 × 3 mm and another with strips of 3 × 10 mm. These FM strips were added in different proportions by the volume of mortar (0%, 0.2%, 0.5%, 0.8%, 1.0%, and 1.5%). In all mortars, the dry bulk density, volume of permeable voids, and water absorption, as well as compressive, flexural, and tensile strengths, were evaluated after a 28-day water immersion curing period. Additionally, two essential properties in masonry mortars were analyzed: air content and shear bond strength. The results indicated that, for both strip sizes, adding FMs up to 0.2% positively affected the flexural and tensile strengths; concerning control mortar, increases of 6% and 1.4%, were recorded, respectively, for the longer strips. At this percentage, the density, air content, and compressive and shear bond strengths are not significantly affected. The results demonstrated that incorporating FMs into mortar mixtures is a promising avenue for sustainable recycling and helps reduce microplastic environmental contamination. Full article

This study aimed to investigate the feasibility of using geopolymer paste (GP) as an adhesive agent for (i) anchoring steel bars in concrete substrates, (ii) repairing concrete, and (iii) repairing limestone and granite masonry blocks commonly found in historic buildings. In this investigation, seven cement-free GP mixes were developed with different combinations of binder materials (slag, silica fume, and metakaolin). The mechanical properties, adhesive performance, and production cost of the developed GP mixes were compared to those of a commercially epoxy adhesive mortar (EAM). The results obtained from this study indicated that the use of GPs enhanced the bonding between steel bars and concrete substrates, achieving bonding strengths that were 19.7% to 49.2% higher than those of control specimens with steel bars directly installed during casting. In concrete repairs, the GPs were able to restore about 60.6% to 87.9% of the original capacity of the control beams. Furthermore, GPs exhibited a promising performance in repairing limestone and granite masonry blocks, highlighting their potential suitability for masonry structures. The best adhesive performance was observed when a ternary binder material system consisting of 70% slag, 20% metakaolin and 10% silica fume was used. This combination, compared to the investigated EAM, showed comparable adhesive properties at a significantly low cost, indicating the viability of GPs as a cost-effective, eco-friendly adhesive agent. Full article

The use of Fabric-Reinforced Cementitious Matrix (FRCM) systems is an innovative method for strengthening structures, particularly masonry, while addressing environmental and economic concerns. Despite their widespread use, characterizing FRCM composites poses challenges due to their complex mechanical behavior and considerable variability in properties. The available standardized testing methods exhibit some inconsistencies, underscoring the need for reliable characterization procedures. This paper presents an experimental study on the bond behavior between FRCM materials and calcarenite stone using a non-standard setup for double shear bond tests. Different FRCM systems are considered, varying the matrix composition and fabric nature. The experimental results are evaluated in terms of maximum stress, slip and data dispersion, alongside comparisons with double shear tests on larger samples and single-lap shear. These findings provide insights into how the mortar nature influences the stress-slip curves, strength, ductility and failure modes. The experimental study demonstrates the repeatability and robustness, particularly in terms of peak strength, of the non-standard setup configuration utilized in the study. The study highlights the importance of reliable characterization procedures for FRCM materials, especially in bond behavior assessments, emphasizing the need for further research to enhance our understanding of their application in structural reinforcement. Full article

Fiber-reinforced cementitious matrix (FRCM) composites have been largely used to strengthen existing concrete and masonry structures in the last decade. To design FRCM-strengthened members, the provisions of the Italian CNR-DT 215 (2018) or the American ACI 549.4R and 6R (2020) guidelines can be adopted. According to the former, the FRCM effective strain, i.e., the composite strain associated with the loss of composite action, can be obtained by combining the results of direct shear tests on FRCM–substrate joints and of tensile tests on the bare reinforcing textile. According to the latter, the effective strain can be obtained by testing FRCM coupons in tension, using the so-called clevis-grip test set-up. However, the complex bond behavior of the FRCM cannot be fully captured by considering only the effective strain. Thus, a cohesive approach has been used to describe the stress transfer between the composite and the substrate and cohesive material laws (CMLs) with different shapes have been proposed. The determination of the CML associated with a specific FRCM–substrate joint is fundamental to capture the behavior of the FRCM-strengthened member and should be determined based on the results of experimental bond tests. In this paper, a procedure previously proposed by the authors to calibrate the CML from the load response obtained by direct shear tests of FRCM–substrate joints is applied to different FRCM composites. Namely, carbon, AR glass, and PBO FRCMs are considered. The results obtained prove that the procedure allows to estimate the CML and to associate the idealized load response of a specific type of FRCM to the corresponding CML. The estimated CML can be used to determine the onset of debonding in FRCM–substrate joints, the crack number and spacing in FRCM coupons, and the locations where debonding occurs in FRCM-strengthened members. Full article

Among the techniques utilized for strengthening masonry structures with advanced materials, the adoption of near-surface mounted (NSM) titanium rods stands out as a promising method for increasing the flexural and shear strength of masonry structures. This method is also known as Bed Joint Reinforcement. Ensuring an effective performance of this technique hinges on establishing a strong bond between the NSM reinforcement and the substrate masonry material. The primary objective of this project was to study the mechanics of this bond using NSM threaded and smooth titanium rods while scrutinizing the impact of key parameters on bond performance. Variables under investigation encompassed the rod type (smooth and threaded), bond length, and the material used to fill the groove (type of mortars). It was found that threaded rods outperformed all other types investigated, and pull-out strengths can be significantly improved through careful selection and optimization of the mortar type and bond length. Full article

Sustainable building materials for integrated (structural and thermal) retrofitting are the need of the hour to retrofit/upgrade the seismic vulnerable and ill-insulated existing building stocks. At the same time, the use of natural fibers and their recyclability could help construct safer and more sustainable buildings. This paper presents three aspects of jute fiber products: (1) the evaluation of the mechanical performance of the jute nets (2.5 cm × 2.5 cm and 2.5 cm and 1.25 cm mesh configurations) through tensile strength tests (with the aim for these to be used in upgrading masonry wall with natural fiber textile reinforced mortars (NFTRM) systems); (2) the hundred percentage recyclability of left-over jute fibers (collected during the net fabrication and failed nets post-tensile strength tests) for the composite mortar preparation; (3) and the evaluation of insulation capacity of the recycled jute net fiber composite mortar (RJNFCM) through thermal conductivity (TC) measurements, when a maximum amount of 12.5% of recycled jute fiber could be added in the mortar mixture at laboratory conditions and with available instruments Notably, when more than the said amount was used, the fiber–mortar bonding was found to be not optimal for the composite mortar preparation. These studies have been carried out considering these products’ applicability for integrated retrofitting purposes. It has been found that the denser mesh configuration (2.5 cm × 1.25 cm) is 35.80% stiffer than the other net configurations (2.5 cm × 2.5 cm). Also, the mesh configuration (2.5 cm × 1.25 cm) shows about 60% more capability to absorb strain energy. TC tests have demonstrated the moderate insulation capacity of these composite mortar samples, and the TC values obtained from the tests range from 0.110 (W/mK) to 0.121 (W/mK). Full article