Masonry Elements Research Articles

3D printable earth-based alkali activated “ink”: Effect of alkali concentration and binder-to-aggregate ratio

This research attempts to investigate the effect of activator concentration (4 mol/L (M) and 8M) and binder-to-aggregate (B:A) ratio (ranging from 1:1 to 1:3 by weight) on extrudability and buildability of 3D printable natural earth-based alkali-activated materials (EAAM). It is found that natural clay in soil, used to replace 25 % of M-sand, imparts higher thixotropy, evident from 90 to 100 % recovery in viscosity compared to 65–80 % for corresponding control (containing only M-sand and no soil). Presence of clay increases the dynamic yield stress than control but reduces the plastic viscosity by 80 – 90 % in EAAM compared to corresponding control where interlocking between sand particles resists smooth extrusion of the material. EAAMs made with 8M NaOH have higher flow retention and maintain 95–100 % recovery in viscosity for longer duration than 4M EAAM. This contributes to superior extrusion quality of 8M EAAM than 4M EAAM. The findings suggest that binder content can be reduced as concentration of NaOH is increased from 4M to 8M. This is evident from lower layer deformation (0.09 % of original height) under self-weight and higher 3D printed buildable height of at least 457 mm in 8M EAAM with B:A of 1:2 compared to a maximum of 375 mm for 4M EAAM at higher B:A of 1:1. Ratios of wet compressive strength to dry compressive strength vary between 0.92 and 1.09 in 8M EAAM compared to 0.79 – 0.85 for 4M EAAM at 28-day age, suggesting lower sensitivity to moisture due to improved clay stabilization. Based on the strength and moisture sensitivity, the developed material can serve as a low-carbon and durable alternative to Portland cement in the construction of masonry elements in buildings, including cavity walls, panels, flooring tiles and façade members.

Simulation of Autogenous Self‐Healing in Lime‐Based Mortars

ABSTRACTThroughout history, architectural heritage has been constructed using masonry, clay or stone elements, and lime‐based mortars. Over time, old buildings are subjected to different degrees of movement and degradation, leading to the formation of microcracks. Water dissolves and transports lime in mortar, but when the water evaporates, the lime is deposited and heals cracks in a process known as autogenous healing. Lime‐based mortars can regain some mechanical properties due to their healing capacity, given certain conditions. In the present work, a constitutive formulation has been developed to simulate cracking and healing in lime‐based mortars. The proposed model captures the residual displacements within cracks, associated with interacting crack surface asperities, as well as the healing effect on mechanical properties. A new approach is described which expresses these mechanisms mathematically within a micromechanical formulation. The proposed model was validated by comparing the outputs with experimental data. The results show that the new continuum micromechanical damage‐healing model could capture the damage‐healing cycle with good accuracy.

Blast resistance of CFRP composite strengthened masonry arch bridge under close-range explosion

Carbon fiber reinforced polymers (CFRP) are recognized for their exceptional strength-to-weight ratio. They offer a viable and effective solution for strengthening and retrofitting masonry bridges, helping to extend their service life, improve structural performance, and meet modern safety and load requirements. Wrapping of CFRP around masonry elements can enhance their confinement and ductility. This flexibility plays a crucial role in preventing sudden brittle failure, allowing for controlled deformation, which is essential for blast resistance. Additionally, CFRP materials possess the ability to flex and absorb energy, which proves beneficial in containing and redistributing forces generated during an explosion, consequently reducing the risk of catastrophic failure. This study employed the coupled Eulerian–Lagrangian (CEL) technique available in the finite element software Abaqus/Explicit to simulate the blast loads. Various detonation scenarios were considered, taking into account factors such as location and their impacts on bridge structures. A detailed micro-model was developed using finite element software and accurate geometric data acquired from FARO laser scanning of the case study. The properties of masonry units and backfill were characterized using the Johnson-Holmquist II damage model and Mohr–Coulomb criteria. The Jones-Wilkins-Lee equation of state (EOS) was applied to replicate the behavior of trinitrotoluene (TNT). In accordance with the JH-II model, the researchers formulated a VUMAT code. The study examined the distinct damage mechanisms and overall structural responses of bridges. By evaluating the blast resistance of individual bridge models, the most critical scenarios were pinpointed. Carbon Fiber Reinforced Polymer (CFRP) was then utilized as a method to fortify bridges against blast loads. A comparison was made between the damage propagation before and after the reinforcement.

In and out of plane behaviour of TRM strengthened heritage masonry elements

This paper presents detailed experimental and analytical investigations into the influence of textile-reinforced mortar (TRM) strengthening on the in-plane and out-of-plane response of unreinforced heritage masonry (URM) elements. The URM wall elements consist of hydraulic lime mortar and fired-clay bricks, and the TRM reinforcement employs mortar-embedded layers of alkali age-resistant glass meshes. Apart from the material characterisation tests on mortars, bricks, and TRM coupons, the experimental programme includes axial compression tests on wallettes, diagonal compression tests on square panels, as well as four-point bending tests on rectangular panels. In the latter, the bending loads are applied either parallel or perpendicular to the bed joints in order to assess the joint layout effect on the behaviour. With the aid of digital image correlation, the in-plane and out-of-plane enhancement in stiffness, strength, and ductility of the masonry elements due to the TRM strengthening is quantified, while the TRM influence on the crack patterns and failure modes is also examined. The results show that the number of mesh layers has a significant influence on the behaviour for the out-of-plane bending tests but plays a less pronounced role in the in-plane shear cases. Modified analytical models for the in-plane shear and out-of-plane bending capacities of reinforced masonry elements, of the type examined in this study, are also proposed and assessed alongside existing codified procedures. The application of current code provisions results in overly conservative estimates. In contrast, the proposed analytical approaches for determining the in-plane and out-of-plane strength provide close prediction of the experimental capacities from this study as well as those from a wider collated database of previous tests, and are therefore suitable for implementation in practical assessment and rehabilitation guidelines.

A Simplified Procedure for the Out-of-Plane Seismic Assessment of Free-Standing URM Elements: Application to the Abandoned Ancient Village of Bussana (Sanremo, Imperia - Italy)

ABSTRACT This paper addresses the safety of connections within urban areas, where free-standing elements that menacingly overlook them are susceptible to potential overturning mechanisms. Such a condition recurs in post-earthquake scenarios and in historical centers abandoned after disasters in seismic-prone areas, which aimed to be restored to create safe pathways for tourists. The paper presents a simplified procedure for the out-of-plane seismic risk assessment of free-standing unreinforced masonry (URM) elements in historical centers. The procedure can be applied to several URM free-standing elements, such as artistic pieces or nonstructural components, but also rocking panels resulting from the collapse of structures in post-event damage scenarios. The procedure is based on the definition of hazard, exposure, and vulnerability, which are combined to assign a risk class to each element and define a priority of intervention. The procedure relies on the kinematic approach but requires a limited number of parameters to be feasible when applied to many elements. Some of them can also be acquired through innovative survey techniques, like unmanned aerial vehicle photogrammetry. To demonstrate its utility, the procedure is applied to the abandoned village of Bussana (Sanremo, Imperia — Italy), severely hit by the 1887 earthquake and partially reoccupied in the 1960s.

Characterization and damage of the historic brick masonry of the Zákupy castle stables

Abstract A chemical-mineralogical analysis and mechanical tests of historical bricks were carried out as part of the construction-technical survey. The objective was to identify the causes of significant masonry decay. The ruined agricultural yard is a national cultural monument. Conservators believe that the historical importance exceeds that of the neighbouring castle. Stables were designed in 1650 by prominent Italian builders Giulio Broggio and Giovanni Domenico Orsi. The building has not been maintained since the conclusion of World War I. After removal from the masonry, the analyzed samples of bricks reached a very high, almost total degree of water saturation - 87-94%. Some bricks are heavily contaminated with nitrates and sulfates, infrared spectrometry analysis showed that calcium nitrate tetrahydrate is the most abundant of the nitrates. The determined average values of physical properties (bulk weight 1764 kg/m3, capillary absorption 13.6% by weight and open porosity 24% by volume) from samples under atmospheric pressure are comparable to the values of masonry bricks produced today. The results of the tests on the bricks from the Zákupy Castle stables construction demonstrate the high manufacturing quality of the masonry elements utilized. Based on the results of the analyses, it can be assumed that three degradation factors contribute to the observed damage to the bricks: high wetting of the masonry (almost total saturation of pores with water), which is most likely long-term lasting, frost cycles - repeated freezing and thawing of water in the bricks during the winter months, and repeated crystallization of water-soluble salts present in pores near the surface.

The In-Plane Seismic Response of Infilled Reinforced Concrete Frames Using a Strut Modelling Approach: Validation and Applications

Reinforced Concrete (RC) buildings often rely on masonry walls to increase their rigidity and strength, distinguishing them from bare frames. Consequently, the lateral capacity of the RC frames is significantly impacted by the presence or absence of these walls. Numerical models are fundamental to understanding this behavior interaction, but the development of robust simplified models is still scarce. Based on this motivation, the reliability of a simplified numerical modelling approach was examined in this study and compared to several experimental tests. An optimized approach was implemented to determine the strut parameters, rather than relying on existing empirical formulae. The reliability of the initial stiffness, maximum strength, and energy dissipation was studied. From the results, the accuracy of the considered modelling strategy can be observed in different types of masonry elements (strong and weak units) with and without openings. The validated simulation approach reveals that the adopted macro-modelling procedure can accurately represent the behavior of infilled masonry frames. The maximum deviation of the prediction of the initial stiffness and maximum strength was found to be around 23% and 14%, respectively. These findings illustrate that the strut model effectively replicates real behavior with a satisfactory level of accuracy. However, using a consistent formula to define the strut can result in significant errors, particularly in strut width.

Influence of PLA impregnation on the performances of vegetable fibers for lime-based composites

In recent years, the application of inorganic lime-based Textile Reinforced Mortar (TRM) for repairing existing masonry structures has gained a relevant interest due to the strong compatibility between masonry elements and the strengthening composite. In addition, several research groups worldwide have recently focused on the possible use of natural fibers for replacing the traditional reinforcement (e.g., steel, fiberglass, basalt, PBO, aramid, carbon, etc.) generally employed for TRM composites. As a matter of fact, the natural fabrics (easily available and biodegradable) present comparable resistance to conventional fabrics, good compatibility with the lime-based mortars and elastic modules compatible with masonry elements. On the other hand, it has been also demonstrated that one of the most relevant aspects on their possible application is related their long-term and durability performances which can be mitigated with coating and impregnation treatments. In this context, the present paper presents the preliminary result of an experimental research aimed at investigating the influence of a biodegradable coating system (PLA - polylactic acid) applied to different types of natural fibers (made of flax and jute) on the resulting performances either from the physical and mechanical standpoint. The results demonstrate a significant improvement of the observed performance of natural fibers that can be more properly employed for the production of natural TRM composites.

Multifunctional sensing mortar for masonry structures: first development and characterization

This study delves into the potential of self-monitoring masonry components constructed with specialized mortars containing conductive carbon-based fillers. The primary objective is to assess their ability to autonomously evaluate their structural integrity. These innovative masonry elements are designed to produce an integrated monitoring system within a structure. This system can effectively identify and respond to changes in structural performance, such as partial damage, crack propagation due to structural anomalies, or extreme loading events. The key to this self-monitoring capacity lies in the application of sensing mortars. These mortars can be used as the bedding material for masonry blocks. Through this approach, the study aims to preliminary characterize and explore the feasibility of cement-based smart mortars for intelligent masonry structures, aiming at diagnosing their own condition. Electromechanical tests on single components and more complex, though small scale, masonry elements allowed to achieve a first optimization of the materials and the building procedure, and to achieve a preliminary characterization of the mechanical, electrical and sensing behaviour. Compressive and bending tests have been coupled to electrical measurements through electrodes applied in the samples. The results of the work demonstrate the potential of the technology to be scaled to larger-scale structures.

Integrated Seismic and Energy Retrofitting of Masonry Elements Strengthened with PCM-enhanced GTRM/FRCM systems

The integration/combination of seismic and energy retrofit measures has been a subject of study for the past decade, exhibiting promising prospects. The main objective of these interventions is to mitigate seismic vulnerability while concurrently enhancing the energy performance and efficiency of new and existing buildings. Integrated approaches can hold the potential for substantial cost savings, time efficiency, and minimal disruption to occupants. The current body of literature emphasizes exploring the benefits of incorporating innovative methods/materials into conventional uncoupled retrofit initiatives. This study focuses on evaluating integrated measures at the panel scale for the prevalent Unreinforced Masonry (URM) typologies in Italy. A design framework has been introduced, aimed at enhancing the seismic capacity of buildings while concurrently improving energy efficiency through the integration of new materials (e.g., highly latent thermal energy storage systems achieved through the integration of Phase Change Materials - PCMs) into retrofit materials. To assess the reduction of the seismic vulnerability, the improvement of the shear strength is estimated by modifying the failure domains, while energy efficiency and thermal-energy storage enhancements are evaluated by using enthalpy-based theories, implemented into open-source software (i.e., FEM-based and through EnergyPlus). Thus, the design variables are those defined by the URM typologies, the adopted retrofitting technique, and the considered envelope. The adopted integrated (seismic and energy retrofitting) solutions will be compared with the standard reference one in terms of the energy consumed by the enclosed building to keep the indoor thermal comfort which also guarantees the target level of structural performance.

Method for calculating compression resistance of reinforced masonry elements using deformation diagrams

Method for calculating compression resistance of reinforced masonry elements using deformation diagrams

Self-sensing concrete masonry structures with intrinsic abilities of strain monitoring and damage detection

Self-sensing cementitious materials are emerging technologies for Structural Health Monitoring (SHM) of civil structures. Their application for SHM of concrete masonry elements was not investigated in previous studies. The effects of triaxial strain/stress states of masonry joints and units on their self-sensing response are still unknown. Therefore, this work aimed to investigate mechanical and self-sensing properties of masonry elements produced with self-sensing mortar joints, solid concrete bricks and/or hollow concrete blocks fabricated with carbon black nanoparticles. The intrinsic abilities of strain monitoring and damage detection were evaluated in piezoresistive tests of masonry prisms, based on variations in the type of unit, mortar bedding approach, bonding arrangement, relative strength of mortar and units, joint thickness and location of self-sensing regions. These variations did not affect significantly the gauge factor of cementitious sensors embedded into the prism units. In contrast, the gauge factor of self-sensing horizontal or vertical joints was statistically affected by most of these variations. Stages of balance and abrupt increases in fractional changes in electrical resistivity (FCRs) during the plastic regime of the prisms provided an anticipated warming associated with the propagation of vertical and diagonal cracks associated with tensile splitting and crushing failure of units. The strong non-linearity on the electrical output of self-sensing joints provided an evidence of the mortar pore collapse. In conclusion, the self-sensing units and mortar joints were found to be promising alternatives for strain monitoring and damage detection in smart concrete masonry structures.

Simplified Analysis of a Masonry Cross Vault Under Dynamic Actions

ABSTRACTDynamic tests performed on masonry cross vaults provide important information to improve the knowledge under seismic actions of these particular structural elements. Under seismic actions, curved masonry elements show a behaviour strongly influenced by several parameters (both physical and mechanical). Their structural behaviour is hard to predict due to the significant variability of the input parameters and the strong heterogeneity of these elements. Refined nonlinear models often require specific numerical calibrations of nonlinear parameters in order to assess the structural capacity of tested element. Conversely, simplified Finite Element models represent useful tools to develop a basic knowledge on the expected structural behaviour. Initial knowledge level in SERA TA blind competition favoured simple assumptions. Therefore, the main goal was to evaluate key information of a masonry vault under dynamic action: triggering and the type of damage, the most stressed areas and the threshold at which evident damage is expected. The results obtained by these preliminary analyses have been compared with the experimental tests.

Fibre-Reinforced Geopolymers (FRGPs) as Inorganic Composites for Flexural Strengthening of Brick Masonry

ABSTRACT This study presents an assessment of externally bonded Fibre-Reinforced GeoPolymers (FRGPs) as strengthening material for masonry structures. Geopolymer matrices can also potentially fulfil the requirements of restoration criteria for historical buildings, with heat-resistant performances generally better than Fibre-Reinforced Polymers (FRPs). Four FRGPs, embedding either unidirectional steel or bidirectional carbon, basalt or glass mesh as reinforcement, were tested by means of local shear and bending tests on fired clay brick specimens, either alone or coupled with hydraulic lime mortar. In addition, the behaviour of each reinforcement exposed to alkaline environments was investigated through tensile tests on coupons. Results confirmed the interesting potential of FRGPs for strengthening masonry elements, highlighting a good performance of steel and carbon reinforcements.

Preliminary Studies on a Lightweight Porous Cement-Based Composite – Gel Concrete

This paper presents some preliminary results of research on light, highly porous cement composites – gel concretes. A material based on Portland cement was tested, the very high porosity of which (over 60%) was obtained by direct gelatinization of starch in a liquid cement slurry. A composite based solely on cement and concretes produced with the addition of metakaolin or zeolite was tested. The basic properties of the concretes obtained in this way were determined, i.e., the volume density in a dry state, the thermal properties, and the compressive strength. In the case of the thermal properties, tests were performed on specimens dried to constant mass, while the test itself was carried out at an average temperature of 10°C. The tests employed an Isomet 2114 apparatus, which uses a non-stationary heat flow technique. The thermal conductivity coefficients and the volumetric specific heat were determined. The compressive strength tests were carried out on cubic specimens with a side of 4 cm after 28 days of curing by air-drying. Four specimens of each type of composite were tested. For composites based solely on Portland cement, the sorption properties of the material were also tested. For this purpose, the method of dynamic water vapor sorption (DVS) was used. As a result, graphs of the sorption and desorption of individual composites of different densities were obtained. Preliminary qualitative tests were also carried out using an electron microscope. The use of the starch gelatinization process directly in the cement slurry made it possible to obtain a very homogeneous material, in which the initial, temporary structure was starch gel, around which, after exceeding the setting time of the cement, the target cement-based structure was formed – gel concrete. The tested materials are innovative, having excellent thermal properties, comparable mechanical properties to lightweight concretes of the same densities, and is formed using an easily available, relatively cheap admixture in the form of starch. They can be used to produce small masonry elements, such as blocks for external walls or other typical prefabricated lightweight concrete elements.

Mutual Effect Between Moisture Transfer and Mechanical Response in Infill Masonry Walls of Reinforced Concrete Building Envelope

The external envelope of buildings with reinforced concrete structures (RCS buildings) is subjected to environmental actions, particularly related to wind-driven rain (WDR), external humidity variations, and rising dampness, which can cause significant variations in moisture content to their unreinforced masonry (URM) infill walls, mainly associated to water penetration across that envelope. The consequent moisture transfer across the envelope can change the mechanical response of the URM infill walls and lead to their cracking, which could aggravate the referred water penetration, with a subsequent increase in the risk of building envelope degradation. In reverse, the effects of mechanical loads on moisture transfer across that envelope can be also relevant, in terms of change in the moisture content of these URM infill walls. The aim here is to analyze this type of mutual effect between moisture transfer and mechanical response in URM infill walls of RCS buildings. Essential elements about the characteristics of moisture transfer across URM infill walls and of the interface resistance with moisture flows are summarily described, and the essential evaluation of the mechanical behavior of URM infill walls when subjected to moisture variations is carried out. Moisture transport characteristics are discussed, focusing on analyses of the behavior of masonry elements when subjected to moisture variations. An initial assessment of the mechanical behavior of URM infill walls when subjected to different moisture variations is made through a compression test of a brick masonry specimen with variable moisture content. Following that analysis, an evaluation is made of the moisture transfer in URM infills, as well as the influence of the interface between layers in that moisture transfer and, subsequently, an assessment is made of hygromechanical couplings. Finally, elements for prevention about the causes of degradation of URM infill related to humidity and mechanical actions in the RCS building envelope are discussed.

Performance of Unreinforced Masonry Walls in Compression: A Review of Design Provisions, Experimental Research, and Future Needs

Unreinforced masonry (URM) is a construction of brick or concrete block unit that is joined together using mortar, without steel reinforcement. Because of the heterogeneous nature and difference in mechanical properties of the masonry elements, analyzing and capturing the structural behaviour of URM walls under various loading conditions is therefore complex. In recent decades, research efforts have been focused on addressing and understanding the compressive behaviour of URM walls from the experimental viewpoint. However, from the existing experimental literature, there is a significant degree of variation in the mechanical and geometric properties of URM walls, especially the comprehensive comparison of apparently equivalent test parameters, which has yet to be examined. It is therefore necessary to highlight and critically examine major results derived from the experimental literature to better understand the performance of URM walls under compressive loads. This review paper presents the assessment performance with regard to axial compressive tests on URM walls, along with comprehensive comparisons among the experimental literature findings on the basis of masonry construction methods and various influencing parameters. Emphasis in the literature has been placed chiefly on the masonry elements, design provisions, axial load, slenderness ratio, openings, and stress–strain response. Based on observations from the study, experimental development trends have been highlighted to identify and outline potential directions for future studies.

Complete stress-strain analysis of masonry prisms under compressive loading-unloading cycles through digital image correlation

This paper presents the findings of an experimental study focused on the behaviour of masonry structures subjected to uniaxial loading-unloading compression. The study's primary objective is to examine the impact of joint mortar on the failure mode and the development of permanent strains using the digital image correlation technique (DIC). Masonry prisms were constructed using two types of fired bricks and five different mortars, each with varying cement and lime contents. The prisms were instrumented with a linear variable differential transformer (LVDT) for displacement measurements and prepared for image processing using DIC. The prisms were then subjected to compression testing until failure to capture their complete behaviour. The experimental results obtained through DIC and LVDT measurements showed good agreement. The DIC technique proved its effectiveness in providing comprehensive strain evaluations of the brick prisms, enabling a detailed stress-strain analysis at a full-scale level. Furthermore, the study revealed that prisms with lower cement content exhibited a more ductile behaviour in the post-peak region, with strain localisation observed at the joint mortar interface.To validate DIC's reliability in characterising masonry's cyclic behaviour, the results obtained from analytical modelling were compared with those derived from DIC. This comparison aimed to confirm the accuracy and consistency of DIC measurements. Overall, this study contributes to our understanding of masonry behaviour under compression and highlights the capabilities of DIC in capturing strain patterns and providing valuable insights into the influence of joint mortar on the structural response of masonry elements.

Ultimate in-plane shear behaviour of clay brick masonry elements strengthened with TRM overlays

This paper studies the response of unreinforced masonry (URM) members made of hydraulic lime mortar and fired clay bricks, commonly found in heritage structures, strengthened with textile reinforced mortar (TRM) overlays. The investigation includes URM and TRM-strengthened diagonal compression tests on square panels, and relatively large-scale wall specimens subjected to combined gravity and lateral cyclic loads. Complementary compression, tension, and interface material tests are also carried out. The diagonal panel tests show that the TRM effectiveness depends in a non-proportional manner on the overlays, render thickness, and substrate strength. The enhancement in stiffness, strength, and ultimate shear strain, using one to four mesh layers on each side, is shown to vary in the range of 49–132%, 102–536%, and 300–556% respectively. It is shown that strut crushing typically governs the response of such low-strength URM masonry elements confined by TRM overlays. The cyclic tests on the comparatively larger walls show that the TRM is effective, shifting the response from URM diagonal tension to rocking, and enhancing the stiffness, strength, and ultimate drift capacity by more than 160%, 30%, and 130%, respectively. It is shown that analytical assessment methods for predicting the response of TRM-strengthened and URM members in terms of stiffness, strength and load-deformation can be reliably adapted. The cumulative contribution of the URM and TRM components, in conjunction with a suitable fibre textile strain, is also found to offer an improved prediction of the shear strength compared to codified procedures. The findings enable the evaluation and improvement of analytical models for determining the main inelastic response parameters of TRM-strengthened masonry and provide information for validating future detailed nonlinear numerical simulations.

Particular Strength Criteria for Microstructural Analysis of Masonry

This study presents a set of "particular" strength criteria of the constituent elements of masonry as a composite material constituted by homogeneous fragments of heterogeneous materials (brick and mortar) and contact interface (shear and normal adhesive strength). This paper proposes the expressions for calculate the values of each particular strength criterion used for the discrete modelling of masonry. The results were obtained based on the experimental study of stresses and failure modes in masonry specimens, mortar samples and brick units. There are determined a set of 8 particular strength criteria, which correspond to the actual work of the masonry constituent elements. Their use in the structural micromodelling of masonry allows to determine the body contact interactions, track the gradual accumulation of local stresses, exclude from the calculation model the elements in which a particular strength criterion has been exceeded, and modelling the degradation process.