Mortar Layer Research Articles

Experimental Research and Numerical Analysis of CFRP Retrofitted Masonry Triplets under Shear Loading.

This paper presents an experimental and numerical study into the shear response of brick masonry triplet prisms under different levels of precompression, as well as samples reinforced with carbon fiber-reinforced polymer (CFRP) strips. Masonry triplets were constructed with two different mortar mix ratios (1:1:3 and 1:1:5). In this study, finite element models for the analysis of shear triplets are developed using detailed micro-modelling (DMM) approach and validated with the experimental data. The failure mechanisms observed in the masonry triplets were simulated using a coupled XFEM-cohesive behaviour approach in ABAQUS finite element software. The nonlinear behaviour of mortar and brick was simulated using the concrete damaged plasticity (CDP) constitutive laws. The cohesive element with zero thicknesses was employed to simulate the behaviour of the unit–mortar interfaces. The extended finite element method (XFEM) was employed to simulate the crack propagation in the mortar layer without an initial definition of crack location. CFRP strips were simulated by 3D shell elements and connected to masonry elements by an interface model. The changes in failure mechanism and shear strength are calculated for varying types of mortar and fiber orientation of CFRP composite. Based on this study, it was concluded that the ultimate shear strength of masonry triplets is increased due to the external bonding of CFRP strips. The performance of masonry specimens strengthened with CFRP strips is assessed in terms of gain in shear strength and post-peak behaviour for all configurations and types of mortar considered. The comparison of FE and experimental results proved that the models have the potential to be used in practice to accurately predict the shear strength and reflect damage progression in unreinforced and CFRP-reinforced masonry triplets under in-plane loading, including the debonding of the CFRP reinforcement. Additionally, XFEM was found to be a powerful technique to be used for the location of crack initiation and crack propagation in the mortar layer.

Thermomechanical characterization and thermal simulation of a new multilayer mortar and a light-weight pozzolanic concrete for building energy efficiency

A brand-new sandwich material has been developed with a pozzolan-granular, plaster composite core and two cement mortar protective layer. The main goal of this study is to test the thermal behavior of a new sandwich material as well as the thermomechanical characteristics of pozzolanic concrete. The effects of granulomere sizes on the thermal properties of sandwich materials, as well as the volume fraction of pozzolan on the thermomechanical properties of lightweight concrete, have been studied. As a reference, mortar and concrete samples were made. The morphology and chemical composition of pozzolan granular were studied using scanning electron microscopy and X-ray fluorescence respectively. An energy building simulation of a prototype by Using TRNSYS simulator software, with variable internal and external walls composition, is performed; in order to evaluate the energy performance of sandwich material and lightweight concrete with optimum mechanical and thermal properties obtained from this work. Experimental results have shown that the incorporation of pozzolan as aggregates in the multilayer material and the concrete improves their thermal behavior. For multilayer material, it was shown that thermal conductivity varies from 0.682 W.m−1.K−1 to 0.42 W.m−1.K−1 for a sandwich sample having a granular size of pozzolan (7–20 mm) compared with reference mortar with 21.17 % mass gain. Concerning effusivity and diffusivity, of the same samples are varied from 723 to 575 J m−2.K−1.s−1/2 and from 3.51 to 2 10–7 m2.s−1 respectively. While for concrete without pozzolanic aggregate compared with a lightweight concrete sample having 100 % of volume fraction of Pozzolan, the thermal conductivity varies from 1.5 W.m−1.K−1 to 0.79 W.m−1.K−1 respectively with 31 % mass gain. Unfortunately, the mechanical performance decreases. The results of the thermal simulation have shown that sandwich material and lightweight concrete might be used in the thermal building envelope and walls. It offers significant reductions in cooling and heating energy consumption of 22 % and 14 %, respectively, as well as a significant yearly decrease in CO2 emissions of roughly 611.57 kg CO2e and 810 KgCO2e. When compared to other common wall materials, the results reveal that the new green construction materials have exceptional self-insulation properties.

Adaptation of the SonReb method to the mea-surement of the compressive strength of a two-layers concrete structure

The three most common building materials which most structures are built from are: timber, steel and Reinforcement Concrete (RC). Estimating the in-situ compressive strength is an imperative issue to evaluate the performance of in-situ concrete structures during their service life. Most codes and technical recommendations indicate that in-situ concrete strength should be estimated by means of cores, possibly supplemented by Non-Destructive tests. In this study a series of ultrasonic refraction measurements on a two layers slabs (mortar over concrete) are carried out in order to recover the velocity of the compression waves of each layer in view of combining the results with the rebound method in order to estimate the compressive strength of the mortar layer. Accuracy of measurements of compression wave propagation velocities and errors on the estimation of the compressive strength are investigated.

Differential inversion using surface wave methods for time-lapse monitoring

Climate-changing, human activities or aging problems create variations in civil engineering structures and materials which, if monitored, bring useful information for maintenance. Time-lapse (TL) monitoring measures the present condition of a given material, named the baseline, and then repeat a successive series of measurements at different times, named repeatlines. By comparing the baseline with one of the repeatlines, material properties’ variations, including weak ones, can be inferred. Surface wave (SW) methods are widely used for TL monitoring, because SW are very energetic and the inversion of their dispersion properties gives a depth-profile of some mechanical parameters. Classical SW inversion uses SW phase velocity (Vph) as inversion input data. It suffers from low sensitivity to the deep medium’s parameters due to high uncertainties in the measurements at low frequencies. TL monitoring can partially overcome the difficulties linked to the estimation of deep variations. In this study, we propose a new strategy for TL monitoring using SW methods, by looking for the relation between the model parameter variations and the data difference within the frame of global inverse problems. For this purpose, we introduce differential inversion (DI) in surface wave methods. Instead of independent inversions of the baseline and repeatlines, DI uses the difference between measured data of baseline and repeatlines as inversion input data. Two approaches have been tested. The first approach uses an innovative method to calculate the data difference, which is called the diagram difference (DD). DD is based on a statistical distance considering the area of interest of the dispersion diagram as a histogram of Vph distribution. This DI is tested experimentally on laboratory-measured data, obtained on three mortar-concrete slabs. The mortar layers of the three slabs have different water-to-cement ratios which change the mechanical properties of each slab. DI shows more concentrated results closer to the true values for both layers compared to the SW inversion using Vph as inversion input data. The second approach uses a linear approximation of Rayleigh wave Vph in the inversion process, in order to relates the data difference with the model parameters variations by using the analytical equation of the sensitivity kernel. Numerical tests show that this approach is limited to model parameter variations less than 5%, beyond which the linear assumption of Rayleigh wave Vph is no longer valid. This approach is tested on three epoxy-resin models, with respect to the 5% variation limitation in the deep layer. The low cost of the computation time is the main feature of this second approach. Its main drawback is that it requires a good estimation of the baseline model in order to correctly calculate the sensitivity kernel. In this case, the first DI approach can be used for a prior estimate of the medium’s variations, since it has a better resolution on the inversion results compared to SW Vph inversion.

Experimental Study and Numerical Analysis of Structural Performance of CRTS II Slab Track under Extreme High Temperature

A ballastless track is susceptible to damage and even failure of structural components under the long-term effects of extremely high temperatures. In this paper, considering the influence of different constraint boundaries, a 1 : 4 scaled model of a ballastless track-bridge structural system was produced and placed in a large-sized environmental chamber. The thermal performance of the track structure was studied by carrying out temperature loading tests at extreme temperatures. In combination with the scaled-down model test data, a 3D nonlinear finite element model was established to investigate the damage evolution of broad-narrow joints under temperature gradient loading. The results are shown as follows: (1) the cement asphalt (CA) mortar layer has a hysteretic effect on the vertical temperature transfer. The most unfavorable structural part is between the track slab and the CA mortar layer of the track structure. (2) The constraint conditions accelerate the rate of temperature transfer, creating disturbances to the internal stresses of the track structure and amplifying the internal stresses induced by the environmental temperature increase. (3) Temperature and longitudinal stresses in the track’s structural layers are highly correlated. There is a significant quadratic regression between internal temperature and structural stresses in different extreme high-temperature environments. (4) As the temperature gradient load increases, the damage occurs at the junction of the broad-narrow joint and tends to expand towards the ends, which has little effect on the compression damage of the broad-narrow joint but significantly increases the tension damage. The research could provide useful guidance for the scientific operation and maintenance of the ballastless track in extreme high-temperature environments.

Masonry Elements Strengthened with TRM: A Review of Experimental, Design and Numerical Methods

Textile-Reinforced Mortar (TRM) is a modern and compatible strengthening strategy for existing masonry, which consists in plastering the walls by means of mortar layers with embedded grids or textiles made of long fibers. TRM can be very useful for the reduction of the seismic vulnerability of masonry buildings, since the fiber-based reinforcement, carrying high tensile stresses, opposes the widening of cracks and provides “pseudo-ductility” to the masonry. The increasing number of available studies on the subject testifies to its relevance but also the lack of a standardized or well-establish approach to quantify the benefits of these systems on the performance of masonry. The present review is aimed at providing a broad overview of how the study of TRM-strengthened masonry elements has been addressed in the literature. In particular, the main features of the different experimental tests are compared, dealing with both in-plane and out-of-plane behavior. Moreover, the different design methods and numerical modeling strategies are presented and discussed.

Analysis and experimental testing of a self-centering controlled rocking wall with buckling-restrained braces at base

A new self-centering controlled rocking wall (CRW) with buckling-restrained braces (BRBs) at the base (SC-CRWBB) is proposed to improve the energy dissipation and self-centering capacities of CRWs. The SC-CRWBB was established by adding unbonded posttensioned tendons (UPTs) at the center and BRBs at two corners of a CRW. The quasi-static test results demonstrated that the proposed SC-CRWBB achieved a satisfactory seismic performance. Structural damage was concentrated in the BRBs, while a few cracks occurred in the surface between the CRW and mortar layer and between the BRBs and CRW. Then, a finite element model (FEM) of the test specimen was created in ABAQUS software to study the influence of the initial stress of the UPTs and sectional area of the BRB core plate on the residual deformation and lateral carrying capacity of the SC-CRWBB. Finally, an analytical method for the investigation of SC-CRWBBs was validated against the test and FE analysis results.

Experimental and analytical assessment on rubberized concrete interlocking grouted masonry walls under eccentric loading

In this study, the concept of interlocking masonry is modified by introducing waste materials, fly ash (FA) and crumb rubber (CR), to overcome the issues of mortared walls and conventional interlocking walls. Therefore, this research is aimed to investigate the behavior of rubberized concrete interlocking grouted masonry walls (RCIGMWs) subjected to eccentric compression loading experimentally. Twelve RCIGMWs of size 1260 mm height × 625 mm width × 125 mm thickness were constructed, by stacking RCIBs in running bond on top of one another without the use of mortar layers, however, the center cores (holes) of the wall panels were filled by pouring the concrete grout into. RCIGMWs were then tested under four axial compression eccentric loading levels including e=0, e=t/6, e=t/3, and e=t/2.5 where the top of the wall panels was considered for eccentricity while the end was maintained flat as a fixed. The bottom support was fixed while the upper end was free. The structural responses including the efficiencyof the walls, axial displacement and lateral deformation, and failure mechanisms were investigated. The experimental findings show that higher compressive eccentricities adversely impacted the behavior responses of RCIGMWs. Under eccentricities greater than kern distance, walls suffered significant loss of their load-bearing capacity. Moreover, higher lateral deflection was recorded at higher eccentricity levels as a result of the developed wall’s bending moment. Vertical splitting failure was observed between the webs and brick shells, which was followed by localized spalling. A global buckling was formed at higher eccentricity levels where the wall bent and the dry bed joint at the upper height of the wall opened and failed prematurely. Analytically, the EC-6 and ACI-530 are able to calculate the load-bearing capacity of the RCIGMWs, however, they tend to underestimate it with increasing the eccentricity while BS 5628–1 provides approximately 90 % precision.

Effect of temperature variations on the bond behavior of FRCM applied to masonry

In the last decades, Fiber Reinforced Cementitious Matrix (FRCM) composites were successfully introduced to repair and strengthen existing masonry structures. The good mechanical performances of these materials determined their efficiency as a strengthening technique; however, their durability is still an open issue. As a matter of fact, FRCM composites may be exposed to a combination of different environmental conditions and, additionally, to temperature variations due to solar radiation. The objective of this research was to study the effects of temperature variations on the bond behavior of a FRCM composite, constituted by a basalt grid and a lime-based mortar matrix, applied to masonry. For this purpose, an experimental investigation on thermally conditioned FRCM-strengthened masonry wallets is presented, in which 14 single-lap shear tests were performed. Before testing, samples were exposed to different target temperatures inside a climatic chamber: 32, 40, 50, 60 and 80 °C. Thermocouples were embedded within the FRCM reinforcing layers at two different depths to detect the inner temperature profiles and to control the conditioning process. The single-lap shear tests were then carried out inside the same climatic chamber, while maintaining the target temperature constant. A decrease in terms of peak-axial stress was observed by increasing temperature, along with a progressive change in the failure mode, from fiber rupture outside the bonded area to fiber slippage within the mortar matrix layers.

Dynamic mechanical properties and wave propagation of composite rock-mortar specimens based on SHPB tests

Filled inclusions in rock discontinuities play a key role in the mechanical characteristics of the rock and thereby influence the stability of rock engineering. In this study, a series of impact tests were performed using a split Hopkinson pressure bar system with high-speed photography to investigate the effect of interlayer strength on the wave propagation and fracturing process in composite rock-mortar specimens. The results indicate that the transmission coefficient, nominal dynamic strength, interlayer closure, and specific normal stiffness generally increase linearly with increasing interlayer stiffness. The cement mortar layer can serve as a buffer during the deformation of composite specimens. The digital images show that tensile cracks are typically initiated at the rock-mortar interface, propagate along the loading direction, and eventually result in a tensile failure regardless of the interlayer properties. However, when a relatively weaker layer is sandwiched between the rock matrix, an increasing amount of cement mortar is violently ejected and slight slabbing occurs near the rock-mortar interface.

Characterization of Coarse Recycled Aggregates Produced from Concretes with Different Strength Levels

With the acceleration of Urban Renewal Program, particularly in large cities of Turkey, the problem of finding land-fills and eliminating construction waste with the least environmental pollution necessitates its value-added recycling. However, the presence of adhered weak mortar layer, comprising 20-70% of recycled concrete aggregate (RCA), limits the use of RCA or lowers its inclusion level in concrete mixtures. Within the scope of this study, limestone- and basalt-bearing RCA obtained from 6 different concrete mixtures with three different water/cement ratios (0.45, 0.60, 0.70) were prepared and their water absorption, specific gravity, dense and loose unit weight, flatness indices, Los Angeles degradation values were determined. The results showed that, increasing w/c ratio of the parent concrete increased water absorption of the resultant RCA. However, the specific gravity, unit weight, abrasion resistance and flakiness index of RCA were decreased by increasing w/c ratio of the parent concrete.

Raman and ATR-FTIR analyses of medieval wall paintings from al-Qarawiyyin in Fez (Morocco)

A multi-analytical study has been undertaken to characterise wall paintings from the al-Qarawiyyin university in Fez, dating back to the 9th century and still in activity, with the aim of identifying the pigments used and going back to the painting techniques adopted by the Moroccan craftsmen of the time. The investigation crossed Raman and ATR-FTIR structural analyses along with XRF elemental ones, as well as colorimetric measurements. The colours and shades of six representative fragments collected during a recent excavation have been examined. Hence, red ochre (mainly hematite) was used to obtain brown-red colour, calcite for white, bistre for carbon-based black, while blue shades were achieved using azurite. Mixtures of pigments were created to widen the colour palette: cinnabar, minium and hematite were identified in orange hues while lapis lazuli and azurite were observed in grey-blue areas. The exploration of mortar layers revealed gypsum, gypsum/calcite and calcite type plasters. Furthermore, the observation of the morphological aspect of the interface between the plaster and the painting layer seems indicating that the lime-secco-painting skill had been the adopted painting technique.

Impact resistance of concrete pavement surface reinforced with fibre mesh

ABSTRACT The surface layer of military airfield pavements is prone to damage, including cracking, abrasion, and spalling. It is proposed to strengthen the pavement mortar layer by laying fiber mesh to solve these issues. In this study, three meshes of carbon fiber, aramid fiber, and basalt fiber were selected for surface reinforcement across six pavement slabs of 1.5m (length) × 1.5m (width) × 0.25m (height). The drop hammer impact test was carried out on the six pavement slabs. The test data were analyzed using impact times, crack development characteristics, and development models on the surface deflection as evaluation indices. The results show that the fiber mesh can effectively improve the impact resistance of concrete pavement slabs. Aramid fiber mesh best strengthened the pavement surface, whereas the basalt fiber mesh had the least strengthening effect. However, the mesh size has a negligible influence on the impact resistance of concrete pavement slabs. The effect of fiber mesh on improving the impact resistance of the concrete pavement slab corner was greater than that of the concrete pavement slab edge midpoint. Considering the performance and cost indicators, within the scope of the study, aramid fiber mesh is the most suitable for surface strengthening of airfield concrete pavement.

Durable life assessment of centrifugal stratified PHC piles in marine environment

This study proposes an analytical approach to assess the durable life of pre-stressed high-strength concrete (PHC) pipe piles exposed to the marine environment with consideration of centrifugal stratification and different end types. The durable life of the PHC pile is divided into two stages: the initiation stage for chloride penetration and the propagation stage for rust accumulation. To simulate the two stages, a two-layer composite cylinder diffusion model and a thick-walled ring mechanical model are developed based on the governing mechanisms. The proposed diffusion model is verified via comparisons with the numerical models with respect to chloride concentration under different stages. Then, extensive parametric studies based on the proposed method are performed to investigate the effects of end type, cover thickness, and steel bar diameter on the durable life of a PHC pipe pile. The results indicate that both increasing the cover thickness and using the closed-ended pile can significantly extend the durable life of a PHC pipe pile. Furthermore, the open-ended pile with a thinner mortar layer has a longer durable life, while the durable life of a closed-ended pile only slightly increases with a larger thickness of the mortar layer.

Multiscale assessment of masonry materials from the roman imperial baths at Sagalassos

The Imperial Roman Baths in Sagalassos, Turkey, were built in the 2nd century C.E. and have been excavated since the 1990s. The harsh environmental conditions, especially during the winter, resulted in the accelerated decay of the building materials, material losses, and serious structural problems in the Baths. This study explores the comprehensive characterization and multiscale assessment of bricks and mortars for effective preservation of the Baths. Experimental results showed that although the interface between building materials weakened after years of accumulated degradation, the individual materials still had higher strength than those from the same period. The material scale finite element model used to understand the damage mechanism showed that brick failure was caused by the tensile stresses accumulated at the brick–mortar interface when some of the mortar crumbled and fell with deterioration. A global sensitivity analysis was also conducted to investigate the impact of individual layer thicknesses on the stress distribution in the brick and mortar composite. Results indicated that thicker bricks resulted in better confinement at mortar layer and smaller tensile stresses at the bricks.

The Effect of Interface Damage between Slab and Mortar Layer on the Dynamic Performances of Vehicle and Track Systems under the High Frequency Train Loads

To investigate the influences of through-transverse mortar disengagement with different lengths and heights on the dynamic responses of vehicle and track systems under the high frequency train loads, a coupled rigid vehicle–flexible track multi-body dynamics (MBD) model with mortar disengagement was established in SIMPACK platforms with the help of ANSYS software. The results indicate that when the mortar disengagement length is no more than 1 m, the responses of vehicle and track systems are hardly influenced by mortar disengagement with an increase rate of no more than 10% except for the slab displacement. When LMD reaches 1.5 m, the maximum slab displacement exceeds the safety limit of 0.5 mm. The vertical wheel–rail contact force and the rail displacement exceed the safety limit with the mortar disengagement length of 2 m and the mortar disengagement height of 1.5 mm. The most increase rates induced by mortar disengagement are 190% and 272% with regards to the slab displacement and the longitudinal tension stress of slab, respectively, which is significantly detrimental to the service life of slab. The proposed approach has the potential to preliminarily determine the critical mortar disengagement size, which is conductive to relieving the pressure of track maintenance while ensuring the service life of track structures and the operation safety and riding comfort of the vehicle.

Testing of Fabric Reinforced Cementitious Matrix in Shear without Substrate

This paper aims at investigating the matrix-to-textile stress transfer in a fabric reinforced cementitious matrix FRCM system, not bonded to any substrate, under shear loads. To this end, direct shear tests are performed on a basalt FRCM specimen introduced into an innovative properly designed four-hinge frame loaded by a universal testing machine. The role of the single components in the global shear behavior of the FRCM is experimentally analyzed. Digital image correlation (DIC) is adopted for evaluating both the displacement and strain fields as well as for detecting the damage. Furthermore, the shear response of the tested FRCM material is reproduced via an effective numerical approach that considers the nonlinear behavior of the mortar and the possible micro-mechanisms that arise between the textile and the matrix, introducing suitable interfaces joining the FRCM constituent layers, i.e. textile and mortar layers. Experimental outcomes highlighted the non-negligible influence of the matrix in the shear response of the composite, both in strength and stiffness. The proven DIC technique demonstrated to be suitable also for this novel test type, since it allows to obtain shear strains, location and amplitude of cracks with satisfying accuracy, such as to make direct shear tests results a benchmark to be used for numerical simulations. Numerical analyses are performed in order to verify the efficiency of the proposed model in reproducing the mechanical behavior of FRCM composites under shear loads and in describing the damage patterns during the loading process.

Tensile Behavior of Textile-Reinforced Mortar: Influence of the Number of Layers and their Arrangement

In the last decade, textile-reinforced mortar (TRM) composites have been introduced as a sustainable solution for the strengthening of masonry structures. As an externally bonded reinforcement system, it consists of textile fibers embedded in an inorganic matrix (e.g., lime or cement mortar) applied to the substrate. Even though many studies have been focused on characterizing the mechanical behavior of TRM composites in recent years, there are still some drawbacks, including their tensile performance and few studies about multilayer textiles arrangement. This work aims at clarifying the effect of adding a second textile layer to TRM composites and investigating how textile arrangement affects the tensile behavior of the composite system. For this purpose, AR-glass and steel-based TRM composites were used in single layer and multilayer with different arrangements embedded in a lime-based mortar. The results show that using two plies of textile mesh improves the tensile response of TRM composites. In addition, it is found that the arrangement of different layers in the matrix influences the TRM response in different stress stages. The addition of a thin layer of mortar between two layers seems to improve the stiffness in uncracked condition and slightly decreases the final strength of TRM. Thus, the present study makes a step toward optimizing the arrangement of textiles in multilayer TRM composites.

A Simplified Modelling Approach for the In-Plane Analysis of Masonry Structures Strengthened by FRCMs

Among the many strengthening techniques introduced for the seismic retrofitting of the masonry structures, FRCM strategies, based on the application of fibre-reinforced composite materials on the masonry surface through inorganic mortar layers, has become object of research due to their good performances in terms of physic and mechanic compatibility with historical substrate, low invasiveness and capacity to improve both the in-plane and the out of plane masonry behaviour increasing the capacity and the ductility of the structure. In this paper, a simplified discrete model is proposed to simulate the in-plane behaviour of masonry panels strengthened by FRCM systems. The proposed modelling approach is based on the DMEM model, whose numerical configuration can adapt to encompass the properties of the externally bonded strengthening system. According to the proposed strategy, the masonry support and the FRCM layers are simulated by an equivalent homogeneous material, discretized by a mesh of shear-deformable articulated quadrilaterals interacting along their edges by means of cohesive-friction links. The model is implemented in OpenSees and validated by simulating experimental shear-diagonal tests, available in literature.

Efficient Use of Graphene Oxide in Layered Cement Mortar.

Graphene oxide (GO) has been found to be an attractive nanomaterial to improve the properties of cementitious composites. However, the use of GO in the industry is limited by its high cost. To achieve a higher cost/performance ratio, GO can be strategically applied in certain parts of cementitious composites structure according to the principle of functionally graded materials. In this study, graded distribution of GO in cement mortar was achieved by sequentially casting a fresh GO-incorporated cement layer on another cement mortar layer. The mechanical properties, especially flexural strength, of layered cement mortar were found to be dependent on the GO content, the delay time, and the interface formed due to layering fabrication. With the GO incorporated in the tensile region only (30% of the total depth), the flexural strength of the layered beam attained 90.91% of that of the beam, with GO uniformly distributed throughout the sample. Based on the results of rapid chloride migration tests, when 12 mm GO-incorporated cement mortar layer was used, the chloride migration coefficient was reduced by 21.45%. It was also found that the measured chloride migration coefficient of layered cement mortar agreed with the series model. The present investigation provides an efficient approach to use GO in cement-based materials from the perspective of mechanical and durability properties.