Mortar Beams Research Articles

Flexural behavior of hollow self compacted mortar ferrocement beam reinforced by GFRP bars

This study aimed to investigate a form of ferrocement that was a hollow ferrocement beam of self-compacting mortar reinforced with various types of metallic (steel bars, steel wire mesh) and non-metallic (GFRP bars, fiber glass mesh) reinforcement. The experimental program comprised casting twenty ferrocement beams with dimensions of 150 × 225 × 2000 mm, incorporating 50 mm of ferrocement thickness and a polystyrene cork core of 50 × 125 mm. The results showed that the hollow ferrocement beams reinforced with GFRP bars and several layers of the fiber glass mesh (one, two and three) gave higher loads by 7.51%, 9.88% and 5.15%, respectively, as well as higher energy by 4.75%, 27% and 15.10%, respectively, However, the ductility of these beams was reduced by 37.84%, 37.33%, and 44.27%, when compared to beams reinforced with steel bars and several layers of steel wire mesh (one, two and three). These beams gave lower first crack loads, high deflections, and wide cracks with no control on crack width compared to beams reinforced with steel. The increasing number of the welded wire mesh and fiber glass mesh layers increases the first crack load, ultimate load, and energy absorption by 20%, 30.25% and 69.2%, respectively, in the ferrocement beams reinforced with (steel bars and steel wire mesh) and 34.36%, 27.1% and 94.92% respectively, in the ferrocement beams reinforced with (GFRB bars and fiber glass mesh) when three layers of mesh were used compared to beams reinforced with bars only without mesh. Also, the study shows that steel wire mesh and fiber glass mesh materials were better at controlling crack width than beams reinforced with bars only without wire mesh. The results showed that the theoretical calculations based on strain and force distribution assumptions that the theoretical and experimental ultimate loads of the beams reinforced with steel were acceptable, with a ratio ranging from 0.98 to 1.12. But, in the beams reinforced with GFRP, the theoretical and experimental ultimate loads of the beams were varied and spaced clearly with a ratio that ranged from 0.82 to 1.36. The study showed that the hollow ferrocement beams reinforced with steel bars and steel wire mesh layers were more efficient than beams reinforced with GFRP bars and fiber glass mesh.

Mechanical properties of mortar beams reinforced by gyroid 3D printed plastic spatial elements

After four decades of technological development, 3-D printing (and other additive manufacturing technologies) is slowly entering research efforts associated with construction and civil engineering. A significant majority of this research effort has focused on 3-D printing of a fresh concrete mix. The authors propose a very different approach for the utilization of 3-D printing in civil engineering based on plastic spatial reinforcing elements for concrete. The mechanical properties of 3-D printed plastics are significantly lower than those of traditional steel re-bars; however, the unconventional and spatial geometric shapes of plastic reinforcement can minimize some of these differences. In the conducted research program, gyroids were harnessed as spatial reinforcing elements that are unachievable using traditional reinforcing techniques. The properties of the tested plastic-mortar elements were highly quasi-plastic and similar to those of good-quality steel fiber-reinforced concrete. The flexural characteristics of plastic-mortar elements enable the testing of possible substitutes for steel reinforcements. Areas of future research and current applications of plastic-mortar elements are discussed.

Flexural characterization and ductility assessment of small-scale mortar beams reinforced with 3D-printed polymers

Additive Manufacturing (AM) is recently getting tremendous attention in many scientific fields. In this research, a civil engineering application of AM is investigated, where thirty small-scale cement mortar prisms reinforced with 3D-printed thermoplastics were tested in flexure. Rebar-like reinforcement were printed using a fused deposition modeling (FDM) printer. Five different thermoplastics were used with three different surface morphologies, obtained by introducing lugs on the rebar surface. The lugs were intended to enhance the reinforcement-matrix bond. Beams were tested in a three-point bending configuration to assess their load–deflection response and flexural ductility. In general, the introduction of lugs increased the load-carrying capacity of the specimen, between 40 and 120%. The ductility of beams was calculated based on displacement and energy methods. Due to the lack of a definite yield point in such composites, modifications to well-established ductility calculation methods are proposed here. The results indicate the capability of thermoplastics to reinforce mortar beams in flexure. Surface morphology has shown to be significantly influential for most of the thermoplastics considered in this study in terms of strength gain and ductility.

Electrical Methods for Sensing Damage in Cement Mortar Beams Combined with Acoustic Emissions.

The temporal variation in terms of the “time-to-failure” parameter of the recordings of the electrical resistance and the acoustic emissions from concurrent measurements in three cement mortar specimens of prismatic shape that were subjected to a three-point bending test until fracture are studied. The novelty of the work at hand lies in the demonstration that the electrical resistance is described by a power law during the last stages of the loading protocols. The onset of the validity of the power law is indicative of the specimens’ imminent fracture, thus providing a useful pre-failure indicator. The above findings are supported by the analysis of the recorded acoustic signals in terms of the F-function and the Ib-value formulations.

Interfacial Bonding Strength in Cement Mortar Beams Reinforced with Metamaterial Bars

Reinforced concrete beam (RCB) elements show low mechanical performance when interfacial bonding strength (IBS) is not well controlled. New tailorable material-structure arrangements - Metamaterials - offer solutions to the IBS problem. This paper analyzes the mechanical characteristics of IBS on RCBs for reinforced cement mortar containing Metamaterial bars (MMB) that were machined from SAE 1020 Carbon steel. Each MMB has a stepped geometrical shape, with a cylindrical bar divided into equal-length segments, along with a ’rise height’ (p) change. Four geometries were defined, i.e., R0− Smooth bar, R1− p = 0.1mm, R2− p =0.3mm and R3− p=0.5mm. Three-point flexural strength tests were performed on the RCBs to determine the maximum bond strength (ML) between the MMB and cement mortar. Images of interfacial regions were obtained using SEM and 3D Roughness Reconstruction software to calculate the average roughness (Ra) and the roughness height (Rz). The reinforcement MMB geometry had a significant impact on the ML results, particularly on the first crack strength and the failure mode. The R3 geometry ML values were higher than the other tested geometries (44.5%). The results of the scale models are encouraging and offer a novel and prospective direction for further experimental and even numerical Metamaterial research to improve interfacial bond strength.

Enabling shape memory effect wires for acting like superelastic wires in terms of showing recentering capacity in mortar beams

Superelastic shape memory alloy (SMA) wires embedded in mortar beams show a recentering capacity, however, shape memory effect wires can provide a prestressing effect after inducing phase transformation. In this study our goal is to empower shape memory effect wires to show recentering capacity by designing a new wire configuration. These wires will thus be able to achieve both a prestressing effect and a recentering capacity in mortar beams. To this end, various shapes of martensitic SMA wires, including as-received, crimped, dog bone, and anchoring reinforced crimped wires, were employed to examine the potential of displaying recentering capacity while preserving the prestressing force in mortar beams. Several monotonic and cyclic three-point bending tests were also conducted to investigate the crack-closing effect, as well as the load bearing of the specimens. To evaluate the effect of temperature and heating procedure, two different methods, namely, a hot air gun and electric current heating, were used to induce phase transformation in shape memory effect wires. The results generally show that for two types of as-received and dog bone wires, the displacement recovery ratio have been reduced about 65% and 74%, respectively, however, for the crimped wire and anchoring reinforced crimped wire, this ratio is almost the same. More importantly, when the results of displacement recovery ratio of crimped wires heated by electrical heating are compared with the available experimental data for superelastic SMA bars, proves the great ability of SME wires to fulfill recentering capacity.

Mechanical performance of mortar mixes reinforced with hemp and fique fibers treated with sodium silicate

Natural fibers have been a replacement option for the plastic fibers used in mortar mixtures, given their ease of achievement and lower extraction cost, this gives them a strong advantage over their potential application as reinforcement. Hemp and fique were added to the mortar matrix, these fibers were superficially treated with sodium hydroxide at 1%, 2%, 5% and 10%. Subsequently, the fibers were immersed in a sodium silicate solution for 24 hours, extracting them and allowing them to dry at room temperature. The fibers were chemically characterized using infrared spectrophotometry, scanning electron microscopy, and gravimetric techniques. Mortar cubes and mortar beams were made evaluating their mechanical performance with the addition of 1% of natural fibers with and without sodium silicate treatment. The results showed that of the untreated fibers, that of hemp is the most resistant compared to that of fique, and the chemical impregnation treatments with sodium silicate improve the mechanical properties of the fibers, in this way the addition of reinforcement in the mortar and the treatment used to improve the mechanical properties of the fibers added in the mixtures improve the flexural strength compared to the control specimen.

Modelling of the fully coupled chemo-mechanical degradation for cement-based materials

The coupling of chemically induced degradation and mechanical damage is fundamental to investigate the durability of load-bearing cement-based materials subject to aggressive environments. This study is devoted to the incorporation of a reactive transport model and non-local damage model to integrate the complete process of chemical degradation and appropriate propagation of mechanical damage in the framework of coupled chemo-mechanical degradation. The chemical degradation of cement-based materials subject to leaching solution is principally concluded as the dissolution of portlandite and decalcification of C–S–H, and the reduction of Young's modulus is evaluated based on the microstructure of cement-based materials by the Mori–Tanaka scheme. The displacement-based non-local damage model is incorporated to capture the post-peak behaviour of the leached mortar beam in three-point bending test. The significance of coupling chemical and mechanical damage for the degraded beam is demonstrated by comparing the fully coupled damage with outcomes of the non-coupled case.

Degradation Monitoring in Reinforced Concrete with 3D Localization of Rebar Corrosion and Related Concrete Cracking

Corrosion of the reinforcement is a major degradation mechanism affecting durability and safety of reinforced concrete (RC) structures. As the corrosion process starts internally, it can take years before visual damage can be noticed on the surface, resulting in an overall degraded condition and leading to large financial costs for maintenance and repair. The acoustic emission (AE) technique enables the continuous monitoring of the progress of internal cracking in a non-invasive way. However, as RC is a heterogeneous material, reliable damage detection and localization remains challenging. This paper presents extensive experimental research aiming at localizing internal damage in RC during the corrosion process. Results of corrosion damage monitoring with AE are presented and validated on three sample scales: small mortar samples (scale 1), RC prisms (scale 2), and RC beams (scale 3). For each scale, the corrosion process was accelerated by imposing a direct current. It is found that the AE technique can detect damage earlier than visual inspection. However, dedicated filtering is necessary to reliably localize AE events. Therefore, AE signals were filtered by a newly developed post-processing protocol which significantly improves the localization results. On the smallest scale, results were confirmed with 3D micro-CT imaging, whereas on scales 2 and 3, results were compared with surface crack width measurements and resulting rebar corrosion levels.

Crack sealing evaluation of self-healing mortar with Sporosarcina pasteurii: Influence of bacterial concentration and air-entraining agent

Microbial induced calcium carbonate precipitation has been recognized as a novel pathway to repair concrete cracks. This study aimed to explore the application of Sporosarcina pasteurii in self-healing mortar preparation, and further investigate the influence of bacterial concentration and air-entraining agent content on crack sealing performance. X-ray diffraction and scanning electron microscope tests were carried out to identify the calcium carbonate in vaterite phase for biomineralization precipitations of S. pasteurii which was utilized for self-healing mortar beam specimens production. Subjected to 3-point-bending test, a V-shape crack was induced from the beam bottom with 0.4 mm width which can be automatically healed due to bacteria metabolic activity. Four different S. pasteurii concentrations, i.e., 0, 2 × 105, 2 × 106 and 2 × 107 cells/ml, were comparatively studied with respect to self-healing mortar property. In general, the higher bacterial concentration corresponded to faster crack healing and 2 × 106 cells/ml was deemed as the proper bacterial concentration. Afterwards, self-healing mortar with various air-entraining agent contents (0%, 0.005%, 0.01%, 0.015% and 0.02% of cementitious material) was also discussed, implying that best flexural strength regain is achieved at 0.01% air-entraining agent. Finally, the crack filling crystals were examined to find bacterial imprints leaving on the surface of calcium carbonate.

Shear Strength of Reinforced Mortar Beams Containing Polyvinyl Alcohol Fibre (PVA)

The current study aims to assess the shear behaviour of reinforced mortar beams including Polyvinyl Alcohol Fibre (PVA) ranges from 0 to 2.25%, fly ash (55%) and silica fume (15%). Fourteen beams were experimentally tested under two concentrated loads. In addition, a finite element model was developed to predict the crack pattern, load–deflection, energy absorption, and shear strength results of the test beams. The studied variables were different percentages of PVA fibres, shear span to depth ratio (a/d), and transverse reinforcement (stirrups) ratio. The fly ash and silica fume were kept constant in all the studied mixes to achieve a compressive strength above 55 MPa at the time of testing (90 days) and to improve PVA-mortar properties. It was found that the inclusion of PVA improves the shear behavior of the tested beams in terms of crack pattern and ductility. It was observed also that reducing a/d led to enhancing the shear capacity without changing the mode of failure. In addition, PVA played the same role as the stirrups and their effect on the ultimate shear capacity was increased with reducing the volume of stirrups. Moreover, the PVA fibres were more effective in lower shear span to depth ratio (a/d = 1.5) giving an enhancement of shear resistance of 221%. The non-linear finite element model showed excellent agreement with the experimental results and the ratio of the predicted to experimental ultimate strength ranged between 0.91 and 1.09. The authors recommend a combination of fly ash, silica fume and at least 1.5% PVA in the presence of minimum stirrups reinforcement (5 $$\Phi$$ 6/m) or adding 2.25% PVA without stirrups to achieve adequate shear behaviour and to improve the ductility of PVA-mortar beams.

Experimental and finite element analysis on flexural behavior of mortar beams with chemically modified kenaf fibers

In this study, raw kenaf fibers (RKF), alkaline treated kenaf fibers (AKF), and alkaline-hydrogen peroxide treated kenaf fibers (AHPKF) were prepared and then incorporated into mortar to evaluate their impact on the flexural behavior of mortar. In addition to the fiber type, the effect of fiber dosage (0.25%, 0.5%, and 0.75% by weight of cement) on flexural behavior was also studied. Finite element analysis (FEA) was conducted to assist in examining the stress and cracking strain within the mortar specimens. The results show that with the increase of fiber dosage, although the compressive strength and flexural strength of the mortar decrease, a huge improvement of flexural toughness can be achieved. By comparing these three types of kenaf fibers, AKF provides the best performance compared to the other two. With the addition of superplasticizer, the flexural behavior of mortar can be further improved. The microstructure analysis provides some insight into the flexural behavior of mortars with chemically modified kenaf fibers. Lastly, the finite element analysis indicates that the presence of fibers in mortar can increase the residual load, slow down crack propagation, and reduce the cracking strain.

Ureolytic MICP-Based Self-Healing Mortar under Artificial Seawater Incubation

Ureolytic microbial-induced calcium carbonate precipitation (MICP) is a promising green technique for addressing sustainable building concerns by promoting self-healing mortar development. This paper deals with bacteria-based self-healing mortar under artificial seawater incubation for the sake of fast crack sealing with sufficient calcium resource supply. The ureolytic MICP mechanism was explored by morphology characterization and compositional analysis. With polyvinyl alcohol fiber reinforcement, self-healing mortar beams were produced and bent to generate 0.4 mm width cracks at the bottom. The crack-sealing capacity was evaluated at an age of 7 days, 14 days, and 28 days, suggesting a 1-week and 2-week healing time for 7-day- and 14-day-old samples. However, the 28-day-old ones failed to heal the cracks completely. The precipitation crystals filling the crack gap were identified as mainly vaterite with cell imprints. Moreover, fiber surface was found to be adhered by bacterial precipitates indicating fiber–matrix interfacial bond repair.

Experimental and numerical analysis of 3D printed cement mortar specimens using inkjet 3DP

Investigations involving the experimental and numerical analysis of inkjet (powder-based) 3DP are relatively limited for cement mortar materials. This study, by using cement mortar specimens, aimed to determine the optimum strength of 3D printed structural members in all three planes by identifying the compressive strength of cubes, the modulus of elasticity and Poisson’s ratio. In addition, this study aimed to analyse and verify the numerical model for 3D printed cementitious mortar (CP) prisms and beams using an inkjet 3D printer by considering the mechanical behaviour of the printed prisms under compression. Robust and optimal mechanical properties of the 3D printed cementitious mortar obtained from laboratory testing were utilised in the simulation of structural components using ABAQUS software. As inputs for simulation, the strength properties of the printed objects in all three cartesian planes were obtained from test results. The obtained results showed that the printed cementitious materials have orthotropic properties and that the results of experiments were consistent with the analytical solutions and hypothesised model for the different geometric shapes. This finding is extremely valuable in determining the optimum features of 3D printed structures.

Preliminary Evaluation of Cement Mortars Containing Waste Silt Optimized with the Design of Experiments Method.

Every year, up to 3 billion tons of non-renewable natural aggregates are demanded by the construction sector and approximately 623 million tons of waste (mining and quarrying) was produced in 2018. Global efforts have been made to reduce the number of virgin aggregates used for construction and infrastructure sectors. According to the revised waste framework directive in Europe, recycling at least 70% of construction and demolition waste materials by 2020 was obligatory for all member states. Nonetheless, quarries must work at full capacity to keep up with the demands, which has made quarry/mining waste management an important aspect during the past decades. Amongst the various recycling methods, quarry waste can be included in cement mortar mixtures. Thus, the current research focuses on producing cement mortars by partially substituting natural sand with the waste silt obtained from the limestone aggregate production in S.A.P.A.B.A. s.r.l. (Italy). A Design of Experiments (DOE) method is proposed to define the optimum mix design, aiming to include waste silt in cement mortar mixtures without affecting the final performance. Three cement mortar beams were produced and tested for each of the 49 randomized mixtures defined by the DOE method. The obtained results validate the design approach and suggest the possibility of substituting up to 20% of natural sand with waste silt in cement mortar mixtures.

Strain, natural frequency, damping coefficient and elastic modulus of mortar beams determined by fiber Bragg grating (FBG) sensors

Abstract Structural health monitoring can detect anomalies in time, allowing the implementation of more efficient maintenance and repair actions in special engineering structures. An alternative in the monitoring and evaluation of structures in civil engineering is the use of optical fibers inscribed with Bragg gratings (FBG or Fiber Bragg Grating). This paper aims to compare available techniques to estimate the elastic module of cementitious composites, as well as contribute to the application of optical fiber sensors in the monitoring of strain, natural vibration frequency, damping coefficient and elastic modulus of mortar beams. The FBG sensors manufactured and calibrated by the authors presented a good precision for measuring those parameters in mortar samples. The results show that FBG sensors and strain gauge sensors present a similar result for strain and estimation of the elastic module (static and dynamic), therefore, bare FBGs could be further investigated for non-destructive testing.

Influence of Portland cement alkalinity on wool-reinforced mortar

Natural wool is a good insulating material, both thermally and acoustically. With the increase in demand for the usage of waste materials, other applications have been found, such as the use of wool as a fibre reinforcement in mortars and concretes. Unfortunately, wool, like other natural organic materials, dissolves in alkaline environments and, consequently, the performance of wool reinforcement cannot be guaranteed for a long time. To address this issue, three series of wool-reinforced mortar beams, with various contents of alkalis in cement, were investigated. The chemical compatibility and the effects of alkalinity on mechanical performance were investigated by testing the beams under three-point bending and, subsequently, by analysing the microstructure of the mortars using energy-dispersive X-ray spectroscopy. The results showed that the lower the alkalinity of the cement paste, the better the resistance of wool fibres in the cementitious matrix, thus guaranteeing larger post-cracking residual stresses in the wool-reinforced mortars.

Prestressing effect of embedded Fe-based SMA wire on the flexural behavior of mortar beams

This paper investigates the stress recovery stress induced in the newly developed Fe-based SMA and then studies the prestressing effect of embedded Fe-SMA wires on the flexural behavior of mortar beams. To evaluate deflection variations of the beams during heating and cooling using an external heating source at the bottom, we increase the temperature in two types of reinforced and unreinforced mortar beams. Under developed prestressing force, several three-point bending tests are carried out to analyze the bending stress in the Fe-SMA reinforced specimens. Moreover, the crack propagation and failure modes of each specimen are investigated. Experimental data indicates that prestressing force can more than double the fracture deformation capacity and decrease the resultants stress by about 28% in both tensile and compressive parts of mortar beams.

Influence of wetting–drying cycles on compressive and flexural strength of cement mortar and CFRP-mortar bond strength

When mortar is exposed to the marine environment, its mechanical properties can degrade due to weathering by seawater spray and capillary rise. This paper investigates the compressive, flexural, and pull-out bond strengths of a commercially available M3 type mortar. Mortar cube and beam specimens were used for the compressive and flexural strength tests and UPV test. Mortar beams were also retrofitted with carbon fibre polymer (CFRP) and their flexural and pull-out bond strengths were investigated. All the specimens, except the control group, were subjected to accelerated wetting and drying cycles (WDC) over a period of nine weeks, where each cycle consisted of four days of wetting in tapwater and seawater at room temperature and three days of drying at 60 °C. A notable decrease in the compressive, flexural, and pull-out strengths of the mortar specimens, along with physical degradation of the mortar, CFRP and epoxy were observed following the WDC. Correlations between flexural and compressive strengths, and pull-out and compressive strengths is proposed, which can be useful in assessing the material properties of mortar during its service life.

The composition of the material phase responsible for the self-healing of macro-cracks in asphalt mortar beams

ABSTRACT Self-healing of asphalt is assumed to be a flow process where bitumen flows into cracks to close them. Hence, the rheological behaviour of bitumen is one of the main factors affecting self-healing together with damage history, healing duration and pressure (external compressive forces or internal thermal expansion). Bitumen-filler interaction influences the flow and it is hypothesised that the material flowing into cracks during self-healing is a mixture of bitumen, filler and eventually fine aggregates. In the paper, the self-healing ratio was determined by mechanical testing and the self-healing was accelerated by an increase of temperature to 100°C. Material draining from asphalt mortar beams into a horizontal gap, representing a crack, was found to be a mixture of bitumen and aggregates with increasing self-healing observed with increasing bitumen and filler content. For the mortar mixture used in this study, a bitumen content of 5.4 wt% was identified to be the limit for self-healing.