Steel Fiber Reinforced Mortar Research Articles

Study on the Influence of Waste Rock Wool on the Properties of Cement Mortar under the Dual Fiber Effect of Polyvinyl Alcohol Fibers and Steel Fibers

In this paper, the effect of waste rock-wool dosage on the workability, mechanical strength, abrasion resistance, toughness and hydration products of PVA and steel fiber-reinforced mortars was investigated. The results showed that the fluidity of the mortar gradually decreased with the increase in the dosage of waste rock wool, with a maximum reduction of 10% at a dosage of 20%. The higher the dosage of waste rock wool, the greater the reduction in compressive strength. The effect of waste rock wool on strength reduction decreases with increasing age. When the dosage of waste rock wool was 10%, the 28 days of flexural and compressive strengths were reduced by 4.73% and 10.59%, respectively. As the dosage of waste rock wool increased, the flexural-to-compressive ratio increased, and at 20%, the maximum value of 28 days of flexural-to-compressive ratio was 0.210, which was increased by 28.05%. At a 5% dosage, the abraded volume was reduced from 500 mm3 to 376 mm3—a reduction of 24.8%. Waste rock wool only affects the hydration process and does not cause a change in the type of hydration products. It promotes the hydration of the cementitious material system at low dosages and exhibits an inhibitory effect at high dosages.

Experimental and numerical evaluation of the out-of-plane bending behavior of masonry walls retrofitted by Steel Fiber Reinforced Mortar coating

The Out-of-Plane (OP) bending behavior of Un-Reinforced Masonry (URM) walls retrofitted by Steel Fiber Reinforced Mortar (SFRM) coating was investigated by performing in-situ experimental tests on two one-way vertically spanning walls. The latter were part of a full-scale two-story hollow block masonry building provided with seismic floor diaphragms and a 30 mm thick SFRM coating applied only on the external surface of the structure. One of the two test walls was tested under monotonic loading whereas the remaining one was subjected to reverse cyclic loading.Non-linear finite element analyses were performed to simulate the behavior of the specimens. To this end, a plane-stress model based on the smeared crack approach was implemented in the commercial code Diana 10.5. The simulations allowed to predict the response of both the strengthened walls and the un-strengthened (reference) member not included in the experimental campaign.The paper reports the results of the experimental tests including some important considerations on the observed failure mechanisms, the resistance and the displacement capacity of the walls. Moreover, the main results of the numerical simulations are reported and compared with those obtained from the tests in order to get a full comprehension of the different mechanisms affecting the response of the specimens.

Analytical prediction of the seismic resistance of masonry buildings retrofitted by Steel Fiber Reinforced Mortar coatings

An extensive experimental program has been performed in the last years at the University of Brescia to show the effectiveness of the in-plane seismic strengthening or repairing of existing masonry buildings by Steel Fiber Reinforced Mortar (SFRM) coatings. In particular, the tests on a full-scale hollow clay block masonry building showed the applicability of the retrofitting technique on the external surface of the structure only.An analytical model already developed and validated is briefly presented in this article and applied to the building experimentally tested. Particular attention is paid to the simplified schematization of the masonry piers based on the fracture lines expected before and after retrofitting. The effectiveness of the analytical model in predicting the seismic resistance of the building is assessed by comparing the analytical results with those obtained from the experimental test.Finally, the analytical model is applied to a real two-story residential building made of concrete hollow units to perform the seismic verification of the structure. The analytical prediction of the global seismic resistance of the building is compared with that obtained from a non-linear static analysis carried out with the finite element program Midas FEA. The results of the comparison will further prove the reliability of the proposed analytical model.

Experimental study and mesoscale finite element modeling of elastic modulus and flexural creep of steel fiber-reinforced mortar

Incorporation of fiber into cementitious materials would affect their mechanical and creep properties. The macro creep test is normally time-consuming and is difficult to evaluate the influence of the microstructures fully. This study investigated experimentally the elastic modulus and flexural creep of mortars with different volume fractions of steel fibers. Then a mesoscale finite element (FE) model consisting of mortar and randomly-distributed steel fibers was developed. The results show that the elastic modulus of mortars increases with increasing volume fraction of steel fiber, but the specific flexural creep exhibits an opposite trend. The influence of volume fraction of steel fiber on the specific flexural creep is more significant than that on the elastic modulus. The mesoscale FE model developed in this study is capable of capturing well the development of elastic modulus and flexural creep of mortars with different volume fractions of steel fibers. The simulated results reveal that fiber orientation is an important factor affecting the elastic modulus and flexural creep of steel fiber-reinforced mortars. The flexural creep (elastic modulus) of steel fiber-reinforced mortar increases (decreases) with increasing fiber rotational angle with respect to the stress direction. Moreover, both the elastic modulus and flexural creep of the mortar containing randomly-distributed steel fibers are equivalent to those of the mortars with steel fibers distributed by a fixed rotational angle of 30° when the volume fraction of steel fiber ranges from 1% to 3%. The findings in this study are expected to provide references to further investigations of elastic and creep properties of fiber-reinforced cementitious materials.

Analytical model for the in-plane resistance of masonry walls retrofitted with steel fiber reinforced mortar coating

Recent experimental tests showed the ability of Steel Fiber Reinforced Mortar (SFRM) coating to significantly improve the in-plane resistance of masonry walls and buildings. International and national structural codes, such as the fib Model Code 2010 (MC2010) and the Italian building code (NTC2018), have introduced fiber reinforced cementitious composites as structural materials for designing structural elements. However, the use of these materials as jacketing of masonry buildings is currently not taken into considerations by any design guidelines as potential seismic retrofitting intervention. Besides the limited availability of experimental data, this gap in design recommendations is closely related to the lack of design equations able to provide the shear and flexural resistance of retrofitted masonry elements.The present work aims at filling this gap by proposing code-oriented formulations for calculating the in-plane lateral resistance of walls strengthened by SFRM overlays. The model has been mainly validated by comparison with the numerical results obtained from a comprehensive parametric study presented and described in the paper. Finally, an example is presented to show a practical application of the model.

Electro-Mechanical Impedance Technique for Assessing the Setting Time of Steel-Fiber-Reinforced Mortar Using Embedded Piezoelectric Sensor

The electro-mechanical impedance (EMI) change in Piezoelectric (PZT) sensors embedded in steel-fiber-reinforced mortar (SFRM) was investigated to assess the material setting time. The EMI was continuously monitored for 12 h by the PZT sensor embedded in SFRM having fiber volume fraction of 0.5%, 1.5%, and 2.0%. The initial and final setting time of the SFRM were estimated using EMI signal change. The penetration resistance test, a conventional test method for the setting time of cement mortar, was also conducted. In the penetration resistance test, it was observed that the initial and the final setting time of SFRM accelerated as the volume fraction of the steel fiber increased. On the other hand, in the EMI sensing technique, the initial and the final setting time of the SFRM were consistent regardless of the fiber volume fraction.

Experimental investigation on flexural behavior of a precast slab joint with perfobond strips and steel fiber-reinforced mortars

This study aims to present a joining method for precast concrete slabs in the replacement work of the degraded concrete slab in existing steel girder bridges. The joint uses perfobond strips along with steel fiber-reinforced mortars, which is expected to be smaller and to offer a short construction time compared with traditional loop joints. Firstly, an optimized mixture of the steel fiber-reinforced mortar with both early strength development and high tensile strength is developed based on material tests. Then, eight joint specimens are fabricated and tested under flexural loads, considering the effects of various parameters associated with the layout, the perforation diameter of perfobond strips, and the curing age of joint materials. Detail discussions on load–deflection relationships, crack patterns, strain behaviors of joint components, and joint resisting mechanisms are presented. It is observed that the flexural behavior of the joint is correlated with the shear behavior of the perfobond strips, which is both significantly affected by the examined parameters. Finally, a simplified estimating method for the joint flexural capacity is then proposed according to the shear capacity of perfobond strips. The results obtained by the proposed method show a good agreement with ones from the experimental results.

Compressive and Diagonal Tension Strengths of Masonry Prisms Strengthened with Amorphous Steel Fiber-Reinforced Mortar Overlay

A technique for strengthening masonry walls by plastering with amorphous steel fiber-reinforced mortar (ASFRM) is investigated through compressive and diagonal tension tests for masonry prisms. The vertical joint between masonry units was not completely filled with mortar to mimic poor workmanship, which is typically reflected in low-cost buildings. The test variables include the number and thickness of mortar overlays, fiber volume fraction, and additional reinforcement using glass fiber mesh or shear connectors. In most strengthened specimens, the ASFRM is not damaged but separated from the masonry prisms after its maximum strength is reached. Additional tests for the bond strength between the ASFRM overlay and masonry surface are conducted to evaluate its contribution to the strengthening effects. Based on experimental observations, equations for predicting the compressive and diagonal tension strengths of masonry prisms strengthened with ASFRM are proposed. The compressive strength can be predicted more accurately by considering the asymmetrical distribution of compressive stress when strengthening is performed on only one side. The diagonal tension strength after strengthening can be predicted by incorporating the contribution of the bond strength between the ASFRM overlay and masonry prism to the initial strength.

Cyclic Test on a Full-Scale Unreinforced Masonry Building Repaired with Steel Fiber-Reinforced Mortar Coating

The present work reports the results of two quasi-static reverse cyclic tests performed on an unreinforced hollow clay block masonry building before and after repairing with a single 30-mm thick layer of mortar applied on the façades. Unlike traditional coating-based retrofitting techniques, the one proposed herein adopts a cement-based mortar reinforced with short high-strength steel fibers randomly diffused in the mortar matrix. In order to assess the effectiveness of the strengthening intervention, a preliminary cyclic test was carried out on the unstrengthened building in order to predamage masonry. The experimental results showed that the repaired structure exhibited a significant improvement of seismic behavior both at the serviceability and ultimate limit state conditions. Moreover, based on the observed ultimate ductility of the retrofitted building, some considerations on the behavior factor are reported.

Enhancement of Compressive and Shear Strength for Concrete Masonry Prisms with Steel Fiber-Reinforced Mortar Overlay

Enhancement of Compressive and Shear Strength for Concrete Masonry Prisms with Steel Fiber-Reinforced Mortar Overlay

Retrofitting unreinforced masonry by steel fiber reinforced mortar coating: uniaxial and diagonal compression tests

Thin layers of mortar reinforced with steel fibers can be applied on one or both sides of bearing walls as an effective seismic strengthening of existing masonry buildings. To assess the effectiveness of this technique, an experimental study on masonry sub-assemblages was carried out at the University of Brescia. This paper summarizes and discusses the main results of the investigation, which included mechanical characterization tests on masonry and its components as well as on the Steel Fiber Reinforced Mortar (SFRM) used to retrofit the masonry samples. Uniaxial and diagonal compression tests were carried out on both unstrengthened wallets and masonry samples retrofitted with 25 mm thick SFRM coating. Both single-sided and double-sided retrofitting configurations for application on wall surfaces were considered. The results highlighted the ability of the technique to improve the compressive and the shear behavior of masonry, even in case of single-sided strengthening. Moreover, no premature debonding of coating was observed. Lastly, the manuscript presents the results of a numerical investigation that was performed both to simulate the diagonal compression tests described in the first part of the paper and to predict the response of panels with different strengthening configurations.

Experimental evaluation of the shear capacity of perfobond strips with steel fiber-reinforced mortar in narrow joint structures

Appropriate transfer of the shear force of a perfobond strip used as a shear connector in steel concrete hybrid structures depends on the restraining effect around the strip, and hence, the arrangement of the surrounding reinforcements is very important to improve the restraining effect. However, when the perfobond strip is arranged in narrow joint structures and when the rapid construction is also required, reinforcements are undesirable on the site. An alternate method to improve the restraining effect around the perfobond strip is to use steel fiber-reinforced mortar (SFRM). This study aims to evaluate appropriately the shear capacity of a perfobond strip with SFRM without surrounding reinforcements for narrow joint structures. Assuming these conditions, pull-out tests were conducted, and the data obtained were considered along with the results of push-out tests conducted in the previous study of the authors. Based on the results of both test series, the impacts of various factors on the shear capacity of the perfobond strip was analyzed comprehensively. The results showed that the shear capacity of a perfobond strip with SFRM increases with the perforation diameter, SFRM compressive strength, volume content of steel fibers in the mortar, and dimensions of the mortar block around the perfobond strip. Moreover, the plasticization of the perfobond steel plate and the difference in boundary conditions between the push-out and pull-out tests also affect the shear capacity of the perfobond strip. An equation was proposed for evaluating the shear capacity of the perfobond strip with SFRM without any surrounding reinforcements for narrow joint structures. The shear capacity obtained using the proposed equation has high correlation with the experimental value for both push-out and pull-out specimens.

Evaluation of the vertical load capacity of masonry arch bridges strengthened with FRCM or SFRM by limit analysis

The large number of existing masonry bridges still in service in the world roadway and railway networks requires that transportation system managers carry out ordinary and extraordinary maintenance. In many of these networks, the need for increasing the speed and/or weight of the traffic loads also entails the design of strengthening interventions aimed at enhancing the load-carrying capacity of masonry bridges. Among the available techniques for the strengthening of these structures, the use of fiber reinforced cementitious matrix (FRCM) composites has gained popularity due to their advantages with respect to more traditional techniques. More recently, the use of steel fiber reinforced mortars (SFRM), has also been investigated for the strengthening of masonry bridges, with promising results. In this paper, a limit analysis for assessing the vertical load-carrying capacity of single-span bridges strengthened with FRCM or SFRM, applied at the intrados, is described, and calibrated using available experimental results. The document highlights the variables that should be considered in such procedure and also discusses the similarities and differences between the two strengthening techniques. A subsequent parametrical analysis shows that both techniques produce comparable increments in the load carrying capacity of the masonry bridges when compared to unstrengthened conditions. In addition, it was seen that if the finite friction between blocks is not considered when performing the limit analysis of masonry bridges, the ultimate load capacity of the arches can be overestimated as the failure mode can be attained due to shear sliding of the masonry blocks, a hinge mechanism or a combination of both.

Investigation of Steel Fiber-Reinforced Mortar Overlay for Strengthening Masonry Walls by Prism Tests

A strengthening method using steel fiber-reinforced mortar (SFRM), proposed for the seismic retrofit of masonry buildings, is verified experimentally in this study. The SFRM is overlaid on masonry walls directly, which is possible to implement while the building is occupied for residence. First, tests of workability and material strengths were conducted for SFRM itself in order to find SFRM mixing ratios appropriate for overlay construction and strengthening. Then, masonry prisms were produced using two types of bricks and strengthened with SFRM for the chosen mixing ratios and test variables such as the number of overlaid sides and the fiber volume fraction. Compressive strength tests and diagonal tension tests for those specimens were conducted. Both compressive and shear strengths were improved the most highly by overlaying the SFRM with a fiber volume fraction of 1.3%, which is the highest among the test variables, on both sides. Overlaid SFRM tends to be detached without cracking almost at the maximum strength in both compression and diagonal tension tests. For red clay brick prisms, the compressive and shear strengths increased by up to 61% and 138%, respectively. For concrete brick prisms, the compressive and shear strengths increased by up to 26% and 67%. Finally, a design formula for the shear strength of strengthened masonry prisms is compared with the experimental results, and it is observed that the design formula gives slightly higher results.

Bond behavior of steel fiber-reinforced mortar (SFRM) applied onto masonry substrate

Masonry was the most used material during the last centuries to build constructions. Most of the existing masonry structures (buildings, bridges, etc.) were built without considering some important structural considerations that are important nowadays. Moreover, due to factors such as the increasing of service loads, materials aging, structural damage, etc., the existing masonry structures require strengthening interventions. The definition of optimal strengthening strategies using traditional and innovative materials is still an important issue of the scientific research. In fact, during the last decade, many researchers focused their attention studying innovative composites materials, such as fiber-reinforced polymers and fiber-reinforced cementitious matrix composites, for the strengthening of existing masonry structures. This research has focused on aspects such as the bond behavior between the substrate and the composite materials, the structural behavior of the strengthened masonry and concrete structures, and the compatibility and reversibility of these materials when bonded to existing substrates. In this study, the bond behavior of a composite material known as steel fiber-reinforced mortar (SFRM), recently used as for the strengthening of existing structures, applied onto masonry structures is analyzed experimentally and numerically. First, the material is characterized experimentally with the aim of getting insight on its behavior and applicability when applied as an innovative technique for the strengthening of masonry and to obtain mechanical parameters required for the numerical models. Mechanical properties of the SFRM studied included flexural and compressive strength, tensile strength, and residual flexural strength. The SFRM bond behavior on masonry substrates was evaluated by means of double shear lap tests. In addition, the experimental tensile and bond behavior of the SFRM is studied numerically through finite-element models validated using the results obtained during the experimental tests. Results show that if an adequate bonded length is provided, the SFRM can fully develop its tensile strength as detachment from the substrate is not observed.

Shear behavior of a perfobond strip with steel fiber-reinforced mortar in a condition without surrounding reinforcements

To sufficiently transmit the shear force of a perfobond strip shear connector in steel–concrete hybrid structures, the arrangement of the surrounding reinforcements is essential to improve the restraining effect around the perfobond strip. However, in cases of joint structures with small dimensions and rush work on site, because the arrangement of reinforcements in the joint is challenging, steel fiber-reinforced mortar (SFRM) can be used along with a perfobond strip to improve the restraining effect around the perfobond strip. This study investigates the shear behavior of a perfobond strip that uses SFRM without surrounding reinforcements. Push-out tests were conducted focusing on the effect of steel fibers inside the SFRM, SFRM compressive strength, perforation diameter, and dimensions of the mortar block around the perfobond strip. Findings of the study confirmed that the steel fibers inside the mortar contribute to the restraining effect around the perfobond strip, thus preventing a rapid drop in the shear force beyond the shear capacity of the perfobond strip. The shear capacity of the perfobond strip combined with SFRM increased with the perforation diameter, SFRM compressive strength, and dimensions of the mortar block around the perfobond strip. Several shear capacity evaluation equations proposed in previous studies are not applicable for evaluating the shear capacity of the perfobond strip that uses SFRM without surrounding reinforcements. Here, the shear capacity of the perfobond strip can be evaluated by considering the correlation between the experimental parameters of this study, but more test data are required.

Quasi-static cyclic tests of confined masonry walls retrofitted with mortar overlays reinforced with either welded-wire mesh or steel fibers

Overlays made of high-slump mortar reinforced with a steel welded-wire mesh are one of the most common techniques to retrofit low-rise confined masonry walls. An alternative to this technique is the use of Steel Fiber-Reinforced Mortar (SFRM) overlays to strengthen and enhance the shear capacity of existing masonry walls. In this paper, test results are presented of two full-scale, multi-hollow clay brick confined walls strengthened with reinforced mortar overlays. The overlays consisted of a high-slump mortar reinforced with a) welded-wire reinforcement in one wall and b) hooked end steel fibers in the second wall. Overall height and length of the walls were 2.5 m and 4.24 m, respectively. Both walls were tested under in-plane, quasi-static, reversed cyclic lateral loads. Performance of the retrofitted walls is evaluated in terms of crack patterns, hysteretic response, and lateral strength and displacement capacity. The test data show that both retrofit techniques performed very well and they each restored the strength and deformation capacity to that of the original walls.

Experimental behaviour of damaged masonry arches strengthened with steel fiber reinforced mortar (SFRM)

In this paper, the results of an experimental campaign aimed to study the behavior of damaged solid clay brick masonry arches strengthened with steel fiber reinforced mortar (SFRM) are presented. Conditions of damage studied included preloading, horizontal displacement of one of the supports, or a combination of both. After damage was produced, the arches were strengthened with one layer of SFRM at the intrados and retested. The performance of the strengthened arches is discussed in terms of failure mode, and variation in the load carrying capacity, ductility and stiffnesses with respect to unstrengthened undamaged condition. The results show that the SFRM strengthening was able to increase significantly the strength and stiffness of the arches, although in some cases such increase was accompanied by a reduction in the specimens’ ductility. In addition, an analytical formulation for the design and assessment of the capacity of masonry arches strengthened with SFRM was developed. Comparison between predicted and experimental values show good agreement, which allowed validating the analytical method.

Strengthening of Masonry Arches with SFRM

Research on the preservation and restoration of masonry arches is of interest for the scientific and civil engineering communities, and the construction industry. Among the open investigation topics in the field, the study of new materials for strengthening masonry arches has gained attention from researchers. In this context, this paper presents the experimental results from destructive tests carried out on a masonry arch strengthened with steel fiber reinforced mortar (SFRM). The tested masonry arch was made of solid clay bricks disposed in a single layer and was strengthened with a single layer of steel FRM bonded at the arch intrados. In order to replicate the possible condition of an existing arch in which acting loads exceeded the member strength, the arch was preloaded before strengthening. The performance of the strengthened arch is discussed in terms of witnessed failure mode, ductility and increase in the load carrying capacity with respect to unstrengthened condition.

Strengthening of Masonry Arches with FRCM Composites: A Review

Research on the preservation and restoration of masonry arches is of interest for the scientific and civil engineering communities, and the construction industry. Among the open investigation topics in the field, the study of new materials for strengthening masonry arches has gained attention from researchers. In this context, this paper presents the experimental results from destructive tests carried out on a masonry arch strengthened with steel fiber reinforced mortar (SFRM). The tested masonry arch was made of solid clay bricks disposed in a single layer and was strengthened with a single layer of steel FRM bonded at the arch intrados. In order to replicate the possible condition of an existing arch in which acting loads exceeded the member strength, the arch was preloaded before strengthening. The performance of the strengthened arch is discussed in terms of witnessed failure mode, ductility and increase in the load carrying capacity with respect to unstrengthened condition.