Papers by Keyword: Fiber Reinforced Concrete (FRC)

Abstract: This paper presents a comprehensive experimental campaign performed on natural stone masonry wallettes jacketed with 14 different combinations of mortars, meshes, and connectors. After characterizing the mortars and the bare masonry, diagonal compression tests were performed on three specimens for each jacketing solution. The performance of a fiber-reinforced, high-performance mortar without reinforcing mesh was investigated, considering its application to one or both sides of the wall, with and without connectors. Then, two different fabric reinforced cementitious matrix solutions were tested, using unidirectional or bidirectional textiles. Finally, the effects of FRP mesh spacing, mortar composition, and connector type and density were explored on reinforced plaster applications. The test outcomes were analyzed in terms of failure mode, tensile strength, and corresponding shear deformation capacity. All combinations proved effective at increasing the tensile strength compared to the bare masonry, with ratios between 1.9 and 4.7.

Abstract: This study is an experimental study aims to examine the effect of utilization of straight, and low cost steel fibers on the impact resistance of concrete. The impact resistance of steel fiber reinforced concrete (SFRC) was assessed using drop weight test as per ACI committee 544. The steel fibers were randomly dispersed in concrete during mixing. Five mixes made with steel fibers dosages of 0% (control mix), 0.5%, 1%, 1.25% and 1.5% by volume of concrete were examined in the study. The results show that mixes containing steel fibers show better impact resistance than plain concrete (control Mix). The results also indicate that increasing the dosage of fiber increases the impact resistance of concrete but up to a certain content of fibers. The maximum increase was recorded at steel fiber dosage of 1.25% by volume of concrete. Also the patterns of failure of the concrete specimens show that fibers are very effective in increasing the concrete toughness which enhance the ductility of concrete and delays the crack initiation.

Abstract: After more than fifty years from the opening of the largely discussed “Autostrada del Sole” Highway in 1964, the infrastructure system in Italy appears marked by the passing of time, similarly to what observed in several other countries worldwide. The great heterogeneity of the Italian landscape has determined a great variety of construction types, such as large span concrete bridges over the northern rivers and large arch concrete bridges over the valleys of the central region. Increment of vehicle traffic and new seismic regulations are setting new requirements to adapt the existing infrastructure, which should be otherwise replaced. Moreover, reinforced concrete (RC) aging and deterioration have led to structural and material degradation, including severe cracking and corrosion. Specialized materials such as High Performance Concrete (HPC) could represent a viable convenient solution for repairing, strengthening and retrofitting of RC structures as both structural capacity and durability can be refurbished. However, alongside high mechanical performance, HPC is characterized by a high cracking sensitivity at very early age, due to its high stiffness and shrinkage. Restrained shrinkage cracking, particularly significant in repaired structures where the existing concrete generates a considerable restraint against the free movement of the repair material, may represent a limit to the effective application of these materials. For this reason, shrinkage compatibility of HPC with the existing concrete substrate needs to be experimentally and numerically assessed. A study is herein presented where, based on experimental tests, different numerical models are developed and compared to assess and eventually minimize the risk of shrinkage cracking in bridge piers strengthened with HPC.

Abstract: The design procedure recently proposed by the same authors and based on a simplified FE model for underground tunnels subjected to internal explosion is extended in this work taking into account different possible positions of the explosive source inside the tunnel. The situation in which the internal explosion is preceded by fire accidents is also analyzed. The reference situation is represented by the explosive source located at the center of the tunnel cross–section. The tunnel geometry considered is that of the metro line in Brescia, Italy. It has an internal diameter of about 8.15 m and is located about 23.1 m below the surface. Six segments and a smaller key segment (6+1) make up the tunnel. The ring has an average width of about 1.5 m. Dynamic analyses were carried out in order to reproduce the blast scenario. The aim of this work is to evaluate the influence of the position of the explosive source on the tunnel dynamic response. An ultimate limit state criterion based on the eccentric ultimate flexural capacity and capable of including fire–blast interaction is adopted. An innovative layered precast tunnel segment solution made of different fiber–reinforced cementitious composites is considered.

Abstract: Concrete structures subjected to impact have shown a higher sensitivity to develop a brittle shear failure than under quasi-static loading. The differences between the dynamic and static behavior are due to the strain-rate dependence of material properties and the presence of inertial forces. Both effects should be accounted for when performing analyses of structures under impact. In the present paper, a simplified three-degree-of-freedom model is used to understand the improved impact response of reinforced concrete when steel fibers are added to the concrete matrix. The analysis shows that the higher capacity for energy absorption of fiber-reinforced concrete (FRC) may avoid local shear failure when the FRC is able to develop strain hardening prior to the peak strength. Various analyses are presented in order to understand the influence of different types and contents of fibers.

Abstract: Steel fibre reinforced concrete (FRC) has higher ductility, it can save amount of convention reinforcement, labour and in consequence costs of the structure. However, broader use of SFRC as construction material is limited among others by lack of design codes. According to the previous study, reliability and safety of ordinary reinforced engineering can be verified using non-linear finite element analysis and several safety formats that are proposed in fib Model Code 2010. In the presented paper, safety formats are applied for fibre reinforced structures such as tunnel lining precast segment and individual approaches are compared. As tensile and shear cracks or compressive crushing can develop in the fibre reinforced concrete under severe conditions, the design combining numerical and experimental investigations together with safety formats is appropriate method how to obtain safe and reliable structure. Finite element method and advanced material models taking into account FRC properties such as shape of tensile softening branch, high toughness and ductility are described in the paper. Since the variability of FRC material properties is rather high, full probabilistic analysis seems to be the most appropriate format for evaluation of structural performance, reliability and safety.

Abstract: Structure and properties of cement composite are time-varying characteristics, depending among others on environmental conditions. The key idea is a struggle for complex research of joint effect of physical, chemical and dynamic loads on the internal structure [1] of cement composite and understanding the correlation between changes in microstructure and macro-scale properties [2, 3]. During the experimental program, specimens will be exposed to combined influence of freeze-thaw cycles [4,5,6], aggressive chemical agents [7] and dynamic loading [8]. The aim is to create a theoretical basis for design of effective cement composites meant to be used in severe environmental conditions.

Abstract: Favourable experience with fibre reinforced concrete (FRC) resulted in its increasing use worldwide. The properties of fibre reinforced concrete are mostly influenced by the type and the amount of fibres. Our experimental study was directed to the possible improvements of the residual flexural strength and the properties of concrete exposed to high temperatures with different fibre cocktails including steel, micro polymer or cellulose fibres. The influence of type and amount of fibres on residual flexural strength in cold state were tested after 300, 500 or 800 °C temperature loading.

Abstract: During fire, one or two faces of structural members experience higher temperatures than other faces and the deterioration on these faces may continue after fire. High temperature exposure above 400 °C causes deterioration in strength, modulus of elasticity and durability of concrete. Inclusion of fibers and air entraining agents in concrete mixes may reduce the destructive effects of high temperatures on concrete. Therefore, 8 groups of 0.45 w/c ratio of concrete were designed by using polypropylene fibers as low melting point fibers and hooked end steel fibers as high melting point fibers and air entraining admixture as a chemical additive. 15 cm cubic concrete specimens were produced and the five sides of the cubes were insulated with gypsum boards to maintain one face heating. An electrical furnace was used to heat concrete to 1000 °C and K-type thermocouples were placed in specimens to monitor temperature distribution in concrete. Moreover, two different re-curing methods, air and water, were applied after heating to see the change in mechanical properties and crack occurrences on the heated surface of concrete specimens. SEM and XRD investigations were conducted on the samples taken from the heated surfaces and the inner parts of the concrete in order to understand the morphological changes due to heating and re-curing. Results showed that deterioration on the surfaces due to high temperature exposure continued during air re-curing process and compressive strength and modulus of elasticity values of these specimens also diminished. On the other hand, compressive strength of water re-cured concrete stayed constant after heating and partial recovery of modulus of elasticity were obtained and the positive effect of water re-curing were observed on polypropylene fiber reinforced concrete prominently.

Abstract: The manufacturing technology of reinforced concrete with the use of steel fibers to improve its mechanical properties is well-known and commonly used in civil engineering. Generally, steel fibers as discontinuous reinforcement of the concrete matrix are used to limit the cracking growth following the load application. Thus, the obtained concrete is characterized by an improvement of the typically brittle behavior of the ordinary matrix, mainly referring to toughness and post-cracking behavior. In this paper the results of a recent experimental campaign carried out at the University of Salento will be discussed. It was designed to study the optimization of concrete mixtures reinforced with recycled steel fibers from end of life tires (ELTs) to be used for the realization of precast panels. This experimental campaign is part of a wider research project aimed to validate the idea that the constituent elements of the ELTs, especially rubber and steel, can be effectively reused in concrete mixtures. Taking into account the high annual amount of ELTs generated around the world and their negative impact on the global environmental sustainability, the recovery of their constituent materials and their reuse as raw materials in different technologies, is certainly an excellent way for a sustainable development.