1,721,014 research outputs found
A comparison between the use of FRP, FRCM and HPM for concrete confinement
No full textThe use of new methods to strengthen and rehabilitate existing concrete and masonry structures is one of the challenges that the engineering community is facing in recent years. In this field, composite materials are acquiring more and more success, due to lower invasiveness and ease of application if compared to more traditional systems (e.g. steel plates or reinforced concrete jacketing). This work, based on experimental investigations, aims to propose a comparison between three different methods as possible strengthening solutions for existing concrete elements. Twenty compression tests were conducted on reduced scale concrete columns, realized by using a low performance concrete, in order to reproduce the poor mechanical properties of most existing structures. Two of them were left unconfined, while the other ones were reinforced by using Fiber Reinforced Polymer (FRP), Fiber Reinforced Cementitious Matrix (FRCM) or High Performance Mortar (HPM) systems. The effectiveness of the different strengthening techniques and the main differences in terms of structural response were investigated. Experimental results were then compared with predictions deriving from guidelines and theoretical models from the literature
Study of environmentally friendly mortars prepared with recycled concrete aggregates and biomass ash
No full textTensile behavior of a glass FRCM system after different environmental exposures
Full text linkThe use of Fabric-Reinforced Cementitious Matrix (FRCM) systems as externally bonded reinforcement for concrete or masonry structures is, nowadays, a common practice in civil engineering. However, FRCM durability against aggressive environmental conditions is still an open issue. In this paper, the mechanical behavior of a glass FRCM system, after being subjected to saline, alkaline and freeze-thaw cycles, has been investigated. The experimental campaign includes tensile tests on the fabric yarns, compression and flexural tests on the matrix and tensile tests (according to AC434) on FRCM prismatic coupons. The effects of the different environmental exposures on the mechanical properties of both the constituent materials and the composite system have been investigated and discussed. Ion chromatography analysis has also been performed to better understand the damage mechanisms induced by environmental exposures and to evaluate the ions' penetration within the inorganic matrix. Alkaline exposure was shown to be the most detrimental for Alkali-Resistant (AR) glass fiber yarns, causing a reduction in tensile strength of about 25%. However, mechanical properties of the FRCM composite seemed not to be particularly affected by any of the artificial aging environments
Concrete columns confined with different composite materials
Full text linkIn the last decades, the need for upgrading, strengthening and retrofitting of existing concrete structures is rapidly growing. Composite materials showed to be an optimal solution to face this problem, combining high efficacy with low invasiveness. The use of Fiber Reinforced Polymers (FRP) to wrap concrete columns has been widely investigated and became a very successful method to improve their structural performances. However, it has been recognized that FRPs, due to the presence of an organic resin, have a few drawbacks, such as poor mechanical behavior at high temperatures, lack of vapor permeability and impossibility to be installed on wet surfaces. This experimental work aims to propose a comparison between three different innovative methods as possible strengthening solutions for existing concrete columns. The structural behavior of 20 reduced scale concrete columns, realized by using a low performance concrete, in order to reproduce the poor mechanical properties of existing structures, was investigated. Two unreinforced column were tested in compression as reference. Six of them where reinforced by applying an external layer of FRP, with different types of fabric reinforcement (made of carbon or PBO fibers). Six columns were reinforced by using the same fabrics coupled with an inorganic matrix (FRCM) instead of epoxy. Six other columns were reinforced by using a layer of High Performance Fiber Reinforced Concrete (HPFRC) of 3 cm thick. Experimental results have been analyzed and performance of the three reinforcement systems have been compared
Tensile behaviour of glass FRCM systems with fabrics’ overlap: Experimental results and numerical modeling
No full textThe use of Fabric Reinforced Cementitious Matrix (FRCM) systems to reinforce existing masonry and concrete structures is nowadays a well-established practice. The mechanical characterization of FRCM systems is of fundamental importance to define the correct parameters needed to design a strengthening intervention. However, some aspects regarding FRCM tensile behaviour need to be further investigated. The aim of this paper is to provide a detailed overview on the mechanical behaviour of FRCM specimens subjected to tensile tests. In this context, the effect of fabrics’ overlapping on the global behaviour of the system is extensively analyzed. Different sample's configurations have been studied: one reinforced with a single layer of bidirectional glass fabric and three others with different fabrics’ overlap lengths, varying between 100 and 200 mm. Digital Image Correlation (DIC) has been also used to measure displacements in experimental testing. A phase-field model, that accounts for brittle fracture of cementitious matrix and fabric reinforcement and possible slippage at the fabric-to-matrix interface, has been developed. The variational formulation has been implemented in a finite element code to simulate the tensile behaviour of FRCM systems and the effects of using different fabrics’ overlap lengths
Uniaxial tensile behavior of ultra-high performance fiber-reinforced concrete (uhpfrc): Experiments and modeling
Full text linkUltra-High Performance Fiber-Reinforced Concrete (UHPFRC) is considered a promising material for many structural applications where high strength and high energy absorption capacity are required. The purpose of this work is to study the uniaxial tensile behavior of soft cast (flowable at casting time) UHPFRC by varying the amount of hooked steel fibers (30-mm long) from 0% up to 2.55% by volume. Direct tensile tests have been performed on dog-bone shaped specimens and Digital Image Correlation (DIC) has been used to measure displacements and deformations and to monitor the evolution of cracks. Then, a phase-field model has been implemented in a FE code and numerical simulations have been performed to better understand the effects of different fiber dosages on the mechanical behavior of UHPFRC composites and on their post-elastic evolution. Concrete matrix and fiber reinforcement have been modeled as brittle and elasto-plastic phases of a mixture, whose internal energies are enriched by non-local damage and plasticity contributions. The different failure mechanisms observed in experiments have been reproduced, including the ductile failure experienced by specimens with sufficiently high fiber dosage, which distinguishes for a strain-hardening phase of matrix multi- micro-cracking that anticipates material failure
Reuse of ground waste glass as aggregate for mortars
No full textThis work was aimed at studying the possibility of reusing waste glass from crushed containers and building demolition as aggregate
for preparing mortars and concrete. At present, this kind of reuse is still not common due to the risk of alkali–silica reaction
between the alkalis of cement and silica of the waste glass. This expansive reaction can cause great problems of cracking and, consequently,
it can be extremely deleterious for the durability of mortar and concrete. However, data reported in the literature show
that if the waste glass is finely ground, under 75 lm, this effect does not occur and mortar durability is guaranteed. Therefore, in this
work the possible reactivity of waste glass with the cement paste in mortars was verified, by varying the particle size of the finely
ground waste glass. No reaction has been detected with particle size up to 100 lm thus indicating the feasibility of the waste glass
reuse as fine aggregate in mortars and concrete. In addition, waste glass seems to positively contribute to the mortar micro-structural
properties resulting in an evident improvement of its mechanical performance
TRM reinforced tuff and fired clay brick masonry: Experimental and analytical investigation on their in-plane and out-of-plane behavior
No full textThe paper presents the results of an experimental campaign aimed at investigating the in-plane and out-of-plane behavior of tuff and fired clay brick masonry panels reinforced by a commercial, not yet tested, Textile Reinforced Mortar (TRM) system. The TRM, consisting of hydraulic lime mortar coupled with a bidirectional glass fabric (total thickness of 30 mm), was applied on both sides of the panels and connected through stainless-steel helical bars. First, a mechanical characterization of the TRM system was carried out, according to recent guidelines (AC434 and CNR-DT215) by means of tensile tests and single-shear bond tests on the two different substrates. Then, the effectiveness of the reinforcement was investigated through uniaxial compression, diagonal compression and three-point bending tests on masonry panels. After that, experimental results were compared to the predictions of recent guidelines and analytical models available in the literature, by using the mechanical parameters obtained from the TRM mechanical characterization. TRM showed to be very effective in increasing the in-plane shear strength of tuff panels, of about 170%, whereas in the case of fired clay brick ones the increase was limited to 33%. Besides, the diagonal compression strength of reinforced specimens seemed to be strongly influenced by the mortar matrix, instead of by the fabric reinforcement, as it usually happens i.e. for Fabric Reinforced Cementitious Matrix (FRCM) systems. Thus, novel simplified analytical formulations to predict the shear strength of reinforced panels by only considering the contribution of the TRM matrix were provided, discussed and compared to current analytical approaches for FRCM systems. As regards the out-of-plane behavior, the TRM system significantly increased the out-of-plane bending strength and ductility of both tuff and fired clay brick panels. The applicability of current analytical approaches, as well as possible amendments, was also investigated. Finally, the compressive behavior of the walls was not substantially modified by the reinforcement, reasonably due to the low axial stiffness of the connectors and, to a minor extent, because they were dry inserted within the masonry and simply folded over the glass fabric
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