1,720,982 research outputs found
On Durability of Fiber Reinforced Concrete
No full textCosts for maintenance and repair of conventional reinforced concrete (RC) buildings and structures have become a serious economical, ecological and social problem. A large percentage of worldwide infrastructure needs repair measures. This situation motivates great care when developing new construction materials, such as Fiber-Reinforced Concrete (FRC), whose enhanced toughness contributes to more durable structures. In fact, fibers could be introduced in RC structures to reduce the cracking phenomena thus helping the structural durability.
In the present paper, fracture behaviour and water permeability of fiber reinforced concrete are studied. The effect of different crack openings is analysed in order to study its influence on the
mechanism of ingress of water
Influence of matrix grade on the mechanical behaviour of fibre-reinforced concrete
No full textMechanical behaviour of fibre-reinforced concrete is influenced both by the properties of the fibres (geometry, aspect ratio, dosage) and the properties of the matrix (concrete grade, curing time, water-to-cement ratio). Many research studies have been published that focus on the influence of different kinds of fibres on the final properties of concrete. Against this the influence of the matrix grade on the mechanical properties of fibre-reinforced concrete is a topic that is almost unexplored. A mechanical characterisation of fibre-reinforced concrete in the hardened and fresh states is carried out, varying the concrete grade, the fibre dosage and the fibre type (steel and polyester). The results of the experimental research indicate the importance of the matrix grade on the bond between the steel fibre and the matrix and, consequently, on the mechanical performances of the composite material. Furthermore the concrete grade also influences the minimum volume fraction of polyester fibres affecting the matrix toughness
Research of correlations between NDT and DT to assess mechanical properties of a soft stone in ancient masonry
No full textA deep knowledge of the physical and mechanical properties of the constituent materials of ancient masonries is of crucial importance in the choice of the proper intervention technique. In case of historical buildings sustainable diagnostic procedures responding to the conservation constraints, should have the lowest degree of intrusion and the fullest respect for their physical integrity. The sample’s extraction from existing structures for laboratory tests is one of the major problems in the field of diagnosis of ancient buildings and this has moved the scientific community to propose alternative non-destructive techniques to evaluate the mechanical and physical properties of the building stones.
In the present work non-destructive and destructive tests have been investigated as tools for assessing the compressive strength of “Lecce stone”, a soft calcarenitic stone used as traditional building materials in the Southern Italy. Ultrasonic pulse velocity (UPV), Schmidt hammer test and compressive tests on microcores have been compared with mechanical destructive tests on cubes in order to found correlations between the results. The final aim is to assess the reliability of the non-destructive investigated methods in describing the mechanical performance of the stone, reducing the use of destructive analyses on masonries
Mechanical and Cracking Behavior of Concrete Beams Reinforced with SteelBars and Short Fibers
No full textIt is well known that fibers embedded in a cementitious matrix enhance its toughness, increase its performance in tension and act as crack arrestors. While the interaction between fibers and concrete, as well as their effect on cracking has been extensively investigated, the interaction between fibers and rebars in a R/C member is still open to investigation. In fact, a consolidated model to predict crack width in structural members embedding fibers can hardly be found in the literature; hence, further experimental efforts are needed to better understand the fiber-reinforcement interaction. Furthermore, the results found in the literature on Fiber-Reinforced Concrete mainly refer to steel fibers, while the effect of other fibers on concrete cracking and on R/C mechanics is a topic still requiring dedicated research efforts.
In this research project, an experimental study on the effect that steel and polyester fibers have on the mechanical and cracking behavior of ordinary reinforced-concrete beams, is presented. The objective is to investigate the role that fiber amount, geometry and type have on the cracking behavior of the beams in terms of crack width and spacing
Ultrasonic pulse velocity test for non-destructive investigations of historical masonries: an experimental study of the effect of frequency and applied load on the response of a limestone
No full textThe ultrasonic pulse velocity (UPV)
method can be conveniently used for non-destructive testing of physical–mechanical properties of the stones within historical masonry, as well as to check the state of damage and microcracking. Before to proceed with in situ measurements, it is important to assess the contribution that both intrinsic characteristics of the stones and external factors may give to the ultrasonic response. In this work the effect of different wave frequencies, sample geometry and application of a compression load on the response of a natural stone to UPV test has been investigated. An extensive experimental campaign in laboratory conditions was carried out on a soft limestone, used in the historical building heritage of the Southern Italy. A negligible UPV dispersion was found at the used frequencies of 1 MHz, 120 and 55 kHz when a compression load was not applied; the measured velocities were found to be influenced by the stone inhomogeneity rather than by the sample size. They showed a slight decrease and still negligible dispersion under load up to the visible damage. Dispersion increased with the cracking progression. This indicates that enhanced capability of UPV, in checking material quality and damage conditions, can be obtained by combining the use of different wave frequencies
Interface analysis between steel bars and recycled steel fiber reinforced concrete
No full textThe positive effect of fibers on the bond of reinforcing bars in concrete is widely recognized and supported in literature; on the contrary information are not available on recycled steel fiber reinforced concrete. The experimental work discussed in this paper represents a part of a wider analysis, performed by the authors, on the mechanical performance of RSFRC. In particular the main objective is to investigate the bond behavior between steel bar and recycled steel fiber (from waste tires) reinforced concrete. To this aim eccentric pull-out test on prismatic samples were designed varying the type of fiber (recycled and industrial steel fibers) and the concrete cover-bar diameter ratio; in addition similar tests were carried out on plain concrete for comparison purpose. The experimental data in terms of peak bond stress, mode of failure and bond stress-slip curves are analyzed and discussed evidencing the good bond performance of specimens realized with recycled steel fiber reinforced concrete compared with both those realized with plain and industrial fiber reinforced concret
Mechanical characterization of fibre reinforced concrete with steel and polyester fibre
No full textA low volume of fibers, typically less than 2%, can be added to concrete to make Fiber Reinforced Concrete (FRC). The presence of fibers reduces the formation of cracks and their growth, thus improving the mechanical properties of the cement matrix and its structural durability.
The ability of FRCs to absorb energy is one of the most important benefits of using fibers into the plain concrete. This is due to the pull-out mechanisms that should occur without fibre rupture. Many tests have been developed to characterize the energy absorption capacity of FRCs using simple loading configurations such as compression, tension and flexure. The bending test is the most widely used because it is simple to be performed and it represents a typical service condition for structural elements.
This paper shows the results of an experimental study based on flexural tests of concrete reinforced with short steel and polyester fibres. Different volumes of fibers and water cement ratios were analysed in order to investigate their influence on the FRC’s toughness and workability. The experimental program involved compression tests and four point bending tests on notched specimens. Durability aspects concerning FRC structures will be also discussed. In particular, water permeability tests were performed in order to evaluate the influence of the fiber type and the fiber volume content on the permeability of the matrix
Cracking behaviour of frc flexural beams without stirrups
No full textThe experimental research presented herein is focused on the study of the flexural behaviour of Fibre Reinforced Concrete (FRC) beams. Ten full scale specimens were prepared and tested under a four point bending scheme. The beams were built without transverse steel reinforcement along the region that was tested with a constant flexural moment and shear null. Experimental variables were the concrete mix, the type of short fibres used as dispersed reinforcement (steel and polymeric fibres) and volume fraction of fibres used in the concrete matrix. Two repetition specimens were tested for each concrete mix. Experimental results show strain monitoring in the longitudinal steel at increasing loads, strain monitoring in compressed concrete, flexural deflection along the beams. The results highlight the great importance of the beneficial role exercised by the short fibres dispersed in the cement matrix in reducing cracking of reinforced concrete (RC) beams. In particular results obtained herein in absence of the web reinforcement provide new original data since it was avoided to have the onset of the cracks along the stirrups. In correspondence of different five load levels the distance, the height and the maximum width of the cracks were also measured over the whole length of the beams, with particular attention to the constant moment region. The steel fibres demonstrated to be more effective than respect to polyester fibres as crack arrestors. The experimental data were also compared to the design values obtained by applying the analytical models of the new FIB Model Code 2010
Analytical prediction of crack width of FRC/RC beams under short and long term bending condition
No full textIt is well known that fibers are effective in modifying the cracking pattern development of concrete structural element, causing an higher number of cracks and, consequently, lower crack spacing values and narrower crack widths compared to the matrix alone. This effect could be exploited to improve durability of Reinforced Concrete (RC) structures, especially of those exposed to aggressive environments. The analytical prediction of crack width and spacing in Fiber Reinforced Concrete (FRC) structural elements in bending is still an open issue. A crack width relationship for RC elements with fibers similar to those developed for classical RC structural members would be desirable for designers. The recent development of important technical design codes, such as RILEM TC 162 TDF and the new MC2010, embrace this idea. However further validation of these models by experimental results are still needed. On the other hand, the study of the influence of a sustained load on crack width in presence of the fiber reinforcement is a topic almost unexplored and important at the same time. In the present work, the cracking behaviour of full-scale concrete beams reinforced with both traditional steel bars and short fibers has been analyzed under short and long term flexural loading. A theoretical prediction of crack width and crack spacing was carried out according to different international design provisions. The analytical results are discussed and compared in order to highlight the differences between the models and to check the reliability of the theoretical predictions on the basis of the experimental data
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