930 research outputs found
Ductilityof fiber-reinforcedself-consolidatingconcreteundermulti-axial compression
Full text linkThe results of 12 multi-axial compression tests performed on cylinders made of self-consolidating concrete, plain (SCC) and reinforced with steel fibers (FR-SCC), are presented. In the experimental campaign, four ‘‘reference'' confining pressures (0, 1, 3 and 10 MPa) were applied on the lateral surface of the specimens. After the first stage of loading, when a hydraulic stress was applied to the cylinders, and progressively increased up to the value of a pre-established confining pressure, a longitudinal compressive load was used to generate crushing of concrete. During this failure, the post-peak behavior of SCC and FR-SCC can be defined by a non-dimensional function that relates the inelastic displacement and the relative stress during softening. Such a function also reveals the ductility of SCC, which increases with the confinement stress and with the fiber volume fraction. In particular, by adding 0.9% in volume of steel fibers, FR-SCC can show practically the same ductility measured in unreinforced SCC with 1MPa of confining pressure. Thus, the presence of an adequate amount of fibers in SCC columns is sufficient to create a sort of distributed confinement
Green public procurement applied to partially precast reinforced concete slabs
Full text linkTo build environmentally friendly public constructions, authorities impose tailoring concrete mixtures with a
minimum content of recycled materials. To satisfy this green public procurement (GPP) in frame structures,
whose mass is mainly distributed on horizontal diaphragms, it is necessary to draw attention to the slabs of
floors. As ready-mixed concrete with recycled materials is not easily available on the market, partially prefabricated
one-way slabs, composed by both cast-in-situ concrete and precast plates (generally called predalles)
were investigated. Only the precast concrete of predalles contained recycled materials, such as supplementary
cementitious materials (SCM) in place of CEM I, recycled concrete aggregate (RCA) and rubber to replace stone
aggregate, and recycled steel fibers (RSF). These materials were used to cast full-scale one-way slabs, subsequentially
tested in three-point bending. A three-stage model, based on the equivalence between the traditional
rebar and RSF, was also introduced to predict the load-deflection responses of the slabs. As results, both numerical
and experimental analyses revealed the effectiveness of RSF, which can be added to concrete mixtures to
compensate the loss of flexural strength that the substitution of virgin materials produces. Thus, if large quantities
of SCM, RCA, rubber, and RSF are in the concrete of predalles, slab can satisfy both GPP and the mechanical
performances, though the cast-in-situ concrete does not contain any recycled material
Optimization of hybrid reinforcement in precast concrete linings using numerical analysis
No full textConcrete mixtures reinforced with a combination of steel rebar and fibers, i.e., Hybrid Reinforced Concretes (HRC), are frequently used in segmental precast tunnel linings. As massive cross-sections are usually adopted in these structures, only the minimum reinforcement is necessary to prevent the brittle failure. To study the brittle/ductile behavior of HRC tunnel segments in bending, the flexural responses of Lightly Reinforced Concrete (LRC) and that of Fiber-Reinforced Concrete (FRC) elements are modelled and combined herein. By means of this combination, the minimum reinforcement of HRC segments can be determined with a new design-by-testing procedure, in which the ductility index DI should be equal to zero. As a result, the minimum hybrid reinforcement can be defined through a linear combination of the minimum area of rebar and the minimum fiber volume fraction of LRC and FRC segments, respectively
A simplified approach to the evaluation of the strength of old concrete
No full textTo design the retrofit and/or conservation of existing reinforced concrete structures, an assessment of concrete strength is generally required. The current methodologies consist of destructive tests, based on uniaxial compression performed on concrete cores extracted from a structure, and/or non-destructive tests, in which the strength of the concrete is indirectly estimated by measuring other physical properties (like ultrasonic pulse velocity). Nevertheless, in several situations (e.g. the seismic vulnerability assessment of long-term service structures), the traditional tests cannot be performed. Hence, a new simplified approach is introduced and described in this paper. This can be applied to structures located in a precise geographical area, where the average strength of concrete (and the relative variance) is a function of the year of construction. Such a relationship is summarised by the so-called strength curves statistically computed from a huge database stored in the Department of Structural and Geotechnical Engineering of Politecnico di Torino (Italy). Relating to a concrete dam and a stadium built during the 1950s and in 1967, respectively, the strength predicted by these curves is in good agreement with the measurements of destructive tests
Case study on High-Performance-Fiber-Reinforced-Concrete manufactures made with recycled steel fibers from End-Life-Tires
No full textAbstract
To minimize the amount of CO2 released into the atmosphere, a variety of revisions regarding the construction industry must be done. One possible approach to modify the sustainability of con-struction industry manufactures is to substitute, partially or completely, the traditional compo-nents with recycled materials. Considering tremendous amount of recycled steel fibers (RSF) from end-of-life tires (ELTs) disposed annually around the world and their negative environmental impact, the recovery of their constituent materials and their reuse as raw materials in different technologies, is certainly an excellent way for a sustainable development. This paper presents a case study of High-Performance-Fiber-Reinforced-Concrete (HPFRC) as a replacement of current industrial component material. As a result, by applying a linear relation we tried to evaluate the suitable volume of fiber to be used in such manufactures
Experimental and numerical analyses of curvilinear masonry structures exposed to high temperatures
No full textDespite masonry arches and vaults are recurring structural members within architectural heritage, experimental and numerical analyses on these structures exposed to fire are still not much addressed. The present paper deals with
ive tests carried out on masonry barrel vaults, made with clay solid bricks, cement-lime mortar, and subjected to
tandard fire at intrados and to different load arrangements on the extrados. Two vaults were also insulated with fire
rotectives to mitigate the effects of elevated temperatures. In addition, a simplified numerical model, previously
ntroduced and herein improved with a more refined thermal analysis, is used to calculate the fire resistance R. As
esults, by comparing the test data and the numerical outcomes, more reliable, but still conservative, predictions of R
an be obtained in the case of barrel vaults
Influence of Cement Type and Curing Conditions on the Flexural Strength and Microstructure of Mortars Reinforced with Sheep Wool Fibers
No full textVarious types of dispersed reinforcement in the form of thin fibers are known to improve the toughness of cement-based materials. In cement-matrix composites, the application of sheep wool, which is an ecological material, annually renewable and completely recyclable, perfectly fits into green and sustainable development. As the wool tends to be damaged by alkaline environment, this paper describes the influence of the cement type on the performances of sheep wool reinforced mortars. Hence, ordinary Portland cement (CEM I 42.5R), limestone Portland cement (CEM II/B-LL 42.5R), and calcium sulfoaluminate cement (SL05 42.5) are analyzed. The latter is known to be low carbon compared to CEM I. Additionally, two conditions, differing on maturity in high or low humidity, at constant temperature of 20°C, are used to cure the specimens. As a result, mechanical properties, and flexural toughness in particular, strongly depend on the type of cement and on the curing conditions. This is true both for the mortar specimens reinforced with sheep wool fibers and for those reinforced with polypropylene fibers, herein considered as reference fibers. © 2022 American Concrete Institute
Two-Stage Cementitious Composites Containing Recycled Steel Fibers
No full textExperimental research performed on fiber-reinforced cement-based composites made with polymeric aggregate and reinforced with recycled steel fibers is presented in this paper. In total, 18 concrete prisms were cast with a two-stage procedure: first, the fibers from end-of-life tires were put in the molds and, subsequently, they were covered by a cementitious grout containing fine (recycled or virgin) aggregate. The two-stage composites showed more than one crack and a deflection-hardening behavior in the post-cracking regime by performing three-point bending tests. Moreover, both flexural and compressive strength increased with the fiber volume fraction. Thus, if the content of recycled materials is suitably selected, the ecological and mechanical performances of the two-stage composites improve and become similar to those of one-stage fiber-reinforced concrete made with only virgin components
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