1,720,971 research outputs found
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
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
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
High-Performance-Fiber-Reinforced-Concrete elements made with recycled steel fibers from End-Life-Tires (Manufatti in calcestruzzo ad alte prestazioni realizzati con fibre di acciaio riciclate da pneumatici fuori uso)
No full textTo minimize the amount of CO2 released into the atmosphere, the construction industry has to change some of the traditional ap-proaches. For instance, to increase the sustainability of concrete, recycled materials can substitute, partially or completely, the traditional components. Considering tremendous amount of recycled steel fibers (RSF) from end-of-life tires (ELTs) disposed an-nually around the world, and their negative environmental impact as well, the recovery of their constituent materials and their re-use as raw materials in concrete is certainly an excellent way for a sustainable development. Accordingly, this paper presents a case study on the replacement of current cement-based composites with a new High-Performance-Fiber-Reinforced-Concrete (HPFRC). Despite the large content of waste materials, the proposed HPFRC can be effectively used in the production of manhole and corrugated slabs. / Per ridurre al minimo la quantità di CO2 in atmosfera, l’industria delle costruzioni deve modificare alcuni processi di produzione. In particolare, per aumentare la sostenibilità dei manufatti in conglomerato cementizio occorre sostituire, parzialmente o totalmente, i componenti tradizionali del calcestruzzo con materiali riciclati. Considerando l'enorme quantità di fibre d'acciaio riciclate da pneumatici fuori uso, ed anche il loro impatto ambientale, il recupero e il riutilizzo di tali materiali nei calcestruzzi fibrorinforzati è sicuramente un’ottima soluzione. Per tale ragione, il presente articolo introduce un nuovo High-Performance-Fiber-Reinforced-Concrete (HPFRC) realizzato con un fibre d’acciaio riciclate. Nonostante gli elevati volumi di materiali di riciclo, l’HPFRC può efficacemente essere utilizzato nell’industria manifatturiera per la produzione di tombini o di onduline a base cementizia
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
Relationship between flexural strength and compressive strength in concrete and ice
Full text linkIce is a locally available material in cold regions, where it is used in temporary constructions and permanent hydraulic structures. Thus, it is of practical interest the introduction of a model capable of computing the flexural strength of ice as function of its compressive strength. Accordingly, three point bend ing test and compression test have been performed for the first time on the same ice prism (40 × 40 × 160 mm3). In accordance with the testing procedure suggested by UNI EN 196 for cement-based mortars, compression loads are applied on the two halves of the specimens previously broken in bending. In this way, the ratio between the modulus of rupture and the compressive strength of ice can be measured. As a result,
although the specific strengths of cement-based materials are higher than those of ice, the flexural/compres sive strength ratio of ice is larger than that obtained in normal strength morta
Optimal content of bio-fibers in structural ice
Full text linkThe use of ice as structural material has two main concerns: the low strength and the brittle failure of the structures. With the aim of finding a solution to these problems, an experimental campaign, performed on fiber-reinforced ice (FRI) samples, made with plain water and bio-fibers, is presented in this paper. In total, 12 ice prisms were cast at − 18 °C with a different content of fibers, and then tested in three-point bending and uniaxial compression. Test results indicate that the presence of a reinforcement increases both flexural and compressive strength with respect to plain ice. Moreover, FRI is a tougher material, as multiple cracking and deflection hardening behavior can be observed in the flexural tests. However, the mechanical performances of plain ice are not always enhanced by the fiber-reinforcement. Therefore, an empirical model, capable of predicting the optimal content of bio-fibers, is also proposed
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
Designing Reinforced Concrete Beams Containing Supplementary Cementitious Materials
No full textIf supplementary cementitious materials (SCMs) are used as binders, the environmental impact produced by cement-based composites can be reduced. Following the substitution strategy to increase sustainability, several studies have been carried out with the aim of measuring the mechanical properties of different concrete systems, in which a portion of Portland cement was substituted with SCMs, such as fly ashes. On the other hand, studies on the structural behavior of reinforced concrete (RC) elements made with SCMs are very scarce. For this reason, in this paper, a new procedure is introduced with the aim of fulfil a new limit state of sustainability, in accordance with the serviceability and ultimate limit states required by building codes. Although the environmental impact of concrete decreases with the reduction of cement content, the proposed approach shows that the carbon dioxide emission of an RC beam is not a monotonic function of the substitution rate of cement with SCMs. On the contrary, there are favorable values of such substitution rates, which fall within a well-defined range
Carbon Dioxide: A Raw Material for Cementitious Mortar
Full text linkBuildings and infrastructures can absorb CO2 from the atmosphere because of the carbonation process that affects the calcium hydroxide of concrete elements. The aim of this research project is to initiate the absorption at casting by adding dry ice pellets to cement-based mortars. Test results demonstrate that the flexural and compressive strength of the mortars are not modified by this addition. Conversely, due to the presence of CO2, the standard deviation of strength reduces with respect to that measured in plain mortars. Thus, carbon dioxide can be considered a valuable resource that improves the mechanical behavior of construction materials
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