1,721,161 research outputs found
La valutazione della sostenibilità di calcestruzzi con scorie di acciaieria tramite un approccio al ciclo di vita
No full textAn experimental study about the possibility of substituting natural aggregates with EAF slag in concrete production
No full textFRCM-confined concrete: Monotonic vs. Cyclic axial loading
No full textIn this work, the experimental behavior of confined concrete specimens subject to axial cyclic load is analyzed in terms of compressive strength, ductility, stress deterioration, plastic strain development, stiffness deterioration, fibers strain exploitation ratio and volumetric dilation. The following variables were considered, and their influence is discussed along the work: geometry of the cross-section (circular, square and two rectangular ones), fiber material (carbon and glass fibers) and number of layers (up to four for carbon-FRCM jackets), loading protocol (cyclic and monotonic). Results demonstrate that the envelope of the stress–strain curves obtained with cyclic loading coincides with the monotonic curve, for the range of variables analyzed here. Further, the stress–strain curve of FRCM-confined concrete has been modeled according to three different behaviors exhibited in this experimental campaign, being purely softening, softening with plateau, and hardening
Techniques for sustainable building materials production: recycling in concrete industry
Full text linkThe excellent mechanical and durability properties, with its large availability and affordable costs, make concrete the most used engineered material, with an estimated worldwide consumption about 6 billion tons per year. The prices of this wide diffusion lie into the relevant environmental emissions associated to concrete industry: concrete production is in fact one of the main responsible of carbon emission in atmosphere, mainly due to cement manufacturing and natural aggregates extraction. Together with the energy requirements, water consumption and generation of construction and demolition waste, these factors contribute to the general appearance that concrete is not particularly compatible with the demands of sustainable development.
Several operations can be applied to limit concrete impacts: the replacement of Portland cement with supplementary cementing materials (SCMs) and the use of recycled aggregates in place of natural resources are solutions that may achieve the aim of reducing concrete emissions during all its life cycle. Between the various recycled materials which can be suitable in concrete applications, promising results were obtained when limited quantities of recycled aggregates from construction and demolition wastes (C&DWs) and from electric arc furnace (EAF) slag are used, generally not affecting mechanical properties and environmental compatibility. Nevertheless, in the most of cases a lack of standardized rules hinder their use at market level, in particular when recycled aggregates or mineral additions come from metallurgical industry.
In this thesis the use of two types of recycled aggregates for structural concrete production is explored: EAF slag as recycled aggregates and recycled aggregates from C&DW. In addition, the use of supplementary cementing materials is analyzed, paying particular attention on the suitability of the application of co-combustion fly ash in structural concrete.
Two extensive experimental campaigns were carried out to analyze the main mechanical and durability-related properties of recycled concrete with EAF slag. Several mixes with increasing substitution ratios were produced, using both the coarse and the fine aggregates. A specific chemical and micro-structural in-depth examination was carried out in order to evaluate the actual stability of the material, the influence of the substitution ratio on hardened concrete properties and to study the aggregates-matrix bond when detrimental cycles were applied to concrete specimens. Once determined the suitability of some of the substitution ratios used, for the first time real-scale reinforced concrete beams with EAF slag were realized and tested for bending and shear failure, and their structural behavior is analyzed and discussed.
The second part of the thesis deals with the use of recycled aggregates coming from C&DWs, to assess their influence on the rheological behavior of fresh concrete. An experimental campaign was conducted, and since slump value is often operator-sensitive, a more quantitative estimate was derived in terms of fundamental physical quantities, such as plastic viscosity and yield stress, by means of viscometer measures. The variables analyzed were the aggregates substitution ratio and proportioning method, the super-plasticizer content and the water/cement ratio.
Lastly, an experimental campaign was performed to compare the effects of two different (SCMs) on mechanical and durability-related properties of structural concrete. Three mixes were produced, where coal and co-combustion fly ashes were used as partial substitute of cement (20% in volume) and compared with a reference concrete.
An environmental impacts’ assessment was also performed, through a Life Cycle Analysis (LCA) framework specifically developed for concrete emissions evaluation, using a cradle-to-gate approach. Assessment is based on Italian LCI data, collected directly from local EAF slag treatment plant, a natural aggregate extractive plant and a C&DW processing plan
Experimental Behavior of Reinforced Concrete Beams with Electric Arc Furnace Slag as Recycled Aggregate
Full text linkThe aim of the present work is to investigate the possibility of partially substituting natural aggregates with Black/Oxidizing Electric Arc Furnace (EAF) slag for Reinforced Concrete (RC) structural elements. International research has been mainly focused on experimental tests on small specimens rather than investigating the behavior of RC structural elements. In this work the experimental behavior of RC beams made with EAF slag as aggregate was studied showing that these beams have both ultimate flexural and shear capacity higher than the corresponding traditional beams. Some comparisons between experimental results and analytical predictions according to the European and US recommendations were also shown. The main result of this work is that the use of steel slag as aggregate in RC structural elements is, in principle, possible, and the rate of substitution could reach the whole part of coarse aggregates obtaining benefits both from an economical and environmental point of view
Sustainability of recycled concretes through life cycle assessment
No full textA significant number of green concrete have been recently designed to meet the growing request of reducing construction industry impacts, saving raw materials and preventing industrial by-products’ discard. Between these, recycled aggregates coming from construction and demolition waste (CDW) and Black/Oxidizing Electric Arc Furnace (EAF) slag have been founded to be suitable for structural concrete applications, when used as replacement of natural coarse aggregates. However it is necessary to solve the arising question about how those recycled materials effectively improve the sustainability of concrete industry. A quantitative estimate of the environmental impacts’ related to the production of those concretes can be performed using several environmental indicators. In this section a review of the available environmental tools, useful to assess concrete impacts, is reported. Particularly Life Cycle Analysis (LCA) and abiotic depletion indicator can be satisfactorily applied to quantify the emission reduction due to the use of recycled aggregates instead of natural gravel in structural concrete. The procedure described in this section can be applied to determine the impacts of other recycled aggregates concretes, practically estimating the environmental footprint of the material
Recycled aggregates for concrete production: State-of-the-art
No full textIn the last decades, problems linked to industrial material landfill disposal has become more and more relevant to society, with cost increases for environment and municipalities. Waste reutilization is attractive to reduce economical costs and potential pollution problems, and preserve natural raw resources. In this context, the promotion of recycling in concrete industry may represent a valid route for sustainable development, preventing natural resources consumption, valorizing recycled materials, and avoiding the landfill of huge amount of materials. Nowadays, there are, among others, two significant possibilities to reduce natural aggregates exploitation: the use of recycled concrete from construction and demolition waste (C&DWs) and the use of slag from metallurgical industrial production. Additionally the use of supplementary cementing materials (SCMs) can reduce the great environmental emissions due to cement use. In this chapter, a review about the most commonly used recycled aggregates is given, i.e. recycled aggregates from C&DW and from metallurgical slag, with a special focus about the available codes and normative which regulate their use in structural concrete
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