Durability performance of concrete made with fine recycled concrete aggregates

Fine recycled aggregates are seen as the last choice in recycling for concrete production. Many references quote their detrimental influence on the most important characteristics of concrete: compressive and tensile strength; modulus of elasticity; water absorption; shrinkage: carbonation and chloride penetration. These two last characteristics are fundamental in terms of the long-term durability of reinforced or prestressed concrete. In the experimental research carried out at IST, part of which has already been published, different concrete mixes (with increasing rates of substitution of fine natural aggregates sand - with fine recycled aggregates from crushed concrete) were prepared and tested. The results were then compared with those for a reference concrete with exactly the same composition and grading curve, but with no recycled aggregates. This paper presents the main results of this research for water absorption by immersion and capillarity, chloride penetration (by means of the chloride migration coefficient), and carbonation resistance, drawing some conclusions on the feasibility of using this type of aggregate in structural concrete, while taking into account any ensuing obvious positive environmental impact

Environmental life cycle assessment of concrete made with fine recycled concrete aggregates

The majority of worldwide structures use concrete as its main material. This happens because concrete is economically feasible, due to its undemanding production technology and case Of use. However, it is widely recognized that concrete production has a strong environmental impact in the planet. Natural aggregates use is one of the most important problems of concrete production nowadays, since they are obtained from limited, and in some countries scarce, resources. In Portugal, although there are enough stone quarries to cover coarse aggregates needs for several more years, Supplies of fine aggregates are becoming scarcer, especially in the northern part of the country. On the other hand, as concrete structures' life cycle comes to an end, an urgent need emerges to establish technically and economically viable solutions for demolition debris, other than for use as road base and quarry fill. This paper presents a partial life cycle assessment (LCA) of concrete made with fine recycled concrete aggregates performed with EcoConcrete tool. EcoConcrete is a tailor-made, interactive, learning and communications tool promoted by the Joint Project Group (JPG) on the LCA of concrete, to qualify and quantify the overall environment impact of concrete products. It consists of an interactive Excel-spreadsheet in which several environmental inputs (material quantities, distances from origin to production Site, production processes) and outputs (material, energy, emissions to air, water, soil or waste) are collected in a life cycle inventory, and are then processed to determine the environmental impact (assessment) of the analysed concrete, in terms of ozone layer depletion, smog or "greenhouse" effect

17-Acetoxymulinic acid

The title compound, [systematic name: 5a-acetoxymethyl-3-isopropyl-8-methyl-1,2,3,3a,4,5,5a,6,7,10,10a,10b-dodecahydro-7,10-endo-epidioxycyclohepta[e]indene-3a-carboxylic acid], C22H32O6 (I), is closely related to methyl 5a-acetoxymethyl-3-isopropyl-8-methyl-1,2,3,3a,4,5,5a,6,7,10,10a,10b-dodecahydro-7,10-endo-epidioxycyclohepta[e]indene-3a-carboxylate, (II) [Brito et al., (2008 [triangle]). Acta Cryst. E64, o1209]. There are two molecules in the asymmetric unit, which are linked by two strong intramolecular O—H ... O hydrogen bonds with graph-set motif R 2 2(8). In both (I) and (II), the conformation of the three fused rings are almost identical. The five-membered ring has an envelope conformation, the six-membered ring has a chair conformation and the seven-membered ring has a boat conformation. The most obvious differences between the two compounds is the observed disorder of the acetoxymethyl fragments in both molecules of the asymmetric unit of (I). This disorder is not observed in (II). The crystal structure and the molecular conformation is stabilized by intermolecular C—H ... O hydrogen bonds. The ability to form hydrogen bonds is different in the two compounds. The crystal studied was a non-merohedral twin, the ratio of the twin components being 0.28 (1):0.72 (1

The influence of curing conditions on the mechanical performance of concrete made with recycled concrete waste

Research on the use of Construction and Demolition Waste (CDW) as recycled aggregate (in particular crushed concrete) for the production of new concrete has by now established the feasibility of this environmentally-friendly use of otherwise harmful waste. However, contrary to conventional concrete (CC), no large applications of concrete made with recycled concrete have been made and there is still a lack of knowledge in some areas of production and performance of recycled aggregate concrete (RAC). One issue concerns curing conditions: these greatly affect the performance of concrete made on site and some potential users of RAC wonder how RAC is affected by far-from-ideal curing conditions. This paper shows the main results of experiments to determine the influence of different curing conditions on the mechanical performance of concrete made with coarse recycled aggregate from crushed concrete. The properties analyzed include compressive strength, splitting tensile strength, modulus of elasticity, and abrasion resistance. The general conclusion in terms of mechanical performance is that RAC is affected by curing conditions roughly in the same way as CC. (C) 2011 Elsevier Ltd. All rights reserved

Physical-chemical and mineralogical characterization of fine aggregates from construction and demolition waste recycling plants

Construction and demolition waste (CDW) represents around 31% of all waste produced in the European Union. It is today acknowledged that the consumption of raw materials in the construction industry is a non-sustainable activity. It is thus necessary to reduce this consumption, and the volume of CDW dumped, by using this waste as a source of raw materials for the production of recycled aggregates. One potential use of these aggregates is their incorporation in reinforced concrete as a replacement of natural aggregates. A concrete that incorporates these aggregates and still performs well requires them to be fully characterized so that their behaviour within the concrete can be predicted. Coarse recycled aggregates have been studied quite thoroughly, because they are simpler to reintroduce in the market as a by-product, and so has the performance of concrete made with them. This paper describes the main results of research designed to characterize the physical and chemical properties of fine recycled aggregates for concrete production and their relationship with mineralogical composition and preprocessing. The constraints of the incorporation of fine aggregates in reinforced concrete are discussed. It is shown that, unless a developed processing diagram is used, this application is not feasible. (C) 2013 Elsevier Ltd. All rights reserved

Comportamento em flexão de vigas de betão armado produzidas com agregados finos reciclados

Apesar de em Portugal existir legislação que permite, mesmo que a pequena escala, a utili-zação de agregados reciclados para a produção de betão, a prática mostra que são raros os casos em que esta solução é implementada, ao contrário de um vasto conjunto de países europeus. No entanto, em Portugal, a utilização da fracção fina dos agregados reciclados (AFR) é restringida ou mesmo proibida. Estudos mais recentes mostram, contudo, que a uti-lização de AFR é possível e que os desempenhos mecânicos obtidos são perfeitamente aceitáveis. Nesta comunicação, são apresentados os ensaios de flexão realizados em vigas de betão armado produzidas com substituição de agregados finos naturais por reciclados, comparando os resultados obtidos em termos de carga e deformação de ruptura, ductilidade, capacidade resistente e fendilhação com os resultados de vigas de referência, em betão convencional.info:eu-repo/semantics/publishedVersio

Sensoriamento remoto aplicado ao mapeamento do uso do solo urbano e de assentamentos ilegais em Montes Claros / MG.

O crescimento das cidades é um fenômeno global, sobretudo nos países em desenvolvimento. No contexto brasileiro, as cidades classificadas como intermediárias ou médias destacam-se como polo convergente de imigrantes, por apresentarem características importantes na atração populacional. Essa situação gera transformações significativas no sistema urbano, como, por exemplo, na forma de ocupação do solo. Esse cenário descreve a realidade da cidade de Montes Claros, uma vez que ela se destaca como polo de uma vasta região que abrange todo o Norte de Minas Gerais. Nesse sentido, o objetivo principal deste artigo foi mapear e analisar o uso do solo da cidade de Montes Claros, através do uso integrado do sensoriamento remoto com o SIG. O uso das geotecnologias, notadamente o sensoriamento remoto, com imagens de alta resolução espacial, e o Sistema de Informações Geográficas (SIG) permitiram extrair dados sobre a organização do uso do solo urbano de Montes Claros. Nesse momento foi possível quantificar e qualificar as classes predominantes nesse espaço. A construção de uma metodologia de mapeamento do espaço intraurbano foi imprescindível para criar uma legenda em níveis hierárquicos, permitindo mapear o uso do solo com vários focos, sendo que o interesse principal era identificar, na classe de baixa renda, as áreas classificadas como favelas. Diante desses resultados, é importante o monitoramento constante, através das geotecnologias, do uso do solo urbano, uma vez que a ocupação ilegal desse solo é um problema recorrente nas cidades médias brasileiras

Experimental assessment of the performance and emissions of a spark-ignition engine using waste-derived biofuels as additives

The use of biofuels for spark ignition engines is proposed to diversify fuel sources and reduce fossil fuel consumption, optimize engine performance, and reduce pollutant emissions. Additionally, when these biofuels are produced from low-grade wastes, they constitute valorisation pathways for these otherwise unprofitable wastes. In this study, ethanol and pyrolysis biogasoline made from low-grade wastes were evaluated as additives for commercial gasoline (RON95, RON98) in tests performed in a spark ignition engine. Binary fuel mixtures of ethanol + gasoline or biogasoline + gasoline with biofuel incorporation of 2% (w/w) to 10% (w/w) were evaluated and compared with ternary fuel mixtures of ethanol + biogasoline + gasoline with biofuel incorporation rates from 1% (w/w) to 5% (w/w). The fuel mix performance was assessed by determination of torque and power, fuel consumption and efficiency, and emissions (HC, CO, and NOx). An electronic control unit (ECU) was used to regulate the air–fuel ratio/lambda and the ignition advance for maximum brake torque (MBT), wide-open throttle (WOT)), and two torque loads for different engine speeds representative of typical driving. The additive incorporation up to 10% often improved efficiency and lowered emissions such as CO and HC relative to both straight gasolines, but NOx increased with the addition of a blend.This work was supported by FCT-Fundação para a Ciência e Tecnologia within the R&D Units, MEtRICs Project Scope: UIDP/04077/2020. Joaquim da Costa was supported through a PhD Grant from Fundo de Desenvolvimento Capital Humano of the Government of Timor Leste

Methyl 5a-acetoxy­methyl-3-isopropyl-8-methyl-1,2,3,3a,4,5,5a,6,7,10,10a,10b-dodeca­hydro-7,10-endo-epidioxy­cylohepta­[e]indene-3a-carboxyl­ate

The mol­ecule of the title compound, C23H34O6, is built up from three fused carbocycles, one five-membered, one six-membered and one seven-membered. The five-membered ring has an envelope conformation, whereas the six-membered ring has a perfect chair conformation and the seven-membered ring has a boat conformation. Intra­molecular C—H⋯O hydrogen bonds together with van der Waals inter­actions stabilize the mol­ecular conformation

The effect of superplasticizers on the workability and compressive strength of concrete made with fine recycled concrete aggregates

The reuse of structural concrete elements to produce new concrete aggregates is accepted as an alternative to dumping them and is favourable to the sustainability of natural reserves. Even though the construction sector is familiar with the use of coarse recycled concrete aggregates, the recycled concrete fines are classified as less noble resources. This research sets out to limit the disadvantages associated with the performance of concrete containing fine recycled concrete aggregates through the use of superplasticisers. Two types of latest generation superplasticisers were used that differ in terms of water reduction capacity and robustness, and the workability, density and compressive strength of each of the compositions analysed were then compared: a reference concrete, with no plasticisers, and concrete mixes with the superplasticisers. For each concrete family mixes with 0%, 10%, 30%, 50% and 100% replacement ratios of fine natural aggregates (FNA) by fine recycled concrete aggregates (FRA) were analysed. Concrete with incorporation of recycled aggregates was found to have poorer relative performance. The mechanical performance of concrete with recycled aggregates and superplasticisers was generally superior to that of the reference concrete with no admixtures and of conventional concrete with lower performance superplasticisers