The alkaline activation of aluminosilicates materials has been motivated by their enhanced thermomechanical properties. Despite the majority of studies comprise the evaluation industrial byproduct of precursors (fly ash and slag), metakaolin (Al2O3.2SiO2) is acknowledged to have structure and chemical composition characteristics that make it very reactive as far as alkaline activation is concerned. In tropical regions of the earth, as is the case in northeastern Brazil, there are some waste (kaolin waste, red brick waste and weathered tropical soils) whose alkaline activation potential have not yet been fully studied. These sources are known to have other metals such as iron in its structure, which might affect the alkaline activation. This paper aims to evaluate the potential of alkaline activation of these wastes. Chemical and structural characterization were performed by means of x-ray fluorescence, x-ray diffraction, infrared spectroscopy and compressive strength. The results indicate that all studied waste presented significant potential as precursor material for alkaline activation.
A utilização de resíduos de construção e demolição (RCD) como materiais de construção na produção de concreto é um tema muito comum nas pesquisas, porém existem lacunas a serem preenchidas ao se considerar estudos de durabilidade contra agentes agressivos. O ataque do sulfato é uma problemática no estudo de concretos, o objetivo deste trabalho é analisar o comportamento de concretos fundidos com a substituição de agregados naturais por resíduos de construção e demolição, quando submetidos ao ataque de sulfatos de magnésio em altas concentrações. Para composição da amostra, os corpos-de-prova foram fundidos com a substituição de grandes agregados nas proporções por massa de 0%, 25%, 50%, 75% e 100%, após um período de cura úmida de 150 dias. em ambiente
Biodegradable containing composites are increasingly present in several industries, mainly because they are renewable but also for their engineering properties. Despite environmentally friendliness has become an issue of paramount importance, the use of natural fibers has some limitations, especially when high temperature exposure is concerned. Geopolymers are known to withstand temperatures as high as 1000°C, preserving significant mechanical properties. This paper aims to explore the potential use of sisal fiber reinforced alkaline activated in high temperature environment. The composites were exposed to direct flame and visual changes and temperature profile were assessed up to 35 minutes. The results shows that material behavior works as an insulation barrier with a c.a. 80% temperature reduction between the direct flame exposed surface to the opposite side. Also, samples with thickness above 5mm maintained their integrity without developing smoke or spreading flame throughout the study time.
Solar energy presents the greatest potential by which to produce heat energy with reduced carbon emissions for power generation. To increase its harvesting and conversion, it is necessary to understand fundamental concepts and develop new materials. Although many processes can obtain selective absorbing surfaces (SAS) for application in solar energy exploitation, including electroplating methods, those processes have not sufficiently investigated the substrate’s treatment impact. The present work investigates 304 stainless steel (SS304) substrates treatment influence on the film’s (coatings) optical properties of SAS based on CrO3 electroplating. For this purpose, three main steps featured in the methodology: substrates treatment, coatings deposition, and physical-chemical characterization. The former was performed by detergent cleaning (DC), acid treatment (AT), and electropolishing (EP). Then, coatings were electroplated towards chromium deposition on the substrates with different deposition times. Finally, films were characterized by Profilometry, UV-Vis-NIR, and IR regions Spectroscopy and Scanning Electron Microscopy (SEM). The results indicated that, in terms of surface treatments on the substrate, the electropolished (EP) substrates presented average roughness values of 35 nm, reflectivity of 5.09%, and clear morphological difference (SEM) when compared to other treatments in this study (DC and AT). A SAS was successfully obtained, and the electropolished substrates (EP) presented coatings with better optical performance than other samples (DC and AT), with absorptivity values around 98% and emissivity of approximately 7%. A relationship between substrate treatment, its roughness, and the impacts on the optical selectivity of SASs was observed. Therefore, electropolishing is presented as a promising treatment for the SASs substrates.
Abstract. Lightweight concrete shows good insulation properties, depending on several parameters such as mix design and aggregate type. Perlite aggregate is one of the most effective aggregates for such a purpose, mainly because of its low thermal conductivity (0.04 W/m. o C), but is not available globally. This paper explores the potential use of another source of thermal efficient aggregate, vermiculite (0.058 W/m. o C) which is available in Brazil and other countries where perlite is absent. Cylindrical samples were cast by using two lightweight aggregates, perlite and vermiculite, and treated with supercritical carbon dioxide. Supercritical carbonation (SCC) of concrete can improve mechanical, thermal and durability features. In this paper, the effect of SCC on the thermal behavior of lightweight mortars was investigated with regards to physical and microstructure features and thermal behavior due to cooling.
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