Effect of the water/binder ratio on the hydration process of Portland cement pastes with silica fume and metakaolin

abstract: The microstructure of cement pastes is important to understand the effect of some parameters in the hydration process. In this context, this study had as objective to evaluate the effect of different water/binder (w/b) ratios in the hydration process of cementitious pastes produced with and without incorporation of silica fume and metakaolin. The pastes were obtained with water/binder ratios of 0.3, 0.4 e 0.5, with replacement, by weight, of Portland cement for silica fume and metakaolin, in the contents of 10% and 20%, respectively. It was performed the X-ray diffraction test of the pastes in the ages of 1, 3, 7, and 28 days, to evaluate the hydration evolution of the cementitious materials. According to the results obtained, it was observed that the cementitious pastes presented similar mineralogical phases, except for the pastes containing metakaolin due to the formation of new aluminate phases. With the increase of the water/binder ratio, the pozzolanic reactions and hydration occurred in greater proportion, standing out the metakaolin with greater reactivity.

Geochemical modeling of the leaching behavior of municipal solid waste bottom ash.

Mineral trace elements (MTE) constitute an environmental restriction on the recycling of municipal solid waste incineration-bottom ash (MSWI-BA). The study of the speciation of MTE and the factors that control their release allows to predict their behavior under different environmental conditions and, consequently, suggest different actions to expand the management of MSWI-BA.A geochemical modeling led to a better understanding of the speciation of MTE. In this study, target elements were barium, copper, lead, nickel and zinc and the factors that control their release were identified.The results show that the leaching of metals as a function of pH mainly depends on the mineralogical phases. On the other hand, the organic matter has an influence in the leaching of MTE (for Ni, Cu and Pb notably); organic matter presents adsorbent or complexation properties. Les éléments traces métalliques (ETM) constituent une restriction environnementale pour le recyclage des mâchefers d'incinération des déchets non dangereux (MIDND). L'étude de la spéciation des ETM et des facteurs qui contrôlent leur mobilité permet de prédire le comportement des MIDND dans différentes conditions environnementales et de suggérer ensuite des actions pour élargir leur gestion. Une modélisation géochimique des MIDND a permis de mieux comprendre la spéciation des ETM. Dans cette étude, les éléments ciblés étaient le baryum, le cuivre, le plomb, le nickel et le zinc et les facteurs qui régissent leur mobilité ont été définis. Les résultats montrent que la lixiviation des métaux en fonction du pH dépend principalement des phases minéralogiques ; la matière organique joue également un rôle en tant qu'adsorbant ou complexant dans la lixiviation de certains éléments (Ni, Cu et Pb, notamment). Mots-clés Mâchefers d'incinération des déchets non dangereux (MIDND), éléments traces métalliques, capacité de neutralisation acide, modélisation géochimique, PhreeqCI.

Development of Eco-Friendly Mortars Produced with Kaolin Processing Waste: Durability Behavior Viewpoint

This study presents the development of new eco-friendly mortar compositions containing kaolin residues (KR) and assesses their durability behavior. Firstly, the natural and calcinated kaolin residues (600 °C, 650 °C, 700 °C, 750 °C, and 800 °C) were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), granulometric analysis, and surface area. The kaolin residue calcinated at 800 °C was chosen to be added to new compositions of mortar because it presented the best pozzolanic performance. The aging tests accomplished in internal (Ei) and external (Ee) environments were applied in mortars with a mass proportion of 1:2:6 (cement + KR: lime: sand), in which the KR, calcinated at 800 °C, replaced the cement in the mass fraction of 0%, 5%, 10%, 15%, 20%, and 30%. The Ei was performed for 30, 60, 90, 180, and 360 days, and the Ee for 90; 210; 360; and 512 days. After the aging tests were completed, the mortar compositions containing KR were evaluated to determine their mineralogical phases (XRD), compressive strength (CS), and thermal behavior (DTA and thermogravimetry). In summary, the KR addition to the mortar compositions decreases the mechanical resistance to compression; however, mortars with a substitution of 10% and 20% presented resistance values within the minimum limit of 2.4 MPa established by ASTM C 270.

Historical glass mosaic tesserae: a multi-analytical approach for their characterization

We present a completely non-destructive approach to analyse a set of historical glass mosaic tesserae. Aim of the study is to obtain a qualitative and quantitative characterization of the glass matrix in terms of elements and mineralogical phases. Several non-destructive techniques have been applied like Particle-Induced X-ray Emission, Particle-Induced Gamma-ray Emission, micro-Raman spectroscopy, neutron resonance capture analysis and neutron activation analysis in order to combine different technique strengths and to explore the effect of different range sizes for the analysis. Yet, best practices require the use of combined analysis and different skills. The paradigm of a non-destructive multi-analytical approach is suggested for a comprehensive investigation in non-homogeneous real samples, like historical glass mosaic tesserae.

Caracterización de partículas metálicas extraídas de cenizas volantes de una planta termoeléctrica de Boyacá-Colombia

In this work, it was studied the by-products of fly ashes, obtained from a thermoelectric power station in Boyacá, Colombia, through magnetic separation. The morphological characterization of the particles was performed by a scanning electron microscopy. Its elemental composition and crystalline structure were studied through energy dispersive spectroscopy and an X-ray diffraction, respectively. The results obtained show the presence of ferrospheres and cenospheres, which are irregular and rough compounds with a high iron content. The mineralogical phases present in the samples are mainly magnetite and hematite, with some traces of mullite. These phases can provide magnetic properties and extend the range of applications of these particles using a simple separation process in fly ashes.

DFT Simulation of the Water Molecule Interaction with the (00l) Surface of Montmorillonite

Montmorillonite is one of the principal mineralogical phases in clay minerals, where its interaction with water and other molecules represents one of the most important aspects and properties for basic science and specific applications. In fact, montmorillonite has many uses in various scientific and technological fields, ranging from environmental remediation to ceramics, food science, and construction/building materials. Several efforts have characterized its structure and physico-chemical properties, especially at the Tetrahedral-Octahedral-Tetrahedral TOT surface. For this purpose, in this work, the authors investigated the structural and electrostatic potential features of the (00l) surface of montmorillonite and the water adsorption process by first principle methods (density functional theory, DFT), considering both static and molecular dynamics approaches. The provided data further extend the knowledge of the modulation of the water molecule adsorption with this important clay mineral.

Heavy Metals as Impurities in the Bayer Production Cycle of the Aluminum Hydroxide from Sierra Leone Bauxite. Preliminary Study

This paper is reporting the data of a preliminary study on heavy metals distribution in the fluid and solid phases involved in dry and classified aluminium hydroxide production through Bayer process. For heavy metals released in the fluid phases, the main source of contamination is the bauxite through its mineralogical phases soluble or insoluble in alkaline solution. It was shown that predominant way to transfer contaminating elements in aluminium hydroxide particles is the occlusion of very fine particles coming from mineralogical phases of bauxite residue. New born mineralogical phases from bauxite residue, like poor crystallized sodalite and cancrinite, are the most active occlusion contaminants

Determination of the microscopic mineralogy of inclusion in an amygdaloidal pillow basalt by fs-LIMS

Depth profiling and atomic intensity correlation studies on mineralogical inclusion embedded in calcium carbonate phase using a miniature laser mass spectrometer are presented. The method allows the determination of complex mineralogical phases.

CHARACTERIZATION OF CLAYS IN THE ZINDER REGION BY X-RAY DIFFRACTION AND X-RAY FLUORESCENCE METHODS

In order to characterizeclays of the Zinder region, 20 samples were taken from the quarries of Magaria, Mirriah, Guidimouni and Kolleram and four composite samples were made and representative of the quarries. These samples were subjected to chemical and mineralogical analyzes. Chemical analysis shows that the materials from these four quarries are aluminosilicates, but in varying proportions. The samplesfrom the Magaria and Kolleramquarries, contain proportions of carbonwhichinducethem a blackishcolor and alkaline and alkaline-earthelements (CaO, K2O, MgO. The samplesfromMirriah and Guidimouni,are veryrich in ironoxide (Fe2O3) whichinduces a reddishcolor. The main mineralogical phases detected by X-ray diffraction in the rawsamples and fine fractions from the four quarrieswere kaolinite, a mica structure close to illite and quartz.Thesequarriesthenconstitutekaolinicdeposits, primary and secondary. Those of Magaria and Kolleram are secondary and less favorable to formulations of ceramicproducts and those of Mirriah and Guidimouni are primary and very favorable to formulations of ceramicproductssuch as potteryfromMirriah.