Effect of calcium sulfate source on the hydration of calcium sulfoaluminate eco-cement

The availability of cements, including eco-cements, with tailored mechanical properties is very important for special applications in the building industry. Here we report a full study of the hydration of calcium sulfoaluminate eco-cements with different sulfate sources (gypsum, bassanite and anhydrite) and two water/cement ratios (0.50 and 0.65). These parameters have been chosen because they are known to strongly modify the mechanical properties of the resulting mortars and concretes. The applied multitechnique characterization includes: phase assemblage by Rietveld method, evolved heat, conductivity, rheology, compressive strength and expansion/retraction measurements. The dissolution rate of the sulfate sources is key to control the hydration reactions. Bassanite dissolves very fast and hence the initial setting time of the pastes and mortars is too short (20 min) to produce homogeneous samples. Anhydrite dissolves slowly so, at 1 hydration-day, the amount of ettringite formed (20 wt%) is lower than that in gypsum pastes (26 wt%) (w/c = 0.50), producing mortars with lower compressive strengths. After 3 hydration-days, anhydrite pastes showed slightly larger ettringite contents and hence, mortars with slightly higher compressive strengths. Ettringite content is the chief parameter to explain the strength development in these eco-cements.Universidad de Málaga. Campus de Excelencia Interncaional Andalucía Tech

Evaluation of draw solutions and commercially available forward osmosis membrane modules for wastewater reclamation at pilot scale

An intensive evaluation of draw solutions (DS) was performed by focusing on the wastewater reuse applications of hybrid forward osmosis (FO) processes. The substances studied were potassium formate, potassium phosphate, magnesium sulphate, sodium chloride, sodium polyacrylate and polyethylene glycol, and their osmotic pressure, conductivity, pH, thermostability, sunlight exposure, toxicity, FO filtration performance and replenishment costs were determined. Additionally, commercially available FO membrane modules were evaluated at pilot scale. The results revealed that the most relevant DS properties for wastewater reuse under the studied conditions were the DS regeneration method, DS replacement price, pH adjustment and toxicity. These properties were shown to be more relevant than filtration flux when a maximum DS osmotic pressure value of 10 bar was used. This was the limit for efficient DS recovery. When the different FO membranes were compared, thin-film composite (TFC) flat-sheet membranes showed the highest flux and the highest salt rejection, and the lowest permeability and salt rejection values were presented by cellulose triacetate (CTA) hollow fibre membranes. Based on the information obtained, a TFC-FO/nanofiltration (NF) demonstration plant will be constructed next to the wastewater treatment plant (WWTP) in San Pedro del Pinatar, in the region of Murcia (Spain). This represents the world's first FO demonstration plant for municipal wastewater reclamation and its results will allow this technology to be evaluated for wastewater reuse for agricultural purpose

Chats as a strategy to encourage the cooperative learning. An investigation on teaching practices of future teachers

Presentamos una investigación en la que se recurre al uso de las Tecnologías de la Información y la Comunicación (TICs) como estrategias para fomentar el aprendizaje cooperativo, concretamente hemos optado por las sesiones de Chat (seminarios virtuales), al entender que este sistema de comunicación entre personas ubicadas en diferentes lugares, permite crear espacios para discutir, compartir experiencias, generar reflexión y por tanto, generar conocimiento compartido. La experiencia se ha desarrollado desde el Prácticum de Magisterio de la especialidad de Educación Física, y el Chat ha sido utilizado para la realización de seminarios y tutorías virtuales. Los objetivos de esta investigación se han centrado en evaluar el Chat como estrategia para fomentar el aprendizaje cooperativo, propiciar la relación y comunicación entre alumnado, tutores y supervisores de diferentes Centros Educativos, y finalmente en realizar un inventario de las estrategias cooperativas puestas en práctica por los implicados en la experiencia. Se trata pues de aprender a cooperar y cooperar para aprender. Los resultados indican que el Chat es una buena estrategia para favorecer el aprendizaje cooperativo, y que el uso del mismo contribuye a potenciar la reflexión crítica de los estudiantes sobre la práctica, el fomento del análisis crítico, el trabajo autónomo y en colaboración con sus colegas.This is an investigation in which information and communication technologies (IT) are used to encourage the cooperative learning. More specifically, we have used Chats (virtual seminars), understanding that this communication system between people in different locations allows the creation of spaces for discussing and sharing experiences. By discussing and sharing experiences, reflection is encouraged, leading to a collective creation of knowledge. This experience was carried out in the teaching practices of future teachers of Physical Education (University of Granada). Chat was used for virtual seminars and tutorships. The objectives of this investigation were to evaluate Chats as a strategy to encourage cooperative learning, relations and communication between students, tutors and supervisors from different institutions. It was also intended to show the different cooperative strategies used by the participants in the experience. In general, it is about learning to cooperate and cooperating to learn. Results show that Chats are a good strategy to encourage cooperative learning, and that the use of Chats helps to create an interactive reflection among students about their practices. They also help to encourage critical analysis and autonomous ways of working, as well as the main competencies required in the initial steps of becoming teachers.Grupo de Investigación FORCE (Formación Centrada en la Escuela) Universidad de Granad

El chat como estrategia para fomentar el aprendizaje cooperativo. Una investigación en el practicum de magisterio

Presentamos una investigación en la que se recurre al uso de las Tecnologías de la Información y la Comunicación (TICs) como estrategias para fomentar el aprendizaje cooperativo, concretamentehemos optado por las sesiones de Chat (seminarios virtuales), al entender que este sistema de comunicación entre personas ubicadas en diferentes lugares, permite crear espacios para discutir,compartir experiencias, generar reflexión y por tanto, generar conocimiento compartido. La experiencia se ha desarrollado desde el Prácticum de Magisterio de la especialidad de Educación Física, y el Chat ha sido utilizado para la realización de seminarios y tutorías virtuales. Los objetivos de esta investigación se han centrado en evaluar el Chat como estrategia para fomentar el aprendizaje cooperativo, propiciar la relación y comunicación entre alumnado,tutores y supervisores de diferentes Centros Educati vos, y finalmente en realizar un inventario de las estrategias cooperativas puestas en práctica por los implicados en la experiencia. Se trata pues de aprender a cooperar y cooperar para aprender.Los resultados indican que el Chat es una buena estrategia para favorecer el aprendizaje cooperativo, y que el uso del mismo contribuye a potenciar la reflexión crítica de los estudiantes sobre la práctica, el fomento del análisis crítico, el trabajo autónomo y en colaboración con sus colegas

In-situ hydration study of sulfobelite eco-cements

ALBA User Meeting and VI AUSE Conferenc

Structure, Atomistic Simulations, and Phase Transition of Stoichiometric Yeelimite

ABSTRACT: Yeelimite, Ca4[Al6O12]SO4, is outstanding as an aluminate sodalite, being the framework of these type of materials flexible and dependent on ion sizes and anion ordering/disordering. On the other hand, yeelimite is also important from an applied perspective as it is the most important phase in calcium sulfoaluminate cements. However, its crystal structure is not well studied. Here, we characterize the room temperature crystal structure of stoichiometric yeelimite through joint Rietveld refinement using neutron and Xray powder diffraction data coupled with chemical soft-constraints. Our structural study shows that yeelimite has a lower symmetry than that of the previously reported tetragonal system, which we establish to likely be the acentric orthorhombic space group Pcc2, with a √2a × √2a × a superstructure based on the cubic sodalite structure. Final unit cell values were a = 13.0356(7) Å, b = 13.0350(7) Å, and c = 9.1677(2) Å. We determine several structures using density functional theory calculations, with the lowest energy structure being Pcc2 in agreement with our experimental result. Yeelimite undergoes a reversible phase transition to a higher-symmetry phase which has been characterized to occur at 470 °C by thermodiffractometry. The higher-symmetry phase is likely cubic or pseudocubic possessing an incommensurate superstructure, as suggested by our theoretical calculations which show a phase transition from an orthorhombic to a tetragonal structure. Our theoretical study also predicts a pressure-induced phase transition to a cubic structure of space group I43m. Finally, we show that our reported crystal structure of yeelimite enables better mineralogical phase analysis of commercial calcium sulfoaluminate cements, as shown by RF values for this phase, 6.9% and 4.8% for the previously published orthorhombic structure and for the one reported in this study, respectively.Universidad de Málaga. Campus de Excelencia Internacional. Andalucía Tech

Reactive belite stabilization mechanisms by boron-bearing dopants

Belite-rich cements hold promise for reduced energy consumption and CO2 emissions, but their use is hindered by the slow hydration rates of ordinary belites. This drawback may be overcome by activation of belite by doping. Here, the doping mechanism of B and Na/B in belites is reported. For B-doping, three solid solutions have been tested: Ca2-x/2□x/2(SiO4)1-x(BO3)x, Ca2(SiO4)1-x(BO3)xOx/2 and Ca2-xBx(SiO4)1-x(BO4)x. The experimental results support the substitution of silicate groups by tetrahedral borate groups with the concomitant substitution of calcium by boron for charge compensation, Ca2-xBx(SiO4)1-x(BO4)x. Otherwise, the coupled Na/B-doping of belite has also been investigated and Ca2-xNax(SiO4)1-x(BO3)x series is confirmed to exist for a large range of x values. Along this series, α'H-C2S is the main phase (for x≥0.10) and is single phase for x=0.25. Finally, a new structural description for borax doping in belite has been developed for α'H-Ca1.85Na0.15(SiO4)0.85(BO3)0.15, which fits better borax activated belite cements in Rietveld mineralogical analysisThis work has been supported by Spanish Ministry of Science and Innovation through MAT2010-16213 research grant which is cofunded by FEDER

Mechanism of stabilization of dicalcium silicate solid solution with aluminium

Stoichiometric dicalcium silicate, Ca2SiO4, displays a well-known polymorphism with temperature. When this phase is doped by a range of elements, belite, one of the main phases of cements, is generated. Here, we thoroughly study the aluminum doping of dicalcium silicate. This type of study is important for cement characterization and also from a basic point of view. Ca2Si1−2xAl2xO4−x□x (x = 0, 0.010, 0.014, 0.03) has been prepared and studied by X-ray powder diffraction and the Rietveld method. The limiting composition has been established as Ca2Si0.972Al0.028O3.986□0.014. The 27Al MAS NMR band located close to ∼−70 ppm is ascribed to tetrahedral environments, in agreement with the proposed aliovalent Si/Al atomic substitution mechanism. Thermal analysis measurements under a wet atmosphere indirectly confirm the increase of oxygen vacancies as the amount of incorporated protons increases with the aluminium content. A thorough electrical characterization has been carried out including overall conductivity measurements under wet and dry atmospheres and conductivity as a function of the oxygen partial pressure. The samples show oxide anion conductivity with a small p-type electronic contribution under oxidizing conditions. These compounds display a very important proton contribution to the overall conductivities under humidified atmospheres.This work has been supported by the Spanish Ministry of Science and Innovation through the research grant MAT2010- 15175 which is co-founded by FEDER and Junta de Andalucía (Spain) through the research grant P10-FQM-6680