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Physical, mechanical and thermal properties of metakaolin-fly ash geopolymers
(Elsevier, 2022-02-16) Gómez-Casero, Miguel Ángel; de-Dios-Arana, Cristina; Bueno-Rodríguez, Juan Salvador; Pérez-Villarejo, Luis; Eliche-Quesada, Dolores
Due to the large coal fly ash (FA) production and its obvious environmental impact, alternative uses of this by-product must be researched. A considerable effort is being made worldwide on research concerning the reuse of FA as a source of alternative raw materials to produce new binder materials. One of the most promising building materials are geopolymers or alkali-activated materials (AAM). In this study, FA (25–75 wt %) was used to evaluate the potential of using this waste as a source of aluminosilicates for the synthesis of geopolymers to replace metakaolin (MK) as precursor. MK and FA geopolymers were also synthesized as a control. Sodium hydroxide and sodium silicate were used as alkaline-activator mix (Na2SiO3/NaOH ratio: 0.92). The geopolymers synthesized were characterized by Fourier Transform Infrared Spectroscopy (FTIR) X-ray diffraction (XRD) and Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM-EDS). The results indicate that control geopolymers, MK and FA geopolymers have similar mechanical and thermal properties. However, the MK-FA blended geopolymers have slightly lower compressive strengths and lower thermal conductivity. The decrease in the properties of the FA and MK-FA blended geopolymers may be due to the high solid/liquid ratio used, since the spherical particles of the FA require less liquid due to their higher workability. However, the obtained geopolymers can be a satisfactory solution for the recovery of waste that results in sustainable construction materials that meet the standard to be used for loadbearing concrete masonry units with insulating properties superior to Portland cement approaching the principles of circular economy.
Comparative study of alkali activated cements based on metallurgical slags, in terms of technological properties developed
(Elsevier, 2022-06-23) Gómez-Casero, Miguel Ángel; Pérez-Villarejo, Luis; Sánchez-Soto, Pedro José; Eliche-Quesada, Dolores
In this work, an investigation on the use of two slags from different origins (electric arc furnace slag (EAFS) and copper slag (CS)) as raw materials in the manufacture of alkali-activated cements has been carried out. A comparison of the different mechanical properties developed by the alkaline activation of each raw material has been studied. Combination of 35 wt% potassium hydroxide (KOH) solution with different concentration (5, 8, 12 and 15 M) and 65 wt% potassium silicate (K2SiO3) solution was used as activating solution to manufacture alkali activated cements. The pastes were cured 24 h in a climatic chamber at 20 °C at 90% of relative humidity, subsequently demoulded and cured at same condition during 1, 7, 28 and 90 days. Alkali activated materials have been characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The physical properties: bulk density, water absorption and apparent porosity, mechanical properties, flexural strength and compressive strength and thermal properties: thermal conductivity have been determined. The results indicate that two types of slags studied are a suitable source of aluminosilicates that can be activated for the manufacture of alkali-activated materials. These precursors are capable of developing high values of flexural and compressive strength and low values of thermal conductivity when optimal concentration of KOH was used. The optimal composition was developed when CS was utilized. Binders with CS and 12 M M ratio achieved compressive strength values up to 70 MPa.
Highly Recommended and Poorly Used: English and Spanish Science Teachers’ Views of Inquiry-based Learning (IBL) and its Enactment
(2020) Romero-Ariza, Marta; Quesada-Armenteros, Antonio; Abril-Gallego, Ana María; Sorensen, Peter; Oliver, Mary Colette
Inquiry pedagogies provide opportunities to meet learning outcomes linked to developing scientific literacy. Within a European project intended at promoting Inquiry Based Learning (IBL), this paper presents quantitative and qualitative data about teachers’ views of IBL and its enactment in England and Spain. Results show that teachers in both countries hold positive views based on benefits to students and science learning and perceive important systemic and personal barriers to the successful implementation, even after decades of political efforts. Teachers express frustration with the lack of time, teaching resources, classroom management and the demands of curriculum delivery, assessment and accountability. There is an emphasis on hands-on activities and students’ motivation but no stress on cognitive and epistemic aspects, showing views not well aligned with current understanding of the type of inquiry that best support learning. Implications for research and practice suggest that there is still a need to expand knowledge about how to support teachers in making the most of this pedagogy
Investigación basada en el diseño en la formación inicialde docentes para una enseñanza integrada de lanaturaleza de la ciencia y el pensamiento crítico
(Universidad de Cádiz, 2021-05-27) Cobo-Huesa, Cristina; Abril-Gallego, Ana María; Romero-Ariza, Marta
Promover el conocimiento didáctico del contenido del profesorado en formación inicial para una enseñanza eficaz de la naturaleza de la ciencia y el pensamiento crítico es uno de los grandes retos a los que debe hacer frente la investigación educativa para mejorar la alfabetización científica de las futuras generaciones. Con el fin de ofrecer propuestas didácticas basadas en la investigación y evaluadas en el contexto real del aula, en este trabajo, se presenta la investigación enfocada al diseño de una propuesta de formación inicial de profesorado para una enseñanza integrada de estos dos constructos. El estudio ilustra el proceso de desarrollo y mejora basada en pruebas y aporta evidencias sobre su eficacia para obtener los resultados buscados, cuantificando el tamaño del efecto con un diseño pre-post test con grupo control.
Changing teachers’ self-efficacy, beliefs and practicesthrough STEAM teacher professional development
(Taylor and Francis Group, 2021-07-06) Romero-Ariza, Marta; Quesada-Armenteros, Antonio; Abril-Gallego, Ana María; Cobo-Huesa, Cristina
This article presents a STEAM education model based on the use ofmeaningful contexts for the integrated acquisition of key learningoutcomes related to different subjects. The model combines inquiryand the use of socio-scientific issues to promote mathematics andscience learning along with the development of critical thinking andthe integration of cultural and fundamental values. The evaluation ofan international teacher professional development programme usinga pre/post-test research design shows the programme’s impact onsecondary school teachers’ self-efficacy beliefs, and teaching prac-tices related to the implemented pedagogical model. The qualitativeanalysis of the teachers’ reflections shows that the most appreciatedaspects of the programme are transferability to practice, the peda-gogical resources offered, the benefits of the model on students’learning, the methodological transformation involved, as well as theopportunity to exchange ideas and practices with colleagues ina professional learning community. These results are of great interestsince they reveal a powerful way to promote transformational tea-cher professional development in the STEAM environment.