Alkali activation of "Pozzolan-calcium aluminate cement" mixtures

Peer ReviewedPostprint (published version

Manual para la redacción de estudios de gestión de RCD en obras de edificación, rehabilitación y demolición

Este Manual se ha desarrollado para dar soporte a los arquitectos, parejadores y project managers para la redacción e implantación de Plan de Gestión de Residuos de Construcción y Demolición y buenas prácticas gremiales, dando soporte a los contratistas a la hora de redactar e implantar Planes de Gestión de RCD.Postprint (published version

Materials a l'arquitectura de Sant Cugat del Vallès

Descripció del recurs: 7 d'abril de 201

The North African and oriental influence in the typologies and rituals of the Roman funerary world of the western end of the Baetica province

Dada la existencia en parte del litoral onubense de un horizonte cultural y poblacional similar al presente en la orilla norteafricana, desde antes de iniciarse la romanización, era de esperar que la continuidad de los intercambios comerciales y poblacionales entre ambas costas, desembocase en la conformación de un horizonte funerario similar, en el que pese a que es posible detectar elementos normativos de la cultura romana, lo que prevalece por encima de todo es el carácter norteafricano de la mayor parte de las prácticas ritualesDue to existence in part of the Huelva’s littoral of a cultural horizon and a similar population at this in the North African coast since before of the beginning of the romanization, it was expected that the continuity of the commercial and population exchanges between both coasts lead in the conformation of a similar funeral horizon, in which in spite of the possibility of detect normative elements of the roman culture, what prevails above all is the North African character of most of the ritual practice

C-S-H gels in blended cements: Study by infrared spectroscopy

ICCC 2015, Beijing, China, 13~16 October 2015; http://iccc2015.csp.escience.cn/dct/page/1C-S-H gel is the main product in the Portland cement (PC) hydration. Of their structure and composition depends the cement properties (strength, durability¿). The mixes of others materials with PC provides new cementitious materials with different properties. Understand the changes produces in the hydration products in these blends improves their use. This work studies the changes produced in the C-S-H gel by means Fourier Transform Infrared Spectroscopy (FTIR). Several samples were studied, PC (as reference system), a system formed by PC and calcium aluminate cement (CAC) with a 75/25 ratio, and two system formed by PC, CAC and calcium sulfate (C¿) with an 85/15 ratio of PC/CAC with 3 and 5% of C¿. All samples were cured in two environmental; at the air and under water, in order to observe the influence of curing. The samples were studied at the 6 hours, 7 days, 12 and 32 months of age. Results show in the PC, it changes to lower wavenumbers in the Q2 units positions over time. This fact indicates a little transformation of structure like-tobermorite to structure like-jennite providing a C-S-H less compact. Addition of CAC in PC hydration decreases the migration of Q2 units to lower wavenumbers indicating that C-S-H structure is more compact in this case. When C¿ is included in the system, this migration of Q2 units is lower and the bands are sharper indicating the structure like tobermorite presence. Other effect visible in the spectra is the decrease of bands due to Q1 units with the addition of CAC. The greater presence of aluminates in the system provides substitutions of Si4+ by Al3+ in the C-S-H structure. This fact produces longer chains reducing the units Q1. Different behaviors are observed in the cured conditions showing higher transformation towards structures like-jennite in the samples cured under water. Several conclusions can be drawn of this work. First, it use of infrared spectroscopy as powerful tool in the cement chemistry field. Not only as characterization technique but also it can be used for obtain structural information about cement phases, both hydrated as anhydrous. Regarding addition of other hydraulic materials at PC, the study shows formation of C-S-H more compact that will provide better mechanical properties. Also the cured conditions have influenced about hydrated products structure.Peer Reviewe

Cements based on kaolinite waste

The cement industry involves high-energy consumption that generates high CO2 emissions into the atmosphere. Environmental concerns can be addressed by replacing parts of Portland cement clinkers with pozzolanic materials in mortars and concrete. Slag, fly ash and silica fume are materials considered for the planned replacement. Research studies on clay minerals, such as kaolinite, are being followed with special attention by the scientific community and the cement industry. It is well known that these minerals require an activation process to transform kaolinite (K) into metakaolinite (MK). MK is an amorphous material from the transformation of K with high pozzolanic activity, which is its capacity to react with the portlandite released during the hydration of Portland cement, generating compounds such as C–S–H gels and some aluminum-phase hydrates. One of the MK production methods is heat treatment controlled by kaolinite at temperatures in the range of 600–900°C. Different residues have been used (coal mining, paper sludge and waste from a drinking water treatment plant) activated at 600°C for 2h to elaborate blended cements. Due to their good behaviour as future eco-efficient additions, this research is a study by x-ray fluorescence (XRF), x-ray diffraction (XRD) and scanning electron microscopy (SEM) of their influence on the performances of blended cement mixtures (binary and ternary one), with substitutions of pozzolan ratio at 28 days of hydration. The porosity of pozzolanic cements decreases because of the formation of hydrated phases during pozzolanic reaction.the Spanish Ministry of the Economy and Competitiveness under coordinated projects BIA2015-65558C3-1-2-3R (MINECO/FEDER

In situ chemical modification of C–S–H induced by CO2 laser irradiation

The final publication is available at Springer via http://dx.doi.org/10.1617/s11527-018-1150-yFire-induced compositional changes lead to strength loss and even failure in cement and concrete. Calcium silicate hydrate (C–S–H) gel, the main product of cement hydration, dehydrates at 25–200 °C, while temperatures of 850–900 °C alter its structure. A Raman spectroscopic study of the amorphous and crystalline phases forming after CO2 laser radiation of cement mortar showed that C–S–H dehydration yielded tricalcium silicate at higher, and dicalcium silicate at lower, temperatures. Post-radiation variations were identified in the position of the band generated by Si–O bond stretching vibrations.Peer ReviewedPostprint (author's final draft

Methodologies for Fostering Critical Thinking Skills from University Students’ Points of View

Developing critical thinking skills appears to be a challenge for higher education institutions. However, little is known about the students’ points of view regarding the methodologies they consider to foster the development of this competence. To answer this question, a total of 263 Spanish university students participated in this study and were asked what they understood by critical thinking and the methodologies they considered to be the most effective for developing it. The results indicated that, based on students’ points of view, there were six methodologies that mainly contributed to developing critical thinking: Debates, project-based learning, practices in real contexts, doing research, cooperative learning, and case studies. These results were unanimous regardless of the student’s understanding of critical thinking: Analyzing/organizing, reasoning/arguing, questioning/asking oneself, evaluating, taking a position/taking a decision, compromising/acting. These findings have important theoretical and practical implications for teachers and educational institutions in relation to the development of critical thinking in higher education.The APC was funded by eDucaR research team through the University of Deusto/Basque Government Contract-Programme

A teachers’ based approach to assessing the perception of critical thinking in Education university students based on their age and gender

In the 21st century, critical thinking (CT) is regularly presented as one of the most important competences to be developed by a majority of educational institutions. Teachers are expected to change and enrich their teaching and learning methodologies so that students could face future challenges. Nonetheless, few are the instruments that measure the perception of critical thinking based on teachers’ conception. The aim of this study is to design and validate an instrument for the assessment of CT in university students based on the conception of CT that university teachers have. For this study, a total of 312 Spanish university students have participated. Based on a good model fit from a Confirmatory Factor Analysis and good reliability indices, the results provide strength to the theoretical model to evaluate critical thinking in university students formed by six dimensions (Analyzing/Organizing; Reasoning/Argumenting; Questioning/Asking oneself; Evaluating; Positioning /Taking decisions, and Acting /Committing oneself) and 42 items. Similarly, age was not a predictor variable for the different dimensions; while gender was statistically in favor of women in some of the dimensions, and tendentially, the dimension of Positioning/Taking decisions, in favor of men. However, despite these differences, the model guaranteed its factorial invariance. These findings have important pedagogical implications for universities in particular, and educational institutions in general, when developing curricula and teaching plans that focus on the development of students’ critical thinking.The publication has been funded by eDucaR research team through the University of Deusto/Basque Government Contract-Programme

New developments in low clinker cement paste mineralogy

The use of industrial waste as a cement addition often changes the composition and development of the hydrated phases and with them matrix performance and durability, in particular at later ages. The effect of the presence in blended cement of 20% to 50% kaolinite based activated carbon waste (ACW) on paste hydration has been characterized by means of XRD, SEM/EDX, TG/DTG, NMR and FTIR to identify and monitor the mineralogical phases forming in materials at ages of up to 180 d. The results showed that the main reaction products forming in the first 7 d included C-S-H gels, C4ACH12 and C4AH13 (hydroxy-AFm). Whilst monocarboaluminate (Mc) content declined with rising percentages of ACW, the amount of hexagonal phase hydroxy-AFm rose. Then microstructure of the C-S-H gels developing in the OPC and the 50% additioned paste differed. Compact C-S-H gel plates, and phyllosilicate-like laminar spongy microplates with high polymerised C-S-H gel formed in the blended cement paste.Peer ReviewedPostprint (author's final draft