ANALYSIS OF BUILDING MATERIALS BY SYNCHROTRON X-RAY IMAGING

Building materials have complex hierarchical microstructures. The largest components are coarse aggregates with dimensions larger than a few centimetres and the smallest ones are the calcium silicate hydrate (C-S-H) gel nanoparticles with sizes smaller than 5 nm. To fully understand the main properties of cement binders and optimize their performances, a sound description of their spatially-resolved contents is compulsory. Furthermore, cement manufacturing is responsible for about 7% of the anthropogenic CO2 emissions and hence, to decrease the CO2 footprint, in a sustainable and cost-effective way, is a top priority. To gain a deeper insight into the microstructures of building materials, synchrotron X-ray ptychographic nanotomography and absorption-based microtomography have been employed. Here we will present three examples of our approach blending quantitative powder diffraction with synchrotron X-ray imaging. Firstly, we will show our comparative work on belite and Portland cement pastes cured at varying temperatures [1]. Synchrotron tomographic data taken at TOMCAT allowed understanding the different hydrating behaviour of both cements. Secondly, ptychographic nanotomographic data taken at cSAXS showed the hydration of CaAl2O4 with curing temperature [2]. Ptychographic data have permitted to characterise the conversion of the aluminate hydrates which is key for durability. The very good contrast in the electron density tomograms will be discussed as well as the porosity induced after the conversion reactions. Finally, we will report our work on Portland cements [3]. The densities and spatial distribution of calcium silicate hydrate (C-S-H) gel and amorphous iron-siliceous hydrogarnet components will be described.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. BIA2017-82391-R UMA18-FEDERJA-09

Multiscale understanding of tricalcium silicate hydration reactions

Tricalcium silicate, the main constituent of Portland cement, hydrates to produce crystalline calcium hydroxide and calcium-silicate-hydrates (C-S-H) nanocrystalline gel. This hydration reaction is poorly understood at the nanoscale. The understanding of atomic arrangement in nanocrystalline phases is intrinsically complicated and this challenge is exacerbated by the presence of additional crystalline phase(s). Here, we use calorimetry and synchrotron X-ray powder diffraction to quantitatively follow tricalcium silicate hydration process: i) its dissolution, ii) portlandite crystallization and iii) C-S-H gel precipitation. Chiefly, synchrotron pair distribution function (PDF) allows to identify a defective clinotobermorite, Ca11Si9O28(OH)2.8.5H2O, as the nanocrystalline component of C-S-H. Furthermore, PDF analysis also indicates that C-S-H gel contains monolayer calcium hydroxide which is stretched as recently predicted by first principles calculations. These outcomes, plus additional laboratory characterization, yielded a multiscale picture for C-S-H nanocomposite gel which explains the observed densities and Ca/Si atomic ratios at the nano- and meso- scales.This work has been supported by Spanish MINECO through BIA2014-57658-C2-2-R, which is co-funded by FEDER, BIA2014-57658-C2-1-R and I3 (IEDI-2016-0079) grants. We also thank CELLS-ALBA (Barcelona, Spain) for providing synchrotron beam time at BL04-MSPD beamline

“Education Network” a new way to teach Chemistry

The complexity of chemistry has implications for the teaching of chemistry. That chemistry is a very complex subject. The majority of the students at University think that chemistry is a difficult discipline and they have difficulty in understanding the concepts. Moreover, students' interest in chemistry decreases the first year at university. The reason for this decrease might be that the contents of chemistry laboratory classes are boring, out of date and lacking of dynamism that students experience through visual media tools. For these reasons, new programs and methodologies should be developed. Those are based on making chemistry relevant through problem solving and collaborative learning hold promise for reforming chemistry education. It is about an education according to circumstances, which is adapted to context and virtual behaviour of people. It's time to CRUSH boredom by transforming your classroom into an Escape Room adventure. School-based escape games are a great teaching tool. The students while playing, learn. The most important point is that they won’t realize they’re doing both at the same time. In this work, an educational gamification experience based on the escape room concept was developed. The first (Do It Yourself) DIY Escape Room was built the year before at Mechanical Engineer Degree started, that took more than three weeks of work. It was presented to other professors to the same subject at different degrees. That DIY Escape Room was modified and adapted to each group. Each professor changed the clues, problems and so on in order to orientate the topic as much as possible to their students.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

X-ray near-field ptychographic nanoimaging of cement pastes

The hydration processes of Portland cements (PC) and blends are complicated as there are many components with great heterogeneity at different length scales. Thus, 3D nanoimaging techniques with high spatial resolution and scanning large fields of view are needed. Here, synchrotron X-ray near-field ptychographic tomography is used to investigate four pastes within 0.2 mm thick capillaries: PC with CaCl2, PC hydration enhanced by C-S-H nucleation seeding, PC partly substituted with metakaolin, and PC partly substituted with metakaolin and limestone. Data analysis emphasis has been placed on the characterization of amorphous components: (i) C-S-H and C-A-S-H gels; (ii) iron aluminium siliceous hydrogarnets; (iii) metakaolin; and (iv) aluminium carboaluminate, AFm-like. Synchrotron ptychotomography yields electron density and absorption coefficient tomograms and the resulting bivariate plots are instrumental for characterising these amorphous components. The attained spatial resolution, ∼220 nm, with very good contrast allowed us to determine nanofeatures including mass densities and spatial distributions of amorphous components. For instance, the C-S-H gel mass density differences between the two type of accelerated pastes are detailed.Funding for open access charge: Universidad de Málaga / CBUA. This research has been partly supported by the research grant PID2019-104378RJ-I00 which is co-funded by ERDF. We acknowledge the Paul Scherrer Institut, Villigen, Switzerland for provision of synchrotron radiation beamtime at cSAXS beamline of the SLS, proposal number 20210147

Preparación y caracterización de cementos belíticos blancos activados con dopantes alcalinos

Activated white cement clinkers with a theoretical 60% (wt) belite (dicalcium silicate) content were prepared at a temperature 100 ºC lower than used to manufacture conventional white Portland cement clinkers. Activation was achieved by adding variable amounts of K2CO 3 or Na2CO 3 to the raw mixes. Rietveld quantitative analysis of X-ray diffraction findings showed that adding the alkalis stabilized the high temperature belite polymorphs. When 2.0% (wt) of Na2O was added, the composition (by wt) found was 16.4(4)% alpha-C2S, 16.7(8)% alpha’-H-C2S, 23.2(6)% beta-C2S, 32.7(7)% total C3S, 9.5(2)% orthorhombic C3A and 1.50(5)% free lime. Due to the high volatilization rate of K2O under the experimental conditions, it stabilized the alpha-type C2S less effectively than Na2O. A calorimetric study was likewise performed to correlate the phase composition with early age hydration (behaviour).Se han preparado clínkeres blancos activados con un porcentaje en peso teórico de belita (silicato dicálcico) del 60%, a una temperatura 100 ºC menor que los clínkeres Portland blancos convencionales. El proceso de activación se ha llevado a cabo añadiendo a las mezclas crudas cantidades variables de K2CO3 o Na2CO 3. Utilizando la difracción de rayos-X y la metodología de Rietveld se ha comprobado la estabilización a temperatura ambiente de porcentajes variables de los polimorfos de alta temperatura de la belita por la adición de alcalinos. De hecho, al añadir 2,0% en peso de Na2O se ha obtenido 16,4(4)% de alfa-C2S, 16,7(8)% de alfa’-H-C2S, 23,2(6)% de beta-C2S, 32,7(7)% de C3S total, 9,5(2)% de C3A ortorrómbico y 1,50(5)% de cal libre, porcentajes en peso. Se ha comprobado que el grado de volatilización de los alcalinos, en estas condiciones de preparación, ha sido muy acusado para el K2O, lo que ha provocado una menor estabilización de los polimorfos tipo-alfa-C2S. Además, se ha realizado un estudio calorimétrico para correlacionar el ensamblaje de fases con el comportamiento de hidratación a edades tempranas

Quantitative analysis of cementitious materials by X-ray ptychographic nanotomography

Cement manufacturing is responsible for ~7% of the anthropogenic CO2 emissions and hence, decreasing the CO2 footprint, in a sustainable, safe, and cost-effective way, is a top priority. It is also key to develop more durable binders as the estimated world concrete stock is 315 Gt which currently results in ~0.3 Gt/yr of concrete demolition waste (CDW). Moreover, models under development predict a skyrocketing increase of CDW to 20–40 Gt/yr by 2100. This amount could not be easily reprocessed as aggregates for new concretes as such volumes would be more than two times the predicted need. Furthermore, concretes have very complex hierarchical microstructures. The largest components are coarse aggregates with dimensions bigger than a few centimetres and the smallest ones are amorphous components and the calcium silicate hydrate gel with nanoparticle sizes smaller than a few nanometres. To fully understand the properties of current and new cement binders and to optimize their performances, a sound description of their spatially-resolved contents is compulsory. However, there is not a tomographic technique that can cover the spatial range of heterogeneity and features of concretes and mortars. This can only be attained within a multitechnique approach overlapping the spatial scales in order to build an accurate picture of the different microstructural features. Here, we have employed far-field and near-field synchrotron X-ray ptychographic nanotomographies to gain a deeper insight into the submicrometer microstructures of Portland cement binders. With these techniques, the available fields of view range from 40 to 300 um with a true spatial resolution evolving between ~50to~300 nm. It is explicitly acknowledged here that other techniques like X-ray synchrotron microtomography are necessary to develop the whole picture accessing to larger fields of view albeit with poorer spatial resolution and without the quantitativeness in the reconstructed electron densities

Hidratación y prestaciones mecánicas de cementos LC3 con arcillas caoliníticas calcinadas españolas

La búsqueda de alternativas que reduzcan esas emisiones es prioritario. Dentro de esas estrategias se encuentra la sustitución parcial de cemento por material cementicio suplementario (SCM, de sus siglas en inglés, Supplementary Cementitious Materials), como es el caso de arcillas calcinadas. En este grupo, se encuentran los denominados cementos LC3, de sus siglas en inglés Limestone Calcined Clay Cement, cuyas emisiones CO2 se reducen hasta un 40% respecto del PC sin adiciones. Según la UNE-EN 197-5 (versión española, julio-2021) para cemento Portland compuesto CEM II/C-M, el clínker podría sustituirse hasta en un 50%p. Este trabajo se centra en cementos LC3 con 52%p de PC 42.5 R, 30%p de arcilla calcinada, 15%p de caliza y 3%p de yeso adicional, y la utilización de 3 arcillas caoliníticas españolas con diferente porcentaje en caolinita (70-83%p), activadas térmicamente a 860ºC y molidas a dos tamaños de partícula relevantes (Dv,50 10 y 5 m). Se abordará el estudio de las pastas de cemento LC3 preparadas en una relación agua/binder (w/b) de 0.40 con superplastificante basado en policarboxilato, a través de su comportamiento reológico, ensamblaje de fases de pastas (RQPA, del inglés Rietveld Quantitative Phase Analysis) a diferentes edades (2, 7, 28 y 120 días) y calorimetrías (20ºC/7d). A modo de ejemplo, LC3 con la arcilla calcinada CVPM3B desprende 50.6 y 135.5 J/g a 2 y 7d, respectivamente, pero con SY1 el calor liberado era 12.9 J/g y 63.0 J/g, respectivamente. Estos valores están justificados principalmente por el mayor área superficial (y menor tamaño de partícula) de CVPM3V (y su estructura local altamente tensionada), a pesar de su menor contenido en caolinita. Finalmente, los resultados se relacionarán con las resistencias mecánicas de los morteros correspondientes.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Doble activación de cementos BYF (belita-ye’elemita-ferrita) y su efecto en pastas y morteros

Los eco-cementos tipo BYF se postulan como una alternativa a los PC (Cementos Portland) por su menor demanda de caliza. Estos están principalmente constituidos por tres fases: Belita (-C2S o -Ca2SiO4), Ye’elemita (C4A3S o Ca4Al6O12(SO4)) y Ferrita (C4AF o Ca2AlFeO5), de ahí sus siglas. Sin embargo, el problema principal de estos cementos son las bajas resistencias mecánicas a edades tempranas, debido a la baja reactividad de la belita a esas edades. Una manera de abordar esta problemática, consiste en activar la belita para tener fases más reactivas, como las formas alfa. Otra manera de activar estos materiales, es mediante el uso de aditivos (aceleradores) cuya finalidad es aumentar la velocidad de algunas reacciones de hidratación de estos cementos optimizando el ensamblaje de fases. Concretamente, en este trabajo se han estudiado dos familias de cementos BYF sintetizados en el laboratorio: estándar (con -C2S) y activado (con α’H-C2S o α’H-Ca2SiO4), denominados st-BYF y B-BYF, respectivamente. En la segunda familia, la fase α’H-C2S se estabilizó por la adición del B2O3 (en forma de bórax) en el proceso de clinkerización. Ambos cementos se prepararon mediante la adición de 10 %p de anhidrita al clínker molturado. Posteriormente, se abordó el estudio del efecto de la relación agua/cemento y de varios aditivos comerciales, como son: B2O3, CaCl2, TIPA (triisopropanolamina) y Master X-Seed (nano C-S-H), sobre la hidratación de las pastas y las prestaciones a edades tempranas. Las pastas se han caracterizado a través de su comportamiento reológico, difracción de rayos-X (laboratorio y sincrotrón), calorimetría y análisis térmico. Estos resultados se discutirán y relacionarán con las resistencias mecánicas de los morteros correspondientes.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Floristic diversity, composition and dominance across Amazonian forest types respond differently to latitude

Aim: The latitudinal biodiversity gradient is considered a first-order biogeographical pattern for most taxonomic groups. Latitudinal variation in plant diversity is not always consistent, and this could be related to the particular characteristics of different forest types. In this study, we compare latitudinal changes in floristic diversity (alpha diversity), composition (beta diversity) and dominance across different tropical forest types: floodplain, terra firme and submontane forests. Location: Western Amazonia (Ecuador, Peru and Bolivia). Taxon: Woody plants. Methods: We inventoried 1978 species and 31,203 individuals of vascular plants with a diameter at breast height ≥ 2.5 cm in 118 0.1-ha plots over an 1800 km latitudinal gradient in three different forest types. The relationships between alpha diversity, latitude and forest type were analysed using generalised linear mixed models. Semi-parametric permutational multivariate analysis of variance was used to investigate the effects of latitude and forest type on beta diversity. Dominant species abundances were correlated with non-metric multidimensional scaling ordination axes to reflect their contributions in shaping changes in beta diversity. Results: Alpha diversity increased towards equatorial latitudes in terra firme and submontane forests but remained relatively constant in floodplains. Beta diversity of all forest types changed with latitude, although less clearly in floodplains. Also, in floodplain forests, there were fewer dominant species contributing to beta diversity and more species homogeneous along the gradient. Main Conclusions: Latitudinal diversity patterns are manifested in alpha and beta diversity since latitude summarizes climatic and edaphic changes. However, we found different responses of each forest type. In floodplain forests, inundation regime is a stronger predictor than latitude, limiting floristic diversity and composition. Changes in dominant species abundance over gradients explained species composition, but floodplain forests harboured more homogeneous dominant species than well drained forests. It is key to study environmental trends and habitat characteristics of each forest type to understand their species diversity and dominance pattern

Aluminum-rich belite sulfoaluminate cements: clinkering and early age hydration

Belite sulfoaluminate (BSA) cements have been proposed as environmentally friendly building materials, as their production may release up to 35% less CO2 into the atmosphere when compared to ordinary Portland cements. Here, we discuss the laboratory production of three aluminum-rich BSA clinkers with nominal mineralogical compositions in the range C2S (50-60%), C4A3$(20- 30$, i.e. a value as close as possible to the nominal composition. Under these experimental conditions, three different BSA clinkers, nominally with 20, 30 and 30 wt% of C4A3$, had 19.6, 27.1 and 27.7 wt$ respectively, as determined by Rietveld analysis. We also studied the complex hydration process of BSA cements prepared by mixing BSA clinkers and gypsum. We present a methodology to establish the phase assemblage evolution of BSA cement pastes with time, including amorphous phases and free water. The methodology is based on Rietveld quantitative phase analysis of synchrotron and laboratory X-ray powder diffraction data coupled with chemical constraints. A parallel calorimetric study is also reported. It is shown that the b-C2S phase is more reactive in aluminum-rich BSA cements than in standard belite cements. On the other hand, C4A3$ reacts faster than the belite phases. The gypsum ratio in the cement is also shown to be an important factor in the phase evolution