Recent studies of cements and concretes by synchrotron radiation crystallographic and cognate methods

The portfolio of available synchrotron radiation techniques is increasing notably for cements and pastes. Furthermore, sometimes the terminology is confusing and an overall picture highlighting similarities and differences of related techniques was lacking. Therefore, the main objective of this work is to review recent advances in synchrotron techniques providing a comprehensive overview. This work is not intended to gather all publications in cement chemistry but to give a unified picture through selected examples. Crystallographic techniques are used for structure determination, quantitative phase analyses and microstructure characterization. These studies are not only carried out in standard conditions but synchrotron techniques are especially suited to non-ambient conditions: high temperatures and pressures, hydration, etc., and combinations. Related crystallographic techniques, like Pair Distribution Function, are being used for the analysis of ill-crystalline phase(s). Furthermore, crystallographic tools are also employed in imaging techniques including scanning diffraction microscopy and tomography and coherent diffraction imaging. Other synchrotron techniques are also reviewed including X-rays absorption spectroscopy for local structure and speciation characterizations; small angle X-ray scattering for microstructure analysis and several imaging techniques for microstructure quantification: full-field soft and hard X-ray nano-tomographies; scanning infrared spectro-microscopy; scanning transmission and fluorescence X-ray tomographies. Finally, a personal outlook is provided.I am grateful to all my coauthors, collaborators, colleagues and PhD students, for all our work together during more than two decades. I thank the University of Malaga and ALBA Synchrotron Light Source for the support and the stirring environments. I acknowledge the Spanish science funding agencies (they change the name quite often) for funding my studentship, to do the PhD and the three summer research stays at Oxford University, to the last ongoing research project. To all synchrotrons I have been allowed to enjoy carrying out experiments: SRS, ESRF, Max-Lab, DLS, APS, SLS and ALBA. Finally, this work has been supported by the Spanish MINECO through the BIA2014-57658-C2-1-R research grant

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

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

Processing and characterisation of standard and doped alite-belite-ye'elimite ecocement pastes and mortars

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cemconres.2019.105911.Cement and Concrete Research 127 (2020) 105911Here, we report the processing optimisation of two laboratory-prepared alite-belite-ye'elimite ecocements (standard and doped) that release to the atmosphere ~13% less CO2 than Portland Cement during fabrication. The processing was optimised through rheological measurements, where homogeneous pastes and mortars were finally prepared through the study and optimisation of both the superplasticiser content and the water-to-cement ratio. Both parameters were correlated with the phase assembly of selected pastes and compressive strength of the corresponding mortars. After optimisation, mortars with high compressive strengths (~72 and ~77 MPa for the standard mortar, and ~41 and ~75 MPa for the doped one, at 7 and 28 days, respectively) were prepared. Furthermore, the important increase in compressive strength from 7 to 28 days of the optimised mortar prepared from the doped ecocement is due to its composition (the higher content of belite jointly with the reaction of its active polymorph (α'H-belite)).This work is part of the PhD of Mr. Jesus D. Zea-Garcia. This research has been supported by Spanish MINECO and FEDER [BIA2017- 82391-R research project and I3 (IEDI-2016-0079) program]

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

The role of raw powder diffraction data in peer review; past, present and future

Scientific data in our community can be classified, in broad terms, in three large categories: raw, reduced and derived data. IUCr has been very active in promoting the sharing of reduced and derived data for decades in independently-verified databases. The need for raw data sharing is clearly increasing, being nowadays technically feasible and likely cost-effective. Powder diffraction (PD) community is a subgroup of the crystallographic community dealing with several goals, mainly (1) average crystal structure determination; (2) quantitative phase analyses; (3) microstructural analyses; and (4) local structure determination and quantitative analyses of nanocrystalline materials. For PD, derived data for objectives (2) and (3) and to a large extend (4) can not be incorporated in ‘standard’ databases. Derived data are not independently validated, and therefore and in my opinion, the need for sharing raw PD data is even more compelling than that of sharing raw single crystal diffraction data. So, if raw diffraction data sharing is approaching, we have the responsibility to ensure that this action is useful. Hence, and as stated by John Helliwell in the introduction of this workshop, two conditions must be fulfilled. On the one hand, and from the computing point of view, the shared data must be findable, accessible, interoperable and reusable – i.e. comply with FAIR standards. However, this is necessary but not sufficient. On the other hand, and from the involved scientific community point of view, the shared data must have sufficient quality. They must be true facts and the ‘FACT and FAIR’ term has been coined. Incorporating raw powder diffraction data ‘check/validation’ in the peer review process, the FACT nature of the raw data could be established. Or at least, a minimum quality level could be ensured. Some ideas (and experiences) will be developed in the meeting, including the use of shared raw powder diffraction data by meticulous reviewers. .....Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. BIA2014-57658 and BIA2017-82391-

Diffraction for industries, businesses and health

Se adjunta abstract en PDF- PDF abstract is attachedBIA2017-82391-R cofinanciado con FEDER Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Belite clinkers with increasing aluminium content: effect of calcium aluminates on calcium silicate hydration

Belite cements (BCs) could have advantages over Portland cements concerning durability, low heat development and the use of less demanding raw materials. The activation of BCs by sulfur addition at the clinkering stage and by fast cooling is well established. However, the reaction rates of the calcium silicate phases, mainly belite, are still not fully understood. This is partly due to the interplay between factors including: i) belite activation during clinkering; ii) role of the calcium aluminates at early hydration ages; and iii) role of the sulfates. In the research reported here, three belite clinkers were prepared with constant values of lime saturation factor, and SO3, Fe2O3 and CaF2 contents. The varied parameter was the amount of Al2O3. The resulting clinkers have overall crystalline reactive calcium aluminate contents of 0.4, 7.9 and 16.7 wt%, respectively. Cements were prepared with similar particle sizes and constant anhydrite content. Here, it is shown that calcium silicate reactivities, both alite and belite, strongly depend upon the calcium aluminate contents. As these amounts increase, the degree of hydration of alite at 1 day decreases: 85, 65 and 50 %. Furthermore, the degree of hydration of belite at 7 days was 50, 35 and 0 %. Thus, there is a strong influence of aluminates in calcium silicate rates of hydration. Moreover, comparing the mechanical properties of the cements with 0.6 and 8.2 wt% amounts of calcium aluminates, the improvements due to the higher reactivity of calcium aluminates at very early ages, seem to be counterbalanced by the lower reactivity of the silicate phases. The reported findings may allow further optimization of early age reactivity of active BCsThe research carried out in Malaga was supported by PID2020-114650RB-I00 research grant from the Spanish Government, which is co-funded by ERDF

Synchrotron pair distribution function approach applied to cement samples

The characterization of the nanocrystalline/amorphous materials is very challenging but the presence of these materials mixed with large amounts of crystalline phases makes the analysis even more complicated. This is the case of cement hydrated samples, since they contain high amounts of crystalline phases jointly with nanocrystalline and amorphous components, making challenging their full characterization. High-energy synchrotron X-ray scattering jointly with the pair distribution function (PDF) methodology is very useful to deeply study complex cement pastes. PDF data give information about the local structure (bonding environments) of the nanocrystalline and amorphous component phases such as cement gels. The main aim of this work is to characterize amorphous/nanocrystalline gels which are present in different cementitious pastes by the PDF approach. Moreover, the PDF technique also gives us quantitatively information about the nanocrystalline and microcrystalline contents. Firstly, the C-S-H gel obtained from the hydration of alite, Ca3SiO5, the main phase of Portland cement, is found to contain two components: a nanocrystalline defective clinotobermorite and an amorphous component which seemed to be monolayers of calcium hydroxide1. Figure below shows the PDF fit of a C-S-H gel formed from the hydration of alite in two selected r-ranges. Secondly, some ye’elimite Ca4Al6O12(SO4) -containing pastes with different sulfate contents have been also studied. The nanocrystalline hydrated phases, such as A-H gel and monosulfoaluminate (AFm) phases have been thoroughly analyzed in the different pastes and the diameters of these nanoparticles have also been reported2. Finally, we will also show here, PDF data for different cement samples (including the Ni sample as standard) that have been collected in two different experimental configurations, i.e., in ID15A beamline at ESRF and in MSPD beamline at ALBA synchrotron3Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This work has been supported by Spanish MinCIU through BIA2014-57658-C2 and BIA2017-82391-R, which are co-funded by FEDER. We also thank CELLS-ALBA (Barcelona, Spain) and ESRF (Grenoble) for providing synchrotron beam time at BL04-MSPD and ID15A, respectively