Preparation and hydration of model ecocement phases. Characterization by diffraction and cognate methods

La producción de cementos de sulfoaluminato de calcio (CSA, del inglés Calcium SulfoAluminate) es más respetuosa para el medio ambiente que la de los cementos Portland ordinarios (OPC, del inglés Ordinary Portland Cement) ya que libera menos CO2. Los cementos CSA presentan un amplio rango de ensamblaje de fases, pero todos contienen en torno a un 50% de ye'elimita además de belita, ferrito aluminato tetracálcico y otros componentes minoritarios. La ye'elimita es muy reactiva y la mayor parte del calor de hidratación se libera durante las ocho primeras horas. Durante la hidratación a edades tempranas, el principal producto cristalino que se forma, debido a la disolución de la ye'elimita en presencia de sulfato, es la fase etringita. Sin embargo, la fase monosulfato se forma cuando no hay una fuente de sulfato soluble en el medio. La ye'elimita, también está incluida (25% en peso) en los cementos belíticos de sulfoaluminato de calcio (BCSA, del inglés Belite Calcium SulfoAluminate). La formulación más común de estos cementos consiste en β-C2S, C4A3S y C4AF. El C2S presenta cinco formas polimórficas. Sin embargo, el polimorfo α'H-C2S es el más activo hidráulicamente, por ello su estabilización juega un papel importante en la preparación de los cementos activados tipo BCSA en el laboratorio y en ensayos industriales. Esta tesis doctoral se ha dividido en dos bloques: i) estudios estructurales de fases anhidras y ii) estudios de hidratación de fases seleccionadas. Para el estudio de la forma β del silicato dicálcico, se preparó la disolución sólida con fórmula general, Ca2Si1-2xAl2xO4-x x. Los materiales se caracterizaron determinándose el límite de la serie cercano a x=0.014. Por otro lado, la muestra α'H-Ca1.85Na0.15(SiO4)0.85(BO3)0.15 se seleccionó para estudiar la estructura cristalina del polimorfo α'H del silicato dicálcico. Para el caso de la ye'elimita, se han preparado dos muestras: una estequiométrica (Ca4Al6O12SO4) y otra dopada (Ca3.8Na0.2Al5.6Fe0.2Si0.2O12SO4) para caracterizar los polimorfos ortorrómbico y pseudocúbico, respectivamente. Mediante estudios termodifractométricos, calorimetría diferencial de barrido y medidas de permitividad se determinó la transición reversible que presentan. Los estudios de hidratación se han realizado usando difracción de rayos-X de polvo de laboratorio con la metodología del estándar externo (factor-G) y/o usando difracción de rayos-X sincrotrón de polvo con la metodología del estándar interno para determinar el ensamblaje de fases incluyendo el material amorfo. Los resultados obtenidos por ambas metodologías muestran una consistencia que permite entender las reacciones de hidratación en función del tiempo. Se ha determinado el papel del polimorfismo de la ye'elimita en los mecanismos de hidratación comparándose la reactividad de ambos polimorfos, obteniéndose importantes diferencias en su cinética y en sus mecanismos de hidratación. Además, se ha estudiado la hidratación de la ye'elimita en combinación con C4AF y con silicato dicálcico. En el caso del estudio de la hidratación con el silicato dicálcico, a los 6 meses, el α'H-C2S se disolvió totalmente, en cambio, se encontraron grandes cantidades de β-C2S sin reaccionar en todas las muestras. Finalmente, se ha determinado el comportamiento de hidratación de la fase C4AF en ausencia y presencia de yeso

Recent Advances in C-S-H Nucleation Seeding for Improving Cement Performances

Reducing cement CO2 footprint is a societal need. This is being achieved mainly by replacing an increasing amount of Portland clinker by supplementary cementitious materials. However, this comes at a price: lower mechanical strengths at early ages due to slow pozzolanic reaction(s). This is being addressed by using accelerator admixtures. In this context, calcium silicate hydrate nucleation seeding seems to have a promising future, as it can accelerate cement and pozzolanic reactions at early ages, optimising their microstructures, without compromising late strength and durability performances. In fact, these features could even be improved. Moreover, other uses are low temperature concreting, precasting, shotconcrete, etc. Here, we focus on reviewing recent reports on calcium silicate hydrate seeding using commercially available admixtures. Current knowledge on the consequences of nucleation seeding on hydration reactions and on early and late mechanical strengths is discussed. It is noted that other features, in addition to the classic alite hydration acceleration, are covered here including the enhanced ettringite precipitation and the very efficient porosity refinement, which take place in the seeded binders. Finally, because the seeded binders seem to be denser, durability properties could also be enhanced although this remains to be properly established.This research has been partly supported by PID2020-114650RB-I00 research grant, Spanish Government, which is co-funded by ERDF. Partial funding for open access charge: Universidad de Málag

Advanced synchrotron studies of ye'elimite-based cement pastes

Synchrotron characterization techniques [1] are being used to study Portland-based cements and recently also CSA and related cements. A key property of these techniques is that they do not require sample preparation, so the microstructures of the pastes can be preserved. The classical application of synchrotron tools is powder diffraction used to determine the crystalline phase content evolution with hydration including the overall amorphous fraction. Furthermore, other most advanced techniques are being applied to ye'elimite-containing pastes such as i) Total Scattering Synchrotron Powder Diffraction (TS-SXPD), and ii) Ptychographic Synchrotron X-ray Computed Tomography (PSXCT). All these applications will be reviewed here. TS-SXPD data coupled with the Pair Distribution Function (PDF) analysis methodology [2] allows having a better insight about the nanocrystalline/amorphous atomic arrangements in the gels. It has been very recently shown that nanogibbsite with very small particles, 3nm, is the main constituent of ye'elimite-gypsum hydration paste [2]. Nanogibbsite particles being smaller than those originated from the hydration of monocalcium aluminate. In addition, PSXCT is a tomographic technique that profits from the partly coherent nature of the synchrotron beam to provide better (smaller) resolution, which can be lower than 100 nm. It also provides the mass densities if the chemical stoichiometries are known. This technique has been applied to ye'elimite hydration to determine the microstructure and chiefly the bulk densities of nanogibbsite [3]. The microstructure evolution at early age was also followed [4]. Figure 1 shows an example of a slide of the electron density tomogram for a ye'elimite paste at 8 days of hydration and the corresponding histogram for the full volume with all phases identified.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.This work has been supported by Spanish MINECO through BIA2014-57658-C2 and BIA2017-82391-R, which are co-funded by FEDER

Early hydration study of standard and doped Alite-Belite-Ye’elimite (ABY) cements through Synchrotron Radiation

The manufacturing of ye'elimite-rich cements releases from 15 to 37%, depending on their composition, less CO2 to the atmosphere than ordinary Portland cement (OPC). BYF cements containing belite, ye’elimite and ferrite as main crystalline phases, are promising eco-friendly binders. Nevertheless, belite, its main phase, shows a slow hydrating behaviour and the mechanical strengths are lower than OPC at early ages. Some alternatives to solve this problem are: i) forming alite jointly with belite and ye’elimite during clinkering, Alite Belite Ye’elimite (ABY) clinkers. The hydration of alite and ye’elimite would develop high mechanical strengths at early ages, and belite contributes to later curing times; ii) a second alternative is the stabilisation of alpha forms of belite using dopants such as boron named here after dABY. In this work, two different types of ABY clinkers (standard and doped) have been prepared and characterized to understand their different hydration mechanisms at the same water-to-cement (w/c) ratio. The clinkers have been prepared using CaF2 and ZnO as mineralizers, and borax as dopant agent to stabilize alpha forms of belite (’H-C2S). Afterwards, 14 wt% of anhydrite (as soluble sulphate source) was added to prepare the corresponding cements. Finally, the hydration study was performed at w/c ratio of 0.5. Here, an in-situ hydration study using synchrotron X-ray powder diffraction (SXRPD) for the first 14 hours of hydration is reported. Moreover, these results will be combined with the ex-situ laboratory X-ray powder diffraction study (LXRPD) at 1 day of hydration and calorimetric results. Rietveld quantitative phase analysis has been used to establish the phase evolution across the time.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO ( BIA2017-82391-R), co-funded by FEDER, and I3 [IEDI-2016-0079]

Water-to-cement ratio influence on low-carbon cements performances

Portland Cement (PC) is the most important active ingredient in most of the construction concrete. However, the PC production is associated with a high carbon dioxide release (around 1 ton of CO2 per ton of PC). One approach to reduce CO2 emissions consists on the reformulation of the clinker with less calcite demanding phases, such as, belite rich clinkers. The drawback of this kind of clinkers is the low reactivity of belite (beta-belite). In order to compensate this problem, belite rich clinkers can be prepared with ye’elimite and ferrite or with alite [known as belite-ye’elimite-ferrite (BYF) and belite-alite-ye’elimite (BAY), respectively]. In addition, it can be improved by using a high reactive belite polymorph, such as alpha-belite. In this work, the hydration and mechanical behaviour of BYF and BAY cements (with beta and/or alpha-belite) with different water-to-cement ratios have been studied. The clinkers were produced using natural raw materials, and were mixed with anhydrite (CaSO4) to prepare the corresponding cements. At early ages, the main hydration products of these cements were ettringite, calcium monosulfoaluminate and amorphous aluminium hydroxide. At later ages, stratlingite, katoite and amorphous C-S-H were found. The compressive strength values of the corresponding mortars were correlated with the mineralogy evolution of the pastes (mainly obtained by XRD and TGA).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. I3-Ramón y Cajal Universidad de Malag

Rietveld Quantitative Phase Analysis of Oil Well Cement: in Situ Hydration Study at 150 Bars and 150 °C

Oil and gas well cements are multimineral materials that hydrate under high pressure and temperature. Their overall reactivity at early ages is studied by a number of techniques including through the use of the consistometer. However, for a proper understanding of the performance of these cements in the field, the reactivity of every component, in real‐world conditions, must be analysed. To date, in situ high energy synchrotron powder diffraction studies of hydrating oil well cement pastes have been carried out, but the quality of the data was not appropriated for Rietveld quantitative phase analyses. Therefore, the phase reactivities were followed by the inspection of the evolution of non‐overlapped diffraction peaks. Very recently, we have developed a new cell specially designed to rotate under high pressure and temperature. Here, this spinning capillary cell is used for in situ studies of the hydration of a commercial oil well cement paste at 150 bars and 150 °C. The powder diffraction data were analysed by the Rietveld method to quantitatively determine the reactivities of each component phase. The reaction degree of alite was 90% after 7 hours, and that of belite was 42% at 14 hours. These analyses are accurate, as the in situ measured crystalline portlandite content at the end of the experiment, 12.9 wt%, compares relatively well with the value determined ex situ by thermal analysis, i.e., 14.0 wt%. The crystalline calcium silicates forming at 150 bars and 150 °C are also discussed.This research was funded by Spanish MINECO, grant number BIA2017‐82391‐R which is co‐funded by FEDER. We thank Marc Malfois for his help during the experiment performed at NCD‐SWEET beamline at ALBA synchrotron. We also thank Marcus Paul (Dyckerhoff GmbH) for providing the OWC sample with its characterization and helpful discussions

In-situ hydration studies of ye’elemite at early ages for understanding eco-cement performances'

Póster; ALBA User Meeting and VI AUSE Conferenc

Synchrotron x-ray pair distribution function: A tool to characterize cement gels

Cement matrices contain large amounts of crystalline phases jointly with amorphous and/or nanocrystalline phases. Consequently, their analyses are very challenging. Synchrotron powder diffraction in combination with the pair distribution function (PDF) methodology is very useful to characterize such complex cement pastes. This work is focused on the study of the short and medium range atomic arrangement(s) in the different nanocrystalline gels which are present in the cement pastes through total scattering Pair Distribution Function quantitative phase analyses.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Acknowledgments: We thank CELLS-ALBA (Barcelona, Spain) for providing synchrotron beam time and the financial support by BIA2014-57658-C2-1-R and BIA2014-57658-C2-2-R, which is co-funded by FEDER. We also thank Dr. Monica Dapiaggi for her contribution with the PDF study of Ca(OH)2 monolayer

In situ hydration imaging study of a ye'elimite paste by ptychographic x-ray computed tomography

Eco-cements are a desirable alternative to ordinary Portland cements because of their lower CO2 footprints. For instance, the manufacture of Calcium SulfoAluminate (CSA) cements is more environmentally friendly than that of Portland cements as their production may decrease CO2 footprint by up to 40%. CSA cements contain ye'elimite, Ca4Al6O12SO4, as main phase. The hydration of ye'elimite leads to hydrated compounds such as crystalline ettringite (AFt), crystalline monosulfoaluminate (AFm) and amorphous aluminum hydroxide gel, Al(OH)3·nH2O. Here, we report the results of a ptychographic X-ray computed tomography (PXCT) study on the in situ hydration of ye'elimite with gypsum at different early ages. PXCT is a nondestructive X-ray imaging technique which provides 3D electron density and attenuation coefficient distributions of cement pastes with an isotropic resolution close to 100 nm allowing distinguishing between component phases with very similar contrast in more conventional absorption-based X-ray tomography. The sample was prepared by hydrating ye'elimite with gypsum. Four datasets were recorded at 48, 53, 58 and 63 hours of hydration. The main aim of this imaging study was to quantify the microstructure evolution, within this time interval, with submicrometer spatial resolution. The different component phases were identified and their mass densities determined. Furthermore, the tomograms were segmented and the volume percentage of each component were determined and compared at the four hydrating ages. The overall porosity content (air and pore solution) decreased from 11.5 to 8.8 vol% and the anhydrous material content (ye'elimite and gypsum) decreased from 14.7 to 7.5 vol% in the studied time interval. Correspondingly, the hydrated content (crystalline ettringite and aluminum hydroxide gel) increased from 73.7 to 83.7 vol%. The time evolution of several anhydrous particles was analyzed to determine the dissolution rate of the ye'elimite particles. Similarly, the pore filling process has also been investigated by quantifying their time evolution. These rates are reported and some insights about the mechanisms of these processes are discussed.This work has been supported by MINECO through BIA2014−57658-C2-1-R and BIA2014-57658-C2-2-R, which is cofunded by FEDER, research grants. We thank SLS for providing beamtime at the cSAXS beamline. We also thank the Swiss National Science Foundation SNF for the support to the work of J.C.d.S. (Grant 137772). Instrumentation development was supported by SNF (R’EQUIP, No. 145056,“OMNY”) and the Competence Centre for Materials Science and Technology (CCMX) of the ETH-Board, Switzerland. In addition, the authors would like to thank Dr. Manuel Guizar-Sicairos for his valuable assistance with the ptychography and PXCT data analysis

Applications of synchrotron x-ray powder diffraction in hydrated cements: high-resolution and high-pressure studies

The main aim of this study is to apply synchrotron radiation techniques for the study of hydrated cement pastes. In particular, the tetracalcium aluminoferrite phase, C4AF in cement nomenclature, is the major iron-containing phase in Ordinary Portland Cement (OPC) and in iron rich belite calcium sulfoaluminate cements. In a first study, the hydration mechanism of pure tetracalcium aluminoferrite phase with water-to-solid ratio of 1.0 has been investigated by HR-SXRPD (high resolution synchrotron X-ray powder diffraction). C4AF in the presence of water hydrates to form mainly an iron-containing hydrogarnet-type (katoite) phase, C3A0.84F0.16H6, as single crystalline phase. Its crystal structure and stoichiometry were determined by the Rietveld method and the final disagreement factors were RWP=8.1% and RF=4.8% [1]. As the iron content in the product is lower than that in C4AF, it is assumed that part of the iron also goes to an amorphous iron rich gel, like the hydrated alumina-type gel, as hydration proceeds. Further results from the high-resolution study will be discussed. In a second study, the behavior of pure and iron-containing katoites (C3AH6 and C3A0.84F0.16H6) under pressure have been analyzed by SXRPD using a diamond anvil cell (DAC) and then their bulk moduli were determined. The role of the pressure transmitting medium (PTM) has also been studied. In this case, silicone oil as well as methanol/ethanol mixtures have been used as PTM. Some “new peaks” were detected in the pattern for C3A0.84F0.16H6 as pressure increases, when using ethanol/methanol as PTM. These new peaks were still present at ambient pressure after releasing the applied pressure. They may correspond to crystalline nordstrandite or doyleite from the crystallization of amorphous aluminium hydroxide. The results from the high-pressure study will also be discussed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Acknowledgments: We thank CELLS-ALBA (Barcelona, Spain) for providing synchrotron beam time. We also thank the financial support by BIA2014-57658-C2-1-R and BIA2014-57658-C2-2-R (FEDER)