30 research outputs found
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 yeâelimite and ferrite or with alite [known as belite-yeâelimite-ferrite (BYF) and belite-alite-yeâelimite (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 MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech.
I3-RamĂłn y Cajal
Universidad de Malag
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 MĂĄlaga. Campus de Excelencia Internacional AndalucĂa 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
Synchrotron Radiation Pair Distribution Function Analysis of Gels in Cements
The analysis of atomic ordering in a nanocrystalline phase with small particle sizes, below 5 nm, is intrinsically complicated because of the lack of long-range order. Furthermore, the presence of additional crystalline phase(s) may exacerbate the problem, as is the case in cement pastes. Here, we use the synchrotron pair distribution function (PDF) chiefly to characterize the local atomic order of the nanocrystalline phases, gels, in cement pastes. We have used a multi r-range analysis approach,
where the ~4â7 nm r-range allows determining the crystalline phase contents; the ~1â2.5 nm r-range
is used to characterize the atomic ordering in the nanocrystalline component; and the ~0.2â1.0 nm
r-range gives insights about additional amorphous components. Specifically, we have prepared
four alite pastes with variable water contents, and the analyses showed that a defective tobermorite, Ca11Si9O28(OH)2 8.5H2O, gave the best fit. Furthermore, the PDF analyses suggest that the calcium silicate hydrate gel is composed of this tobermorite and amorphous calcium hydroxide. Finally, this approach has been used to study alternative cements. The hydration of monocalcium aluminate and yeâelimite pastes yield aluminum hydroxide gels. PDF analyses show that these gels are constituted of nanocrystalline gibbsite, and the particle size can be as small as 2.5 nmThis 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. Finally, we thank Prof. Simon Billinge, Long Yang and Monica Dapiaggi for their help with the PDF script and simulations for Ca(OH)2 scattering dat
Pair distribution function studies in cementitious systems
The analysis of amorphous/nanocrystalline phase(s) within cement matrices that contain high amounts of crystalline phase(s) is very challenging. Synchrotron techniques can be very useful to characterize such complex samples.1 This work is focused on total scattering Pair Distribution Function (PDF) quantitative phase analyses in selected real-space ranges for a better understanding of the binding gel(s). Powder diffraction data collected in BL04-MSPD beamline have been analyzed by PDF and Rietveld methodologies to determine nanocrystalline and microcrystalline phase contents. The comparison between both methodologies allows us to have a better insight about the nanocrystalline/microcrystalline components which coexist in cement pastes. Three sets of hydrated model samples have been studied: i) monocalcium aluminate, CaAl2O4, the main component of calcium aluminate cements, ii) yeâelimite, Ca4Al6SO16, the main component of calcium sulfoaluminate cements, and iii) tricalcium silicate, Ca3SiO5, the main component of Portland cements.
For the CaAl2O4 paste, the PDF fit shows that the aluminum hydroxide gel has a gibbsite local structure with an average particle size close to 5 nm.2 Figure 1 shows the final fit for CaAl2O4 paste in two different real-space regions. On the contrary, for Ca4Al6SO16 paste, it has been found that the particle size of the aluminum hydroxide gel is below 3 nm. Moreover, the Ca3SiO5 paste contains a different nanocrystalline gel, C-S-H, which has also been thoroughly studied. Different crystal structures (including Tobermorite, Clinotobermorite and Jennite) have been tested to find the structural model that fits better the experimental data. The results from this ongoing investigation will be reported and discussed.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech.
This work has been supported by Spanish MINECO through BIA2014-57658-C2-1-R and BIA2014-57658-C2-2-R, which is co-funded by FEDER, research grants. We also thank CELLS-ALBA for providing synchrotron beam time at BL04-MSPD
Clinkering of calcium sulfoaluminate clinkers: polymorphism of ye'elimite
The manufacture of CSA cements is more environmentally friendly than that of OPC as it releases
less CO2. This reduction depends on CSA composition and is due to three factors: i) less emissions
from decarbonation in the kilns; ii) lower clinkering temperature, consequently less fuel is needed, and
iii) it is easier to grind, implying a depletion in indirect emissions.
CSA cements are prepared by mixing the clinker with different amounts of calcium sulfate as a set
regulator. Their main performances are fast setting time (followed by a rapid hardening), good chemical
resistance and, depending on the amount of the added sulfate source they can work as
shrinkage controllers.
CSA cements present a wide range of phase assemblages, but all of them contain over 50 wt% of
ye'elimite (C4A3s) jointly with belite (C2S), tetracalcium aluminoferrite (C4AF) and other minor
components such as CA, Cs, CsH2 and so on [1]. Ye'elimite is also included (~25 wt%) in BYF (Belite-
Ye'elimite-Ferrite) or BAY (Belite-Alite-Ye'elimite) clinkers.
Ye'elimite has a sodalite type structure with general composition, M4[T6O12]X. Stoichiometric ye'elimite
crystal structure at room temperature will be described in detailed. The role of different amounts of
minor elements on the synthetic procedure and crystal structures will be also presented [2,3].
This keynote will be also focused on a revision of the effect of raw materials on the mineralogical
composition of CSA, BYF and BAY. Specifically, the role of main elements contents in the ye'elimite
formation in these systems will be described. Moreover, the effect of minor elements on the
polymorphism of both ye'elimite and belite, especially on BYF and BAY clinkers, will be presented
[4,5,6].Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech. Spanish MINECO and FEDER [BIA2017-82391-R] research project and I3 [IEDI-2016-0079] program
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
Hydration development and thermal performance of calcium sulphoaluminate cements containing microencapsulated phase change materials
Publicado en: (Cement and Concrete Research 132 (2020) 106039)Microencapsulated phase change materials (MPCM) incorporated in buildings walls can reduce indoor temperature fluctuations, conserving energy and enhancing thermal comfort. MPCM were incorporated in calcium sulphoaluminate cement (CSA) at high concentrations to achieve a significant effect on the thermal properties. The cement hydration development was studied by isothermal calorimetry and laboratory X-ray powder diffraction (LXRPD). The hydration mechanism was not affected by the addition of MPCM. In order to obtain homogeneous mortars in the presence of MPCM, a superplasticizer (SP) was used. However, the SP causes a significant delay of the hydration. Although the mineralogical composition of the hydrated pastes did not change with the addition of MPCM, the mechanical strengths decrease dramatically. This decrease is well described by the Bolomey equation, assuming MPCMs act as air voids. This is a physical effect due to the high volume of MPCM, and not due to a change in the hydration chemistry.We gratefully acknowledge funding from the Research Council of
Norway, project number 238198. The authors gratefully acknowledge
PhD. Luis Miguel Ordoñez at Kheme Chemical S.L. and Eng. Rino Nilsen
at Ăstfold University College for technical assistance
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]
X-ray diffraction, cements and environment, three worlds in one
This keynote lecture will be focused on the strategies for reducing CO2 emissions in the cement production. Concretely, the production of ecocements with optimised formulations that yield reductions in CO2 emissions of up to 25%, when compared to OPC production. Phase assemblage has to be carefully optimised to be competitive and these new ecocements should develop compressive strengths of at least 50 MPa at 28 days of hydration. Optimised compositions of several ecocements will be discussed, but all of them are ye'elimite or calcium sulphoaluminate containing ones: belite-ye'elimite-ferrite (BYF), belite-alite-ye'elimite (BAY) and ye'elimite rich ones (CSA). The clinkering temperature of BYF and BAY has to be established to obtain the targeted phase assemblages. Moreover, the stabilisation of alpha-forms of belite is needed to develop high mechanical strengths at early ages. The benefits of the use of waste materials (such as fly ash or slag) as additions to ecocements are three-fold: lower CO2 emissions due to clinker replacement; valorisation of âuselessâ products that need a lot of landscape and the consequent efficient consumption of raw materials; and to enhance mechanical properties of the corresponding mortars. The design of appropriate CSA, BYF and BAY mortars, with the final aim of knowing and controlling the hydration mechanisms, will be presented. Particularly, the role of i) type and amount of set regulator (gypsum, anhydrite, etc.), ii) water/cement ratio (w/c); iii) superplasticiser; and iv) pozzolanic additions will be discussed. The role of these parameters in the microstructure and hydraulic behaviour has been investigated through traditional techniques as well as advanced synchrotron characterisation. The formers include laboratory/synchrotron X-ray powder diffraction combined with Rietveld methodology (to obtain phase assemblage), electron microscopy techniques for paste microstructure determination, rheological studies (to control the effect of the different additives, w/c ratio and setting time retarders) and mechanical tests (setting times, compressive strengths and dimensional stability). The latters comprise a group of techniques available at synchrotrons such as: i) high temperature x-ray diffraction for clinkering studies and ii) total scattering data to be analysed by pair distribution function, PDF.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech.
PhD D. Londono-Zuluaga thanks Colciencias and Enlaza Mundos program PhD grant. Spanish MINECO (BIA2014-57658-C2-2-R, which is co-funded by FEDER, BIA2014-57658-C2-1-R and I3 (IEDI-2016-0079) grants) are acknowledged
Alite calcium sulfoaluminate cement: chemistry and thermodynamics
Calcium sulfoaluminate (CA) cements can combine the favourable characteristics of Portland cement (PC) with those of CA clinkers. The first is a thermodynamic study demonstrating that the production of a-CA clinker can be readily produced in a standard process by controlling the oxygen and sulfur dioxide fugacity in the atmosphere. This allows for the stabilisation of yeâelimite to the higher temperatures required for alite stability. The second result establishes that when using fluorine to mineralise a-C$A clinker production, the iron content in the clinker is also an important variable. Although the exact mechanism of alite stabilisation is not known, it is shown that alite formation increases with the combination of calcium fluoride and iron (III) oxide in the mix