16,635 research outputs found
Clinkering and hydration study of non-active and active Belite-Alite-Ye'elimite (BAY) cements
The aim of AIM is to promote industry-driven, interdisciplinary research in material science and engineering in order to provide leading-edge, sustainable solutions to the challenges facing engineers in todayâs changing society and environment. http://www.ucl.ac.uk/aim/conference-info/37ccsThe manufacturing process of ye'elimite rich cements emit about 15-37% less CO2 to the atmosphere than OPC. Cements that contain belite, yeâelimite and ferrite, known as BYF cements, are promising eco-friendly binders. However, belite, their main phase, shows a slow hydrating behaviour; therefore the corresponding mortars present lower mechanical strengths than OPC at early ages. To solve this problem, BYF clinkers can be activated by: i) forming alite jointly with belite and yeâelimite during clinkering, known as BAY clinkers. The alite and yeâelimite reaction with water should develop high mechanical strengths at early ages, besides, belite contributes to later curing times. ii) A second activation is based on the stabilisation of alpha forms of belite by dopants. The objective of this work is to obtain two types of BAY clinkers (standard and active BAY) using CaF2 as mineraliser and borax as dopant agent to stabilize alpha forms of belite phase. After that, anhydrite was added as sulphate source to obtain the corresponding cements. The hydration behaviour of these cements has been studied through rheological and x-ray diffraction measurements, the latter combined with Rietveld quantitative phase analysis. In addition, mechanical and dimensional properties of BAY mortars are also presented and discussed.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech
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 realâworld
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 nonâoverlapped 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 BIA2017â82391âR which is coâfunded
by FEDER.
We thank Marc Malfois for his help during the experiment performed at NCDâSWEET
beamline at ALBA synchrotron. We also thank Marcus Paul (Dyckerhoff GmbH) for providing the OWC
sample with its characterization and helpful discussions
A critical assessment of the dislocation-driven model for superplasticity in yttria tetragonal zirconia polycrystals
In this paper, the origin of the threshold stress in pure 3 mol %-yttria
tetragonal zirconia polycrystals (YTZP) is analysed in detail. At this regard,
the two explanations reported in literature are discussed thoroughly. One of
them invokes dislocation activity as the origin for such quantity, whereas the
other one is based upon yttrium segregation at the grain boundaries. Crirical
assessment for both of them is performed, and it has allowed concluding that
the dislocation activity observed by Morita and Hiraga is just an artifact
created during sample preparation. Thence, segregation at the grain boundaries
seems to be the only mechanism accounting for a threshold stress and its
temperature and grain size dependence
Early hydration study of standard and doped Alite-Belite-Yeâelimite (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, yeâelimite 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 yeâelimite during clinkering, Alite Belite Yeâelimite (ABY) clinkers. The hydration of alite
and yeâelimite 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 (âH-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 MĂĄlaga. Campus de Excelencia Internacional AndalucĂa 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 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
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