Aluminum hydroxide gel characterization within a calcium aluminate cement paste by combined Pair Distribution Function and Rietveld analyses

Cuesta, Ana; Ichikawa, Rodrigo Uchida; Londoño-Zuluaga, Diana; Torre, Ángeles G. De la; Santacruz, Isabel; Turrillas, X.; Aranda, Miguel Á. G.

doi:10.1016/j.cemconres.2017.02.025

Cited by 45 publications

(37 citation statements)

References 51 publications

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“…These pastes contain a crystalline phase, hydrogarnet, and a nanocrystalline phase, aluminum hydroxide gel, as previously reported for a related sample [32]. No anhydrous calcium aluminate was found in any paste.…”

Section: Calcium Aluminate Pastessupporting

confidence: 48%

“…The temperatures for the two main water loss steps, nanocrystalline gel and hydrogarnet, are located around 260 and 300 • C, and they are partly overlapped. The expected water loss depends upon the sample composition (and water content of the aluminum hydroxide gel), as previously reported [32].…”

Section: Calcium Aluminate Pastesmentioning

confidence: 93%

“…It was shown that this phase was nanocrystalline gibbsite, with an average particle size close to 5.5 nm [32].…”

Section: X-ray Pair Distribution Function Analysismentioning

confidence: 99%

“…The second type of cementitious system studied was calcium aluminate pastes, which were initially studied by the PDF methodology in a previous publication [32] with a fixed water-solid ratio of 1.0. Here, we expand the research by varying the water-to-solid ratio, which is known to affect the hydration.…”

Section: Calcium Aluminate Pastesmentioning

confidence: 99%

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Synchrotron Radiation Pair Distribution Function Analysis of Gels in Cements

et al. 2017

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Abstract: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~4-7 nm r-range allows determining the crystalline phase contents; the~1-2.5 nm r-range is used to characterize the atomic ordering in the nanocrystalline component; and the~0.2-1.0 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, Ca 11 Si 9 O 28 (OH) 2 ·8.5H 2 O, 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 ye'elimite 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 nm.

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Section: Calcium Aluminate Pastessupporting

confidence: 48%

Section: Calcium Aluminate Pastesmentioning

confidence: 93%

“…It was shown that this phase was nanocrystalline gibbsite, with an average particle size close to 5.5 nm [32].…”

Section: X-ray Pair Distribution Function Analysismentioning

confidence: 99%

Section: Calcium Aluminate Pastesmentioning

confidence: 99%

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Synchrotron Radiation Pair Distribution Function Analysis of Gels in Cements

et al. 2017

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“…In addition, the formation of AFm-type phases at late ages is avoided by the addition of gypsum and anhydrite being ettringite the only crystalline phase formed in this reaction medium. Furthermore, the particle size [22], water content and the calcium uptake of amorphous aluminium hydroxide gels in ye'elimite eco-cements have been established with Ca contents being minor but not negligible [23].…”

Section: Hydration Of Ye'elimitementioning

confidence: 99%

X-ray diffraction, cements and environment, three worlds in one.

et al. 2018

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Abstract. This keynote lecture will be focused on the strategies for reducing CO 2 emissions in the cement production. Concretely, the production of ecocements with optimised formulations that yield reductions in CO 2 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 CO 2 emissions due to clinker replacement; valorisation of "useless" 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).

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