Rheological and hydration characterization of calcium sulfoaluminate cement pastes

Calcium sulfoaluminate (CSA) cements are currently receiving a lot of attention because their manufacture produces less CO2 than ordinary Portland cement (OPC). However, it is essential to understand all parameters which may affect the hydration processes. This work deals with the study of the effect of several parameters, such as superplasticizer (SP), gypsum contents (10, 20 and 30 wt%) and w/c ratio (0.4 and 0.5), on the properties of CSA pastes during early hydration. This characterization has been performed through rheological studies, Rietveld quantitative phase analysis of measured x-ray diffraction patterns, thermal analysis and mercury porosimetry for pastes, and by compressive strength measurements for mortars. The effect of the used SP on the rheological properties has been established. Its addition makes little difference to the amount of ettringite formed but strongly decreases the large pore fraction in the pastes. Furthermore, the SP role on compressive strength is variable, as it increases the values for mortars containing 30 wt% gypsum but decreases the strengths for mortars containing 10 wt% gypsum.This work has been supported by Spanish Ministry of Science and Innovation through MAT2010- 16213 research grant, which is co-funded by FEDER, and Ramón y Cajal Fellowship (RYC-2008- 03523)

Hydration studies of calcium sulfoaluminate cements blended with fly ash

The main objective of this work is to study the hydration and properties of calciumsulfoaluminate cement pastes blended with fly ash (FA) and the corresponding mortars at different hydration ages. Laboratory X-ray powder diffraction, rheological studies, thermal analysis, porosimetry and compressive strength measurements were performed. The analysis of the diffraction data by Rietveld method allowed quantifying crystalline phases and overall amorphous contents. The studied parameters were: i) FA content, 0, 15 and 30 wt.%; and ii) water addition, water-to-CSA mass ratio (w/CSA = 0.50 and 0.65), and water-to-binder mass ratio (w/b = 0.50). Finally, compressive strengths after 6 months of 0 and 15 wt.% FA [w/CSA = 0.50] mortars were similar: 73 ± 2 and 72 ± 3 MPa, respectively. This is justified by the filler effect of the FA as no strong evidences of reactivity of FA with CSA were observed. These results support the partial substitution of CSA cements with FA with the economic and environmental benefitsThis work has been supported by Spanish MINECO through MAT2010-16213 research grant, which is co-funded by FEDER. I. Santacruz thanks a Ramón y Cajal fellowship, RYC-2008-03523

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

Rietveld quantitative phase analysis with molybdenum radiation

Building materials are very complex samples of worldwide importance; hence quantitative knowledge of their mineralogical composition is necessary to predict performances. Rietveld quantitative phase analysis (RQPA) allows a direct measurement of the crystalline phase contents of cements. We highlight in this paper the use of laboratory X-ray powder diffraction (LXRPD) employing high-energy radiation, molybdenum (Mo), for attaining the RQPA of cements. Firstly, we evaluate the accuracy of RQPA employing a commercial calcium sulfoaluminate clinker with gypsum. In addition to MoKα1 and MoKα1,2 radiations, Cu and synchrotron patterns are also analyzed for the sake of comparison. Secondly, the assessment of the accuracy of RQPA results obtained using different radiations (synchrotron, Mo, and Cu) and geometries (reflection and transmission) is performed by analyzing two well-known commercial samples. As expected, for LXRPD data, accuracy in the RQPA results improves as the irradiated volume increases. Finally, three very complex aged hydrated cements have been analyzed using MoKα1-LXRPD and Synchrotron-XRPD. The main overall outcome of this work is the benefit for RQPA of using strictly monochromatic MoKα1 radiation. Best laboratory results arise from MoKα1 data as the effective tested volume is much increased but peak overlapping is not swelledUniversidad de Málaga. Campus de Excelencia Internacional. Andalucía Tech

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)

Effect of calcium sulfate source on the hydration of calcium sulfoaluminate eco-cement

The availability of cements, including eco-cements, with tailored mechanical properties is very important for special applications in the building industry. Here we report a full study of the hydration of calcium sulfoaluminate eco-cements with different sulfate sources (gypsum, bassanite and anhydrite) and two water/cement ratios (0.50 and 0.65). These parameters have been chosen because they are known to strongly modify the mechanical properties of the resulting mortars and concretes. The applied multitechnique characterization includes: phase assemblage by Rietveld method, evolved heat, conductivity, rheology, compressive strength and expansion/retraction measurements. The dissolution rate of the sulfate sources is key to control the hydration reactions. Bassanite dissolves very fast and hence the initial setting time of the pastes and mortars is too short (20 min) to produce homogeneous samples. Anhydrite dissolves slowly so, at 1 hydration-day, the amount of ettringite formed (20 wt%) is lower than that in gypsum pastes (26 wt%) (w/c = 0.50), producing mortars with lower compressive strengths. After 3 hydration-days, anhydrite pastes showed slightly larger ettringite contents and hence, mortars with slightly higher compressive strengths. Ettringite content is the chief parameter to explain the strength development in these eco-cements.Universidad de Málaga. Campus de Excelencia Interncaional Andalucía Tech

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

Póster; ALBA User Meeting and VI AUSE Conferenc

In-situ hydration study of sulfobelite eco-cements

ALBA User Meeting and VI AUSE Conferenc

Conocimientos, actitudes y prácticas sobre el papanicolaou en mujeres en edad fértil con vida sexual activa que acuden al programa de planificación familiar del Centro de Atención Primaria Jairo Bismarck Moncada del Municipio de Somoto, Departamento de Madriz en el periodo del 1° Febrero al 31 de Marzo del 2014

Actualmente Nicaragua vive problemas de salud propios del subdesarrollo y uno de los más importantes que afecta a la población femenina de nuestro país lo representa el Cáncer del Cérvix Uterino, los datos oficiales del Ministerio de Salud lo ubican como la primera causa de morbimortalidad que afecta a las mujeres Nicaragüenses, ya que la mujer representa el eje de la familia, por tanto la muerte de una mujer tiene efectos en mucha mayor población que a su vez resulta vulnerable a otra serie de afectaciones. Este comportamiento mantiene datos similares a los relacionados a la población de América Latina. El comportamiento epidemiológico está relacionado a Condiciones Socio Económicas de pobreza, un bajo nivel cultural y además con una influencia de la población bastante importante, que provoca que los niveles de cobertura y de diagnóstico precoz sean mínimos, el país mantiene desde hace muchos años datos constantes: Por un lado una pobre cobertura y por el otro la aparición de las lesiones cada vez más graves, en la población femenina de menor edad. Se ha demostrado la realización de la toma de la Citología Cervico vaginal (Papanicolaou) es el método de elección muy importante, ya que tanto su nivel de sensibilidad como de especificidad son muy altos y esto permite el impulso de programas de captación oportuna de las mujeres todavía en momentos cuando las lesiones son tratables y mejor aún curables. El desarrollar una mayor cobertura y una mejor captación y aprovechamiento de esta técnica requiere el impulsar en nuestra población el uso de herramientas de conocimiento que mejoren en principio el mal manejo de la información, superando la gran dificultad de los mitos, tabúes y las complicaciones que esto conllev

Quantitative phase Analisis: A comparative study of Mo and Cu strictly monochromatic radiations

A comparison of the Rietveld quantitative phase analyses (RQPA) obtained using Cu-Kα1, Mo-Kα1, and synchrotron strictly monochromatic radiations is presented. The main aim is to test a simple hypothesis: high energy Mo-radiation, combined with high resolution laboratory X-ray powder diffraction optics, could yield more accurate RQPA, for challenging samples, than well-established Cu-radiation procedure(s). In order to do so, three set of mixtures with increasing amounts of a given phase (spiking-method) were prepared and the corresponding RQPA results have been evaluated. Firstly, a series of crystalline inorganic phase mixtures with increasing amounts of an analyte was studied in order to determine if Mo-Kα1 methodology is as robust as the well-established Cu-Kα1 one. Secondly, a series of crystalline organic phase mixtures with increasing amounts of an organic compound was analyzed. This type of mixture can result in transparency problems in reflection and inhomogeneous loading in narrow capillaries for transmission studies. Finally, a third series with variable amorphous content was studied. Limit of detection in Cu-patterns, ~0.2 wt%, are slightly lower than those derived from Mo-patterns, ~0.3 wt%, for similar recording times and limit of quantification for a well crystallized inorganic phase using laboratory powder diffraction was established ~0.10 wt%. However, the accuracy was comprised as relative errors were ~100%. Contents higher than 1.0 wt% yielded analyses with relative errors lower than 20%. From the obtained results it is inferred that RQPA from Mo-Kα1 radiation have slightly better accuracies than those obtained from Cu-Kα1. This behavior has been established with the calibration graphics obtained through the spiking method and also from Kullback-Leibler distance statistic studies. We explain this outcome, in spite of the lower diffraction power for Mo-radiation (compared to Cu-radiation), due to the larger volume tested with Mo, also because higher energy minimize pattern systematic errors and the microabsorption effect.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech