X-Ray Computed Tomography.

En esta ponencia se presenta una breve introducción a la técnica: Tomografía Computerizada de Rayos-X. Además, se presenta el tomógrafo ubicado en la Unidad de Difracción de Rayos-X y Tomografía Computerizada de los Servicios Centrales de Apoyo a la Investigación, SkyScan 2214 (Bruker S.L.), así como los experimentos que se están llevando a cabo (incluyendo estudios donde se combina tanto la difracción de rayos-X como la tomografía).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

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

Rietveld Quantitative Phase Analysis of OPC Clinkers, Cements and Hydration Products

Universidad de Málaga. Campus de Excelencia Interacional. Andalucía Tech

Time-dependent monitoring of cement hydration by combined laboratory x-ray microtomography and powder diffraction

Following the reaction degree of amorphous phases in cements is very challenging. It becomes even harder when some additions (supplementary cementitious materials) are employed. Nowadays, calcined clays are attracting a lot of attention as it is possible to reduce the clinker factor by 50%, which leads to a 40% CO2 cement footprint reduction. Thus, the aim of our overall project is to follow the reaction degree of amorphous anhydrous cement phases (for instance metakaolin) to yield different amorphous phase(s) (f.i. C-A-S-H gel) by combined X-ray micro-computed tomography (μCT) and powder diffraction (PD) analyses at different ages of hydration. Furthermore, some microstructural features, like porosity, can also be mapped out which are important for durability.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

In-situ Molibdenum X-ray powder diffraction study of the early hydration of cementitious systems on a humidity chamber

The durability of cement-based construction materials depends on the environmental conditions during their service life. A further factor is the microstructure of the cement bulk, established by formation of cement hydrates. The development of the phases and microstructure under given conditions is responsible of the high strength of cementitious materials. The investigation on the early hydration behavior of cements and cementing systems has been for a long time a very important area of research: understanding the chemical reactions that lead to hardening is fundamental for the prediction of performances and durability of the materials. The production of 1 ton of Ordinary Portland Cement, OPC, releases into the atmosphere ~0.97 tons of CO2. This implies that the overall CO2 emissions from the cement industry are 6% of all anthropogenic carbon dioxide. An alternative to reduce the CO2 footprint consists on the development of eco-cements composed by less calcite demanding phases, such as belite and ye'elimite. That is the case of Belite-Ye’elimite cements (BY). Since the reactivity of belite is not quick enough, these materials develop low mechanical strengths at intermediate hydration ages. A possible solution to this problem goes through the production of cements which jointly contain alite with the two previously mentioned phases, named as Belite-Alite-Ye’elimite (BAY) cements. The reaction of alite and ye'elimite with water will develop cements with high mechanical strengths at early ages, while belite will contribute to later values. The final goal is to understand the hydration mechanisms of a variety of cementing systems (OPC, BAY and pure phases) as a function of water content, superplasticizer additives and type and content of sulfate source. In order to do so, in-situ laboratory humidity chambers with Molybdenum X-ray Powder diffraction are employed. In the first 2h of hydration, reaction degree (α) of ye'elimite had been decreased for superplasticizer.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

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

Accuracy in Cement Hydration Investigations: Combined X-ray Microtomography and Powder Diffraction Analyses

Cement hydration is a very complex set of processes. The evolution of the crystalline phases during hydration can be accurately followed by X-ray powder diffraction data evaluated by the Rietveld method. However, accurate measurements of some microstructural features, including porosity and amorphous content developments, are more challenging. Here, we combine laboratory X-ray powder diffraction and computed microtomography ( CT) to better understand the results of the CT analyses. Two pastes with different water–cement ratios, 0.45 and 0.65, filled within capillaries of two sizes, = 0.5 and 1.0 mm, were analysed at 50 days of hydration. It was shown that within the spatial resolution of the measured CTs, ~2 m, the water capillary porosity was segmented within the hydrated component fraction. The unhydrated part could be accurately quantified within 2 vol% error. This work is a first step to accurately determining selected hydration features like the hydration degree of amorphous phases of supplementary cementitious materials within cement blends.This research has been supported by PID2019-104378RJ-I00 and PID2020-114650RB-I00 (Spanish Science Ministry) research grants, which are co-funded by ERDF. IRS is thankful for funding from PTA2019-017513–I

The aquatic systems of Doñana (SW Spain): watersheds and frontiers

Doñana includes an extraordinary variety of aquatic systems. They are broadly classified according to their location (on either aeolian sands or marshland) as their hydrology largely depends on the geomorphology of their basins. Their chemical composition is mainly influenced by rainfall, evaporative concentration, groundwater discharge, biogeochemical interactions at the sediment-water interface, and the quality composition of their watersheds. The influence of the watershed can be studied at different scales of observation. Rainfall infiltration in sandy soils is usually high so surface runoff becomes a rare event of very short duration during floods which, nonetheless, exerts a huge influence on the limnology of temporary ponds on aeolian sands. The water quality of the Doñana marshland, on the contrary, is influenced by long-term processes taking place on large-scale areas: sediment deposition, eutrophication and heavy metal pollution. The review of the main literature on the limnology of the Doñana aquatic systems during the past two decades, enable us to make a comparison in time focusing on the interactions at the frontier between terrestrial and aquatic systems within watersheds. Presently, the eastern area of the Doñana marshland is particularly affected by the low quality of the incoming flowing water compared with the more isolated southern marshes within the National Park. Water from the lower strech of the Guadiamar River ("Entremuros"), that floods the marshes of "Lucio El Cangrejo Grande", showed a significant correlation between inorganic suspended solids and total P (r=0.807, p<0.05) during 2003-04, indicating an important contribution of inorganic particulates to the eutrophication of this area. The northern streams of the "Arroyo del Partido" watershed have not significantly improved their water quality in the last two decades despite the construction of two waste-water treatment plants, being total P correlated to dissolved phosphate concentration (r=0.995, p<0.01) during 2003-05. A general increase in NO3 - concentrations have been detected in all studied aquatic systems of the Doñana marshland, including those with the highest water quality ("Arroyo de la Rocina") during the last two decades. Despite wetland management requires a watershed approach, successive hydrologic projects in Doñana have failed to address the great spatio-temporal variability of processes affecting water quality in this area.Doñana alberga una extraordinaria variedad de sistemas acuáticos que se clasifican de forma general según su localización, bien en las arenas o en la marisma, ya que su hidrología depende, fundamentalmente, de la geomorfología de sus cuencas. La composición química de sus aguas varía en función de la lluvia, la evaporación, la descarga freática, las interacciones biogeoquímicas en la interfase agua-sedimento y el estado ecológico de sus cuencas. La influencia de la cuenca se puede estudiar a escalas distintas. La lluvia se infiltra fácilmente en la arena por lo que la escorrentía se convierte en un episodio raro y breve que, sin embargo, afecta considerablemente al funcionamiento limnológico de las lagunas temporales sobre arenas. Por el contrario, la calidad del agua en la marisma de Doñana está afectada por procesos extensos y largos, como la sedimentación, la eutrofización y la contaminación por metales pesados. Una revisión de la bibliografía limnológica permite realizar un estudio comparativo de las últimas dos décadas, centrado en las interacciones que tienen lugar en las fronteras entre los ecosistemas terrestres y acuáticos que comparten las cuencas de estos cuerpos de agua. Actualmente, la zona Este de la marisma está especialmente afectada por la baja calidad de las aguas de entrada en comparación con la zona Sur del Parque Nacional que se encuentra más alejada de estos aportes. El agua que discurre por el último tramo del encauzamiento del río Guadiamar ("Entremuros") inunda las marismas cercanas ("Lucio El Cangrejo Grande") y mostró una correlación significativa entre la carga de materia inorgánica en suspensión y la concentración de P total (r=0.807, p<0.05) durante el periodo 2003-04, indicando la importante contribución del material particulado inorgánico en la eutrofización de esta zona. En la zona Norte, la calidad del agua en los arroyos de la cuenca del Partido no ha mejorado significativamente en la últimas dos décadas, a pesar de la construcción y funcionamiento de dos estaciones depuradoras de aguas residuales. Las concentraciones de P total y fosfato disuelto en el agua se encontraron altamente correlacionadas (r=0.995, p<0.01) durante el periodo 2003-05. En las dos últimas décadas, se ha detectado un incremento de la concentración de NO3 - en los sistemas acuáticos estudiados en la marisma, incluído áquel con la mejor calidad del agua ("Arroyo de la Rocina"). A pesar de que nadie duda que la gestión de los humedales require una estrategia a nivel de cuenca hidrográfica, los sucesivos proyectos hidrológicos que se desarrollan en Doñana no llegan a abarcar la gran escala espacio-temporal de los procesos que afectan a la calidad de su aguas

Natural radiactivity from building materials in Spain

The industrial construction sector is very important in Spain. Building materials used in this industry are sources of radiation from natural radionuclides they contain. The European Commission published some recommendations to facilitate the trade of these materials in the E.U. The studies about this subject have increased notably during last years. This, probably, can be associated with the increase interest from natural radiation radiological risk on indoor exposure.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Consejo de Seguridad Nuclear. CSN-201