Recent Advances in C-S-H Nucleation Seeding for Improving Cement Performances.

Reducing cement CO2 footprint is a societal need. This is being achieved mainly by replacing an increasing amount of Portland clinker by supplementary cementitious materials. However, this comes at a price: lower mechanical strengths at early ages due to slow pozzolanic reaction(s). This is being addressed by using accelerator admixtures. In this context, calcium silicate hydrate nucleation seeding seems to have a promising future, as it can accelerate cement and pozzolanic reactions at early ages, optimising their microstructures, without compromising late strength and durability performances. In fact, these features could even be improved. Moreover, other uses are low temperature concreting, precasting, shotconcrete, etc. Here, we focus on reviewing recent reports on calcium silicate hydrate seeding using commercially available admixtures. Current knowledge on the consequences of nucleation seeding on hydration reactions and on early and late mechanical strengths is discussed. It is noted that other features, in addition to the classic alite hydration acceleration, are covered here including the enhanced ettringite precipitation and the very efficient porosity refinement, which take place in the seeded binders. Finally, because the seeded binders seem to be denser, durability properties could also be enhanced although this remains to be properly established.

Portland and Belite Cement Hydration Acceleration by C-S-H Seeds with Variable w/c Ratios.

The acceleration of very early age cement hydration by C-S-H seeding is getting attention from scholars and field applications because the enhanced early age features do not compromise later age performances. This acceleration could be beneficial for several low-CO2 cements as a general drawback is usually the low very early age mechanical strengths. However, the mechanistic understanding of this acceleration in commercial cements is not complete. Reported here is a contribution to this understanding from the study of the effects of C-S-H gel seeding in one Portland cement and two belite cements at two widely studied water-cement ratios, 0.50 and 0.40. Two commercially available C-S-H nano-seed-based admixtures, i.e., Master X-Seed 130 and Master X-Seed STE-53, were investigated. A multi-technique approach was adopted by employing calorimetry, thermal analysis, powder diffraction (data analysed by the Rietveld method), mercury intrusion porosimetry, and mechanical strength determination. For instance, the compressive strength at 1 day for the PC (w/c = 0.50) sample increased from 15 MPa for the unseeded mortar to 24 and 22 MPs for the mortars seeded with the XS130 and STE53, respectively. The evolution of the amorphous contents was determined by adding an internal standard before recording the powder patterns. In summary, alite and belite phase hydrations, from the crystalline phase content evolutions, are not significantly accelerated by C-S-H seedings at the studied ages of 1 and 28 d for these cements. Conversely, the hydration rates of tetracalcium alumino-ferrate and tricalcium aluminate were significantly enhanced. It is noted that the degrees of reaction of C4AF for the PC paste (w/c = 0.40) were 10, 30, and 40% at 1, 7, and 28 days. After C-S-H seeding, the values increased to 20, 45, and 60%, respectively. This resulted in larger ettringite contents at very early ages but not at 28 days. At 28 days of hydration, larger amounts of carbonate-containing AFm-type phases were determined. Finally, and importantly, the admixtures yielded larger amounts of amorphous components in the pastes at later hydration ages. This is justified, in part, by the higher content of amorphous iron siliceous hydrogarnet from the enhanced C4AF reactivity.

Outcome of Renal Transplantation in Children Given Rabbit Anti-Thymocyte Globulin (rATG) as Induction Therapy.

BACKGROUND: Induction immunosuppressive therapy is used to prevent rejection and maintain allograft function in transplantation. Rabbit antithymocyte globulin (rATG), a T-cell depleting antibody, is the most commonly used induction agent for kidney transplantation. To date there is still limited data on outcomes of pediatric kidney transplants with rATG as induction therapy. METHODS: Retrospective single-center study of first-time kidney transplant recipients ≤18 years old who received rATG induction between 2005 and 2019 at the National Kidney and Transplant Institute. Data were collected up to 1 year post transplant. RESULTS: Eleven patients were included in the study. They received rATG at 1.5 mg/kg/dose (±0.3 mg/kg/dose) once a day for 3 days. Patient survival was 100% at 6 months, and 90.9% at 1 year. Graft survival was 90.9% at 6 months, and 81.8% at 1 year. Four patients (36.4%) had a glomerular filtration rate of <60 at 1 year. One died of sepsis at 7 months. One patient (9.1%) had acute allograft rejection with recurrence of disease, C3 glomerulopathy, on day 13. A total of 3 patients (27.3%) developed leukopenia and 4 patients (36.4%) developed thrombocytopenia. The majority were anemic at baseline (9.7 mg/dL), and a significant increase in the mean hemoglobin was seen at 4 weeks (11.6 mg/dL) to 1 year (13 mg/dL). Incidence of recurrent infections was 9.1% (with culture growth) and 36.4% (no culture growth). Hypertension remained unchanged before and after transplant. CONCLUSIONS: Induction with single dose rATG at 1.5 mg/kg/dose (±0.3 mg/kg/dose) for 3 days provided effective and safe outcomes in pediatric kidney transplant patients in this study.

Strategies to apply 3Rs in preclinical testing.

Animal experimentation has been fundamental in biological and biomedical research. To guarantee the maximum quality, efficacy and/or safety of products intended for the use in humans in vivo testing is necessary; however, for over 60 years, alternative methods have been developed in response to the necessity to reduce the number of animals used in experimentation, to guarantee their welfare; resorting to animal models only when strictly necessary. The three Rs (Replacement, Reduction, and Refinement), seek to ensure the rational and respectful use of laboratory animals and maintain an adequate projection in terms of bioethical considerations. This article describes different approaches to apply 3Rs in preclinical experimentation for either research or regulatory purposes.

Effect of Boron and Water-to-Cement Ratio on the Performances of Laboratory Prepared Belite-Ye'elimite-Ferrite (BYF) Cements.

The effect of superplasticiser, borax and the water-to-cement ratio on BYF hydration and mechanical strengths has been studied. Two laboratory-scale BYF cements-st-BYF (with ß-C2S and orthorhombic C4A3S¯) and borax-activated B-BYF (with α'H-C2S and pseudo-cubic C4A3S¯)-have been used, and both show similar particle size distribution. The addition of superplasticiser and externally added borax to BYF pastes has been optimised through rheological measurements. Optimised superplasticiser contents (0.3, 0.4 and 0.1 wt % for st-BYF, B-BYF and st-BYF with externally added 0.25 wt % B2O3, respectively) result in low viscosities yielding homogeneous mortars. The calorimetric study revealed that st-BYF is more reactive than B-BYF, as the values of heat released are 300-370 J/g and 190-210 J/g, respectively, after 7 days of hydration; this fact is independent of the water-to-cement ratio. These findings agree with the higher degree of hydration at 28 days of ß-C2S in st-BYF (from 45 to 60%) than α'H-C2S in B-BYF (~20 to 30%). The phase assemblage evolution has been determined by LXRPD coupled with the Rietveld method and MAS-NMR. The formation of stratlingite is favoured by increasing the w/c ratio in both systems. Finally, the optimisation of fresh BYF pastes jointly with the reduction of water-to-cement ratio to 0.40 have allowed the achieving of mortars with compressive strengths over 40 MPa at 7 days in all systems. Moreover, the st-BYF mortar, where borax was externally added, achieved more than 70 MPa after 28 days. The main conclusion of this work does not support Lafarge's approach of adding boron/borax to the raw meal of BYF cements. This procedure stabilises the alpha belite polymorph, but its reactivity, in these systems, is lower and the associated mechanical strengths poorer.

Keys to discern the Phoenician, Punic and Roman mining in a typical coastal environment through the multivariate study of trace element distribution.

Trace element concentrations in the Cartagena Bay coastal record reveal a contribution of natural processes. However, the influence of anthropogenic factors predominates in the last three millennia, particularly aerosol deposition linked to mining and industrial activities in the area. The coastal record of Cartagena can be considered a preserved environment, suitable to search for regional human activity fingerprinting, specifically that related to the deposition of heavy metals such as Pb and Cu. A multivariate statistical analysis was carried out to clarify the geochemical behaviour of trace and major elements. Our study design represents a novel approach to assign natural contributions, such as eolian and riverine input, to coastal deposits, and organic matter preservation under anoxic environments. Therefore, synergies obtained by the simultaneous study of multivariate statistics and enrichment factors allow robust conclusions about palaeoenvironmental evolution and human activities. Anthropogenic influence suggested that Pb mining and metallurgy began during the Chalcolithic period, with considerable inputs of Pb and Cu to atmospheric pollution during Phoenician, Punic and Roman times.

Características, evolución clínica y factores asociados a la mortalidad en UCI de los pacientes críticos infectados por SARS-CoV-2 en España: estudio prospectivo, de cohorte y multicéntrico / Patient characteristics, clinical course and factors associated to ICU mortality in critically ill patients infected with SARS-CoV-2 in Spain: a prospective, cohort, multicentre study

ANTECEDENTES: No se ha reportado plenamente la evolución clínica de los pacientes críticos de COVID-19 durante su ingreso en la unidad de cuidados intensivos (UCI), incluyendo las complicaciones médicas e infecciosas y terapias de soporte, así como su asociación con la mortalidad en ICU. OBJETIVO: El objetivo de este estudio es describir las características clínicas y la evolución de los pacientes ingresados en UCI por COVID-19, y determinar los factores de riesgo de la mortalidad en UCI de dichos pacientes. MÉTODOS: Estudio prospectivo, multi-céntrico y de cohorte, que incluyó a los pacientes críticos de COVID-19 ingresados en 30 UCIs de España y Andorra. Se incluyó a los pacientes consecutivos de 12 de Marzo a 26 de Mayo de 2020 si habían fallecido o habían recibido el alta de la UCI durante el periodo de estudio. Se reportaron los datos demográficos, síntomas, signos vitales, marcadores de laboratorio, terapias de soporte, terapias farmacológicas, y complicaciones médicas e infecciosas, realizándose una comparación entre los pacientes fallecidos y los pacientes dados de alta. RESULTADOS: Se incluyó a un total de 663 pacientes. La mortalidad general en UCI fue del 31% (203 pacientes). Al ingreso en UCI los no supervivientes eran más hipoxémicos [SpO2 sin mascarilla de no reinhalación, de 90 (RIC 83-93) vs 91 (RIC 87-94); p < 0,001] y con mayor puntuación en la escala SOFA - Evaluación de daño orgánico secuencial - [SOFA, 7 (RIC 5-9) vs 4 (RIC 3-7); p < 0,001]. Las complicaciones fueron más frecuentes en los no supervivientes: síndrome de distrés respiratorio agudo (SDRA) (95% vs 89%; p = 0,009), insuficiencia renal aguda (IRA) (58% vs 24%; p < 10−16), shock (42% vs 14%; p < 10−13), y arritmias (24% vs 11%; p < 10−4). Las súper-infecciones respiratorias, infecciones del torrente sanguíneo y los shock sépticos fueron más frecuentes en los no supervivientes (33% vs 25%; p = 0,03, 33% vs 23%; p = 0,01 y 15% vs 3%, p = 10−7), respectivamente. El modelo de regresión multivariable reflejó que la edad estaba asociada a la mortalidad, y que cada año incrementaba el riesgo de muerte en un 1% (95%IC: 1-10, p = 0,014). Cada incremento de 5 puntos en la escala APACHE II predijo de manera independiente la mortalidad [OR: 1,508 (1,081, 2,104), p = 0,015]. Los pacientes con IRA [OR: 2,468 (1,628, 3,741), p < 10−4)], paro cardiaco [OR: 11,099 (3,389, 36,353), p = 0,0001], y shock séptico [OR: 3,224 (1,486, 6,994), p = 0,002] tuvieron un riesgo de muerte incrementado. CONCLUSIONES: Los pacientes mayores de COVID-19 con puntuaciones APACHE II más altas al ingreso, que desarrollaron IRA en grados II o III y/o shock séptico durante la estancia en UCI tuvieron un riesgo de muerte incrementado. La mortalidad en UCI fue del 31%

BACKGROUND: The clinical course of COVID-19 critically ill patients, during their admission in the intensive care unit (UCI), including medical and infectious complications and support therapies, as well as their association with in-ICU mortality has not been fully reported. OBJECTIVE: This study aimed to describe clinical characteristics and clinical course of ICU COVID-19 patients, and to determine risk factors for ICU mortality of COVID-19 patients. METHODS: Prospective, multicentre, cohort study that enrolled critically ill COVID-19 patients admitted into 30 ICUs from Spain and Andorra. Consecutive patients from March 12th to May 26th, 2020 were enrolled if they had died or were discharged from ICU during the study period. Demographics, symptoms, vital signs, laboratory markers, supportive therapies, pharmacological treatments, medical and infectious complications were reported and compared between deceased and discharged patients. RESULTS: A total of 663 patients were included. Overall ICU mortality was 31% (203 patients). At ICU admission non-survivors were more hypoxemic [SpO2 with non-rebreather mask, 90 (IQR 83-93) vs 91 (IQR 87-94); p < 0.001] and with higher sequential organ failure assessment score [SOFA, 7 (IQR 5-9) vs 4 (IQR 3-7); p < 0.001]. Complications were more frequent in non-survivors: acute respiratory distress syndrome (ARDS) (95% vs 89%; p = 0.009), acute kidney injury (AKI) (58% vs 24%; p < 10−16), shock (42% vs 14%; p < 10−13), and arrhythmias (24% vs 11%; p < 10−4). Respiratory super-infection, bloodstream infection and septic shock were higher in non-survivors (33% vs 25%; p = 0.03, 33% vs 23%; p = 0.01 and 15% vs 3%, p = 10−7), respectively. The multivariable regression model showed that age was associated with mortality, with every year increasing risk-of-death by 1% (95%CI: 1-10, p = 0.014). Each 5-point increase in APACHE II independently predicted mortality [OR: 1.508 (1.081, 2.104), p = 0.015]. Patients with AKI [OR: 2.468 (1.628, 3.741), p < 10−4)], cardiac arrest [OR: 11.099 (3.389, 36.353), p = 0.0001], and septic shock [OR: 3.224 (1.486, 6.994), p = 0.002] had an increased risk-of-death. CONCLUSIONS: Older COVID-19 patients with higher APACHE II scores on admission, those who developed AKI grades II or III and/or septic shock during ICU stay had an increased risk-of-death. ICU mortality was 31%

Patient characteristics, clinical course and factors associated to ICU mortality in critically ill patients infected with SARS-CoV-2 in Spain: A prospective, cohort, multicentre study. / Características, evolución clínica y factores asociados a la mortalidad en UCI de los pacientes críticos infectados por SARS-CoV-2 en España: estudio prospectivo, de cohorte y multicéntrico.

BACKGROUND: The clinical course of COVID-19 critically ill patients, during their admission in the intensive care unit (UCI), including medical and infectious complications and support therapies, as well as their association with in-ICU mortality has not been fully reported. OBJECTIVE: This study aimed to describe clinical characteristics and clinical course of ICU COVID-19 patients, and to determine risk factors for ICU mortality of COVID-19 patients. METHODS: Prospective, multicentre, cohort study that enrolled critically ill COVID-19 patients admitted into 30 ICUs from Spain and Andorra. Consecutive patients from March 12th to May 26th, 2020 were enrolled if they had died or were discharged from ICU during the study period. Demographics, symptoms, vital signs, laboratory markers, supportive therapies, pharmacological treatments, medical and infectious complications were reported and compared between deceased and discharged patients. RESULTS: A total of 663 patients were included. Overall ICU mortality was 31% (203 patients). At ICU admission non-survivors were more hypoxemic [SpO2 with non-rebreather mask, 90 (IQR 83 to 93) vs. 91 (IQR 87 to 94); P<.001] and with higher sequential organ failure assessment score [SOFA, 7 (IQR 5 to 9) vs. 4 (IQR 3 to 7); P<.001]. Complications were more frequent in non-survivors: acute respiratory distress syndrome (ARDS) (95% vs. 89%; P=.009), acute kidney injury (AKI) (58% vs. 24%; P<10-16), shock (42% vs. 14%; P<10-13), and arrhythmias (24% vs. 11%; P<10-4). Respiratory super-infection, bloodstream infection and septic shock were higher in non-survivors (33% vs. 25%; P=.03, 33% vs. 23%; P=.01 and 15% vs. 3%, P=10-7), respectively. The multivariable regression model showed that age was associated with mortality, with every year increasing risk-of-death by 1% (95%CI: 1 to 10, P=.014). Each 5-point increase in APACHE II independently predicted mortality [OR: 1.508 (1.081, 2.104), P=.015]. Patients with AKI [OR: 2.468 (1.628, 3.741), P<10-4)], cardiac arrest [OR: 11.099 (3.389, 36.353), P=.0001], and septic shock [OR: 3.224 (1.486, 6.994), P=.002] had an increased risk-of-death. CONCLUSIONS: Older COVID-19 patients with higher APACHE II scores on admission, those who developed AKI grades ii or iii and/or septic shock during ICU stay had an increased risk-of-death. ICU mortality was 31%.

A multivariate examination of the timing and accumulation of potentially toxic elements at Las Conchas bog (NW Spain).

The inorganic content of the well-preserved 3.2-m record of Las Conchas bog (NW Spain), covering 8000 cal yr BP., was analysed. To study natural vs. human contributions, we applied an innovative approach, namely the sequential study of multivariate statistics (factor analysis followed by clustering of the factor score matrix) and enrichment factors (EFs). The increasing weight of potentially toxic elements (PTEs) such as the geochemical association of Zn, Pb and Cd (EFs higher than 10, 20 and 40 in the last two centuries) was revealed, and corroborated by the contrast between the contents of anthropogenic Pb and total Rare Earth Elements (a suitable proxy for natural geogenic supplies). Furthermore, elements such as Hg, Tl and As also showed enrichment in the most recent samples of the study core. Some of them are commonly associated with global atmospheric transport; however, in this case, their increasing contents could also be explained by nearby industrial and mining activities. In summary, severe pollution was observed in the uppermost part of the record, thereby pointing to an important environmental concern. Given that local and regional sources of PTEs, such as mining and heavy industry, especially Zn smelting, were probably the main historical causes of this contamination and that some of these industries are still active, we consider that our findings deserve further attention.

High-pressure and -temperature spinning capillary cell for in situ synchrotron X-ray powder diffraction.

In situ research of materials under moderate pressures (hundreds of bar) is essential in many scientific fields. These range from gas sorption to chemical and biological processes. One industrially important discipline is the hydration of oil well cements. Existing capillary cells in this pressure range are static as they are easy to design and operate. This is convenient for the study of single-phase materials; however, powder diffraction quantitative analyses for multiphase systems cannot be performed accurately as a good powder average cannot be attained. Here, the design, construction and commissioning of a cost-effective spinning capillary cell for in situ powder X-ray diffraction is reported, for pressures currently up to 200 bar. The design addresses the importance of reducing the stress on the capillary by mechanically synchronizing the applied rotation power and alignment on both sides of the capillary while allowing the displacement of the supports needed to accommodate different capillaries sizes and to insert the sample within the tube. This cell can be utilized for multiple purposes allowing the introduction of gas or liquid from both ends of the capillary. The commissioning is reported for the hydration of a commercial oil well cement at 150 bar and 150°C. The quality of the resulting powder diffraction data has allowed in situ Rietveld quantitative phase analyses for a hydrating cement containing seven crystalline phases.

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 real-world 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 non-overlapped 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 h, and that of belite was 42% at 14 h. 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.

Quantitative disentanglement of nanocrystalline phases in cement pastes by synchrotron ptychographic X-ray tomography.

Mortars and concretes are ubiquitous materials with very complex hierarchical microstructures. To fully understand their main properties and to decrease their CO2 footprint, a sound description of their spatially resolved mineralogy is necessary. Developing this knowledge is very challenging as about half of the volume of hydrated cement is a nanocrystalline component, calcium silicate hydrate (C-S-H) gel. Furthermore, other poorly crystalline phases (e.g. iron siliceous hydrogarnet or silica oxide) may coexist, which are even more difficult to characterize. Traditional spatially resolved techniques such as electron microscopy involve complex sample preparation steps that often lead to artefacts (e.g. dehydration and microstructural changes). Here, synchrotron ptychographic tomography has been used to obtain spatially resolved information on three unaltered representative samples: neat Portland paste, Portland-calcite and Portland-fly-ash blend pastes with a spatial resolution below 100 nm in samples with a volume of up to 5 × 104 µm3. For the neat Portland paste, the ptychotomographic study gave densities of 2.11 and 2.52 g cm-3 and a content of 41.1 and 6.4 vol% for nanocrystalline C-S-H gel and poorly crystalline iron siliceous hydrogarnet, respectively. Furthermore, the spatially resolved volumetric mass-density information has allowed characterization of inner-product and outer-product C-S-H gels. The average density of the inner-product C-S-H is smaller than that of the outer product and its variability is larger. Full characterization of the pastes, including segmentation of the different components, is reported and the contents are compared with the results obtained by thermodynamic modelling.

A Comparative Study of Experimental Configurations in Synchrotron Pair Distribution Function.

The identification and quantification of amorphous components and nanocrystalline phases with very small crystal sizes, smaller than ~3 nm, within samples containing crystalline phases is very challenging. However, this is important as there are several types of systems that contain these matrices: building materials, glass-ceramics, some alloys, etc. The total scattering synchrotron pair distribution function (PDF) can be used to characterize the local atomic order of the nanocrystalline components and to carry out quantitative analyses in complex mixtures. Although the resolution in momentum transfer space has been widely discussed, the resolution in the interatomic distance space has not been discussed to the best of our knowledge. Here, we report synchrotron PDF data collected at three beamlines in different experimental configurations and X-ray detectors. We not only discuss the effect of the resolution in Q-space, Qmax ins of the recorded data and Qmax of the processed data, but we also discuss the resolution in the interatomic distance (real) space. A thorough study of single-phase crystalline nickel used as standard was carried out. Then, selected cement-related samples including anhydrous tricalcium and dicalcium silicates, and pastes derived from the hydration of tricalcium silicate and ye'elimite with bassanite were analyzed.

Criticality in failure under compression: Acoustic emission study of coal and charcoal with different microstructures.

A systematic study of acoustic emission avalanches in coal and charcoal samples under slow uniaxial compression is presented. The samples exhibit a range of organic composition in terms of chemical elements as well as different degrees of heterogeneity in the microstructure. The experimental analysis focuses on the energies E of the individual acoustic emission events as well as on the time correlations between successive events. The studied samples can be classified into three groups. The more homogeneous samples (group I) with pores in the micro and nanoscales, with signatures of hardening effects in the stress-strain curves, exhibit the cleanest critical power-law behavior for the energy distributions g(E)dE∼E^{-ε}dE with a critical exponent ε=1.4. The more heterogeneous samples with voids, macropores, and granular microstructures (group III), show signatures of weakening effects and a larger effective exponent close to the value ε=1.66, but in some cases truncated by exponential damping factors. The rest of the samples (group II) exhibit a mixed crossover behavior still compatible with an effective exponent ε=1.4 but clearly truncated by exponential factors. These results suggest the existence of two possible universality classes in the failure of porous materials under compression: one for homogeneous samples and another for highly heterogeneous samples. Concerning time correlations between avalanches, all samples exhibit very similar waiting time distributions although some differences for the Omori aftershock distributions cannot be discarded.

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.

Integrating knowledge exchange and the assessment of dryland management alternatives - A learning-centered participatory approach.

The adoption of sustainable land management strategies and practices that respond to current climate and human pressures requires both assessment tools that can lead to better informed decision-making and effective knowledge-exchange mechanisms that facilitate new learning and behavior change. We propose a learning-centered participatory approach that links land management assessment and knowledge exchange and integrates science-based data and stakeholder perspectives on both biophysical and socio-economic attributes. We outline a structured procedure for a transparent assessment of land management alternatives, tailored to dryland management, that is based on (1) principles of constructivism and social learning, (2) the participation of stakeholders throughout the whole assessment process, from design to implementation, and (3) the combination of site-specific indicators, identified by local stakeholders as relevant to their particular objectives and context conditions, and science-based indicators that represent ecosystem services of drylands worldwide. The proposed procedure follows a pattern of eliciting, challenging, and self-reviewing stakeholder perspectives that aims to facilitate learning. The difference between the initial baseline perspectives and the final self-reviewed stakeholder perspectives is used as a proxy of learning. We illustrate the potential of this methodology by its application to the assessment of land uses in a Mediterranean fire-prone area in East Spain. The approach may be applied to a variety of socio-ecological systems and decision-making and governance scales.

Variation in soil enzyme activity as a function of vegetation amount, type, and spatial structure in fire-prone Mediterranean shrublands.

Fire-prone Mediterranean shrublands may be seriously threatened by land degradation due to progressive opening of the vegetation cover driven by increasing drought and fire recurrence. However, information about the consequences of this opening process for critical ecosystem functions is scant. In this work, we studied the influence of vegetation amount, type, and spatial pattern in the variation of extracellular soil enzyme activity (acid phosphatase, ß-glucosidase, and urease) in fire-prone shrublands in eastern Spain. Soil was sampled in vegetation-patch and open-interpatch microsites in 15 shrubland sites affected by large wildfires in 1991. On average, the activities of the three enzymes were 1.5 (ß-glucosidase and urease) to 1.7 (acid phosphatase) times higher in soils under vegetation patches than in adjacent interpatches. In addition, phosphatase activity for both microsites significantly decreased with the fragmentation of the vegetation. This result was attributed to a lower influence of roots -the main source of acid phosphatase- in the bigger interpatches of the sites with lower patch cover, and to feedbacks between vegetation pattern, redistribution of resources, and soil quality during post-fire vegetation dynamics. Phosphatase activity was also 1.2 times higher in patches of resprouter plants than in patches of non-resprouters, probably due to the faster post-fire recovery and older age of resprouter patches in these fire-prone ecosystems. The influence on the studied enzymes of topographic and climatic factors acting at the landscape scale was insignificant. According to our results, variations in the cover, pattern, and composition of vegetation patches may have profound impacts on soil enzyme activity and associated nutrient cycling processes in fire-prone Mediterranean shrublands, particularly in those related to phosphorus.

Mechanism of stabilization of dicalcium silicate solid solution with aluminium.

Stoichiometric dicalcium silicate, Ca2SiO4, displays a well-known polymorphism with temperature. When this phase is doped by a range of elements, belite, one of the main phases of cements, is generated. Here, we thoroughly study the aluminum doping of dicalcium silicate. This type of study is important for cement characterization and also from a basic point of view. Ca2Si(1-2x)Al(2x)O(4-x)□(x) (x = 0, 0.010, 0.014, 0.03) has been prepared and studied by X-ray powder diffraction and the Rietveld method. The limiting composition has been established as Ca2Si0.972Al0.028O3.986□0.014. The (27)Al MAS NMR band located close to ~-70 ppm is ascribed to tetrahedral environments, in agreement with the proposed aliovalent Si/Al atomic substitution mechanism. Thermal analysis measurements under a wet atmosphere indirectly confirm the increase of oxygen vacancies as the amount of incorporated protons increases with the aluminium content. A thorough electrical characterization has been carried out including overall conductivity measurements under wet and dry atmospheres and conductivity as a function of the oxygen partial pressure. The samples show oxide anion conductivity with a small p-type electronic contribution under oxidizing conditions. These compounds display a very important proton contribution to the overall conductivities under humidified atmospheres.