Evaluación de cementos obtenidos por activación alcalina de ceniza de carbón con NaOH curados a bajas temperaturas

The temperature at which the alkaline activation process takes place is a significant factor in the evolution of the mechanical properties of coal ash cementitious base material. In this work, the influence of temperature (8 a 38 °C) and curing time (3 and 28 days) on the mechanical properties of the alkaline synthesis of two coal ashes was evaluated through the study of the mineralogical evolution of the cementitious phases by XRD and FTIR. We found that the type of zeolite, a synthesis product, depends on the study factors. For values above 28 °C and at least 7 days, alkalinely activated cements with compressive strength above 20 MPa were achieved. Other parameters, such as SiO2/Al2O3 ratio, percentage of unburned coal and particle-size distribution, should be taken into account in the variation of mechanical performance.La temperatura a la cual se desarrolla el proceso de activación alcalina es un factor significativo en la evolución de las propiedades mecánicas de material cementante base ceniza de carbón. En este trabajo se evaluó, a través del estudio de la evolución mineralógica de las fases cementantes por DRX y FTIR, la influencia de la temperatura (8 a 38 °C) y tiempo (3 y 28 días) de curado sobre las propiedades mecánicas de la síntesis alcalina de dos cenizas de carbón. Se encontró que el tipo de zeolita, producto de la síntesis, depende de los factores de estudio. Para valores superiores a 28 °C y mínimo 7 días, se lograron cementos activados alcalinamente con resistencias superiores a 20 MPa. Otros parámetros, como la relación SiO2/Al2O3, el porcentaje de carbón inquemado y la distribución del tamaño de partícula, se deben de tener en cuenta en la variación del desempeño mecánico

Seasonal analysis of the atmosphere during five years by using microwave radiometry over a mid-latitude site

This work focuses on the analysis of the seasonal cycle of temperature and relative humidity (RH) profiles and integrated water vapor (IWV) obtained from microwave radiometer (MWR) measurements over the mid-latitude city of Granada, southern Spain. For completeness the study, the maximum atmospheric boundary layer height (ABLHmax) is also included. To this end, we have firstly characterized the HATPRO-RPG MWR errors using 55 co-located radiosondes (RS) by means of the mean-bias (biasbar) profile and the standard deviation (SDbias) profile classified under all-weather conditions and cloud-free conditions. This characterization pointed out that temperature from HATPRO-MWR presents a very low biasbar respects RS mostly below 2.0 km agl, ranging from positive to negative values under all-weather conditions (from 1.7 to -0.4 K with SDbias up to 3.0 K). Under cloud-free conditions, the bias was very similar to that found under all-weather conditions (1.8 to -0.4 K) but with smaller SDbias (up to 1.1 K). The same behavior is also seen in this lower part (ground to 2.0 km agl) for RH. Under all-weather conditions, the mean RH bias ranged from 3.0 to -4.0% with SDbias between 10 and 16.3% while under cloud-free conditions the bias ranged from 2.0 to -0.4% with SDbias from 0.5 to 13.3%. Above 2.0 km agl, the SDbias error increases considerably up to 4 km agl (up to -20%), and then decreases slightly above 7.0 km agl (up to -5%). In addition, IWV values from MWR were also compared with the values obtained from the integration of RS profiles, showing a better linear fit under cloud-free conditions (R2 = 0.96) than under all-weather conditions (R2 = 0.82). The mean bias under cloud-free conditions was -0.80 kg/m2 while for all-weather conditions it was -1.25 kg/m2. Thus, the SDbiasfor all the statistics (temperature, RH and IWV) of the comparison between MWR and RS presented higher values for all-weather conditions than for cloud-free conditions ones. It points out that the presence of clouds is a key factor to take into account when MWR products are used. The second part of this work is devoted to a seasonal variability analysis over five years, leading us to characterize thermodynamically the troposphere over our site. This city atmosphere presents a clear seasonal cycle where temperature, ABLHmax and IWV increase from winter to summer and decrease in autumn, meanwhile RH decreases along the warmer seasons. This city presents cold winters (mean daily maximum temperature: 10.6 ± 1.1 °C) and dry/hot summers (mean daily maximum temperature of 28.8 ± 0.9 °C and mean daily maximum of surface RH up to 55.0 ± 6.0%) at surface (680 m asl). Moreover, considering temporal trends, our study pointed out that only temperature and RH showed a linear increase in winters with a mean-rate of (0.5 ± 0.1) °C/year and (3.4 ± 1.7) %/year, respectively, from ground to 2.0 km agl, meanwhile IWV presented a linear increase of 1.0 kg·m-2/year in winters, 0.78 kg·m-2/year in summers and a linear decrease in autumns of -0.75 kg·m-2/year.Andalusia Regional Government through project P12-RNM-2409Spanish Ministry of Economy and Competitiveness through projects CGL2013-45410-R, CGL2015-73250-JIN and CGL2016-81092-RJuan de la Cierva grant IJCI-2016-3000

Study of the reaction stages of alkali-activated cementitious materials using microcalorimetry

The roles of sodium hydroxide, calcium hydroxide and temperature on heat flow evolution and its relation to the reaction stages of alkali-activated coal fly ash were evaluated. The response surface method was used to analyse data. Both the heat flow and kinetic parameters were determined by the deconvolution of microcalorimetric signals at 25, 35 and 45°C. The studied factors were found to have a strong influence on the dissolution of ash rich in aluminium units, on the diffusion-nucleation processes and its growth, both initial and final. A sodium hydroxide concentration of 8 M guaranteed optimal reorganisation of the dissolved units to form the reaction products. Calcium hydroxide altered the aluminium distribution in the paste, acting as nucleation spots and intervening in the formation of initial and final reaction products. High temperatures were found to favour the efficiency of the alkali activation, increasing the rate constant and simplifying the expiration of energy barriers. Knowledge of the heat flow evolution in these kinds of cementitious materials will allow manipulation of the characteristics of the mixtures in both the fresh and hardened state

New insights into the early reaction of alkali activated slag cements

Resumen del trabajo presentado 2nd Workshop Calcium-Silicate Hydrates Containing Aluminium (C-A-S-H II), celebrado en Empa, Dübendorf (Switzerland) del 23 al 24 de abril de 2018

Hygroscopic growth study in the framework of EARLINET during the SLOPE i campaign: Synergy of remote sensing and in situ instrumentation

This study focuses on the analysis of aerosol hygroscopic growth during the Sierra Nevada Lidar AerOsol Profiling Experiment (SLOPE I) campaign by using the synergy of active and passive remote sensors at the ACTRIS Granada station and in situ instrumentation at a mountain station (Sierra Nevada, SNS). To this end, a methodology based on simultaneous measurements of aerosol profiles from an EARLINET multi-wavelength Raman lidar (RL) and relative humidity (RH) profiles obtained from a multi-instrumental approach is used. This approach is based on the combination of calibrated water vapor mixing ratio (r) profiles from RL and continuous temperature profiles from a microwave radiometer (MWR) for obtaining RH profiles with a reasonable vertical and temporal resolution. This methodology is validated against the traditional one that uses RH from co-located radiosounding (RS) measurements, obtaining differences in the hygroscopic growth parameter (?) lower than 5% between the methodology based on RS and the one presented here. Additionally, during the SLOPE I campaign the remote sensing methodology used for aerosol hygroscopic growth studies has been checked against Mie calculations of aerosol hygroscopic growth using in situ measurements of particle number size distribution and submicron chemical composition measured at SNS. The hygroscopic case observed during SLOPE I showed an increase in the particle backscatter coefficient at 355 and 532nm with relative humidity (RH ranged between 78 and 98%), but also a decrease in the backscatter-related Ångström exponent (AE) and particle linear depolarization ratio (PLDR), indicating that the particles became larger and more spherical due to hygroscopic processes. Vertical and horizontal wind analysis is performed by means of a co-located Doppler lidar system, in order to evaluate the horizontal and vertical dynamics of the air masses. Finally, the Hänel parameterization is applied to experimental data for both stations, and we found good agreement on ? measured with remote sensing (?532 0.48 ± 0.01 and ?355 0.40 ± 0.01) with respect to the values calculated using Mie theory (?532 0.53 ± 0.02 and ?355 0.45 ± 0.02), with relative differences between measurements and simulations lower than 9% at 532nm and 11% at 355nm. © Author(s) 2018