RESUMENEste artículo evalúa el desempeño de morteros y hormigones basados en mezclas de escoria siderúrgica (GBFS)/metacaolín (MK), activadas alcalinamente expuestos a temperaturas altas. Se identifica una elevada estabilidad en morteros con contenidos de MK de hasta un 60% cuando se exponen a temperaturas de 600 ºC, con una resistencia residual de 20 MPa posterior a la exposición a esta temperatura. Por otra parte, la exposición a temperaturas más elevadas conduce al agrietamiento de los hormigones como consecuencia de una elevada contracción de la matriz cementante y las restricciones por efecto de los áridos, especialmente en aquellos especímenes con cementantes que contienen altos contenidos de MK. Se identifican diferencias significativas en las propiedades de absorción de agua de morteros y hormigones, y esto se relaciona con las divergencias en el desempeño de estos materiales posterior a la exposición a temperaturas altas. Esto indica que el desempeño a temperaturas elevadas de morteros de activación alcalina no es completamente transferible a hormigones, ya que los sistemas difieren en permeabilidad. Las diferencias en los coeficientes de expansión térmica entre matriz cementante y los áridos gruesos contribuyen al macrofisuramiento del material y su consecuente reducción de propiedades mecánicas.Palabras claves: cementos alcalinos, altas temperaturas, escoria siderúrgica, metacaolín, propiedades mecánicas. SUMMARYThis paper assesses the performance of mortars and concretes based on alkali activated granulated blastfurnace slag (GBFS)/metakaolin (MK) blends when exposed to high temperatures. High stability of mortars with contents of MK up to 60 wt.% when exposed to 600°C is identified, with residual strengths of 20 MPa following exposure to this temperature. On the other hand, exposure to higher temperatures leads to cracking of the concretes, as a consequence of the high shrinkage of the binder matrix and the restraining effects of the aggregate, especially in those specimens with binders containing high MK content. A significant difference is identified between the water absorption properties of mortars and concretes, and this is able to be correlated with divergences in their performance after exposure to high temperatures. This indicates that the performance at high temperatures of alkali-activated mortars is not completely transferable to concrete, because the systems differ in permeability. The differences in the thermal expansion coefficients between the binder matrix and the coarse aggregates contribute to the macrocracking of the material, and the consequent reduction of mechanical properties. . La principal diferencia entre estas dos clases de cementantes es la presencia de calcio en la escoria lo que promueve la formación de una estructura compuesta fundamentalmente por geles de silicatos cál-cicos hidratados (C-(A)-S-H) (2), mientras que en los geopolímeros se forman geles del tipo aluminosilicato sódi-co hidratado (N-A-S-H) (4). KeywordsEl uso tanto de metacaolín como de escoria activada a...

Can a theoretical inclusion model — specifically, the differential effective medium (DEM) model — match experimental velocity data in rocks that are not necessarily made of inclusions, such as clastics? It is indeed possible in some cases by using an almost constant inclusion aspect ratio (AR) within wide ranges of porosity and mineralogy. We approach this question by using empirical velocity-porosity equations as proxies for data. By finding a DEM inclusion AR to match these equations, we find that the required range of AR is narrow. Moreover, a constant AR of about 0.13 can be used to accurately match empirical relations in competent sand, shale, and quartz/calcite mixtures. This finding can be utilized practically to predict [Formula: see text] from [Formula: see text]; describe velocity-frequency dispersion between low-frequency and ultrasonic experiments; predict the dry-frame elastic properties from ultrasonic data on liquid-saturated samples where Gassmann’s fluid substitution is not applicable; predict the attenuation of P-wave velocity; and establish tight constraints for ranges of possible variation of [Formula: see text] and [Formula: see text] at a given porosity in some mineralogies. When we apply this approach to laboratory data rather than empirical equations, we confirm a positive answer to the main question, with all applications of this result still valid.

Tight gas reservoirs are often defined as gas-bearing sandstones or carbonates having in-situ permeabilities to gas less than 0.1 mD (Holditch, 2006; Smith et al., 2009). Tight gas reservoir rocks can be at different in-situ physical conditions: deep or shallow; over- or underpressured; high temperature or low temperature; and under different stress states. The reservoir-forming rock can have different textures such as shaley and silty unconsolidated sandstones or clean-cemented sandstones. These different rocks produce gas at low rates. Tight reservoir rocks can be blanket or lenticular, homogeneous or heterogeneous, and can contain a single layer or multiple layers, be fractured or unfractured, and mainly produce dry natural gas.

We offer an effective-medium model for estimating the elastic properties of high-porosity marine calcareous sediment and diatomite. This model treats sediment as a pack of porous elastic grains. The effective elastic moduli of the porous grains are calculated using the differential effective-medium ͑DEM͒ model, whereby the intragranular ellipsoidal inclusions have a fixed aspect ratio and are filled with seawater. Then the elastic moduli of a pack of these spherical grains are calculated using a modified ͑scaled to the critical porosity͒ upper Hashin-Shtrikman bound above the critical porosity and modified lower ͑carbonates͒ and upper ͑opal͒ Hashin-Shtrikman bounds below the critical porosity. The best match between the model-predicted compressional-and shearwave velocities and Ocean Drilling Program ͑ODP͒ data from three wells is achieved when the aspect ratio of intragranular pores is 0.5. This model assigns finite, nonzero values to the shear modulus of high-porosity marine sediment, unlike the suspension model commonly used in such depositional settings. The approach also allows one to obtain a satisfactory match with laboratory diatomite velocity data.

No abstract