Geotechnical Properties of Low Calcium and High Calcium Fly Ash

In this paper, a comparative study has been made for physical and engineering properties of low calcium and high calcium Indian fly ash. The grain size distribution of fly ash is independent of lime content. Fly ash particles of size >75 μm are mostly irregular in shape whereas finer fractions are spherical for low calcium fly ash. For high calcium fly ash, chemical and mineralogical differences have been observed for different size fractions. Compared to low calcium fly ash, optimum moisture content is low and maximum dry density is high for high calcium fly ash. Optimum moisture content is directly proportional and maximum dry density is inversely proportional to the carbon content. The mode and duration of curing have significant effect on strength and stress–strain behavior of compacted fly ash. The gain in strength with time for high calcium fly ash is very high compared to that of low calcium fly ash due to presence of reactive minerals and glassy phase.     

Fluid inclusion studies of the Abawso gold prospect,near the Ashanti Belt,Ghana

The major Ghanaian lode gold deposits are preferentially aligned along the western and eastern contacts of the Kumasi Basin with the Ashanti and Sefwi Belts, respectively. The investigated area of the Abawso small-scale concession, covering the workings of the old Ettadom mine, is situated 3 km west of the lithological contact of the Birimian metavolcanic rocks of the Akropong Belt in the east with the Birimian metasedimentary rocks of the Kumasi Basin in the west. The rocks of the Abawso concession represent a steeply NW-dipping limb of a SE-verging anticline with an axis plunging to the SW. Quartz veining occurs predominantly in the form of en échelon dilatational veins along NNE–SSW-striking shear zones of a few metres width and shows evidence of brittle and ductile deformation. Also stockwork-style quartz veining occurs in the vicinity of the main shaft of the old Ettadom mine. Hydrothermal alteration includes sericitisation, sulphidation and locally carbonatisation. The auriferous quartz veins mainly follow the trend of brittle to ductile deformed quartz veins; however, some occur in stockwork. Fluid inclusion studies reveal a large number of H₂O inclusions along intragranular trails in auriferous quartz vein samples, as well as an overall dominance of H₂O and H₂O-CO₂ inclusions over CO₂ inclusions. Textural observations and physico-chemical fluid inclusion properties indicate post-entrapment modifications for all quartz vein samples due to grain boundary migration recrystallisation. This process is interpreted to be responsible for the generation of the CO₂ inclusions from a H₂O-CO₂ parent fluid. In comparison with mineralisation at the Ashanti and Prestea deposits, which are characterised by CO₂±N₂ inclusions, the observed inclusion assemblage may be due to a shallower crustal level of mineralisation, or different degrees and styles of recrystallisation, or a less pronounced development of laminated quartz veins due to comparably restricted pressure fluctuations. Furthermore, the microthermometric observations allow the reconstruction of a possible retrograde P-T path, depicting near-isothermal decompression in the P-T range of the brittle/ductile transition.Editorial handling: E. Frimmel     

Kinetics and Equilibrium Sorption Studies of 4-Nitrophenol on pyrolyzed and activated oil shale residue

Sorption of the organic pollutant 4-nitrophenol (4-NP) by pyrolyzed and activated Jordanian oil-shale was studied. Pyrolyzed oil shale was prepared using a fluidized bed reactor at 520 °C in the presence of nitrogen. Physical activation was carried out by treating the pyrolyzed oil shale with CO₂ at 830 °C, while chemical activation was achieved by using KOH and ZnCl₂ as impregnating agents. Batch kinetics and isotherm studies were conducted to evaluate the sorption process. Effects of contact time, initial sorbate concentration, sorbent concentration, temperature, pH and inorganic salts (NaCl and KCl) on the sorption process by the different sorbents were considered. Chemically activated oil shale, pretreated with ZnCl₂, gave the highest uptake of 4-NP. The isotherm experimental data fit reasonably well to Langmuir, Freundlich and Redlich-Paterson models. Three kinetic models, namely the Morris-Weber, Lagergren, and Pseudo-Second-Order model (PSOM), were applied to represent the experimental results for both pyrolyzed and ZnCl₂-oil shale sorbents.     

Dauphiné twinning and texture memory in polycrystalline quartz. Part 3: texture memory during phase transformation

Samples of quartz-bearing rocks were heated above the α (trigonal)–β (hexagonal) phase transformation of quartz (625–950°C) to explore changes in preferred orientation patterns. Textures were measured both in situ and ex situ with neutron, synchrotron X-ray and electron backscatter diffraction. The trigonal–hexagonal phase transformation does not change the orientation of c- and a-axes, but positive and negative rhombs become equal in the hexagonal β-phase. In naturally deformed quartzites measured by neutron diffraction a perfect texture memory was observed, i.e. crystals returned to the same trigonal orientation they started from, with no evidence of twin boundaries. Samples measured by electron back-scattered diffraction on surfaces show considerable twinning and memory loss after the phase transformation. In experimentally deformed quartz rocks, where twinning was induced mechanically before heating, the orientation memory is lost. A mechanical model can explain the memory loss but so far it does not account for the persistence of the memory in quartzites. Stresses imposed by neighboring grains remain a likely cause of texture memory in this mineral with a very high elastic anisotropy. If stresses are imposed experimentally the internal stresses are released during the phase transformation and the material returns to its original state prior to deformation. Similarly, on surfaces there are no tractions and thus texture memory is partially lost.     

Cobalt‐Bearing Grunerite in the Metamorphosed Banded Iron Formation in Orissa,India

Banded iron formation (BIF) comprising high grade iron ore are exposed in Gorumahisani‐Sulaipat‐Badampahar belt in the east of North Orissa Craton, India. The ores are multiply deformed and metamorphosed to amphibolite facies. The mineral assemblage in the BIF comprises grunerite, magnetite/martite/goethite and quartz. Relict carbonate phases are sometimes noticed within thick iron mesobands. Grunerite crystals exhibit needles to fibrous lamellae and platy form or often sheaf‐like aggregates in linear and radial arrangement. Accicular grunerite also occur within intergranular space of magnetite/martite. Grunerite needles/accicules show higher reflectivity in chert mesoband and matching reflectance with that of adjacent magnetite/martite in iron mesoband. Some grunerite lamellae sinter into micron size magnetite platelets. This grunerite has high ferrous oxide and cobalt oxide content but is low in Mg‐ and Mn‐oxide compared to the ones, reported from BIFs, of Western Australia, Nigeria, France, USA and Quebec. The protolith of this BIF is considered to be carbonate containing sediments, with high concentrations of Fe and Si but lower contents of cobalt and chromium ± Mg, Mn and Ni. During submarine weathering quartz, sheet silicate (greenalite) and Fe‐Co‐Cr (Mg‐Mn‐Ni)‐carbonate solid solution were formed. At the outset of the regional metamorphic episode grunerite, euhedral magnetite and recrystalized quartz were developed. Magnetite was grown at the expense of carbonate and later martitized under post‐metamorphic conditions. With the increasing grade of metamorphism greenalite transformed to grunerite.     

Considerations on the European Standard EN 14157 Test Methods: Abrasion Resistance of Natural Stones Used for Flooring in Buildings

In Europe, the Wide Wheel abrasion (WWA) test and the B?hme abrasion (BA) test are among the most widely used standard test methods for determining abrasion resistance of natural stones, the former being the reference test method in EN 14157 Standard. However, it is stated in the Annex-A (Informative) of EN 14157 Standard that very limited data are available to provide correlations between these two test methods. To be able to fill this gap, in this study, 25 different natural stones belonging to sedimentary, metamorphic and igneous groups were tested for their abrasion resistance as well as physico-mechanical properties. Also, for a better interpretation of abrasion resistance characteristics of the tested stone materials, relationships between abrasion resistance and physico-mechanical properties were statistically examined. A statistically significant linear correlation (R ² = 0.85; P value = 0.000) was established between the WWA test and the BA test, which could be used in practice for converting the measured abrasion resistance values from one testing method to another. It was also found that the correlation between these two test methods improved significantly (R ² = 0.93; P value = 0.001) when relatively high-porosity stone materials (porosity ≥1%) were separately evaluated. Both methods of abrasion resistance employed in the present study showed statistically significant linear correlations with uniaxial compressive strength and Brazilian tensile strength, the former proving to be a more influencing parameter on resistance to abrasion. Also, from the point view of representing actual abrasion mechanism of stone materials in practice, the necessity of simulating multi-directional foot traffic in abrasion testing methods was discussed. In this respect, the reference test method in the EN 14157 Standard was criticized for not fully meeting this requirement. It was also pointed out that the reference method could have some drawbacks when applied to coarse-grained granitic rocks having cleavable minerals such as plagioclase and orthoclase feldspars.     

Trends in the frequency of synoptic types in central-southern Chile in the period 1961–2012 using the Jenkinson and Collison synoptic classification

Atmospheric circulation patterns in southern Chile (42° 30′ S) were studied in order to determine and analyse the most characteristic synoptic types and their recent trends, as well as to gain an understanding of how they are associated with low-frequency variability patterns. According to the Jenkinson and Collison (J&C) classification method, a 16-point grid of sea-level pressure data was employed. The findings reveal that some synoptic types show statistically significant trends with a 95% confidence level, positively for anticyclonic westerly hybrids (AW) and advective types for third and fourth quadrant wind flows (W, NW, and N) and negatively for SW and cyclonic hybrids (CS and CSW). A model has been constructed of the linear regression of some weather types with teleconnections that most affect Chile: the undetermined types (U), AW were associated with El Niño or the warm phase of the Pacific Decadal Oscillation (PDO), whereas the cyclonic northerly and cyclonic northeasterly types (CN and CNE) were associated with La Niña or cool phase of the PDO. The weather types associated with Antarctic Oscillation (AAO) in its positive phase are anticyclonic northerly and northeasterly and northerly advection types, while in its negative phase are cyclonic southwesterly and advection types.     

Climate Suitability for Stable Malaria Transmission in Zimbabwe Under Different Climate Change Scenarios

Climate is one factor that determines the potential range of malaria. As such, climate change may work with or against efforts to bring malaria under control. We developed a model of future climate suitability for stable Plasmodium falciparum malaria transmission in Zimbabwe. Current climate suitability for stable malaria transmission was based on the MARA/ARMA model of climatic constraints on the survival and development of the Anopheles vector and the Plasmodium falciparum malaria parasite. We explored potential future geographic distributions of malaria using 16 projections of climate in 2100. The results suggest that, assuming no future human-imposed constraints on malaria transmission, changes in temperature and precipitation could alter the geographic distribution of malaria in Zimbabwe, with previously unsuitable areas of dense human population becoming suitable for transmission. Among all scenarios, the highlands become more suitable for transmission, while the lowveld and areas with low precipitation show varying degrees of change, depending on climate sensitivity and greenhouse gas emission stabilization scenarios, and depending on the general circulation model used. The methods employed can be used within or across other African countries.     

拟合水工设计反应谱的人工地震波的生成与Huang变换校正

根据非平稳输入下建立的功率谱与均值反应谱之间的关系,合成基于水工设计反应谱的人工地震波,并对其幅值进行修正,降低了高频区误差作用.为了解决加速度时程积分后的速度、位移时程的零线漂移现象,利用Huang变换得到加速度时程的固有模态函数,这种最低频率固有模态函数分量通常情况下代表原始信号的趋势或均值;再对去掉均值后的加速度时程进行积分,得到的速度、位移时程不存在零线漂移问题.