Quantitative Analysis of Experimental and Synthetic Microstructures for Sedimentary Rock

A quantitative comparison between the experimental microstructure of a sedimentary rock and three theoretical models for the same rock is presented. The microstructure of the rock sample (Fontainebleau sandstone) was obtained by microtomography. Two of the models are stochastic models based on correlation function reconstruction, and one model is based on sedimentation, compaction and diagenesis combined with input from petrographic analysis. The porosity of all models closely match that of the experimental sample and two models have also the same two point correlation function as the experimental sample. We compute quantitative differences and similarities between the various microstructures by a method based on local porosity theory. Differences are found in the degree of anisotropy, and in fluctuations of porosity and connectivity. The stochastic models differ strongly from the real sandstone in their connectivity properties, and hence need further refinement when used to model transport.Comment: to appear in Physica A (1999), in prin

Estimation of corrosion resistance of curing mixtures based on coal-bearing rocks from Western Donbass

Purpose. Substantiation of possible use of coal-bearing rocks as a replacement for a part of the filler in the preparation of shotcrete for lining of mine workings in the conditions of mineralized mine water. Methods. The research is based on carrying out corrosion testing of concrete specimens by dipping them into mine water. Chemical analysis of mine waters composition has been completed. A scanning microscope was used to study the state of concrete specimens microstructure. Findings. A comparative analysis was conducted to evaluate of the cement rock resistance to mineralized water, depending on the composition of the starting components for the grouting and shotcrete mixtures is carried out. The change in the chemical composition of mine water after soaking concrete specimens in it is defined. Photographs of concrete specimens microstructure after soaking in ordinary and mineralized water for 6 and 8 months are shown. Originality. Curing mixtures based on coal-bearing rocks from Western Donbass are mineralized water resistant and can act as a quality protection from aggressive water filtrationdue to the properties of rocks used as a filler. Practical implications. The results can be used for the rational choice of the composition of the concrete mixture with the replacement of filler part with mine rock. That will enhance the long-term stability of the mine working lined by these compositions.Мета. Обґрунтування можливості використання вуглевміщуючих порід у якості заміни частини заповнювача в процесі приготування бетону для кріплення гірничих виробок в умовах мінералізованих шахтних вод. Методика. Робота базується на проведенні корозійних випробувань бетонних зразків шляхом занурення їх у шахтну воду. Виконано хімічний аналіз складу шахтних вод. Використаний растровий мікроскоп для дослідження стану мікроструктури бетонних зразків. Результати. Виконано порівняльний аналіз оцінки стійкості цементного каменю до впливу мінералізованої води залежно від складу вихідних компонентів для тампонажних, торкрет-бетонних і набризкбетонних сумішей. Визначено зміну хімічного складу шахтної води після витримки у ній бетонних зразків. Наведено фотографії мікроструктури бетонних зразків після витримки у нормальних умовах та мінералізованої води протягом 6 і 8 місяців. Наукова новизна. Твердіючі суміші на основі вуглевміщуючих порід Західного Донбасу достатньо стійкі до впливу мінералізованих вод та є якісною протифільтраційною завісою завдяки властивостям порід, використаних у якості заповнювача. Практична значимість. Отримані результати можуть бути використані для раціонального підбору складу бетонної суміші із заміною частини заповнювача шахтної породою, що дозволить підвищити тривалу стійкість гірничої виробки, закріпленої з використанням даних складів.Цель. Обоснование возможности использование углевмещающих пород в качестве замены части заполнителя в процессе приготовления бетона для крепления горных выработок в условиях минерализованных шахтных вод. Методика. Работа базируется на проведении коррозионных испытаний бетонных образцов путем погружения их в шахтную воду. Выполнен химический анализ состава шахтных вод. Использован растровый микроскоп для исследования состояния микроструктуры бетонных образцов. Результаты. Выполнен сравнительный анализ оценки устойчивости цементного камня к воздействию минерализованной воды в зависимости от состава исходных компонентов для тампонажных, торкрет-бетонных и набрызгбетонных смесей. Определено изменение химического состава шахтной воды после выдержки в ней бетонных образцов. Представлены фотографии микроструктуры бетонных образцов после выдержки в нормальных условиях и минерализованной воде в течение 6 и 8 месяцев. Научная новизна. Твердеющие смеси на основе углевмещающих пород Западного Донбасса устойчивы к влиянию минерализованных вод и являются качественной противофильтрационной завесой благодаря свойствам пород, использованных в качестве заполнителя. Практическая значимость. Полученные результаты могут быть использованы для рационального подбора состава бетонной смеси с заменой части заполнителя шахтной породой, что позволит повысить длительную устойчивость горной выработки, закрепленной с использованием данных составов.The authors express their gratitude to the administration of the Department of Construction, Geotechnics and Geomechanics of the National Mining University (Dnipropetrovsk, Ukraine), represented by O. Shashenko and A. Solodiankin, as well as to all those who helped in carrying out works related to preparation of this paper

Micro-dynamics of ice

No abstract available

Reactive infiltration instability amplifies the difference between geometric and reactive surface areas in natural porous materials

Reactive infiltration instability (RII) drives the development of many natural and engineered flow systems. These are encountered e.g. in hydraulic fracturing, geologic carbon storage and well stimulation in enhanced oil recovery. The surface area of the rocks changes as the pore structure evolves. We combined a reactor network model with grey scale tomography to seek the morphological interpretation for differences among geometric, reactive and apparent surface areas of dissolving natural porous materials. The approach allowed us to delineate the experimentally convoluted variables and study independently the effects of initial geometry and macroscopic flowrate. Simulations based on North Sea chalk microstructure showed that geometric surface not only serves as the interface for water-rock interactions but also represents the regional transport heterogeneities that can be amplified indefinitely by dissolutive percolation. Hence, RII leads to channelization of the solid matrix, which results in fluid focusing and an increase in geometric surface area. Fluid focusing reduces the reactive surface area and the residence time of reactants, both of which amplify the differences in question, i.e. they are self-supporting. Our results also suggested that the growing and merging of microchannels near the fluid entrance leads to the macroscopic "fast initial dissolution" of chemically homogeneous materials.Comment: 37 pages, 12 figure

Determining the unsaturated hydraulic conductivity of a compacted sand-bentonite mixture under constant volume and free-swell conditions

Highly compacted sand-bentonite mixtures are often considered as possible engineered barriers in deep high-level radioactive waste disposals. In-situ, the saturation of these barriers from their initially unsaturated state is a complex hydro-mechanical coupled process in which temperature effects also play a role. The key parameter of this process is the unsaturated hydraulic conductivity of the barrier. In this paper, isothermal infiltration experiments were conducted to determine the unsaturated hydraulic conductivity according to the instantaneous profile method. To do so, total suction changes were monitored at different locations along the soil specimen by using resistivity relative humidity probes. Three constant volume infiltration tests were conducted showing, unexpectedly, a decrease of the hydraulic conductivity during infiltration. One test performed under free-swell conditions showed the opposite and standard trend. These observations were interpreted in terms of microstructure changes during wetting, both under constant volume and free swell conditions

Wave propagation through alumina-porous alumina laminates

A Brazilian disk geometry of an alumina layered composite with alternating dense and porous layers was dynamically loaded using a Split-Hopkinson Pressure Bar (SHPB)apparatus under compression. High-speed imaging and transmitted force measurements were used to gain an insight into stress wave propagation and mitigation through such a layered system. Uniformly distributed porosities of 20 and 50 vol % were introduced into the interlayers by the addition of fine graphite particles which volatilized during heat treatment. Brazilian disk samples were cut from the cylinders which were drilled out of the sintered laminated sample. The disks were subjected to dynamic impact loading in perpendicular and parallel orientations to the layers in order to investigate the influence of the direction of impact. The dynamic failure process of the layered ceramic consisted of the initiation and propagation of the cracks mainly along the interphases of the layers. Upon impact, the impact energy was dissipated through fracture in parallel orientation (0 deg) but transmitted in perpendicular (90 deg) orientations. The high degree of correlation between the transmitted force, microstructure and orientation in which the layered systems were impacted is discussed.Comment: 39 pages, 14 figures, 2 tables. Accepted for publication in the Journal of the European Ceramic Societ