The increase to the proportion of fluxed pellets in the blast furnace burden is a useful way to reduce the carbon emissions in the ironmaking process.In this study,the interaction between calcium carbonate and iron or...The increase to the proportion of fluxed pellets in the blast furnace burden is a useful way to reduce the carbon emissions in the ironmaking process.In this study,the interaction between calcium carbonate and iron ore powder and the mineralization mechanism of fluxed iron ore pellet in the roasting process were investigated through diffusion couple experiments.Scanning electron microscopy with energy dispersive spectroscopy was used to study the elements’diffusion and phase transformation during the roasting process.The results indicated that limestone decomposed into calcium oxide,and magnetite was oxidized to hematite at the early stage of preheating.With the increase in roasting temperature,the diffusion rate of Fe and Ca was obviously accelerated,while the diffusion rate of Si was relatively slow.The order of magnitude of interdiffusion coefficient of Fe_(2)O_(3)-CaO diffusion couple was 10^(−10) m^(2)·s^(−1) at a roasting temperature of 1200℃for 9 h.Ca_(2)Fe_(2)O_(5) was the initial product in the Fe_(2)O_(3)-CaO-SiO_(2) diffusion interface,and then Ca_(2)Fe_(2)O_(5) continued to react with Fe_(2)O_(3) to form CaFe_(2)O_(4).With the expansion of the diffusion region,the sillico-ferrite of calcium liquid phase was produced due to the melting of SiO_(2) into CaFe_(2)O_(4),which can strengthen the consolidation of fluxed pellets.Furthermore,andradite would be formed around a small part of quartz particles,which is also conducive to the consolidation of fluxed pellets.In addition,the principle diagram of limestone and quartz diffusion reaction in the process of fluxed pellet roasting was discussed.展开更多
The hydrocarbon generation effectiveness of lacustrine limestone has been gradually proven. The Da'anzhai Member limestone is the most important Jurassic oil-producing layer in the central Sichuan Basin, and the c...The hydrocarbon generation effectiveness of lacustrine limestone has been gradually proven. The Da'anzhai Member limestone is the most important Jurassic oil-producing layer in the central Sichuan Basin, and the characteristics of limestone organic matter are often overlooked. 175 typical samples of different lithologies from 19 wells were systematically analyzed to determine hydrocarbon generation, controlling factors and formation models by analyses of organic matter, minerals, elements, isotopes and petrography. (1) Lacustrine paleoenvironments can be beneficial for the enrichment of organic matter in limestone. A favorable environment would be a quiet, low-energy zone in a warm and humid climate with an appropriate supply of terrestrial inputs. (2) Lacustrine limestone has a higher organic matter conversion rate, and a lower hydrocarbon generation threshold than argillaceous source rocks, and can be effective source rock. (3) The mud-bearing shell limestone from the forebeach to the lake slope is thick, with a relatively high abundance of organic matter, and its hydrocarbon generation is effective. This study can clarify the effectiveness and enrichment of the limestone organic matters in the study area, and contribute to an understanding of hydrocarbon generation for full-rock system in a lacustrine mixed sedimentary environment.展开更多
Aptian is characterized by widespread deposition of organic-rich sediment.The Aptian bitumen limestone horizon,which is thin decimetre-thick sequences,locally crops out in the Kircaova area,Eastern Black Sea Region(Ea...Aptian is characterized by widespread deposition of organic-rich sediment.The Aptian bitumen limestone horizon,which is thin decimetre-thick sequences,locally crops out in the Kircaova area,Eastern Black Sea Region(Eastern Pontides).They are well correlated with Aptian bitumen limestone in the other Tethys Reams.They are proposed as episodes of increased organic matter.However,background factors controlling organic matter enrichment are poorly known.In this study,we present new inorganic geochemistry,including trace elements,rare earth elements(REE),redox-sensitive elements(RSE),stable-isotopes(δ~(18)O andδ~(13)C),and total organic carbon(TOC).We integrated new geochemical data with existing stratigraphy,paleontology,and organic chemistry data to provide new insight into the depositional environment and paleoclimate conditions during Aptian.The lacustrine bitumen limestone(LBL)samples have variedδ~(13)C(ave.-1.45‰)andδ~(18)O(ave.-4.50‰).They possess distinct REE patterns,with an average of REE(ave.14.45 ppm)and Y/Ho(ave.35)ratios.In addition,they have variable Nd/YbN(0.28-0.81;ave.0.56)and Ce/Ce*(0.68-0.97;ave.0.86),and relatively high Eu^(*)/Eu(1.23-1.53;ave.1.35).They display seawater signatures with reduced oxygen conditions.The enrichment in RSE(Mo,Cu,Ni,and Zn)and the low Mo/TOC(0.70-3.69;ave.2.41)support a certain degree of water restriction.The high Sr/Ba,Sr/Cu,Ga/Rb,and K/Al records of the LBL facies suggest hot house climatic conditions.The sedimentary environment was probably an isolated basin that is transformed from the marine basin.In addition to depositional conditions,the regional parameters such as the climate,increased run-off period,nutrient levels,alkalinity level,and dominant carbonate producers favored the enrichment in organic matter of LBL facies.Thus,extreme greenhouse palaeoclimate conditions have an important role in organic matter enrichment in the isolated basin.Our results are conformable with the published data from marine,semi-restricted basin,and lacustrine settings in the different parts of the Tethys margin.Thus,this approach provides the first insight into the Aptian greenhouse paleo-climate conditions of the Eastern Black Sea Region,NE Turkey.展开更多
Vertical orthogonal joints are a common feature in shallow crustal rocks.There are several competing theories for their formation despite the ubiquity.We examined the exceptional exposures of orthogonal joints in flat...Vertical orthogonal joints are a common feature in shallow crustal rocks.There are several competing theories for their formation despite the ubiquity.We examined the exceptional exposures of orthogonal joints in flat-lying Ordovician limestone beds from the Havre-Saint-Pierre Region in Quebec,Canada(north shore of Saint-Lawrence River)to test conceptual models of joint formation in a natural setting.In the region,the spacing of cross-joints is consistently larger than the spacing of systematic joints by a factor of 1.5 approximately.The joint-spacing-to-bed-thickness ratios(s/t)are much larger in these beds(s/t=4.3 for systematic joints,and 6.4 for cross-joints)than those in higher strained strata along the south shore of the Saint-Lawrence River(s/t=1),highlighting the effect of tectonic strain in decreasing fracture spacing and block size.The high values of s/t indicate that cross-joint formation was unlikely caused by a switch from compression to tension once a critical s/t ratio for systematic joints was reached(as hypothesized in previous studies).We proposed a new model for the formation of orthogonal joint systems where the principal stress axes locally switch during the formation of systematic fractures.The presence of ladder-shaped orthogonal joints suggests a state of effective stress withσ_(1)^(∗)≫0>σ_(2)^(∗)>σ_(3)^(∗)and whereσ_(2)^(∗)-σ_(3)^(∗)is within the range of fracture strength variability at the time of fracture.This research provides a new mechanical model for the formation of orthogonal joint systems and cuboidal blocks.展开更多
Compared with the control sample without limestone powder(LP), the mechanical properties of the sample with 30% LP can be significantly improved by using a small amount of water reducer to reduce the water-cement rati...Compared with the control sample without limestone powder(LP), the mechanical properties of the sample with 30% LP can be significantly improved by using a small amount of water reducer to reduce the water-cement ratio, without significantly affecting the fluidity of the fresh mixture and increasing the economic cost. In addition, compared with the sole addition of limestone powder, dual addition of metakaolin and limestone powder can effectively improve the strengths. The reason of this phenomenon was investigated by means of XRD, TG-DTG, SEM, LF-NMR and isothermal calorimetry, etc. The reactive aluminum-rich phases in metakaolin react with limestone powder in the hydration process, and the formed calcium carboaluminate reduces the porosity and makes the hardened paste denser. The addition of ground granulated blast furnace slag can also improve the strength of the specimen added with limestone powder, whereas, the effect is inferior to that of metakaolin, for the ground granulated blast furnace slag contains less reactive aluminate phases, and accordingly, the amount of calcium carboaluminate generated is lower than that of metakaolin.展开更多
Reef limestone is a biogenic sedimentary rock widely distributed in coral reef areas, acting as an important foundation for coast construction. Due to its special biogenic origin, reef limestone is different from conv...Reef limestone is a biogenic sedimentary rock widely distributed in coral reef areas, acting as an important foundation for coast construction. Due to its special biogenic origin, reef limestone is different from conventional rocks both in terms of rock structure and mechanical properties. In this study, mesoscale uniaxial compression experiments with five different loading directions were conducted on two kinds of reef limestones from the Maldives Islands and the South China Sea, respectively. The real-time high-resolution videos and images of failure processes were recorded simultaneously to investigate the fracture evolution and fracture surface roughness of reef limestones. It demonstrated that the reef limestones belonged to extremely soft to soft rocks, and their uniaxial compressive strength (UCS) values fluctuated with high discreteness. The mesoscale mechanical properties of reef limestones were highly anisotropic and mainly controlled by pore structure. The occurrence of dissolution pores in reef limestone tended to intensify mechanical anisotropy. With the integration of the fracture initiation and propagation features of reef limestones, it is supposed that the intrinsic mechanism of anisotropy was probably attributed to the differences in coral growth direction and dissolution. Furthermore, the quantified fracture surface roughness was revealed to have a good consistency with density and UCS for the reef limestones from the South China Sea. The findings are helpful for providing theoretical and experimental references for engineering construction in coral reef areas.展开更多
The problem of low disposal and utilization rate of bulk industrial solid waste needs to be solved.In this paper,a high-activity admixture composed of steel slag-phosphate slag-limestone powder was proposed for most o...The problem of low disposal and utilization rate of bulk industrial solid waste needs to be solved.In this paper,a high-activity admixture composed of steel slag-phosphate slag-limestone powder was proposed for most of the solid waste with low activity and a negative impact on concrete workability,combining the characteristics of each solid waste.The paper demonstrates the feasibility and explains the principle of the composite system in terms of water requirement of standard consistency,setting time,workability,and mechanical properties,combined with the composition of the phases,hydration temperature,and microscopic morphology.The results showed that the steel slag:phosphate slag:limestone=5:2:3 gave the highest activity of the composite system,over 92%.Besides,the composite system had no significant effect on water demand and setting time compared to cement,and it could significantly increase the 7 and 28 d activity of the system.The composite system delayed the exothermic hydration of the cement and reduced the exothermic heat but had no effect on the hydration products.Therefore,the research in this paper dramatically improved the solid waste dissipation in concrete,reduced the amount of cement in concrete and positively responded to the national slogan of carbon neutral and peaking.展开更多
Ordinary Portland Cement (OPC) is by mass the largest manufactured product on Earth, responsible for approximately 6% - 8% of global anthropogenic carbon dioxide emissions (CO<sub>2</sub>) and 35% of indus...Ordinary Portland Cement (OPC) is by mass the largest manufactured product on Earth, responsible for approximately 6% - 8% of global anthropogenic carbon dioxide emissions (CO<sub>2</sub>) and 35% of industrial CO<sub>2</sub> emissions. On average 0.8 to 0.9 ton of CO<sub>2</sub> is emitted to produce one ton of OPC. In this paper, partial substitution of clinker (30% - 35%) by the calcined clay-limestone mixture was investigated in order to produce an eco-cement (LC3). Analyzes by XRF, XRD and ATG/ATD have characterized different components, determined the calcination temperature and selected the right clay which can act as effective Supplementary Cementitious Material (SCM). Mechanical tests on mortar carried out over a period of 90 days. The WBCSD/WRI “Greenhouse Gas Protocol” methodology then allowed the calculation of CO<sub>2</sub> emissions into the atmosphere. Three types of clay are available in the Songololo Region. The kaolinite is the principal clay mineral and its content varies from 27% to 34%. The sum of kaolinite and amorphous phase which enable clay to react with cementitious material ranges from 57% to 60%. The SiO<sub>2</sub> content ranges from 33% to 76%, the Alumina content from 12% to 20% so that the ratio Al<sub>2</sub>O<sub>3</sub>/SiO<sub>2</sub> is on the higher side (0.17 - 0.53). The calcination window is between 750°C and 850°C and the best clay which can act as SCM identified. The clinker’s substitution reduced CO<sub>2</sub> emissions from 0.824 ton of CO<sub>2</sub> for one ton of OPC to 0.640 ton of CO<sub>2</sub> for one ton of LC3, means 22% less emissions. The compressive strengths developed by LC3 vary from 8.91 to 57.6 MPa (Day 1 to Day 90), exceed those of references 32.5 cement and are close to 42.5 cement. In view of the results, LC3 cement can be considered for industrial trials.展开更多
Limestones of different facies in the Senegal basin are most commonly used as aggregates, regardless of their petrographic properties. These differences may influence their behaviour. The aim of this paper is to study...Limestones of different facies in the Senegal basin are most commonly used as aggregates, regardless of their petrographic properties. These differences may influence their behaviour. The aim of this paper is to study the stratigraphy and characterise the limestones of the Bandia and Popenguine quarries. Sampling and geochemical and geotechnical characterisation were carried out on these limestones. The results show the presence of several very different facies in the Paleocene formation. The geochemical study shows that the Bandia limestones (Bd2) have the highest CaCO<sub>3</sub> percentages (98.54%) and the highest SiO<sub>2</sub> percentages were recorded in the Popenguine limestones (Pop2). The study also gives MDE values of 22.38 and LA of 22, which are acceptable for use in road construction. It is important to carry out a complete study in order to select the right materials for optimal use.展开更多
Low grade dumped limestone sample having high silica of 8.1%, 36.8% CaO, and 3% Al2O3 has been studied with the aim to reduce the silica level to below 3% for its utilization in iron making. Beneficiation study of the...Low grade dumped limestone sample having high silica of 8.1%, 36.8% CaO, and 3% Al2O3 has been studied with the aim to reduce the silica level to below 3% for its utilization in iron making. Beneficiation study of the sample was initiated with desliming of the feed sample of -100 μm to remove the siliceous ultrafine particles and to improve the feed quality. Flotation study was carried out by column flotation technique varying the collector dosage, superficial air flow velocity and froth depth to assess their effect on silica reduction and CaO recovery. It was observed that increased collector dosage and superficial air velocity increases the recovery of CaO, and increase in the froth depth reduces the mass flow and silica content in the concentrate. The best result was found at 1.25 cm/sec superficial air velocity, 25 cm froth depth, 1.25 kgpt collector dosage and concentrate assayed 47.3% CaO, 2.8% silica with 72% CaO recovery.展开更多
The management of overburden is an important task in open pit exploitations. Site topography and morphology as well as geological and geotechnical properties of natural and remoulded materials are the most important f...The management of overburden is an important task in open pit exploitations. Site topography and morphology as well as geological and geotechnical properties of natural and remoulded materials are the most important factors affecting the disposal phase. Economic and environmental requirements must be followed in order to achieve the best reclamation results, keeping into account site constraints such as slope stability, hauling and dumping issues, and interactions with groundwater. This paper deals with the above mentioned issues, illustrating a rational approach applied on the case of a large limestone quarry where the thickness of the overburden is relevant and the spoil material has to be dumped in a flooded pit. The proposed multidisciplinary approach led to the selection of most suitable methods for excavation, transportation and disposal. The selection was based on a detailed laboratory and site characterisation that defined favorable and adverse factors to be considered during the preliminary study of a large quarrying project.展开更多
The development of a multiple level underground mine is a complex task in which geology,engineering,ground control,and unit operations are integrated into a single mine design.The components are interdependent and mus...The development of a multiple level underground mine is a complex task in which geology,engineering,ground control,and unit operations are integrated into a single mine design.The components are interdependent and must function cohesively to ensure a profitable underground mining operation.To optimize reserve recovery,mine planning should begin from the lowest level and progress up.This limits any misjudgments or oversights of a given level affecting the underlying levels and ensures the ability to maximize recovery from each level.Mine planning should start with the exploration and characterization of the geologic setting.Once the reserve geology and quality is well understood,then mine planning can begin with respect to the following:(1)orientation of mine works with respect to horizontal stress;(2)access to the reserve;(3)determination of opening widths;(4)selection of back,floor horizons and pillar centers;(5)selection of development and secondary mining heights;(6)appropriate inter-burden thicknesses;and(7)examining the stability of the multiple level mine through numerical modeling.The multiple level mine design process and decisions are presented through a case history example.The theme is that there is one opportunity to"get it right"and many chances to overlook a small aspect within the design that will plague the mine throughout all levels and through the entirety of its operating life.展开更多
This paper outlines the results of experimental study of the dynamic rock failure based on the comparison of dry and saturated limestone samples obtained during the dynamic compression and split tests. The tests were ...This paper outlines the results of experimental study of the dynamic rock failure based on the comparison of dry and saturated limestone samples obtained during the dynamic compression and split tests. The tests were performed using the Kolsky method and its modifications for dynamic splitting. The mechanical data(e.g. strength, time and energy characteristics) of this material at high strain rates are obtained. It is shown that these characteristics are sensitive to the strain rate. A unified interpretation of these rate effects, based on the structuraletemporal approach, is hereby presented. It is demonstrated that the temporal dependence of the dynamic compressive and split tensile strengths of dry and saturated limestone samples can be predicted by the incubation time criterion. Previously discovered possibilities to optimize(minimize) the energy input for the failure process is discussed in connection with industrial rock failure processes. It is shown that the optimal energy input value associated with critical load, which is required to initialize failure in the rock media, strongly depends on the incubation time and the impact duration. The optimal load shapes, which minimize the momentum for a single failure impact, are demonstrated. Through this investigation, a possible approach to reduce the specific energy required for rock cutting by means of high-frequency vibrations is also discussed.展开更多
Carbonate precipitation and hydrothermal reaction are the two major processes that remove Mg from seawater.Mg isotopes are significantly(up to 5%)fractionated during carbonate precipitation by preferential incorporati...Carbonate precipitation and hydrothermal reaction are the two major processes that remove Mg from seawater.Mg isotopes are significantly(up to 5%)fractionated during carbonate precipitation by preferential incorporation of ^(24)Mg,while hydrothermal reactions are associated with negligible Mg isotope fractionation by preferential sequestration of^( 26)Mg.Thus,the marine Mg cycle could be reflected by seawater Mg isotopic composition(δ^(26)Mg_(sw)),which might be recorded in marine carbonate.However,carbonates are both texturally and compositionally heterogeneous,and it is unclear which carbonate component is the most reliable for reconstructing δ^(26)Mg_(sw).In this study,we measured Mg isotopic compositions of limestone samples collected from the early Carboniferous Huangjin Formation in South China.Based on petrographic studies,four carbonate components were recognized:micrite,marine cement,brachiopod shell,and mixture.The four components had distinct δ^(26)Mg:(1)micrite samples ranged from -2.86% to -2.97%;(2)pure marine cements varied from -3.40% to -3.54%,while impure cement samples containing small amount of Rugosa coral skeletons showed a wider range(-3.27% to-3.75%);(3)values for the mixture component were-3.17% and -3.49%;and (4)brachiopod shells ranged from -2.20% to -3.07%,with the thickened hinge area enriched in ^( 24)Mg.Due to having multiple carbonate sources,neither the micrite nor the mixture component could be used to reconstruct δ^(26)Mg_(sw).In addition,the marine cement was homogenous in Mg isotopes,but lacking the fractionation by inorganic carbonate precipitation that is prerequisite for the accurate determination of δ^(26)Mg_(sw).Furthermore,brachiopod shells had heterogeneous C and Mg isotopes,suggesting a significant vital effect during growth.Overall,the heterogeneous δ^(26)Mg of the Huangjin limestone makes it difficult to reconstruct δ^(26)Mg_(sw)using bulk carbonate/calcareous sediments.Finally,δ^(26)Mg_(sw)was only slightly affected by the faunal composition of carbonate-secreting organisms,even though biogenic carbonate accounts for more than 90% of marine carbonate production in Phanerozoic oceans and there is a wide range(0.2%–4.8%)of fractionation during biogenic carbonate formation.展开更多
This research aimed to investigate the changing mechanism of hydro-geochemistry in Ordovician limestone karst(OL) water induced by mountainous coal mining activities. Thus, the hydrogeochemistry evolution of OL water ...This research aimed to investigate the changing mechanism of hydro-geochemistry in Ordovician limestone karst(OL) water induced by mountainous coal mining activities. Thus, the hydrogeochemistry evolution of OL water over 40 years within a typical northern mountainous coal mine named Fengfeng Mine was studied by using Piper diagram, Gibbs scheme, ions correlation and Principal component analysis(PCA) methods. Results showed that, except for HCO3^-, the ions of Ca^2+, Mg^2+, SO4^2-,Na^++K^+, Cl^- and total dissolution solids(TDS) values all increased by years as mining continues. Different hydro-geochemical characteristics in different periods can reflect different water-rock interactions.Accordingly, sulfates dissolution gradually took place of carbonates in water-rock interaction. Especially,OL water-rock interactions in different periods were all affected by rock weathering and evaporationconcentration together. At last, evaporationconcentration co-effect dominated the hydrogeochemistry evolution slowly, along with significant cations exchange over years.展开更多
Nonlinear model predictive control(NMPC)scheme is an effective method of multi-objective optimization control in complex industrial systems.In this paper,a NMPC scheme for the wet limestone flue gas desulphurization(W...Nonlinear model predictive control(NMPC)scheme is an effective method of multi-objective optimization control in complex industrial systems.In this paper,a NMPC scheme for the wet limestone flue gas desulphurization(WFGD)system is proposed which provides a more flexible framework of optimal control and decision-making compared with PID scheme.At first,a mathematical model of the FGD process is deduced which is suitable for NMPC structure.To equipoise the model’s accuracy and conciseness,the wet limestone FGD system is separated into several modules.Based on the conservation laws,a model with reasonable simplification is developed to describe dynamics of different modules for the purpose of controller design.Then,by addressing economic objectives directly into the NMPC scheme,the NMPC controller can minimize economic cost and track the set-point simultaneously.The accuracy of model is validated by the field data of a 1000 MW thermal power plant in Henan Province,China.The simulation results show that the NMPC strategy improves the economic performance and ensures the emission requirement at the same time.In the meantime,the control scheme satisfies the multiobjective control requirements under complex operation conditions(e.g.,boiler load fluctuation and set point variation).The mathematical model and NMPC structure provides the basic work for the future development of advanced optimized control algorithms in the wet limestone FGD systems.展开更多
Three dimensional (3D) microscopic distributions of dolomite and calcite in a limestone sample have been analyzed with a data-constrained modeling (DCM) technique using synchrotron radiation-based multi-energy X-ray c...Three dimensional (3D) microscopic distributions of dolomite and calcite in a limestone sample have been analyzed with a data-constrained modeling (DCM) technique using synchrotron radiation-based multi-energy X-ray computed tomography (CT) data as constraints. In order to optimize the experimental parameters, X-ray CT simulations and DCM analysis of a numerical phantom consisting of calcite (CaCO3) and dolomite (CaMg(CO3)2) have been used to investigate the effects on the predicted results in relation to noise, X-ray energy and sample-to-detector distance (SDD). The simulation results indicate that the optimal X-ray energies are 25 and 35 keVs, and the SDD is 10 mm. The high resolution 3D distributions of mineral phases of a natural limestone have been obtained. The results are useful for quantitative understanding of mineral, porosity, and physical property distributions in relation to oil and gas reservoirs hosted in carbonate rocks, which account for more than half of the world’s conventional hydrocarbon resources. The case studied is also instructive for the applicability of the DCM methods for other types of composite materials with modest atomic number contrasts between the mineral phases.展开更多
The systematic experiment regarding the general uniaxial compression test and the creep deformations of the typical limestones from the surrounding rock of the highway tunnels were made.The relationship between the ax...The systematic experiment regarding the general uniaxial compression test and the creep deformations of the typical limestones from the surrounding rock of the highway tunnels were made.The relationship between the axial stress and the delayed deformation steady value was obtained from the creep tests under low loading stresses.By the least square method,the parameters of Nishihara creep model were calculated from the creep curves.The results indicate that the strain change always lags behind the increase of stress,and the long-term strength of the limestone is about 80.6% of the stress at the volumetric strain reversal which is obtained from the conventional uniaxial compression test.展开更多
Mortar prisms were made with three different cementitious materials (with or without mineral admixture) plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, the mortars were submerg...Mortar prisms were made with three different cementitious materials (with or without mineral admixture) plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, the mortars were submerged in 2% magnesium sulfate solution at different temperatures (5 ℃, 20 ℃ and alternate temperature between 5 ℃ and 20 ℃) for a year. The appearance and strength development were measured on these immersed prisms at intervals, and samples selected from the surface of prisms were examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results show that the influence of temperature on the resistance to sulfate attack of mortar is related to the binder compositions. A higher temperature leads to a quicker strength loss and appearance deterioration of the mortar without mineral admixture. For blended cements, a higher temperature is favorable for the pozzolanic reaction of mineral admixture and the overall deterioration of mortar is reduced with the increasing temperature. When the mineral admixture has a lower reactivity, such influence of temperature on the resistance to sulfate attack of mortar containing admixtures becomes greater. At the three different solution temperatures, two blended cements show significantly improved resistances to sulfate attack. After 1 year of exposure to magnesium sulfate solutions, the formation of thaumasite was checked in the OPC mortars at both 5 ℃ and 20 ℃. It is concluded that the thaumasite formation is not limited to structures at low temperature (less than 15 ℃).展开更多
The Canadian Nuclear Safety Commission(CNSC), Canada's nuclear regulator, conducts regulatory research in order to develop independent knowledge on safety aspects related to the deep geological disposal of radioac...The Canadian Nuclear Safety Commission(CNSC), Canada's nuclear regulator, conducts regulatory research in order to develop independent knowledge on safety aspects related to the deep geological disposal of radioactive wastes. In Canada, the Cobourg limestone of the Michigan Basin is currently considered as a potential host formation for geological disposal. The understanding of the hydromechanical behavior of such a host rock is one of the essential requirements for the assessment of its performance as a barrier against radionuclide migration. The excavation of galleries and shafts of a deep geological repository(DGR) can induce damage to the surrounding rock. The excavation damaged zone(EDZ) has higher permeability and reduced strength compared to the undisturbed rock and those factors must be considered in the design and safety assessment of the DGR. The extent and characteristics of the EDZ depend on the size of the opening, the rock type and its properties, and the in situ stresses, among other factors. In addition, the extent and characteristics of the EDZ can change with time due to rock strength degradation, evolution of fractures within the EDZ, and the redistribution of pore pressure around the excavation. In this research project initiated by the CNSC, the authors conducted experimental and theoretical research in order to assess the hydro-mechanical behavior of the Cobourg limestone under undamaged and damaged conditions, both in the short and long terms. The short-term behavior was investigated by a program of triaxial tests with the measurement of permeability evolution on specimens of Cobourg limestone. The authors formulate a coupled hydro-mechanical model to simulate the stress-strain response and evolution of the permeability during those triaxial tests. Using creep and relaxation data from a similar limestone, the model was extended to include its long-term strength degradation. The model successfully simulated both the short-and long-term hydro-mechanical behavior of the limestone during those tests. This provides confidence that the main physical processes have been adequately understood and formulated.展开更多
基金support of Shanxi Province Major Science and Technology Projects,China (No.20191101002).
文摘The increase to the proportion of fluxed pellets in the blast furnace burden is a useful way to reduce the carbon emissions in the ironmaking process.In this study,the interaction between calcium carbonate and iron ore powder and the mineralization mechanism of fluxed iron ore pellet in the roasting process were investigated through diffusion couple experiments.Scanning electron microscopy with energy dispersive spectroscopy was used to study the elements’diffusion and phase transformation during the roasting process.The results indicated that limestone decomposed into calcium oxide,and magnetite was oxidized to hematite at the early stage of preheating.With the increase in roasting temperature,the diffusion rate of Fe and Ca was obviously accelerated,while the diffusion rate of Si was relatively slow.The order of magnitude of interdiffusion coefficient of Fe_(2)O_(3)-CaO diffusion couple was 10^(−10) m^(2)·s^(−1) at a roasting temperature of 1200℃for 9 h.Ca_(2)Fe_(2)O_(5) was the initial product in the Fe_(2)O_(3)-CaO-SiO_(2) diffusion interface,and then Ca_(2)Fe_(2)O_(5) continued to react with Fe_(2)O_(3) to form CaFe_(2)O_(4).With the expansion of the diffusion region,the sillico-ferrite of calcium liquid phase was produced due to the melting of SiO_(2) into CaFe_(2)O_(4),which can strengthen the consolidation of fluxed pellets.Furthermore,andradite would be formed around a small part of quartz particles,which is also conducive to the consolidation of fluxed pellets.In addition,the principle diagram of limestone and quartz diffusion reaction in the process of fluxed pellet roasting was discussed.
基金supported by the National Natural Science Foundation of China(Grants 41902131 and 41821002 and 4169130014).
文摘The hydrocarbon generation effectiveness of lacustrine limestone has been gradually proven. The Da'anzhai Member limestone is the most important Jurassic oil-producing layer in the central Sichuan Basin, and the characteristics of limestone organic matter are often overlooked. 175 typical samples of different lithologies from 19 wells were systematically analyzed to determine hydrocarbon generation, controlling factors and formation models by analyses of organic matter, minerals, elements, isotopes and petrography. (1) Lacustrine paleoenvironments can be beneficial for the enrichment of organic matter in limestone. A favorable environment would be a quiet, low-energy zone in a warm and humid climate with an appropriate supply of terrestrial inputs. (2) Lacustrine limestone has a higher organic matter conversion rate, and a lower hydrocarbon generation threshold than argillaceous source rocks, and can be effective source rock. (3) The mud-bearing shell limestone from the forebeach to the lake slope is thick, with a relatively high abundance of organic matter, and its hydrocarbon generation is effective. This study can clarify the effectiveness and enrichment of the limestone organic matters in the study area, and contribute to an understanding of hydrocarbon generation for full-rock system in a lacustrine mixed sedimentary environment.
文摘Aptian is characterized by widespread deposition of organic-rich sediment.The Aptian bitumen limestone horizon,which is thin decimetre-thick sequences,locally crops out in the Kircaova area,Eastern Black Sea Region(Eastern Pontides).They are well correlated with Aptian bitumen limestone in the other Tethys Reams.They are proposed as episodes of increased organic matter.However,background factors controlling organic matter enrichment are poorly known.In this study,we present new inorganic geochemistry,including trace elements,rare earth elements(REE),redox-sensitive elements(RSE),stable-isotopes(δ~(18)O andδ~(13)C),and total organic carbon(TOC).We integrated new geochemical data with existing stratigraphy,paleontology,and organic chemistry data to provide new insight into the depositional environment and paleoclimate conditions during Aptian.The lacustrine bitumen limestone(LBL)samples have variedδ~(13)C(ave.-1.45‰)andδ~(18)O(ave.-4.50‰).They possess distinct REE patterns,with an average of REE(ave.14.45 ppm)and Y/Ho(ave.35)ratios.In addition,they have variable Nd/YbN(0.28-0.81;ave.0.56)and Ce/Ce*(0.68-0.97;ave.0.86),and relatively high Eu^(*)/Eu(1.23-1.53;ave.1.35).They display seawater signatures with reduced oxygen conditions.The enrichment in RSE(Mo,Cu,Ni,and Zn)and the low Mo/TOC(0.70-3.69;ave.2.41)support a certain degree of water restriction.The high Sr/Ba,Sr/Cu,Ga/Rb,and K/Al records of the LBL facies suggest hot house climatic conditions.The sedimentary environment was probably an isolated basin that is transformed from the marine basin.In addition to depositional conditions,the regional parameters such as the climate,increased run-off period,nutrient levels,alkalinity level,and dominant carbonate producers favored the enrichment in organic matter of LBL facies.Thus,extreme greenhouse palaeoclimate conditions have an important role in organic matter enrichment in the isolated basin.Our results are conformable with the published data from marine,semi-restricted basin,and lacustrine settings in the different parts of the Tethys margin.Thus,this approach provides the first insight into the Aptian greenhouse paleo-climate conditions of the Eastern Black Sea Region,NE Turkey.
基金The authors express their gratitude to the Natural Sciences and Engineering Research Council of Canada for financial support through a Discovery Grant(Grant No.06408).
文摘Vertical orthogonal joints are a common feature in shallow crustal rocks.There are several competing theories for their formation despite the ubiquity.We examined the exceptional exposures of orthogonal joints in flat-lying Ordovician limestone beds from the Havre-Saint-Pierre Region in Quebec,Canada(north shore of Saint-Lawrence River)to test conceptual models of joint formation in a natural setting.In the region,the spacing of cross-joints is consistently larger than the spacing of systematic joints by a factor of 1.5 approximately.The joint-spacing-to-bed-thickness ratios(s/t)are much larger in these beds(s/t=4.3 for systematic joints,and 6.4 for cross-joints)than those in higher strained strata along the south shore of the Saint-Lawrence River(s/t=1),highlighting the effect of tectonic strain in decreasing fracture spacing and block size.The high values of s/t indicate that cross-joint formation was unlikely caused by a switch from compression to tension once a critical s/t ratio for systematic joints was reached(as hypothesized in previous studies).We proposed a new model for the formation of orthogonal joint systems where the principal stress axes locally switch during the formation of systematic fractures.The presence of ladder-shaped orthogonal joints suggests a state of effective stress withσ_(1)^(∗)≫0>σ_(2)^(∗)>σ_(3)^(∗)and whereσ_(2)^(∗)-σ_(3)^(∗)is within the range of fracture strength variability at the time of fracture.This research provides a new mechanical model for the formation of orthogonal joint systems and cuboidal blocks.
基金Funded by the National Natural Science Foundation of China (Nos.51972249, 52172026, 51772226)。
文摘Compared with the control sample without limestone powder(LP), the mechanical properties of the sample with 30% LP can be significantly improved by using a small amount of water reducer to reduce the water-cement ratio, without significantly affecting the fluidity of the fresh mixture and increasing the economic cost. In addition, compared with the sole addition of limestone powder, dual addition of metakaolin and limestone powder can effectively improve the strengths. The reason of this phenomenon was investigated by means of XRD, TG-DTG, SEM, LF-NMR and isothermal calorimetry, etc. The reactive aluminum-rich phases in metakaolin react with limestone powder in the hydration process, and the formed calcium carboaluminate reduces the porosity and makes the hardened paste denser. The addition of ground granulated blast furnace slag can also improve the strength of the specimen added with limestone powder, whereas, the effect is inferior to that of metakaolin, for the ground granulated blast furnace slag contains less reactive aluminate phases, and accordingly, the amount of calcium carboaluminate generated is lower than that of metakaolin.
基金supported by the National Natural Science Foundation of China(Grant Nos.41977248 and 42207219)the Key Research Program of the Institute of Geology and Geophysics,Chinese Academy of Sciences(CAS)(Grant No.IGGCAS-201903).
文摘Reef limestone is a biogenic sedimentary rock widely distributed in coral reef areas, acting as an important foundation for coast construction. Due to its special biogenic origin, reef limestone is different from conventional rocks both in terms of rock structure and mechanical properties. In this study, mesoscale uniaxial compression experiments with five different loading directions were conducted on two kinds of reef limestones from the Maldives Islands and the South China Sea, respectively. The real-time high-resolution videos and images of failure processes were recorded simultaneously to investigate the fracture evolution and fracture surface roughness of reef limestones. It demonstrated that the reef limestones belonged to extremely soft to soft rocks, and their uniaxial compressive strength (UCS) values fluctuated with high discreteness. The mesoscale mechanical properties of reef limestones were highly anisotropic and mainly controlled by pore structure. The occurrence of dissolution pores in reef limestone tended to intensify mechanical anisotropy. With the integration of the fracture initiation and propagation features of reef limestones, it is supposed that the intrinsic mechanism of anisotropy was probably attributed to the differences in coral growth direction and dissolution. Furthermore, the quantified fracture surface roughness was revealed to have a good consistency with density and UCS for the reef limestones from the South China Sea. The findings are helpful for providing theoretical and experimental references for engineering construction in coral reef areas.
基金Key Research and Development Plan of Shaanxi Province(2019TSLGY05-04).
文摘The problem of low disposal and utilization rate of bulk industrial solid waste needs to be solved.In this paper,a high-activity admixture composed of steel slag-phosphate slag-limestone powder was proposed for most of the solid waste with low activity and a negative impact on concrete workability,combining the characteristics of each solid waste.The paper demonstrates the feasibility and explains the principle of the composite system in terms of water requirement of standard consistency,setting time,workability,and mechanical properties,combined with the composition of the phases,hydration temperature,and microscopic morphology.The results showed that the steel slag:phosphate slag:limestone=5:2:3 gave the highest activity of the composite system,over 92%.Besides,the composite system had no significant effect on water demand and setting time compared to cement,and it could significantly increase the 7 and 28 d activity of the system.The composite system delayed the exothermic hydration of the cement and reduced the exothermic heat but had no effect on the hydration products.Therefore,the research in this paper dramatically improved the solid waste dissipation in concrete,reduced the amount of cement in concrete and positively responded to the national slogan of carbon neutral and peaking.
文摘Ordinary Portland Cement (OPC) is by mass the largest manufactured product on Earth, responsible for approximately 6% - 8% of global anthropogenic carbon dioxide emissions (CO<sub>2</sub>) and 35% of industrial CO<sub>2</sub> emissions. On average 0.8 to 0.9 ton of CO<sub>2</sub> is emitted to produce one ton of OPC. In this paper, partial substitution of clinker (30% - 35%) by the calcined clay-limestone mixture was investigated in order to produce an eco-cement (LC3). Analyzes by XRF, XRD and ATG/ATD have characterized different components, determined the calcination temperature and selected the right clay which can act as effective Supplementary Cementitious Material (SCM). Mechanical tests on mortar carried out over a period of 90 days. The WBCSD/WRI “Greenhouse Gas Protocol” methodology then allowed the calculation of CO<sub>2</sub> emissions into the atmosphere. Three types of clay are available in the Songololo Region. The kaolinite is the principal clay mineral and its content varies from 27% to 34%. The sum of kaolinite and amorphous phase which enable clay to react with cementitious material ranges from 57% to 60%. The SiO<sub>2</sub> content ranges from 33% to 76%, the Alumina content from 12% to 20% so that the ratio Al<sub>2</sub>O<sub>3</sub>/SiO<sub>2</sub> is on the higher side (0.17 - 0.53). The calcination window is between 750°C and 850°C and the best clay which can act as SCM identified. The clinker’s substitution reduced CO<sub>2</sub> emissions from 0.824 ton of CO<sub>2</sub> for one ton of OPC to 0.640 ton of CO<sub>2</sub> for one ton of LC3, means 22% less emissions. The compressive strengths developed by LC3 vary from 8.91 to 57.6 MPa (Day 1 to Day 90), exceed those of references 32.5 cement and are close to 42.5 cement. In view of the results, LC3 cement can be considered for industrial trials.
文摘Limestones of different facies in the Senegal basin are most commonly used as aggregates, regardless of their petrographic properties. These differences may influence their behaviour. The aim of this paper is to study the stratigraphy and characterise the limestones of the Bandia and Popenguine quarries. Sampling and geochemical and geotechnical characterisation were carried out on these limestones. The results show the presence of several very different facies in the Paleocene formation. The geochemical study shows that the Bandia limestones (Bd2) have the highest CaCO<sub>3</sub> percentages (98.54%) and the highest SiO<sub>2</sub> percentages were recorded in the Popenguine limestones (Pop2). The study also gives MDE values of 22.38 and LA of 22, which are acceptable for use in road construction. It is important to carry out a complete study in order to select the right materials for optimal use.
文摘Low grade dumped limestone sample having high silica of 8.1%, 36.8% CaO, and 3% Al2O3 has been studied with the aim to reduce the silica level to below 3% for its utilization in iron making. Beneficiation study of the sample was initiated with desliming of the feed sample of -100 μm to remove the siliceous ultrafine particles and to improve the feed quality. Flotation study was carried out by column flotation technique varying the collector dosage, superficial air flow velocity and froth depth to assess their effect on silica reduction and CaO recovery. It was observed that increased collector dosage and superficial air velocity increases the recovery of CaO, and increase in the froth depth reduces the mass flow and silica content in the concentrate. The best result was found at 1.25 cm/sec superficial air velocity, 25 cm froth depth, 1.25 kgpt collector dosage and concentrate assayed 47.3% CaO, 2.8% silica with 72% CaO recovery.
文摘The management of overburden is an important task in open pit exploitations. Site topography and morphology as well as geological and geotechnical properties of natural and remoulded materials are the most important factors affecting the disposal phase. Economic and environmental requirements must be followed in order to achieve the best reclamation results, keeping into account site constraints such as slope stability, hauling and dumping issues, and interactions with groundwater. This paper deals with the above mentioned issues, illustrating a rational approach applied on the case of a large limestone quarry where the thickness of the overburden is relevant and the spoil material has to be dumped in a flooded pit. The proposed multidisciplinary approach led to the selection of most suitable methods for excavation, transportation and disposal. The selection was based on a detailed laboratory and site characterisation that defined favorable and adverse factors to be considered during the preliminary study of a large quarrying project.
文摘The development of a multiple level underground mine is a complex task in which geology,engineering,ground control,and unit operations are integrated into a single mine design.The components are interdependent and must function cohesively to ensure a profitable underground mining operation.To optimize reserve recovery,mine planning should begin from the lowest level and progress up.This limits any misjudgments or oversights of a given level affecting the underlying levels and ensures the ability to maximize recovery from each level.Mine planning should start with the exploration and characterization of the geologic setting.Once the reserve geology and quality is well understood,then mine planning can begin with respect to the following:(1)orientation of mine works with respect to horizontal stress;(2)access to the reserve;(3)determination of opening widths;(4)selection of back,floor horizons and pillar centers;(5)selection of development and secondary mining heights;(6)appropriate inter-burden thicknesses;and(7)examining the stability of the multiple level mine through numerical modeling.The multiple level mine design process and decisions are presented through a case history example.The theme is that there is one opportunity to"get it right"and many chances to overlook a small aspect within the design that will plague the mine throughout all levels and through the entirety of its operating life.
基金supported by IHC Merwede B.V. as well as by Russian Foundation for Basic Research (Grant Nos. 13-0100349 and 14-01-31510)Russian Science Foundation (“support and development”, Grant No. 14-19-01637)Saint Petersburg University (Grant No. 6.38.243.2014)
文摘This paper outlines the results of experimental study of the dynamic rock failure based on the comparison of dry and saturated limestone samples obtained during the dynamic compression and split tests. The tests were performed using the Kolsky method and its modifications for dynamic splitting. The mechanical data(e.g. strength, time and energy characteristics) of this material at high strain rates are obtained. It is shown that these characteristics are sensitive to the strain rate. A unified interpretation of these rate effects, based on the structuraletemporal approach, is hereby presented. It is demonstrated that the temporal dependence of the dynamic compressive and split tensile strengths of dry and saturated limestone samples can be predicted by the incubation time criterion. Previously discovered possibilities to optimize(minimize) the energy input for the failure process is discussed in connection with industrial rock failure processes. It is shown that the optimal energy input value associated with critical load, which is required to initialize failure in the rock media, strongly depends on the incubation time and the impact duration. The optimal load shapes, which minimize the momentum for a single failure impact, are demonstrated. Through this investigation, a possible approach to reduce the specific energy required for rock cutting by means of high-frequency vibrations is also discussed.
基金supported by the Natural Science Foundation of China (41272017, 41322021, and 41172001)the China Postdoctoral Science Foundation (2014M55006)
文摘Carbonate precipitation and hydrothermal reaction are the two major processes that remove Mg from seawater.Mg isotopes are significantly(up to 5%)fractionated during carbonate precipitation by preferential incorporation of ^(24)Mg,while hydrothermal reactions are associated with negligible Mg isotope fractionation by preferential sequestration of^( 26)Mg.Thus,the marine Mg cycle could be reflected by seawater Mg isotopic composition(δ^(26)Mg_(sw)),which might be recorded in marine carbonate.However,carbonates are both texturally and compositionally heterogeneous,and it is unclear which carbonate component is the most reliable for reconstructing δ^(26)Mg_(sw).In this study,we measured Mg isotopic compositions of limestone samples collected from the early Carboniferous Huangjin Formation in South China.Based on petrographic studies,four carbonate components were recognized:micrite,marine cement,brachiopod shell,and mixture.The four components had distinct δ^(26)Mg:(1)micrite samples ranged from -2.86% to -2.97%;(2)pure marine cements varied from -3.40% to -3.54%,while impure cement samples containing small amount of Rugosa coral skeletons showed a wider range(-3.27% to-3.75%);(3)values for the mixture component were-3.17% and -3.49%;and (4)brachiopod shells ranged from -2.20% to -3.07%,with the thickened hinge area enriched in ^( 24)Mg.Due to having multiple carbonate sources,neither the micrite nor the mixture component could be used to reconstruct δ^(26)Mg_(sw).In addition,the marine cement was homogenous in Mg isotopes,but lacking the fractionation by inorganic carbonate precipitation that is prerequisite for the accurate determination of δ^(26)Mg_(sw).Furthermore,brachiopod shells had heterogeneous C and Mg isotopes,suggesting a significant vital effect during growth.Overall,the heterogeneous δ^(26)Mg of the Huangjin limestone makes it difficult to reconstruct δ^(26)Mg_(sw)using bulk carbonate/calcareous sediments.Finally,δ^(26)Mg_(sw)was only slightly affected by the faunal composition of carbonate-secreting organisms,even though biogenic carbonate accounts for more than 90% of marine carbonate production in Phanerozoic oceans and there is a wide range(0.2%–4.8%)of fractionation during biogenic carbonate formation.
基金Key Laboratory of Water Resource Protection and Utilization in Coal Mining(Grant No.SHJT-17-42.17)Fundamental Research Funds for the Central Universities of China(Grant Nos.3142018009,3142017100)Key Laboratory of Mine Geological Hazards Mechanism and Control Project(KF2017-13).Figure 7 PCA plot of hydro-chemistry of Ordovician limestone karst(OL)water samples from different years.
文摘This research aimed to investigate the changing mechanism of hydro-geochemistry in Ordovician limestone karst(OL) water induced by mountainous coal mining activities. Thus, the hydrogeochemistry evolution of OL water over 40 years within a typical northern mountainous coal mine named Fengfeng Mine was studied by using Piper diagram, Gibbs scheme, ions correlation and Principal component analysis(PCA) methods. Results showed that, except for HCO3^-, the ions of Ca^2+, Mg^2+, SO4^2-,Na^++K^+, Cl^- and total dissolution solids(TDS) values all increased by years as mining continues. Different hydro-geochemical characteristics in different periods can reflect different water-rock interactions.Accordingly, sulfates dissolution gradually took place of carbonates in water-rock interaction. Especially,OL water-rock interactions in different periods were all affected by rock weathering and evaporationconcentration together. At last, evaporationconcentration co-effect dominated the hydrogeochemistry evolution slowly, along with significant cations exchange over years.
基金Financial support from the National Key R&D Program of China(No.2017YFB0601805)。
文摘Nonlinear model predictive control(NMPC)scheme is an effective method of multi-objective optimization control in complex industrial systems.In this paper,a NMPC scheme for the wet limestone flue gas desulphurization(WFGD)system is proposed which provides a more flexible framework of optimal control and decision-making compared with PID scheme.At first,a mathematical model of the FGD process is deduced which is suitable for NMPC structure.To equipoise the model’s accuracy and conciseness,the wet limestone FGD system is separated into several modules.Based on the conservation laws,a model with reasonable simplification is developed to describe dynamics of different modules for the purpose of controller design.Then,by addressing economic objectives directly into the NMPC scheme,the NMPC controller can minimize economic cost and track the set-point simultaneously.The accuracy of model is validated by the field data of a 1000 MW thermal power plant in Henan Province,China.The simulation results show that the NMPC strategy improves the economic performance and ensures the emission requirement at the same time.In the meantime,the control scheme satisfies the multiobjective control requirements under complex operation conditions(e.g.,boiler load fluctuation and set point variation).The mathematical model and NMPC structure provides the basic work for the future development of advanced optimized control algorithms in the wet limestone FGD systems.
文摘Three dimensional (3D) microscopic distributions of dolomite and calcite in a limestone sample have been analyzed with a data-constrained modeling (DCM) technique using synchrotron radiation-based multi-energy X-ray computed tomography (CT) data as constraints. In order to optimize the experimental parameters, X-ray CT simulations and DCM analysis of a numerical phantom consisting of calcite (CaCO3) and dolomite (CaMg(CO3)2) have been used to investigate the effects on the predicted results in relation to noise, X-ray energy and sample-to-detector distance (SDD). The simulation results indicate that the optimal X-ray energies are 25 and 35 keVs, and the SDD is 10 mm. The high resolution 3D distributions of mineral phases of a natural limestone have been obtained. The results are useful for quantitative understanding of mineral, porosity, and physical property distributions in relation to oil and gas reservoirs hosted in carbonate rocks, which account for more than half of the world’s conventional hydrocarbon resources. The case studied is also instructive for the applicability of the DCM methods for other types of composite materials with modest atomic number contrasts between the mineral phases.
基金Project(50774090) supported by the National Natural Science Foundation of China
文摘The systematic experiment regarding the general uniaxial compression test and the creep deformations of the typical limestones from the surrounding rock of the highway tunnels were made.The relationship between the axial stress and the delayed deformation steady value was obtained from the creep tests under low loading stresses.By the least square method,the parameters of Nishihara creep model were calculated from the creep curves.The results indicate that the strain change always lags behind the increase of stress,and the long-term strength of the limestone is about 80.6% of the stress at the volumetric strain reversal which is obtained from the conventional uniaxial compression test.
基金Funded by the National Natural Science Foundation of China (No. 50408016) the "863" High-Tech Research and Development Program of China (No. 2005AA332010)
文摘Mortar prisms were made with three different cementitious materials (with or without mineral admixture) plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, the mortars were submerged in 2% magnesium sulfate solution at different temperatures (5 ℃, 20 ℃ and alternate temperature between 5 ℃ and 20 ℃) for a year. The appearance and strength development were measured on these immersed prisms at intervals, and samples selected from the surface of prisms were examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results show that the influence of temperature on the resistance to sulfate attack of mortar is related to the binder compositions. A higher temperature leads to a quicker strength loss and appearance deterioration of the mortar without mineral admixture. For blended cements, a higher temperature is favorable for the pozzolanic reaction of mineral admixture and the overall deterioration of mortar is reduced with the increasing temperature. When the mineral admixture has a lower reactivity, such influence of temperature on the resistance to sulfate attack of mortar containing admixtures becomes greater. At the three different solution temperatures, two blended cements show significantly improved resistances to sulfate attack. After 1 year of exposure to magnesium sulfate solutions, the formation of thaumasite was checked in the OPC mortars at both 5 ℃ and 20 ℃. It is concluded that the thaumasite formation is not limited to structures at low temperature (less than 15 ℃).
基金the Canadian Nuclear Safety Commission for funding this project
文摘The Canadian Nuclear Safety Commission(CNSC), Canada's nuclear regulator, conducts regulatory research in order to develop independent knowledge on safety aspects related to the deep geological disposal of radioactive wastes. In Canada, the Cobourg limestone of the Michigan Basin is currently considered as a potential host formation for geological disposal. The understanding of the hydromechanical behavior of such a host rock is one of the essential requirements for the assessment of its performance as a barrier against radionuclide migration. The excavation of galleries and shafts of a deep geological repository(DGR) can induce damage to the surrounding rock. The excavation damaged zone(EDZ) has higher permeability and reduced strength compared to the undisturbed rock and those factors must be considered in the design and safety assessment of the DGR. The extent and characteristics of the EDZ depend on the size of the opening, the rock type and its properties, and the in situ stresses, among other factors. In addition, the extent and characteristics of the EDZ can change with time due to rock strength degradation, evolution of fractures within the EDZ, and the redistribution of pore pressure around the excavation. In this research project initiated by the CNSC, the authors conducted experimental and theoretical research in order to assess the hydro-mechanical behavior of the Cobourg limestone under undamaged and damaged conditions, both in the short and long terms. The short-term behavior was investigated by a program of triaxial tests with the measurement of permeability evolution on specimens of Cobourg limestone. The authors formulate a coupled hydro-mechanical model to simulate the stress-strain response and evolution of the permeability during those triaxial tests. Using creep and relaxation data from a similar limestone, the model was extended to include its long-term strength degradation. The model successfully simulated both the short-and long-term hydro-mechanical behavior of the limestone during those tests. This provides confidence that the main physical processes have been adequately understood and formulated.
