Natural cemented calcareous sand and limestone are highly complex and not well understood in terms of the me-chanical behavior due to the difficulty of obtaining undisturbed samples from far sea.This paper proposes an...Natural cemented calcareous sand and limestone are highly complex and not well understood in terms of the me-chanical behavior due to the difficulty of obtaining undisturbed samples from far sea.This paper proposes an artificial method in a laboratory setting using microbial-induced carbonate precipitation(MICP)to simulate the natural process of cementation of limestone.The artificially cemented sand has a high degree of similarity with the natural weakly limestone in three aspects:(1)the mineral composition of the cemented material is also granular calcite and acicular aragonite;(2)the microstructure in interconnected open pore network can be gradually closed and contracted with cementation.The porosity reaches to approximately 9.2%;(3)both the stress-strain relationship and the unconfined strength closely resemble that of natural weakly limestone.Furthermore,both static and dynamic behaviors of artificial limestone were studied by quasi-static compression tests and Split Hopkinson Pressure Bar(SHPB)tests,finding that the unconfined strength of weakly artifical limestone exponentially increases with increasing strain rate.A rate-dependent bond strength was proposed and implemented in software to reveal the mechanism of strain rate effects.It is found that the loading velocity is too high to keep in sync with the initiation and propagation of cracks under impact loading.This delay-induced viscosity may restrict the movement of the surrounding balls,thus increasing resistance.展开更多
Introduction The widespread use of cement in concrete leads to increased carbon emissions,so the demand for supplementary cementitious materials increases significantly.Limestone powder and steel slag powder are widel...Introduction The widespread use of cement in concrete leads to increased carbon emissions,so the demand for supplementary cementitious materials increases significantly.Limestone powder and steel slag powder are widely used as supplementary cementitious materials in modern concrete.However,for UHPC and self-compacting concrete,an extremely low water/binder(W/B)ratio is on one hand a key factor in achieving ultra-high strength and ultra-low porosity of the materials,on the other hand,also leads to the deterioration of the rheological properties of the fresh paste.Meanwhile,the existing researches focus on the influence of single limestone powder or steel slag powder on the mechanical properties or microstructure of cement-based materials.Little work on the influence of steel slag powder or limestone powder on the rheological properties of composite paste at an extremely low water/binder ratio has been investigated quantitatively.The mechanism of the effect of steel slag powder or limestone powder on the rheological properties of composite paste at extremely low water/binder ratios is still unclear.In this work,the effects of steel slag powder and limestone powder on the rheological properties of composite paste at different low water/binder ratios were analyzed via determining the flow diameter,setting time,marsh cone flow time,rheological parameters,and total organic carbon content.Methods A composite paste was prepared with P.I 42.5 ordinary Portland cement,steel slag powder,limestone powder,blast furnace slag and silica fume as raw materials in a certain proportion.To achieve the preparation of composite paste with extremely low water/binder ratios,a polycarboxylate superplasticizer with a water/reducing rate of 40%(Jiangsu Subot New Materials Co.,Ltd.,China)was used.The dosage of polycarboxylate superplasticizer for the composite paste with different water/binder ratios of 0.16 and 0.21 was 2%and 0.8%,respectively.Composite pastes with different proportions of steel slag powder or limestone powder at water/binder ratios of 0.16 and 0.21 were prepared.The flow diameter(i.e.,the larger the flow diameter,the better the fluidity),setting time(i.e.,the time when the fluidity is lost)and marsh cone flow time(i.e.,the shorter the flow time,the better the fluidity)were determined to analyze the fluidity of the composite pastes.the rheological properties of composite paste at a water/binder ratio of 0.16 for rheological properties tests were determined,and the rheological parameters were obtained by the H-B model.The adsorption performance of the polycarboxylate superplasticizer was analyzed by testing the TOC content.Results and discussion When the ratio of water/binder is 0.16,both limestone powder and steel slag powder initially increase the flow diameter of the composite paste.However,the fluidity of the composite paste decreases over time,and the reduction is more pronounced with steel slag powder.This is because the nucleation and hydration promotion effect of limestone powder can reduce the loss rate of flow diameter,while the rough particles of steel slag powder increase the internal friction force,resulting in a decrease in the flow diameter of composite paste.Adding limestone powder and steel slag powder both shortens the setting time and marsh cone flow time of the composite paste.However,the steel slag powder addition of 30%delays the final setting time due to its delaying effect.Also,limestone powder can enhance the thixotropy and reduce the yield stress and plastic viscosity,thereby improving the rheological properties.In contrast,steel slag powder can increase the yield stress and plastic viscosity,thereby weakening the rheological properties and thixotropy.Steel slag powder and limestone powder both can enhance the adsorption effect of polycarboxylate superplasticizer.Steel slag powder has a stronger adsorption effect.The composite paste containing limestone powder has a higher free water content.This is because the rough and porous surface of steel slag itself and the uneven particle shape lead to the physical adsorption of polycarboxylate superplasticizer molecules on the surface of steel slag particles,thereby reducing the effective content of the water reducer dispersion.Increasing the water/binder ratio to 0.21 results in a decrease in the flow diameter of the composite paste.Furthermore,the setting time and marsh cone flow time can prolong due to the reduction in the dosage of polycarboxylate superplasticizer.Conclusions The results showed that the fluidity loss rate of composite paste with limestone powder could be lower than that of composite paste with steel slag powder.Compared to steel slag powder,the addition of limestone powder reduced the setting time and marsh cone flow time of the composite paste.The addition of limestone powder could shorten the yield stress and plastic viscosity of the composite paste.Therefore,the composite paste with limestone powder had better rheological properties and stronger thixotropy rather than that with steel slag powder.The addition of limestone powder could improve the rheological properties of the composite paste.Compared to composite paste with limestone powder,a better adsorption effect of polycarboxylate superplasticizer on the surface of the composite binder with steel slag powder could be obtained.The free water content of the composite paste with limestone powder was still higher than that of the composite paste with steel slag powder.The fluidity and rheological properties of the composite paste with limestone powder could be better.The comprehensive analysis indicated that a positive effect of limestone powder on rheological properties of composite paste at an extremely low water/binder ratio could be more dominant than that of steel slag powder.展开更多
The production processes for Si and FeSi have traditionally been considered slag-free.However,recent excavations have revealed significant accumulation of CaO–SiO_(2)–Al_(2)O_(3)slag within the furnaces.This accumul...The production processes for Si and FeSi have traditionally been considered slag-free.However,recent excavations have revealed significant accumulation of CaO–SiO_(2)–Al_(2)O_(3)slag within the furnaces.This accumulation can obstruct the flow of materials and gases,resulting in lower metal yield and higher energy consumption.The main objective of the current work is to enhance our understanding of slag formation during Si and FeSi production.We investigate slag formation through the dissolution of limestone and iron oxide in quartz and condensate,focusing on the reactions between these materials at a gram scale.Our findings indicate that most slag reaches equilibrium relatively quickly at temperatures starting from 1673 K.Notably,slag formation starts at lower temperature when the iron source is present (1573 K) compared to when only CaO is involved (1673 K).The minor elements tend to accumulate at quartz grain boundaries prior to slag formation.Furthermore,the slag produced from condensate contains less SiO_(2)than that generated from quartz with limestone.The type of quartz source and SiO_(2)phase appears to have little influence on slag formation.Good wettability is a significant factor in reaction between quartz and slag.FactSage calculations indicates that the viscosity of the slag ranges from 0.02 to 14.4 Pa·s under furnace conditions,comparable to the viscosity of honey or motor oil at room temperature.展开更多
As the main geomaterials for coral reefs oil or gas extraction and underground infrastructure construction,coral reef limestone demonstrates significantly distinct mechanical responses compared to terrigenous rocks.To...As the main geomaterials for coral reefs oil or gas extraction and underground infrastructure construction,coral reef limestone demonstrates significantly distinct mechanical responses compared to terrigenous rocks.To investigate the mechanical behaviour of coral reef limestone under the coupling impact of size and strain rate,the uniaxial compression tests were conducted on reef limestone samples with length-to-diameter(L/D)ratio ranging from 0.5 to 2.0 at strain rate ranging from 10^(−5)·s^(−1)to 10^(−2)·s^(−1).It is revealed that the uniaxial compressive strength(UCS)and residual compressive strength(RCS)of coral reef limestone exhibits a decreasing trend with L/D ratio increasing.The dynamic increase factor(DIF)of UCS is linearly correlated with the logarithm of strain rate,while increasing the L/D ratio further enhances the DIF.The elastic modulus increases with strain rate or L/D ratio increasing,whereas the Poisson’s ratio approximates to a constant value of 0.24.The failure strain increases with strain rate increasing or L/D ratio decreasing,while the increase in L/D ratio will inhibit the enhancing effect of the strain rate.The high porosity and low mineral strength are the primary factors contributing to a high RCS of 16.7%–64.9%of UCS,a lower brittleness index and multiple irregular fracture planes.The failure pattern of coral reef limestone transits from the shear-dominated to the splitting-dominated failure with strain rate increasing or L/D ratio decreasing,which is mainly governed by the constrained zones induced by end friction and the strain rate-dependent crack propagation.Moreover,a predictive formula incorporating coupling effect of size and strain rate for the UCS of reef limestone was established and verified to effectively capture the trend of UCS.展开更多
The Early Eocene Sui Main Limestone(SML)reservoirs in the Qadirpur area are significant hydrocarbon-producing formations but suffer from low permeability and poor reservoir characteristics that lead to well abandonmen...The Early Eocene Sui Main Limestone(SML)reservoirs in the Qadirpur area are significant hydrocarbon-producing formations but suffer from low permeability and poor reservoir characteristics that lead to well abandonment.Although commonly used,conventional stimulation techniques such as hydraulic fracturing and acidizing pose environmental risks,high costs,and sensitivity to fluctuations in crude oil prices.Meanwhile,cryogenic liquid nitrogen(LN2)treatment has emerged as an innovative,eco-friendly alternative due to its thermal shock effects,which enhance rock permeability and porosity.Herein,SML core samples are treated with LN2 for 30,60,and 90 min to obtain samples designated as SML_30,SML_60,and SML_90,respectively.These are examined using X-ray diffraction(XRD),atomic force microscopy(AFM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),nanoindentation,and petrophysical measurements to evaluate the changes in their petrophysical,morphological,and micromechanical properties.The post-treatment analysis reveals that LN2 cooling effectively induces micro-cracks,with fracture widths of up to 40μm,along with a substantial increase in surface roughness from 350 to 942 nm.Additionally,micromechanical analysis indicates notable changes in the indentation modulus due to stress-induced alterations in the rock matrix.At optimal LN2 exposure(90 min),the porosity and permeability of the SML sample is more than doubled.These findings provide valuable insights into LN2-induced reservoir enhancements,thereby contributing to a better understanding of fluid flow behavior and hydrocarbon recovery in tight gas reservoirs.Thus,LN2 treatment presents a promising,cost-effective,and environmentally sustainable alternative to conventional stimulation methods.展开更多
High-plastic clays with significant volume change due to moisture variations present critical challenges to civil engineering structures.Limestone calcined clay cement(LC3),an innovative and sustainable hydraulic bind...High-plastic clays with significant volume change due to moisture variations present critical challenges to civil engineering structures.Limestone calcined clay cement(LC3),an innovative and sustainable hydraulic binder,demonstrates significant potential for improving the engineering characteristics of such soils.Nevertheless,the impact of LC3 on the physico-mechanical characteristics of treated soil under a cyclic wet-dry environment remains unclear.This study for the first time investigates LC3's impact on the long-term durability of treated high-plastic clays through comprehensive macro-micro testing including physical,mechanical,mineralogical,and microstructural investigations with an emphasis on wet-dry cycles.The results revealed that LC3 treatment exhibits significant resistance to wet-dry cycles by completely mitigating the swelling potential,and a considerable reduction in plasticity resulting in enhanced workability.The compressibility and shear strength parameters have been significantly improved to several orders of magnitude.However,after six wet-dry cycles,a slight to modest reduction is observed,but overall durability remains superior to untreated soil.Cohesive and structural bonding ratios quantitatively assessed the impact of wet-dry cycles emphasizing the advantage of LC3 treatment.According to mineralogical and microstructural evaluation,the mechanism behind the adverse effects of wet-dry cycles on the compressibility and strength behavior of LC3-treated soil is mainly attributed to:(1)weakening of CSH/C(A)SH and ettringite(AFt)phases by exhibiting lower peak intensities;and(2)larger pore spaces due to repeated wet-dry cycles.These findings highlight LC3's performance in enhancing the long-term behavior and resilience of treated soils in real-world scenarios,providing durable solutions for infrastructure challenges.展开更多
Coral reef limestone(CRL)constitutes a distinctive marine carbonate formation with complex mechanical properties.This study investigates the multiscale damage and fracture mechanisms of CRL through integrated experime...Coral reef limestone(CRL)constitutes a distinctive marine carbonate formation with complex mechanical properties.This study investigates the multiscale damage and fracture mechanisms of CRL through integrated experimental testing,digital core technology,and theoretical modelling.Two CRL types with contrasting mesostructures were characterized across three scales.Macroscopically,CRL-I and CRL-II exhibited mean compressive strengths of 8.46 and 5.17 MPa,respectively.Mesoscopically,CRL-I featured small-scale highly interconnected pores,whilst CRL-II developed larger stratified pores with diminished connectivity.Microscopically,both CRL matrices demonstrated remarkable similarity in mineral composition and mechanical properties.A novel voxel average-based digital core scaling methodology was developed to facilitate numerical simulation of cross-scale damage processes,revealing network-progressive failure in CRL-I versus directional-brittle failure in CRL-II.Furthermore,a damage statistical constitutive model based on digital core technology and mesoscopic homogenisation theory established quantitative relationships between microelement strength distribution and macroscopic mechanical behavior.These findings illuminate the fundamental mechanisms through which mesoscopic structure governs the macroscopic mechanical properties of CRL.展开更多
In recent years,drilling data from wells Pengshen 10,Heshen 9,Tongshen 17 and Zhengyang 1 in the Sichuan Basin have confirmed the presence of a set of porous reef-beach limestone reservoirs in the Upper Permian Changx...In recent years,drilling data from wells Pengshen 10,Heshen 9,Tongshen 17 and Zhengyang 1 in the Sichuan Basin have confirmed the presence of a set of porous reef-beach limestone reservoirs in the Upper Permian Changxing Formation,which breaks the traditional view that deep carbonate oil and gas are only distributed in porous dolomite reservoirs and karst fracture-cavity limestone reservoirs.Through core and thin section observations,geochemical analysis,and well-seismic based reservoir identification and tracking,the study on formation mechanism of pores in deep reef-beach limestone reservoirs is carried out,this study provides insights in four aspects.(1)Porous reef-beach limestone reservoirs are developed in the Changxing Formation in deep-buried layers.The reservoir space is composed of intergranular pores,framework pores,intra-fossil pores,moldic pores and dissolution pores,which are formed in depositional and epigenetic environments.(2)The intermittently distributed porous reef-beach complexes are surrounded by relatively dense micrite limestone,which leads to the formation of local abnormal high-pressure inside the reef-beach complexes with the temperature increased.(3)The floor of the Changxing Formation reservoir is composed with interbedded tight mudstone and limestone of the Upper Permian Wujiaping Formation,and the roof is the tight micrite limestone interbedded with mudstone of the first member of Lower Triassic Feixianguan Formation.Under the clamping of dense roof and floor,the abnormal high-pressure in the Changxing Formation is formed.Abnormal high-pressure(overpressured compartment)is the key to maintain the pores formed in the depositional and epigenetic environments in deep-buried layers.(4)Based on the identification of roof,floor and reef-beach complexes,the favorable reef-beach limestone reservoir distribution area of 10.3×10^(4) km^(2) is predicted by well-seismic integration.These insights lay the theoretical foundation for the development of deep porous limestone reservoirs,expand the new field of exploration of deep-buried limestone reservoirs in the Sichuan Basin.展开更多
Catastrophic failure in engineering structures of island reefs would occur when the tertiary creep initiates in coral reef limestone with a transition from short-to long-term load.Due to the complexity of biological s...Catastrophic failure in engineering structures of island reefs would occur when the tertiary creep initiates in coral reef limestone with a transition from short-to long-term load.Due to the complexity of biological structures,the underlying micro-behaviors involving time-dependent deformation are poorly understood.For this,an abnormal phenomenon was observed where the axial and lateral creep deformations were mutually independent by a series of triaxial tests under constant stress and strain rate conditions.The significantly large lateral creep deformation implies that the creep process cannot be described in continuum mechanics regime.Herein,it is hypothesized that sliding mechanism of crystal cleavages dominates the lateral creep deformation in coral reef limestone.Then,approaches of polarizing microscope(PM)and scanning electronic microscope(SEM)are utilized to validate the hypothesis.It shows that the sliding behavior of crystal cleavages combats with conventional creep micro-mechanisms at certain condition.The former is sensitive to time and strain rate,and is merely activated in the creep regime.展开更多
Accurately predicting the mechanical behaviour of geological materials is crucial for ensuring the safety of geotechnical structures.However,calibrating advanced models for heterogeneous rocks,such as Copenhagen limes...Accurately predicting the mechanical behaviour of geological materials is crucial for ensuring the safety of geotechnical structures.However,calibrating advanced models for heterogeneous rocks,such as Copenhagen limestone,which exhibits diverse properties due to silicification,cementation,and glaciotectonic fractures,poses significantchallenges.Deterministic approaches often encounter limitations due to data variability and scarcity.Upon embracing a probabilistic approach,recent research emphasises the importance of considering correlations among geotechnical properties to reduce structural variability.This study focuses on the Hoek-Brown(H-B)constitutive model,addressing the challenges of determining parameters,especially with scattered data.The objective is to establish a comprehensive multivariate distribution function encompassing seven pivotal intact rock properties,which are crucial for calibrating the H-B model in the compression zone.Notably,three distinct distribution functions were developed based on the bulk density of intact samples,informed by observed behaviours under triaxial loading(σ_(1)-σ_(3)plane).Rigorous validation using an independent database,including unconfined compressive strength(UCS)and tensile tests,demonstrates the effectiveness of the constructed distributions.The analyses reveal the fundamental role of bulk density through correlations with other parameters.The validated model was employed to back analyse large-scale triaxial tests of layered rock mass samples.The results indicated that under compressive loading,the weakest layer determines the strength and stiffness of the samples when variability within the representative volume is significant.The proposed equivalent rock mass stiffness showed excellent agreement with the observed response.This study establishes a set of probabilistically calibrated H-B multivariate models and provides a practical tool for reliability-based design of underground constructions within Copenhagen limestone.展开更多
Reef limestone is buried in the continental shelf and marine environment.Understanding the mechanisms governing filter cake formation in coral reef limestone strata is essential for various engineering activities in c...Reef limestone is buried in the continental shelf and marine environment.Understanding the mechanisms governing filter cake formation in coral reef limestone strata is essential for various engineering activities in coastal areas,including slurry pressure balanced(SPB)shield tunneling,which are currently not well understood.This study systematically investigates the slurry infiltration characteristics of different coral reef limestone types with inherent anisotropy,identified by growth line orientations,through a series of micro-infiltration column tests.Multiple slurry concentrations and pressures were used to analyze their effects on slurry infiltration dynamics and filter cake formation.Pre-and post-infiltration CT scanning was conducted to examine skeletal morphology and reconstruct the pore network structure of coral reef limestone samples.The results show that while increased slurry concentrations and pressures generally improve filter cake formation,excessive pressure can compromise filter cake integrity.By employing Dijkstra’s algorithm in a pore network model,the study identified primary seepage pathways,highlighting the significant role of near-vertical throat clusters in the infiltration process.A comprehensive analysis of pore structure and connectivity indices before and after infiltration revealed that the orientation of growth lines in coral reef limestone is the primary factor influencing macroscopic slurry infiltration behavior.These findings offer valuable insights for the design and execution of tunneling projects through coral reef limestone formations,especially in coastal regions.展开更多
Coral reef limestone at different depositional depths and facies differ remarkably on the textural and mineralogical characteristics,owing to the complex sedimentary diagenesis.To explore the effects of pore structure...Coral reef limestone at different depositional depths and facies differ remarkably on the textural and mineralogical characteristics,owing to the complex sedimentary diagenesis.To explore the effects of pore structure and mineral composition associated with diagenetic variation on the mechanical behavior of reef limestone,a series of quasi-static and dynamic compression tests along with microscopic examinations were performed on the reef limestone at shallow and deep burial depths.It is revealed that the shallow reef limestone(SRL)is classified as a porous aragonite-type carbonate rock with high porosity(55.3±3.2)%and pore connectivity.In comparison,the deep reef limestone(DRL)is mainly composed of dense calcite-type calcium carbonate with low porosity(4.9±1.6)%and pore connectivity.The DRL strengthened and stiffened by the tight grain framework consistently displays much higher values of the dynamic compressive strength,elastic modulus,brittleness index,and specific energy absorption than those of the SRL.The gap between two types of limestone further increases with an increase in strain rate.It appears that the failure pattern of SRL is dominated by the inherent defects like weak bonding interfaces and growth lines,revealed by the intricate fracturing network and mixed failure.Likewise,although the preexisting megapores in DRL may affect the crack propagation on pore tips to a certain distance,it hardly alters the axial splitting failure of DRL under impacts.The stress wave propagation and attenuation in SRL is primarily controlled by the reflection and diffusion caused by plenty mesopores,as well as an energy dissipation in layer-wise pore collapse and adjacent grain crushing,while the stress wave in DRL is highly hinged on the insulation and diffraction induced by the isolated megapores.This process is accompanied by the energy dissipation behavior of inelastic deformation resulted from the pore-emanated microcracking.展开更多
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
Leaf trait networks(LTNs)visualize the intricate linkages reflecting plant trait-functional coordination.Typical karst vegetation,developed from lithological dolomite and limestone,generally exhibits differential comm...Leaf trait networks(LTNs)visualize the intricate linkages reflecting plant trait-functional coordination.Typical karst vegetation,developed from lithological dolomite and limestone,generally exhibits differential communities,possibly due to habitat rock exposure,soil depth,and soil physicochemical properties variations,leading to a shift from plant trait variation to functional linkages.However,how soil and habitat quality affect the differentiation of leaf trait networks remains unclear.LTNs were constructed for typical dolomite and limestone habitats by analyzing twenty-one woody plant leaf traits across fifty-six forest subplots in karst mountains.The differences between dolomite and limestone LTNs were compared using network parameters.The network association of soil and habitat quality was analyzed using redundancy analysis(RDA),Mantle's test,and a random forest model.The limestone LTN exhibited significantly higher edge density with lower diameter and average path length when compared to the dolomite LTN.It indicates LTN differentiation,with the limestone network displaying a more compact architecture and higher connectivity than the dolomite network.The specific leaf phosphorus and leaf nitrogen contents of dolomite LTN,as well as the leaf mass and leaf carbon contents of limestone LTN,significantly contributed to network degree and closeness,serving as crucial node traits regulating LTN connectedness.Additionally,both habitat LTNs significantly correlated with soil nitrogen and phosphorus,stoichiometric ratios,pH,and organic carbon,as well as soil depth and rock exposure rates,with soil depth and rock exposure showing greater relative importance.Soil depth and rock exposure dominate trait network differentiation,with the limestone habitat exhibiting a more compact network architecture than the dolomite habitat.展开更多
A ternary system comprising Ca_(20)Al_(26)Mg_(3)Si_(3)O_(68)(Q-phase),limestone,and metakaolin is proposed,and its hydration behavior,hydration product phases,microstructure,and mechanical properties are investigated ...A ternary system comprising Ca_(20)Al_(26)Mg_(3)Si_(3)O_(68)(Q-phase),limestone,and metakaolin is proposed,and its hydration behavior,hydration product phases,microstructure,and mechanical properties are investigated and compared with pure Q-phase cement.The results indicate that the ternary system exhibits exceptional and sustained compressive strength even under a 40℃environment,significantly outperforming pure Q-phase.The mechanism lies in that metakaolin effectively inhibits the transformation of metastable phase.Meanwhile,the interactions among Q-phase,limestone,and metakaolin further enhance the cementitious performance.The ternary system effectively addresses potential issues of strength loss in Q-phase cement application,and as a low-carbon cementitious material system,it holds promising potential applications.展开更多
Osmotic water alters the physicochemical properties and internal structures of limestone.This issue is particularly critical in tunnel construction across mountainous regions with aquifers,where pressurized groundwate...Osmotic water alters the physicochemical properties and internal structures of limestone.This issue is particularly critical in tunnel construction across mountainous regions with aquifers,where pressurized groundwater can destabilize the limestone-based surrounding rock.Thus,systematic research into the physicochemical properties and pore structure changes in the limestone under pressurized water is essential.Additionally,it is essential to develop an interpretable mathematical model to accurately depict how pressurized osmotic water weakens limestone.In this research,a specialized device was designed to simulate the process of osmotic laminar flow within limestone.Then,four main tests were conducted:mass loss,acoustic emission(AE),mercury intrusion porosimetry(MIP),and fluorescence analysis.Experimental results gained from tests led to the development of a“Particle-pore throat-water film”model.Proposed model explains water-induced physicochemical and pore changes in limestone under osmotic pressure and reveals evolutionary mechanisms as pressure increases.Based on experimental results and model,we found that osmotic pressure not only alters limestone composition but also affects pore throats larger than 0.1μm.Furthermore,osmotic pressure expands pore throats,enhancing pore structure uniformity,interconnectivity,and permeability.These effects are observed at a threshold of 7.5 MPa,where cohesive forces within the mineral lattice are surpassed,leading to the breakdown of erosion-resistant layer and a significant increase in hydrochemical erosion.展开更多
The topological attributes of fracture networks in limestone,subject to intense hydrodynamics and intricate geological discontinuities,substantially influence the mechanical and hydraulic characteristics of the rock m...The topological attributes of fracture networks in limestone,subject to intense hydrodynamics and intricate geological discontinuities,substantially influence the mechanical and hydraulic characteristics of the rock mass.The dynamical evolution of fracture networks under stress is crucial for unveiling the interaction patterns among fractures.However,existing models are undirected graphs focused on stationary topology,which need optimization to depict fractures'dynamic development and rupture process.To compensate for the time and destruction terms,we propose the damage network model,which defines the physical interpretation of fractures through the ternary motif.We focus primarily on the evolution of node types,topological attributes,and motifs of the fracture network in limestone under uniaxial stress.Observations expose the varying behavior of the nodes'self-dynamics and neighbors'adjacent dynamics in the fracture network.This approach elucidates the impact of micro-crack behaviors on large brittle shear fractures from a topological perspective and further subdivides the progressive failure stage into four distinct phases(isolated crack growth phase,crack splay phase,damage coalescence phase,and mechanical failure phase)based on the significance profile of the motif.Regression analysis reveals a positive linear and negative power correlation between fracture network density and branch number to the rock damage resistance,respectively.The damage network model introduces a novel methodology for depicting the interaction of two-dimensional(2D)projected fractures,considering the dynamic spatiotemporal development characteristics and fracture geometric variation.It helps dynamically characterize properties such as connectivity,permeability,and damage factors while comprehensively assessing damage in rock mass fracture networks.展开更多
To investigate the impact of limestone powder on the chloride ion concentration coefficient of cement pastes,various techniques such as scanning electron microscopy(SEM),X-ray diffraction(XRD),thermogravimetric analys...To investigate the impact of limestone powder on the chloride ion concentration coefficient of cement pastes,various techniques such as scanning electron microscopy(SEM),X-ray diffraction(XRD),thermogravimetric analysis(TGA),and mercury-porosimetry(MIP)were employed in this paper.The findings demonstrate that the creation of Friedel's salt is inversely associated with the addition of limestone powder,that is,Friedel's salt production is lessened by adding more limestone powder,however,the coefficient of chloride ion concentration initially decreased and then increased again,as does the porosity,and most likely the pore size as well.The specific surface area of limestone powder has increased,and the content of Friedel’s salt increased first and then decreased.However,the shifting trend of Friedel's salt and chloride ion concentration coefficient is in direct opposition,and the pore structure was therefore significantly enhanced.The results of this study offer robust theoretical backing for the inclusion of limestone powder in concrete and provide a positive assessment of its potential applications.展开更多
Different sedimentary zones in coral reefs lead to significant anisotropy in the pore structure of coral reef limestone(CRL),making it difficult to study mechanical behaviors.With X-ray computed tomography(CT),112 CRL...Different sedimentary zones in coral reefs lead to significant anisotropy in the pore structure of coral reef limestone(CRL),making it difficult to study mechanical behaviors.With X-ray computed tomography(CT),112 CRL samples were utilized for training the support vector machine(SVM)-,random forest(RF)-,and back propagation neural network(BPNN)-based models,respectively.Simultaneously,the machine learning model was embedded into genetic algorithm(GA)for parameter optimization to effectively predict uniaxial compressive strength(UCS)of CRL.Results indicate that the BPNN model with five hidden layers presents the best training effect in the data set of CRL.The SVM-based model shows a tendency to overfitting in the training set and poor generalization ability in the testing set.The RF-based model is suitable for training CRL samples with large data.Analysis of Pearson correlation coefficient matrix and the percentage increment method of performance metrics shows that the dry density,pore structure,and porosity of CRL are strongly correlated to UCS.However,the P-wave velocity is almost uncorrelated to the UCS,which is significantly distinct from the law for homogenous geomaterials.In addition,the pore tensor proposed in this paper can effectively reflect the pore structure of coral framework limestone(CFL)and coral boulder limestone(CBL),realizing the quantitative characterization of the heterogeneity and anisotropy of pore.The pore tensor provides a feasible idea to establish the relationship between pore structure and mechanical behavior of CRL.展开更多
In caves and monuments, biocorrosion caused by bats occurs partly under accumulations of guano. Tests were carried out both at cave temperature and under hot conditions in the laboratory on 4 different limestones. A c...In caves and monuments, biocorrosion caused by bats occurs partly under accumulations of guano. Tests were carried out both at cave temperature and under hot conditions in the laboratory on 4 different limestones. A comparison of the results obtained using these two methods shows that the processes leading to the weathering of the limestones are the same, and that the hot laboratory tests accelerate them in a well-constrained way. The higher the porosity and capillarity of the limestone, the faster the weathering process. The presence of large calcite crystals also favors weathering. In caves, the ablation rates obtained (8 mm/ka) are sufficient to destroy engravings in a few decades. In monuments, ablation rates are even higher because of the temperature, and could theoretically reach 32 cm/ka in extreme conditions at 80˚C. The laboratory test developed here can be adapted to the temperature of each case study. It has already demonstrated the mechanisms that lead from weathering to the formation of a phosphate crust.展开更多
基金The authors would like to acknowledge the support of the National Natural Science Foundation of China(No.52279097,No.51779264)Blue and Green Project of Jiangsu Province.
文摘Natural cemented calcareous sand and limestone are highly complex and not well understood in terms of the me-chanical behavior due to the difficulty of obtaining undisturbed samples from far sea.This paper proposes an artificial method in a laboratory setting using microbial-induced carbonate precipitation(MICP)to simulate the natural process of cementation of limestone.The artificially cemented sand has a high degree of similarity with the natural weakly limestone in three aspects:(1)the mineral composition of the cemented material is also granular calcite and acicular aragonite;(2)the microstructure in interconnected open pore network can be gradually closed and contracted with cementation.The porosity reaches to approximately 9.2%;(3)both the stress-strain relationship and the unconfined strength closely resemble that of natural weakly limestone.Furthermore,both static and dynamic behaviors of artificial limestone were studied by quasi-static compression tests and Split Hopkinson Pressure Bar(SHPB)tests,finding that the unconfined strength of weakly artifical limestone exponentially increases with increasing strain rate.A rate-dependent bond strength was proposed and implemented in software to reveal the mechanism of strain rate effects.It is found that the loading velocity is too high to keep in sync with the initiation and propagation of cracks under impact loading.This delay-induced viscosity may restrict the movement of the surrounding balls,thus increasing resistance.
文摘Introduction The widespread use of cement in concrete leads to increased carbon emissions,so the demand for supplementary cementitious materials increases significantly.Limestone powder and steel slag powder are widely used as supplementary cementitious materials in modern concrete.However,for UHPC and self-compacting concrete,an extremely low water/binder(W/B)ratio is on one hand a key factor in achieving ultra-high strength and ultra-low porosity of the materials,on the other hand,also leads to the deterioration of the rheological properties of the fresh paste.Meanwhile,the existing researches focus on the influence of single limestone powder or steel slag powder on the mechanical properties or microstructure of cement-based materials.Little work on the influence of steel slag powder or limestone powder on the rheological properties of composite paste at an extremely low water/binder ratio has been investigated quantitatively.The mechanism of the effect of steel slag powder or limestone powder on the rheological properties of composite paste at extremely low water/binder ratios is still unclear.In this work,the effects of steel slag powder and limestone powder on the rheological properties of composite paste at different low water/binder ratios were analyzed via determining the flow diameter,setting time,marsh cone flow time,rheological parameters,and total organic carbon content.Methods A composite paste was prepared with P.I 42.5 ordinary Portland cement,steel slag powder,limestone powder,blast furnace slag and silica fume as raw materials in a certain proportion.To achieve the preparation of composite paste with extremely low water/binder ratios,a polycarboxylate superplasticizer with a water/reducing rate of 40%(Jiangsu Subot New Materials Co.,Ltd.,China)was used.The dosage of polycarboxylate superplasticizer for the composite paste with different water/binder ratios of 0.16 and 0.21 was 2%and 0.8%,respectively.Composite pastes with different proportions of steel slag powder or limestone powder at water/binder ratios of 0.16 and 0.21 were prepared.The flow diameter(i.e.,the larger the flow diameter,the better the fluidity),setting time(i.e.,the time when the fluidity is lost)and marsh cone flow time(i.e.,the shorter the flow time,the better the fluidity)were determined to analyze the fluidity of the composite pastes.the rheological properties of composite paste at a water/binder ratio of 0.16 for rheological properties tests were determined,and the rheological parameters were obtained by the H-B model.The adsorption performance of the polycarboxylate superplasticizer was analyzed by testing the TOC content.Results and discussion When the ratio of water/binder is 0.16,both limestone powder and steel slag powder initially increase the flow diameter of the composite paste.However,the fluidity of the composite paste decreases over time,and the reduction is more pronounced with steel slag powder.This is because the nucleation and hydration promotion effect of limestone powder can reduce the loss rate of flow diameter,while the rough particles of steel slag powder increase the internal friction force,resulting in a decrease in the flow diameter of composite paste.Adding limestone powder and steel slag powder both shortens the setting time and marsh cone flow time of the composite paste.However,the steel slag powder addition of 30%delays the final setting time due to its delaying effect.Also,limestone powder can enhance the thixotropy and reduce the yield stress and plastic viscosity,thereby improving the rheological properties.In contrast,steel slag powder can increase the yield stress and plastic viscosity,thereby weakening the rheological properties and thixotropy.Steel slag powder and limestone powder both can enhance the adsorption effect of polycarboxylate superplasticizer.Steel slag powder has a stronger adsorption effect.The composite paste containing limestone powder has a higher free water content.This is because the rough and porous surface of steel slag itself and the uneven particle shape lead to the physical adsorption of polycarboxylate superplasticizer molecules on the surface of steel slag particles,thereby reducing the effective content of the water reducer dispersion.Increasing the water/binder ratio to 0.21 results in a decrease in the flow diameter of the composite paste.Furthermore,the setting time and marsh cone flow time can prolong due to the reduction in the dosage of polycarboxylate superplasticizer.Conclusions The results showed that the fluidity loss rate of composite paste with limestone powder could be lower than that of composite paste with steel slag powder.Compared to steel slag powder,the addition of limestone powder reduced the setting time and marsh cone flow time of the composite paste.The addition of limestone powder could shorten the yield stress and plastic viscosity of the composite paste.Therefore,the composite paste with limestone powder had better rheological properties and stronger thixotropy rather than that with steel slag powder.The addition of limestone powder could improve the rheological properties of the composite paste.Compared to composite paste with limestone powder,a better adsorption effect of polycarboxylate superplasticizer on the surface of the composite binder with steel slag powder could be obtained.The free water content of the composite paste with limestone powder was still higher than that of the composite paste with steel slag powder.The fluidity and rheological properties of the composite paste with limestone powder could be better.The comprehensive analysis indicated that a positive effect of limestone powder on rheological properties of composite paste at an extremely low water/binder ratio could be more dominant than that of steel slag powder.
基金financially supported by the Norwegian Ferroalloy Producers Research Association (FFF) and the Research Council of Norway through KSP project 326581 Recursive。
文摘The production processes for Si and FeSi have traditionally been considered slag-free.However,recent excavations have revealed significant accumulation of CaO–SiO_(2)–Al_(2)O_(3)slag within the furnaces.This accumulation can obstruct the flow of materials and gases,resulting in lower metal yield and higher energy consumption.The main objective of the current work is to enhance our understanding of slag formation during Si and FeSi production.We investigate slag formation through the dissolution of limestone and iron oxide in quartz and condensate,focusing on the reactions between these materials at a gram scale.Our findings indicate that most slag reaches equilibrium relatively quickly at temperatures starting from 1673 K.Notably,slag formation starts at lower temperature when the iron source is present (1573 K) compared to when only CaO is involved (1673 K).The minor elements tend to accumulate at quartz grain boundaries prior to slag formation.Furthermore,the slag produced from condensate contains less SiO_(2)than that generated from quartz with limestone.The type of quartz source and SiO_(2)phase appears to have little influence on slag formation.Good wettability is a significant factor in reaction between quartz and slag.FactSage calculations indicates that the viscosity of the slag ranges from 0.02 to 14.4 Pa·s under furnace conditions,comparable to the viscosity of honey or motor oil at room temperature.
基金supported by the National Natural Science Foundation of China(Nos.52222110,52401354,and 52301353).
文摘As the main geomaterials for coral reefs oil or gas extraction and underground infrastructure construction,coral reef limestone demonstrates significantly distinct mechanical responses compared to terrigenous rocks.To investigate the mechanical behaviour of coral reef limestone under the coupling impact of size and strain rate,the uniaxial compression tests were conducted on reef limestone samples with length-to-diameter(L/D)ratio ranging from 0.5 to 2.0 at strain rate ranging from 10^(−5)·s^(−1)to 10^(−2)·s^(−1).It is revealed that the uniaxial compressive strength(UCS)and residual compressive strength(RCS)of coral reef limestone exhibits a decreasing trend with L/D ratio increasing.The dynamic increase factor(DIF)of UCS is linearly correlated with the logarithm of strain rate,while increasing the L/D ratio further enhances the DIF.The elastic modulus increases with strain rate or L/D ratio increasing,whereas the Poisson’s ratio approximates to a constant value of 0.24.The failure strain increases with strain rate increasing or L/D ratio decreasing,while the increase in L/D ratio will inhibit the enhancing effect of the strain rate.The high porosity and low mineral strength are the primary factors contributing to a high RCS of 16.7%–64.9%of UCS,a lower brittleness index and multiple irregular fracture planes.The failure pattern of coral reef limestone transits from the shear-dominated to the splitting-dominated failure with strain rate increasing or L/D ratio decreasing,which is mainly governed by the constrained zones induced by end friction and the strain rate-dependent crack propagation.Moreover,a predictive formula incorporating coupling effect of size and strain rate for the UCS of reef limestone was established and verified to effectively capture the trend of UCS.
文摘The Early Eocene Sui Main Limestone(SML)reservoirs in the Qadirpur area are significant hydrocarbon-producing formations but suffer from low permeability and poor reservoir characteristics that lead to well abandonment.Although commonly used,conventional stimulation techniques such as hydraulic fracturing and acidizing pose environmental risks,high costs,and sensitivity to fluctuations in crude oil prices.Meanwhile,cryogenic liquid nitrogen(LN2)treatment has emerged as an innovative,eco-friendly alternative due to its thermal shock effects,which enhance rock permeability and porosity.Herein,SML core samples are treated with LN2 for 30,60,and 90 min to obtain samples designated as SML_30,SML_60,and SML_90,respectively.These are examined using X-ray diffraction(XRD),atomic force microscopy(AFM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),nanoindentation,and petrophysical measurements to evaluate the changes in their petrophysical,morphological,and micromechanical properties.The post-treatment analysis reveals that LN2 cooling effectively induces micro-cracks,with fracture widths of up to 40μm,along with a substantial increase in surface roughness from 350 to 942 nm.Additionally,micromechanical analysis indicates notable changes in the indentation modulus due to stress-induced alterations in the rock matrix.At optimal LN2 exposure(90 min),the porosity and permeability of the SML sample is more than doubled.These findings provide valuable insights into LN2-induced reservoir enhancements,thereby contributing to a better understanding of fluid flow behavior and hydrocarbon recovery in tight gas reservoirs.Thus,LN2 treatment presents a promising,cost-effective,and environmentally sustainable alternative to conventional stimulation methods.
基金The financial support of the National Natural Science Foundation of China(Grant No.42030714)the National Key R&D Program of China(Grant No.2019YFC1509900)is greatly acknowledged.
文摘High-plastic clays with significant volume change due to moisture variations present critical challenges to civil engineering structures.Limestone calcined clay cement(LC3),an innovative and sustainable hydraulic binder,demonstrates significant potential for improving the engineering characteristics of such soils.Nevertheless,the impact of LC3 on the physico-mechanical characteristics of treated soil under a cyclic wet-dry environment remains unclear.This study for the first time investigates LC3's impact on the long-term durability of treated high-plastic clays through comprehensive macro-micro testing including physical,mechanical,mineralogical,and microstructural investigations with an emphasis on wet-dry cycles.The results revealed that LC3 treatment exhibits significant resistance to wet-dry cycles by completely mitigating the swelling potential,and a considerable reduction in plasticity resulting in enhanced workability.The compressibility and shear strength parameters have been significantly improved to several orders of magnitude.However,after six wet-dry cycles,a slight to modest reduction is observed,but overall durability remains superior to untreated soil.Cohesive and structural bonding ratios quantitatively assessed the impact of wet-dry cycles emphasizing the advantage of LC3 treatment.According to mineralogical and microstructural evaluation,the mechanism behind the adverse effects of wet-dry cycles on the compressibility and strength behavior of LC3-treated soil is mainly attributed to:(1)weakening of CSH/C(A)SH and ettringite(AFt)phases by exhibiting lower peak intensities;and(2)larger pore spaces due to repeated wet-dry cycles.These findings highlight LC3's performance in enhancing the long-term behavior and resilience of treated soils in real-world scenarios,providing durable solutions for infrastructure challenges.
基金the National Key Research and Development Program of China(No.2021YFC3100800)the National Natural Science Foundation of China(Nos.42407235 and 42271026)the Project of Sanya Yazhou Bay Science and Technology City(No.SCKJ-JYRC-2023-54).
文摘Coral reef limestone(CRL)constitutes a distinctive marine carbonate formation with complex mechanical properties.This study investigates the multiscale damage and fracture mechanisms of CRL through integrated experimental testing,digital core technology,and theoretical modelling.Two CRL types with contrasting mesostructures were characterized across three scales.Macroscopically,CRL-I and CRL-II exhibited mean compressive strengths of 8.46 and 5.17 MPa,respectively.Mesoscopically,CRL-I featured small-scale highly interconnected pores,whilst CRL-II developed larger stratified pores with diminished connectivity.Microscopically,both CRL matrices demonstrated remarkable similarity in mineral composition and mechanical properties.A novel voxel average-based digital core scaling methodology was developed to facilitate numerical simulation of cross-scale damage processes,revealing network-progressive failure in CRL-I versus directional-brittle failure in CRL-II.Furthermore,a damage statistical constitutive model based on digital core technology and mesoscopic homogenisation theory established quantitative relationships between microelement strength distribution and macroscopic mechanical behavior.These findings illuminate the fundamental mechanisms through which mesoscopic structure governs the macroscopic mechanical properties of CRL.
基金Supported by the National Natural Science Foundation of China(U23B20154)General Program of the National Natural Science Foundation of China(42372169)。
文摘In recent years,drilling data from wells Pengshen 10,Heshen 9,Tongshen 17 and Zhengyang 1 in the Sichuan Basin have confirmed the presence of a set of porous reef-beach limestone reservoirs in the Upper Permian Changxing Formation,which breaks the traditional view that deep carbonate oil and gas are only distributed in porous dolomite reservoirs and karst fracture-cavity limestone reservoirs.Through core and thin section observations,geochemical analysis,and well-seismic based reservoir identification and tracking,the study on formation mechanism of pores in deep reef-beach limestone reservoirs is carried out,this study provides insights in four aspects.(1)Porous reef-beach limestone reservoirs are developed in the Changxing Formation in deep-buried layers.The reservoir space is composed of intergranular pores,framework pores,intra-fossil pores,moldic pores and dissolution pores,which are formed in depositional and epigenetic environments.(2)The intermittently distributed porous reef-beach complexes are surrounded by relatively dense micrite limestone,which leads to the formation of local abnormal high-pressure inside the reef-beach complexes with the temperature increased.(3)The floor of the Changxing Formation reservoir is composed with interbedded tight mudstone and limestone of the Upper Permian Wujiaping Formation,and the roof is the tight micrite limestone interbedded with mudstone of the first member of Lower Triassic Feixianguan Formation.Under the clamping of dense roof and floor,the abnormal high-pressure in the Changxing Formation is formed.Abnormal high-pressure(overpressured compartment)is the key to maintain the pores formed in the depositional and epigenetic environments in deep-buried layers.(4)Based on the identification of roof,floor and reef-beach complexes,the favorable reef-beach limestone reservoir distribution area of 10.3×10^(4) km^(2) is predicted by well-seismic integration.These insights lay the theoretical foundation for the development of deep porous limestone reservoirs,expand the new field of exploration of deep-buried limestone reservoirs in the Sichuan Basin.
基金supported by the National Natural Science Foundation of China(Grant Nos.41877267,41877260)the Priority Research Program of the Chinese Academy of Science(Grant No.XDA13010201).
文摘Catastrophic failure in engineering structures of island reefs would occur when the tertiary creep initiates in coral reef limestone with a transition from short-to long-term load.Due to the complexity of biological structures,the underlying micro-behaviors involving time-dependent deformation are poorly understood.For this,an abnormal phenomenon was observed where the axial and lateral creep deformations were mutually independent by a series of triaxial tests under constant stress and strain rate conditions.The significantly large lateral creep deformation implies that the creep process cannot be described in continuum mechanics regime.Herein,it is hypothesized that sliding mechanism of crystal cleavages dominates the lateral creep deformation in coral reef limestone.Then,approaches of polarizing microscope(PM)and scanning electronic microscope(SEM)are utilized to validate the hypothesis.It shows that the sliding behavior of crystal cleavages combats with conventional creep micro-mechanisms at certain condition.The former is sensitive to time and strain rate,and is merely activated in the creep regime.
文摘Accurately predicting the mechanical behaviour of geological materials is crucial for ensuring the safety of geotechnical structures.However,calibrating advanced models for heterogeneous rocks,such as Copenhagen limestone,which exhibits diverse properties due to silicification,cementation,and glaciotectonic fractures,poses significantchallenges.Deterministic approaches often encounter limitations due to data variability and scarcity.Upon embracing a probabilistic approach,recent research emphasises the importance of considering correlations among geotechnical properties to reduce structural variability.This study focuses on the Hoek-Brown(H-B)constitutive model,addressing the challenges of determining parameters,especially with scattered data.The objective is to establish a comprehensive multivariate distribution function encompassing seven pivotal intact rock properties,which are crucial for calibrating the H-B model in the compression zone.Notably,three distinct distribution functions were developed based on the bulk density of intact samples,informed by observed behaviours under triaxial loading(σ_(1)-σ_(3)plane).Rigorous validation using an independent database,including unconfined compressive strength(UCS)and tensile tests,demonstrates the effectiveness of the constructed distributions.The analyses reveal the fundamental role of bulk density through correlations with other parameters.The validated model was employed to back analyse large-scale triaxial tests of layered rock mass samples.The results indicated that under compressive loading,the weakest layer determines the strength and stiffness of the samples when variability within the representative volume is significant.The proposed equivalent rock mass stiffness showed excellent agreement with the observed response.This study establishes a set of probabilistically calibrated H-B multivariate models and provides a practical tool for reliability-based design of underground constructions within Copenhagen limestone.
文摘Reef limestone is buried in the continental shelf and marine environment.Understanding the mechanisms governing filter cake formation in coral reef limestone strata is essential for various engineering activities in coastal areas,including slurry pressure balanced(SPB)shield tunneling,which are currently not well understood.This study systematically investigates the slurry infiltration characteristics of different coral reef limestone types with inherent anisotropy,identified by growth line orientations,through a series of micro-infiltration column tests.Multiple slurry concentrations and pressures were used to analyze their effects on slurry infiltration dynamics and filter cake formation.Pre-and post-infiltration CT scanning was conducted to examine skeletal morphology and reconstruct the pore network structure of coral reef limestone samples.The results show that while increased slurry concentrations and pressures generally improve filter cake formation,excessive pressure can compromise filter cake integrity.By employing Dijkstra’s algorithm in a pore network model,the study identified primary seepage pathways,highlighting the significant role of near-vertical throat clusters in the infiltration process.A comprehensive analysis of pore structure and connectivity indices before and after infiltration revealed that the orientation of growth lines in coral reef limestone is the primary factor influencing macroscopic slurry infiltration behavior.These findings offer valuable insights for the design and execution of tunneling projects through coral reef limestone formations,especially in coastal regions.
基金supported by the National Natural Science Foundation for Excellent Young Scholars of China(No.52222110)the Natural Science Foundation of Jiangsu Province(No.BK20211230).
文摘Coral reef limestone at different depositional depths and facies differ remarkably on the textural and mineralogical characteristics,owing to the complex sedimentary diagenesis.To explore the effects of pore structure and mineral composition associated with diagenetic variation on the mechanical behavior of reef limestone,a series of quasi-static and dynamic compression tests along with microscopic examinations were performed on the reef limestone at shallow and deep burial depths.It is revealed that the shallow reef limestone(SRL)is classified as a porous aragonite-type carbonate rock with high porosity(55.3±3.2)%and pore connectivity.In comparison,the deep reef limestone(DRL)is mainly composed of dense calcite-type calcium carbonate with low porosity(4.9±1.6)%and pore connectivity.The DRL strengthened and stiffened by the tight grain framework consistently displays much higher values of the dynamic compressive strength,elastic modulus,brittleness index,and specific energy absorption than those of the SRL.The gap between two types of limestone further increases with an increase in strain rate.It appears that the failure pattern of SRL is dominated by the inherent defects like weak bonding interfaces and growth lines,revealed by the intricate fracturing network and mixed failure.Likewise,although the preexisting megapores in DRL may affect the crack propagation on pore tips to a certain distance,it hardly alters the axial splitting failure of DRL under impacts.The stress wave propagation and attenuation in SRL is primarily controlled by the reflection and diffusion caused by plenty mesopores,as well as an energy dissipation in layer-wise pore collapse and adjacent grain crushing,while the stress wave in DRL is highly hinged on the insulation and diffraction induced by the isolated megapores.This process is accompanied by the energy dissipation behavior of inelastic deformation resulted from the pore-emanated microcracking.
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(NSFC:32260268)the Science and Technology Project of Guizhou Province[(2021)General-455]the Guizhou Hundred-level Innovative Talents Project[Qian-ke-he platform talents(2020)6004-2].
文摘Leaf trait networks(LTNs)visualize the intricate linkages reflecting plant trait-functional coordination.Typical karst vegetation,developed from lithological dolomite and limestone,generally exhibits differential communities,possibly due to habitat rock exposure,soil depth,and soil physicochemical properties variations,leading to a shift from plant trait variation to functional linkages.However,how soil and habitat quality affect the differentiation of leaf trait networks remains unclear.LTNs were constructed for typical dolomite and limestone habitats by analyzing twenty-one woody plant leaf traits across fifty-six forest subplots in karst mountains.The differences between dolomite and limestone LTNs were compared using network parameters.The network association of soil and habitat quality was analyzed using redundancy analysis(RDA),Mantle's test,and a random forest model.The limestone LTN exhibited significantly higher edge density with lower diameter and average path length when compared to the dolomite LTN.It indicates LTN differentiation,with the limestone network displaying a more compact architecture and higher connectivity than the dolomite network.The specific leaf phosphorus and leaf nitrogen contents of dolomite LTN,as well as the leaf mass and leaf carbon contents of limestone LTN,significantly contributed to network degree and closeness,serving as crucial node traits regulating LTN connectedness.Additionally,both habitat LTNs significantly correlated with soil nitrogen and phosphorus,stoichiometric ratios,pH,and organic carbon,as well as soil depth and rock exposure rates,with soil depth and rock exposure showing greater relative importance.Soil depth and rock exposure dominate trait network differentiation,with the limestone habitat exhibiting a more compact network architecture than the dolomite habitat.
基金Funded by the National Natural Science Foundation of China(No.52172026)the Science and Technology Development Project of China Railway Design Corporation(Nos.2023A0226407 and 2023B03040003)。
文摘A ternary system comprising Ca_(20)Al_(26)Mg_(3)Si_(3)O_(68)(Q-phase),limestone,and metakaolin is proposed,and its hydration behavior,hydration product phases,microstructure,and mechanical properties are investigated and compared with pure Q-phase cement.The results indicate that the ternary system exhibits exceptional and sustained compressive strength even under a 40℃environment,significantly outperforming pure Q-phase.The mechanism lies in that metakaolin effectively inhibits the transformation of metastable phase.Meanwhile,the interactions among Q-phase,limestone,and metakaolin further enhance the cementitious performance.The ternary system effectively addresses potential issues of strength loss in Q-phase cement application,and as a low-carbon cementitious material system,it holds promising potential applications.
基金funded by the National Key R&D Program of China(2023YFC3806800).
文摘Osmotic water alters the physicochemical properties and internal structures of limestone.This issue is particularly critical in tunnel construction across mountainous regions with aquifers,where pressurized groundwater can destabilize the limestone-based surrounding rock.Thus,systematic research into the physicochemical properties and pore structure changes in the limestone under pressurized water is essential.Additionally,it is essential to develop an interpretable mathematical model to accurately depict how pressurized osmotic water weakens limestone.In this research,a specialized device was designed to simulate the process of osmotic laminar flow within limestone.Then,four main tests were conducted:mass loss,acoustic emission(AE),mercury intrusion porosimetry(MIP),and fluorescence analysis.Experimental results gained from tests led to the development of a“Particle-pore throat-water film”model.Proposed model explains water-induced physicochemical and pore changes in limestone under osmotic pressure and reveals evolutionary mechanisms as pressure increases.Based on experimental results and model,we found that osmotic pressure not only alters limestone composition but also affects pore throats larger than 0.1μm.Furthermore,osmotic pressure expands pore throats,enhancing pore structure uniformity,interconnectivity,and permeability.These effects are observed at a threshold of 7.5 MPa,where cohesive forces within the mineral lattice are surpassed,leading to the breakdown of erosion-resistant layer and a significant increase in hydrochemical erosion.
基金supported by the National Natural Science Foundation of China(Grant No.52090081)the State Key Laboratory of Hydroscience and Engineering(Grant No.2022-KY-02).
文摘The topological attributes of fracture networks in limestone,subject to intense hydrodynamics and intricate geological discontinuities,substantially influence the mechanical and hydraulic characteristics of the rock mass.The dynamical evolution of fracture networks under stress is crucial for unveiling the interaction patterns among fractures.However,existing models are undirected graphs focused on stationary topology,which need optimization to depict fractures'dynamic development and rupture process.To compensate for the time and destruction terms,we propose the damage network model,which defines the physical interpretation of fractures through the ternary motif.We focus primarily on the evolution of node types,topological attributes,and motifs of the fracture network in limestone under uniaxial stress.Observations expose the varying behavior of the nodes'self-dynamics and neighbors'adjacent dynamics in the fracture network.This approach elucidates the impact of micro-crack behaviors on large brittle shear fractures from a topological perspective and further subdivides the progressive failure stage into four distinct phases(isolated crack growth phase,crack splay phase,damage coalescence phase,and mechanical failure phase)based on the significance profile of the motif.Regression analysis reveals a positive linear and negative power correlation between fracture network density and branch number to the rock damage resistance,respectively.The damage network model introduces a novel methodology for depicting the interaction of two-dimensional(2D)projected fractures,considering the dynamic spatiotemporal development characteristics and fracture geometric variation.It helps dynamically characterize properties such as connectivity,permeability,and damage factors while comprehensively assessing damage in rock mass fracture networks.
基金Funded by the National Natural Science Foundation of China(No.52008304)the Natural Science Foundation of Fujian Province(No.2023J05021)the Startup Foundation of Scientific Research by Fuzhou University(Nos.XRC-18016 and GXRC21060)。
文摘To investigate the impact of limestone powder on the chloride ion concentration coefficient of cement pastes,various techniques such as scanning electron microscopy(SEM),X-ray diffraction(XRD),thermogravimetric analysis(TGA),and mercury-porosimetry(MIP)were employed in this paper.The findings demonstrate that the creation of Friedel's salt is inversely associated with the addition of limestone powder,that is,Friedel's salt production is lessened by adding more limestone powder,however,the coefficient of chloride ion concentration initially decreased and then increased again,as does the porosity,and most likely the pore size as well.The specific surface area of limestone powder has increased,and the content of Friedel’s salt increased first and then decreased.However,the shifting trend of Friedel's salt and chloride ion concentration coefficient is in direct opposition,and the pore structure was therefore significantly enhanced.The results of this study offer robust theoretical backing for the inclusion of limestone powder in concrete and provide a positive assessment of its potential applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.41877267 and 41877260)the Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA13010201).
文摘Different sedimentary zones in coral reefs lead to significant anisotropy in the pore structure of coral reef limestone(CRL),making it difficult to study mechanical behaviors.With X-ray computed tomography(CT),112 CRL samples were utilized for training the support vector machine(SVM)-,random forest(RF)-,and back propagation neural network(BPNN)-based models,respectively.Simultaneously,the machine learning model was embedded into genetic algorithm(GA)for parameter optimization to effectively predict uniaxial compressive strength(UCS)of CRL.Results indicate that the BPNN model with five hidden layers presents the best training effect in the data set of CRL.The SVM-based model shows a tendency to overfitting in the training set and poor generalization ability in the testing set.The RF-based model is suitable for training CRL samples with large data.Analysis of Pearson correlation coefficient matrix and the percentage increment method of performance metrics shows that the dry density,pore structure,and porosity of CRL are strongly correlated to UCS.However,the P-wave velocity is almost uncorrelated to the UCS,which is significantly distinct from the law for homogenous geomaterials.In addition,the pore tensor proposed in this paper can effectively reflect the pore structure of coral framework limestone(CFL)and coral boulder limestone(CBL),realizing the quantitative characterization of the heterogeneity and anisotropy of pore.The pore tensor provides a feasible idea to establish the relationship between pore structure and mechanical behavior of CRL.
文摘In caves and monuments, biocorrosion caused by bats occurs partly under accumulations of guano. Tests were carried out both at cave temperature and under hot conditions in the laboratory on 4 different limestones. A comparison of the results obtained using these two methods shows that the processes leading to the weathering of the limestones are the same, and that the hot laboratory tests accelerate them in a well-constrained way. The higher the porosity and capillarity of the limestone, the faster the weathering process. The presence of large calcite crystals also favors weathering. In caves, the ablation rates obtained (8 mm/ka) are sufficient to destroy engravings in a few decades. In monuments, ablation rates are even higher because of the temperature, and could theoretically reach 32 cm/ka in extreme conditions at 80˚C. The laboratory test developed here can be adapted to the temperature of each case study. It has already demonstrated the mechanisms that lead from weathering to the formation of a phosphate crust.
