Oxygen isotope(δ^(18)O)of paleolake water is a key indicator for reconstructing the formation temperature and diagenetic history of lacustrine carbonate minerals.In this study,we use clumped isotopes(Δ_(47))of lacus...Oxygen isotope(δ^(18)O)of paleolake water is a key indicator for reconstructing the formation temperature and diagenetic history of lacustrine carbonate minerals.In this study,we use clumped isotopes(Δ_(47))of lacustrine shell limestones to determine the surface erosion thickness and δ^(18)O of Early Jurassic lake water in the northern Sichuan Basin.We analyzed nine shell limestone and seventeen shale samples from the Early Jurassic Da'anzhai Member(J_(1)z^(4))in the Yuanba area.Whether the shell's shapes are well or partially preserved,the J_(1)z^(4)shell limestones in the Yuanba area show no significant recrystallization and dull cathodoluminescence.These characteristics suggest that the shell limestones did not undergo significant diagenetic alteration during late burial.The Δ_(47)values of the J_(1)z^(4)shell limestones range from 0.448±0.005‰to 0.463±0.006‰,yielding clumped isotope temperature(T_(Δ47))of 64.4±0.8 to 69.7±1.4℃,which is significantly higher than the Early Jurassic paleotemperature.It suggests that the Δ_(47)of shell limestones was altered by solid-state reordering,meaning the T_(Δ47)does not reflect the initial formation temperatures.By integrating organic matter's maturation model(Easy%R_(o))of coexisting shales with Δ_(47)solid-state reordering model of calcite,we constrained the maximum burial temperature(~170℃)and the initial formation temperature(~28℃)of these shell limestones.Based on reported paleotemperature gradient,we estimated that the surface erosion thickness was about 1500 m.Furthermore,using the determined initial formation temperatures and conventional oxygen isotope thermometer,we determined that the δ^(18)O values of the Early Jurassic lake water in the Sichuan Basin,which ranged from-10.8‰to-8.0‰(SMOW).The reconstructed paleo temperature and δ^(18)O of lake water suggest that the Early Jurassic in the Sichuan Basin was warm and humid,which was favorable for the deposition of organic-rich lacustrine shale.The methods developed in this study,which employ Δ_(47)of shell limestones to reconstruct the maximum burial temperature and paleolake environmental conditions,demonstrate broad applicability to the Sichuan Basin and similar lacustrine basins.展开更多
The molybdenum-nickel deposits in Shuidong District of Nayong County （Guizhou Province, Southwest China） are found mainly in black shale series of Lower Cambrian Niutitang Formation, which is another Mo-Ni-rich regi...The molybdenum-nickel deposits in Shuidong District of Nayong County （Guizhou Province, Southwest China） are found mainly in black shale series of Lower Cambrian Niutitang Formation, which is another Mo-Ni-rich region besides Zunyi District （Guizhou province）. Our systematic study on the Mo-Ni deposits in Tangjiaba of Nayong reveals that layered coarse-grained limestones, spherical beaded limestones concretions are hosted at the lower seam of the Mo-Ni deposits. Its strong negative carbon isotope anomaly （the carbon isotope value of the coarse-grained limestones varies from -2.148‰ to 8.223‰） is similar to that in the modern submarine black smoker chimney. The carbon in the coarse-grained limestones from black rock series of Nayong County might be deep source inorganic carbon. The seams, coarse-grained limestones, ore-bearing coarse-grained limestones and the roof and floor of the deposits are characterized by co-variation on the trace element spider diagram, showing good homology. The extraordinary enrichment of Ag, As and Sb resembles hydrothermal sedimentation. Pro-Earth＇s core elements Se is strongly enriched in Ni-Mo ore-bearing coarse-grained limestones. The ore-bearing rock series has an extremely low Th/U value （0.012-0.19）; in the logU-logTh Cartesian Coordinates, the samples of the roof and floor of the deposits and ore-bearing coarse-grained limestones are found in the East Pacific tise; and the samples of coarse-grained limestones are found between the paleo-hydrothermal dedimentary area and the East Pacific tise. The chondrite-normalized rare earth element patterns of the Ni-Mo deposits show LREE enrichment, Ce negative anomaly, and Eu negative anomaly （which is supposed to be influenced by the deep magmatic processes in an extensional environment） resembles the rare earth element distribution patterns of the fluid and its sediments in modern submarine hydrothermal system. It proves that coarse-grained limestones is characterized by typical hydrothermal limestones, being closely related with the genesis of Mo-Ni deposits in Nayong County, which provides new evidence for hydrothermal sedimentary genesis of Mo-Ni deposit and negative carbon anomaly in the basal Cambrian on a global scale.展开更多
This study examines the rare earth elements and yttrium(REY)concentrations of twenty-five samples from the reef outcrop exposed along the Lianglitage Mountain in the Ordovician,Tarim Basin in China.The concentration a...This study examines the rare earth elements and yttrium(REY)concentrations of twenty-five samples from the reef outcrop exposed along the Lianglitage Mountain in the Ordovician,Tarim Basin in China.The concentration analysis provides constraints on the paleoenvironment during reef deposition.Based on the detailed sedimentology and petrographic work,we divide the reef facies into four sub-facies:the base facies,reef-core facies,reef-flank facies,and sealing facies.The geochemical data(such as major and trace elements,carbon and oxygen isotopes,and REYs)are further used to study the coeval seawater characteristics as well as potential diagenesis overprints.The result indicated that the diagenesis has little effect on the REY patterns of the reefal limestones.The REY concentrations of the reefal limestones are overall low(ranging from 3.69 to 19.60 ppm,arithmetic mean=10.22 ppm,SD=5.4).The PAAS-normalized REY patterns are consistently flat compared to the typical well-oxidized,shallow marine water patterns.However,the light REE(LREE)depletions,positive La anomalies,negative Ce anomalies and positive Y anomalies,suggest that these reefal limestones are likely an indicative of contemporaneous seawater REY signals.The seawater-like Y/Ho ratios(average at 37.51)further support that REY signals in these limestones are likely a reflection of seawater with little diagenetic modifications.The low Y/Ho ratios presented only in the reef-flank facies and sealing facies are likely a suggestion of detrital contamination.Hence,this study confirms that REY patterns of the limestones at the base facies and reef-core facies can record ancient seawater information,and reefs can be used as a potential geochemical proxy for paleoenvironment studies throughout the Earth’s history.展开更多
The main aim of this work is to study the possibility of using different Emirati limestones for the production of quicklime. Representative limestone samples have been collected to represent the Triassic, Jurassic, Cr...The main aim of this work is to study the possibility of using different Emirati limestones for the production of quicklime. Representative limestone samples have been collected to represent the Triassic, Jurassic, Cretaceous, Eocene and Oligocene ages. The limestone samples have been characterized for their microstructure, mineral and chemical composition, physico-mechanical characteristics, thermal behavior using polarizing and scanning microscopes together with X-ray micro-tomography, XRD-IR, XRF, Archimedes and Mercury intrusion methods and DTA-TGA, respectively. Post characterization, the samples were fired in electrical muffle furnace for calcination under the firing conditions (800℃ to 1100℃) for (0.25 – 2 h). Then the lime grains have been characterized for their hydration rate, free lime content, pore-distribution and microfabric.展开更多
This study presents an analysis of magnetic susceptibility and natural gamma radioactivity as indirect indicators of impurities in Cretaceous limestones of the Sabinas basin, as well as of the possible relation of the...This study presents an analysis of magnetic susceptibility and natural gamma radioactivity as indirect indicators of impurities in Cretaceous limestones of the Sabinas basin, as well as of the possible relation of these physical properties with the changes in the sedimentation environment. Both of these physical properties indicate changes in the degree of impurities and the mineralogical composition of this rock, principally in its organic matter and detritus content. Considering that the sedimentation environment determines the impurities in these rocks, possible environmental conditions at different levels of the Cretaceous were suggested using the magnetic susceptibility, total gamma radiation and potassium values, as well as the uranium and thorium concentration in the limestones. The analyses suggest variations in the depth of water table of the basin, which are mainly related to transgressions and marine regressions.展开更多
Massive limestones were used in construction of ancient Egyptian tombs, temples, obelisks and other sculptures. These stones are always exposed to physico-mechanical deterioration and destructive forces, leading to pa...Massive limestones were used in construction of ancient Egyptian tombs, temples, obelisks and other sculptures. These stones are always exposed to physico-mechanical deterioration and destructive forces, leading to partial or total collapse. The task of reassembling this type of artifacts represents a big challenge for the conservators. Recently, the researchers are turning to new technologies to improve the properties of traditional adhesive materials and techniques used in re-assembly of broken massive stones. The epoxy resins are used extensively in stone conservation and re-assembly of broken stones because of their outstanding mechanical properties. The adding of nanoparticles to polymeric adhesives at low percentages may lead to substantial improvements of their mechanical performances in structural joints and massive objects. The aim of this study is to evaluate the effectiveness of montmorillonite clay, calcium carbonate, and silicon dioxide nanoparticles for enhancing the performances of epoxy adhesives used in re-assembly of archaeological massive limestones. Scanning electron microscopy (SEM) was employed in order to investigate the morphology of the prepared nanocomposites, and the distribution of nanoparticles inside the composites. Artificial aging, tensile, compressive, and elongation strength tests were used to evaluate the efficiency of epoxy-nanocomposites. The results showed that the epoxy-clay nanocomposites exhibited superior tensile, compressive, and elongation strength, in addition to improving the mechanical properties of stone joints.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
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
The Ching-dar syncline is located to the west of the city of Birjand, in the east of han. The ca. 500 m thick studied section at the eastern flank of the syncline contains a sequence of almost continuous shallow- mari...The Ching-dar syncline is located to the west of the city of Birjand, in the east of han. The ca. 500 m thick studied section at the eastern flank of the syncline contains a sequence of almost continuous shallow- marine limestones that exhibit no major sedimentary breaks or evidence for volcanic activity. Skeletal grains consist of large benthic foraminifera and green algae whereas non-skeletal grains are mostly peloids and intraclasts. They were deposited on a shallow-marine carbonate ramp. The limestones have undergone extensive diagenetic processes with varying intensities, the most important of which are micritization, cementation, compaction （chemical and mechanical）, internal filling and stylolitization. Chemical analysis of the limestone samples revealed high calcium and low magnesium content. Major and minor element values were used to determine the original carbonate mineralogy of these lime- stones. Petrographic evidence and elemental values indicate that calcite was the original carbonate mineral in the limestones of the Ching-dar syncline. The elemental composition of the Ching-dar car- bonates also demonstrates that they have stabilized in a meteoric phreatic environment. Variation of Sr/ Ca vs. Mn values suggests that diagenetic alteration occurred in an open geochemical system.展开更多
Carbon and oxygen XRF spectra were studied using a WDXRF(WD X-ray fluorescence)spectrometer S8 TIGER(Bruker AXS,Germany).XRF spectra were obtained from the samples of the calcareous spar(CaCO3)(pure calcium carbonate)...Carbon and oxygen XRF spectra were studied using a WDXRF(WD X-ray fluorescence)spectrometer S8 TIGER(Bruker AXS,Germany).XRF spectra were obtained from the samples of the calcareous spar(CaCO3)(pure calcium carbonate),the limestones,the graphite,the microcrystalline cellulose,various organic compounds and prepared mixtures on the basis of the calcareous spar with addition of the graphite and the microcrystalline cellulose.The studied samples of the limestones are characterized by high concentrations of calcite(98.5-99%).Main objective of this investigation is to develop WDXRF technique for the determination of C(total)and O(total).Optimal instrumental measuring conditions were selected experimentally for quantitative determination of C(total)and O(total).The calculated values of the ILD(instrumental limit of the detection)vary from 0.0215%for C(total)to 0.0331%for O(total),respectively.The obtained values of the LDM(limit of determination of the XRF method)do not exceed 0.08%for C(total)and O(total).The RSDs(relative standard deviations)values do not exceed 1.0%in all cases.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
Different treatment technologies have been efficiently applied to remove heavy metals from waste- water. Efforts have been made to find out the most economic water treatment technology by using low cost and easily acc...Different treatment technologies have been efficiently applied to remove heavy metals from waste- water. Efforts have been made to find out the most economic water treatment technology by using low cost and easily accessible natural materials. On the other hand, heavy metals are the most threatening groundwater contaminants because of their toxicity and harmful effects on human and biota. This review discusses the use of natural geological materials for heavy metal removal in aqueous systems. Special attention has been devoted to natural limestone through a systematic inventory of relevant published reports. The removal of toxic metals may include different mechanisms （e.g., physisorption, chemisorptions, precipitation, etc.）, depending on the physico-chemical properties of the material and the removed metal. Sorption of toxic metals （e.g., Pb, Cu, Cd, Zn, Cr, Hg, etc.） onto natural limestone involved precipitation of metal carbonate as a predominant removal process, but often subordinated by adsorption and ion exchange, depending on the physico-chemical properties of the studied limestone.展开更多
Major, trace and rare earth elements were measured in 27 samples of the Middle to Late Permian limestones from the Tieqiao section located on the marginal zone of an isolated platform （Laibin, South China）. Shale-no...Major, trace and rare earth elements were measured in 27 samples of the Middle to Late Permian limestones from the Tieqiao section located on the marginal zone of an isolated platform （Laibin, South China）. Shale-normalized REE＋Y patterns of all samples show notably negative Ce anomalies （0.21-0.66, average 0.33）, slightly positive Gd anomalies （1.08-1.30, average 1.20）, and positive Y anomalies with superchondritic Y/Ho ratios （36-91, average 55）, which are consistent with those of modern shallow seawater. Their relative LREEs enrichment with higher NdsN/YbsN ratios （0.58-1.80） than those of modern shallow seawater （0.21-0.50） suggests complicated sources of REEs for all samples. Compared with geochemical features of sediments influenced by terrigenous particles and hydrothermal fluids, it is concluded that ambient shallow seawater was the primary source of REEs in these limestones. Comparing the indicators of REE＋Y elements （ZREE, NdsN/YbsN, Ce/Ce＊, Gd/Gd＊, Eu/Eu＊ and Y/Ho） in limestones with those in bedded cherts from the Tieqiao section, we consider that limestone and bedded chert have similar sources of REE＋Y elements： ambient shallow seawater with more or less hydrothermal fluids. In addition, there is a completely negative correlation between CaCO3 and SiO2 contents in limestones and bedded cherts. These results imply that precipitation of CaCO3 was inhibited by that of SiO2 which was derived mainly from hydrothermal fluid, es- pecially in bedded cherts from the Tieqiao section.展开更多
There are 8 hayers of the Fusulinid-bearing limestone distributed widely and stably in the upper Carboniferous series of Shanxi, their unified names and sequence from bottom upward being Wuming Limestone, Wujiayu Lime...There are 8 hayers of the Fusulinid-bearing limestone distributed widely and stably in the upper Carboniferous series of Shanxi, their unified names and sequence from bottom upward being Wuming Limestone, Wujiayu Limestone, Miaogou Limestone, Maogou Limestone, Xiedao Limestone, Dongdayao Limestone, Fucheng Limestone and Xiaodonggou Limestone (Table 1).展开更多
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
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
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
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
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
Among the rolling hills and vineyards of the Tuscan countryside lies one of the most impressive tourist attractions not only in Italy,but in the entire world-a cascade(小瀑布)of white limestone pools overflowing with ...Among the rolling hills and vineyards of the Tuscan countryside lies one of the most impressive tourist attractions not only in Italy,but in the entire world-a cascade(小瀑布)of white limestone pools overflowing with warm turquoise(绿松石色)water known as Cascate del Mulino.展开更多
基金supported by National Natural Science Foundation of China(42372148)。
文摘Oxygen isotope(δ^(18)O)of paleolake water is a key indicator for reconstructing the formation temperature and diagenetic history of lacustrine carbonate minerals.In this study,we use clumped isotopes(Δ_(47))of lacustrine shell limestones to determine the surface erosion thickness and δ^(18)O of Early Jurassic lake water in the northern Sichuan Basin.We analyzed nine shell limestone and seventeen shale samples from the Early Jurassic Da'anzhai Member(J_(1)z^(4))in the Yuanba area.Whether the shell's shapes are well or partially preserved,the J_(1)z^(4)shell limestones in the Yuanba area show no significant recrystallization and dull cathodoluminescence.These characteristics suggest that the shell limestones did not undergo significant diagenetic alteration during late burial.The Δ_(47)values of the J_(1)z^(4)shell limestones range from 0.448±0.005‰to 0.463±0.006‰,yielding clumped isotope temperature(T_(Δ47))of 64.4±0.8 to 69.7±1.4℃,which is significantly higher than the Early Jurassic paleotemperature.It suggests that the Δ_(47)of shell limestones was altered by solid-state reordering,meaning the T_(Δ47)does not reflect the initial formation temperatures.By integrating organic matter's maturation model(Easy%R_(o))of coexisting shales with Δ_(47)solid-state reordering model of calcite,we constrained the maximum burial temperature(~170℃)and the initial formation temperature(~28℃)of these shell limestones.Based on reported paleotemperature gradient,we estimated that the surface erosion thickness was about 1500 m.Furthermore,using the determined initial formation temperatures and conventional oxygen isotope thermometer,we determined that the δ^(18)O values of the Early Jurassic lake water in the Sichuan Basin,which ranged from-10.8‰to-8.0‰(SMOW).The reconstructed paleo temperature and δ^(18)O of lake water suggest that the Early Jurassic in the Sichuan Basin was warm and humid,which was favorable for the deposition of organic-rich lacustrine shale.The methods developed in this study,which employ Δ_(47)of shell limestones to reconstruct the maximum burial temperature and paleolake environmental conditions,demonstrate broad applicability to the Sichuan Basin and similar lacustrine basins.
基金sponsored by the Doctoral Fund of Ministry of Education of China (Grant no.20105201110002)Research Fund of Guizhou Province and Doctoral Programme Fund of Guizhou University
文摘The molybdenum-nickel deposits in Shuidong District of Nayong County （Guizhou Province, Southwest China） are found mainly in black shale series of Lower Cambrian Niutitang Formation, which is another Mo-Ni-rich region besides Zunyi District （Guizhou province）. Our systematic study on the Mo-Ni deposits in Tangjiaba of Nayong reveals that layered coarse-grained limestones, spherical beaded limestones concretions are hosted at the lower seam of the Mo-Ni deposits. Its strong negative carbon isotope anomaly （the carbon isotope value of the coarse-grained limestones varies from -2.148‰ to 8.223‰） is similar to that in the modern submarine black smoker chimney. The carbon in the coarse-grained limestones from black rock series of Nayong County might be deep source inorganic carbon. The seams, coarse-grained limestones, ore-bearing coarse-grained limestones and the roof and floor of the deposits are characterized by co-variation on the trace element spider diagram, showing good homology. The extraordinary enrichment of Ag, As and Sb resembles hydrothermal sedimentation. Pro-Earth＇s core elements Se is strongly enriched in Ni-Mo ore-bearing coarse-grained limestones. The ore-bearing rock series has an extremely low Th/U value （0.012-0.19）; in the logU-logTh Cartesian Coordinates, the samples of the roof and floor of the deposits and ore-bearing coarse-grained limestones are found in the East Pacific tise; and the samples of coarse-grained limestones are found between the paleo-hydrothermal dedimentary area and the East Pacific tise. The chondrite-normalized rare earth element patterns of the Ni-Mo deposits show LREE enrichment, Ce negative anomaly, and Eu negative anomaly （which is supposed to be influenced by the deep magmatic processes in an extensional environment） resembles the rare earth element distribution patterns of the fluid and its sediments in modern submarine hydrothermal system. It proves that coarse-grained limestones is characterized by typical hydrothermal limestones, being closely related with the genesis of Mo-Ni deposits in Nayong County, which provides new evidence for hydrothermal sedimentary genesis of Mo-Ni deposit and negative carbon anomaly in the basal Cambrian on a global scale.
基金supported by the National Natural Science Foundation of China(grant number 51574208)the National 973 Program of China(grant number 2012CB214802)+1 种基金the China Geological Survery Project(grant number DD20190217)the China Scholar Council(grant number 201606400023)for providing the financial support
文摘This study examines the rare earth elements and yttrium(REY)concentrations of twenty-five samples from the reef outcrop exposed along the Lianglitage Mountain in the Ordovician,Tarim Basin in China.The concentration analysis provides constraints on the paleoenvironment during reef deposition.Based on the detailed sedimentology and petrographic work,we divide the reef facies into four sub-facies:the base facies,reef-core facies,reef-flank facies,and sealing facies.The geochemical data(such as major and trace elements,carbon and oxygen isotopes,and REYs)are further used to study the coeval seawater characteristics as well as potential diagenesis overprints.The result indicated that the diagenesis has little effect on the REY patterns of the reefal limestones.The REY concentrations of the reefal limestones are overall low(ranging from 3.69 to 19.60 ppm,arithmetic mean=10.22 ppm,SD=5.4).The PAAS-normalized REY patterns are consistently flat compared to the typical well-oxidized,shallow marine water patterns.However,the light REE(LREE)depletions,positive La anomalies,negative Ce anomalies and positive Y anomalies,suggest that these reefal limestones are likely an indicative of contemporaneous seawater REY signals.The seawater-like Y/Ho ratios(average at 37.51)further support that REY signals in these limestones are likely a reflection of seawater with little diagenetic modifications.The low Y/Ho ratios presented only in the reef-flank facies and sealing facies are likely a suggestion of detrital contamination.Hence,this study confirms that REY patterns of the limestones at the base facies and reef-core facies can record ancient seawater information,and reefs can be used as a potential geochemical proxy for paleoenvironment studies throughout the Earth’s history.
文摘The main aim of this work is to study the possibility of using different Emirati limestones for the production of quicklime. Representative limestone samples have been collected to represent the Triassic, Jurassic, Cretaceous, Eocene and Oligocene ages. The limestone samples have been characterized for their microstructure, mineral and chemical composition, physico-mechanical characteristics, thermal behavior using polarizing and scanning microscopes together with X-ray micro-tomography, XRD-IR, XRF, Archimedes and Mercury intrusion methods and DTA-TGA, respectively. Post characterization, the samples were fired in electrical muffle furnace for calcination under the firing conditions (800℃ to 1100℃) for (0.25 – 2 h). Then the lime grains have been characterized for their hydration rate, free lime content, pore-distribution and microfabric.
文摘This study presents an analysis of magnetic susceptibility and natural gamma radioactivity as indirect indicators of impurities in Cretaceous limestones of the Sabinas basin, as well as of the possible relation of these physical properties with the changes in the sedimentation environment. Both of these physical properties indicate changes in the degree of impurities and the mineralogical composition of this rock, principally in its organic matter and detritus content. Considering that the sedimentation environment determines the impurities in these rocks, possible environmental conditions at different levels of the Cretaceous were suggested using the magnetic susceptibility, total gamma radiation and potassium values, as well as the uranium and thorium concentration in the limestones. The analyses suggest variations in the depth of water table of the basin, which are mainly related to transgressions and marine regressions.
文摘Massive limestones were used in construction of ancient Egyptian tombs, temples, obelisks and other sculptures. These stones are always exposed to physico-mechanical deterioration and destructive forces, leading to partial or total collapse. The task of reassembling this type of artifacts represents a big challenge for the conservators. Recently, the researchers are turning to new technologies to improve the properties of traditional adhesive materials and techniques used in re-assembly of broken massive stones. The epoxy resins are used extensively in stone conservation and re-assembly of broken stones because of their outstanding mechanical properties. The adding of nanoparticles to polymeric adhesives at low percentages may lead to substantial improvements of their mechanical performances in structural joints and massive objects. The aim of this study is to evaluate the effectiveness of montmorillonite clay, calcium carbonate, and silicon dioxide nanoparticles for enhancing the performances of epoxy adhesives used in re-assembly of archaeological massive limestones. Scanning electron microscopy (SEM) was employed in order to investigate the morphology of the prepared nanocomposites, and the distribution of nanoparticles inside the composites. Artificial aging, tensile, compressive, and elongation strength tests were used to evaluate the efficiency of epoxy-nanocomposites. The results showed that the epoxy-clay nanocomposites exhibited superior tensile, compressive, and elongation strength, in addition to improving the mechanical properties of stone joints.
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.
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.
文摘The Ching-dar syncline is located to the west of the city of Birjand, in the east of han. The ca. 500 m thick studied section at the eastern flank of the syncline contains a sequence of almost continuous shallow- marine limestones that exhibit no major sedimentary breaks or evidence for volcanic activity. Skeletal grains consist of large benthic foraminifera and green algae whereas non-skeletal grains are mostly peloids and intraclasts. They were deposited on a shallow-marine carbonate ramp. The limestones have undergone extensive diagenetic processes with varying intensities, the most important of which are micritization, cementation, compaction （chemical and mechanical）, internal filling and stylolitization. Chemical analysis of the limestone samples revealed high calcium and low magnesium content. Major and minor element values were used to determine the original carbonate mineralogy of these lime- stones. Petrographic evidence and elemental values indicate that calcite was the original carbonate mineral in the limestones of the Ching-dar syncline. The elemental composition of the Ching-dar car- bonates also demonstrates that they have stabilized in a meteoric phreatic environment. Variation of Sr/ Ca vs. Mn values suggests that diagenetic alteration occurred in an open geochemical system.
基金The equipment of the Center for Collective Use“Geodynamics and Geochronology”of the Institute of the Earth’s Crust of the SB RAS was used in this work within the framework of the grant No.075-15-2021-682。
文摘Carbon and oxygen XRF spectra were studied using a WDXRF(WD X-ray fluorescence)spectrometer S8 TIGER(Bruker AXS,Germany).XRF spectra were obtained from the samples of the calcareous spar(CaCO3)(pure calcium carbonate),the limestones,the graphite,the microcrystalline cellulose,various organic compounds and prepared mixtures on the basis of the calcareous spar with addition of the graphite and the microcrystalline cellulose.The studied samples of the limestones are characterized by high concentrations of calcite(98.5-99%).Main objective of this investigation is to develop WDXRF technique for the determination of C(total)and O(total).Optimal instrumental measuring conditions were selected experimentally for quantitative determination of C(total)and O(total).The calculated values of the ILD(instrumental limit of the detection)vary from 0.0215%for C(total)to 0.0331%for O(total),respectively.The obtained values of the LDM(limit of determination of the XRF method)do not exceed 0.08%for C(total)and O(total).The RSDs(relative standard deviations)values do not exceed 1.0%in all cases.
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Different treatment technologies have been efficiently applied to remove heavy metals from waste- water. Efforts have been made to find out the most economic water treatment technology by using low cost and easily accessible natural materials. On the other hand, heavy metals are the most threatening groundwater contaminants because of their toxicity and harmful effects on human and biota. This review discusses the use of natural geological materials for heavy metal removal in aqueous systems. Special attention has been devoted to natural limestone through a systematic inventory of relevant published reports. The removal of toxic metals may include different mechanisms （e.g., physisorption, chemisorptions, precipitation, etc.）, depending on the physico-chemical properties of the material and the removed metal. Sorption of toxic metals （e.g., Pb, Cu, Cd, Zn, Cr, Hg, etc.） onto natural limestone involved precipitation of metal carbonate as a predominant removal process, but often subordinated by adsorption and ion exchange, depending on the physico-chemical properties of the studied limestone.
基金financially supported by the National S&T Major Project(Grant No.2011ZX05008)National Natural Science Foundation of China(Grant Nos.41273001 and 41103018)
文摘Major, trace and rare earth elements were measured in 27 samples of the Middle to Late Permian limestones from the Tieqiao section located on the marginal zone of an isolated platform （Laibin, South China）. Shale-normalized REE＋Y patterns of all samples show notably negative Ce anomalies （0.21-0.66, average 0.33）, slightly positive Gd anomalies （1.08-1.30, average 1.20）, and positive Y anomalies with superchondritic Y/Ho ratios （36-91, average 55）, which are consistent with those of modern shallow seawater. Their relative LREEs enrichment with higher NdsN/YbsN ratios （0.58-1.80） than those of modern shallow seawater （0.21-0.50） suggests complicated sources of REEs for all samples. Compared with geochemical features of sediments influenced by terrigenous particles and hydrothermal fluids, it is concluded that ambient shallow seawater was the primary source of REEs in these limestones. Comparing the indicators of REE＋Y elements （ZREE, NdsN/YbsN, Ce/Ce＊, Gd/Gd＊, Eu/Eu＊ and Y/Ho） in limestones with those in bedded cherts from the Tieqiao section, we consider that limestone and bedded chert have similar sources of REE＋Y elements： ambient shallow seawater with more or less hydrothermal fluids. In addition, there is a completely negative correlation between CaCO3 and SiO2 contents in limestones and bedded cherts. These results imply that precipitation of CaCO3 was inhibited by that of SiO2 which was derived mainly from hydrothermal fluid, es- pecially in bedded cherts from the Tieqiao section.
文摘There are 8 hayers of the Fusulinid-bearing limestone distributed widely and stably in the upper Carboniferous series of Shanxi, their unified names and sequence from bottom upward being Wuming Limestone, Wujiayu Limestone, Miaogou Limestone, Maogou Limestone, Xiedao Limestone, Dongdayao Limestone, Fucheng Limestone and Xiaodonggou Limestone (Table 1).
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.
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.
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.
基金National Key Research and Development Program of China (No.2021YFC3100800)the National Natural Science Foundation of China (Nos.42407235 and 42271026)+1 种基金the Project of Sanya Yazhou Bay Science and Technology City (No.SCKJ-JYRC-2023-54)supported by the Hefei advanced computing center
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.
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.
文摘Among the rolling hills and vineyards of the Tuscan countryside lies one of the most impressive tourist attractions not only in Italy,but in the entire world-a cascade(小瀑布)of white limestone pools overflowing with warm turquoise(绿松石色)water known as Cascate del Mulino.
