Chloride ions(Cl^(-))have been shown to impact the long-lasting nature of reinforced concrete.However,Cl^(-)that are already bound inside the concrete will not lead to the deterioration of the concrete’s characterist...Chloride ions(Cl^(-))have been shown to impact the long-lasting nature of reinforced concrete.However,Cl^(-)that are already bound inside the concrete will not lead to the deterioration of the concrete’s characteristics.The composition of the cement-based material,including the type of cement and auxiliary materials,greatly influences the ability of the material to bind Cl^(-),and varied components result in varying binding beha-vior of the Cl^(-).Simultaneously,the Cl^(-)binding process in concrete is influenced by both the internal and exterior surroundings,as well as the curing practices.These factors impact the hydration process of the cement and the internal pore structure of the concrete.Currently,mathematical theories and molecular dynamics simulations have increasingly been employed as the prevalent methods for examining the binding behaviors of Cl^(-)in concrete.These techniques are extensively utilized for predicting the lifespan and conducting microscopic studies of reinforced concrete in Cl^(-)settings.This work proposes recommendations for future research based on a summary of experimental and simulation investigations on Cl^(-)binding.Which will offer theoretical guidance for studying the binding of Cl^(-)in cement-based materials.展开更多
A slurry-phase carbonation technique was utilized,employing argon oxygen decarburization slag(AOD slag)as a source of calcium and MgCl_(2) as a regulator for the crystal morphology of acicular aragonite.Subsequently,t...A slurry-phase carbonation technique was utilized,employing argon oxygen decarburization slag(AOD slag)as a source of calcium and MgCl_(2) as a regulator for the crystal morphology of acicular aragonite.Subsequently,the carbonated AOD slag,enriched with acicular aragonite,was employed in fabricating composite cementitious materials,followed by an analysis of their evolution in hydration heat,hydration products,and microscopic morphology.Additionally,it delved into the mechanism through which acicular aragonite enhances the stength of composite cementitious materials.Moreover,advanced simulation software for engineering and sciences(ABAQUS)was utilized to simulate the compressive performance of composite mortar with varying dosages of acicular aragonite.The findings demonstrate that the carbonated AOD slag,containing 83.4%acicular aragonite(with an average aspect ratio of 21.31),exhibited commendable compatibility with cement.Moderate integration of carbonated AOD slag facilitated the formation of calcium sulfoaluminate hydrate(AFt)phases.The acicular aragonite within the cementitious matrix showcased remarkable filling effects.As the dosage of carbonated AOD slag increased,flexural and compressive strengths of cement mortar initially rose before declining.Upon reaching a 6%cement inclusion of carbonated AOD slag,the various constituents of the cementitious material displayed optimal synergy.The numerical simulation results confirmed the experimental findings,demonstrating a favorable increase in compressive strength and flexural strength with the addition of acicular aragonite.The acicular aragonite strengthened the matrix by serving bridging and pull-out functions.展开更多
The study aims to investigate the carbonated water erosion mechanism of lining concrete in tunnels traversing karst environment and enhance its resistance.In this study,dynamic carbonated water erosion was simulated t...The study aims to investigate the carbonated water erosion mechanism of lining concrete in tunnels traversing karst environment and enhance its resistance.In this study,dynamic carbonated water erosion was simulated to assess erosion depth,microstructure,phase migrations,and pore structure in various tunnel lining cement-based materials.Additionally,Ca^(2+)leaching was analyzed,and impact of Ca/Si molar ratio in hydration products on erosion resistance was discussed by thermodynamic calculations.The results indicate that carbonated water erosion caused rough and porous surface on specimens,with reduced portlandite and CaCO_(3) content,increased porosity,and an enlargement of pore size.The thermodynamic calculations indicate that the erosion is spontaneous,driven by physical dissolution and chemical reactions dominated by Gibbs free energy.And the erosion reactions proceed more spontaneously and extensively when Ca/Si molar ratio in hydration products was higher.Therefore,cement-based materials with higher portlandite content exhibit weaker erosion resistance.Model-building concrete,with C-S-H gel and portlandite as primary hydration products,has greater erosion susceptibility than shotcrete with ettringite as main hydration product.Moreover,adding silicon-rich mineral admixtures can enhance the erosion resistance.This research offers theory and tech insights to boost cement-based material resistance against carbonated water erosion in karst tunnel engineering.展开更多
In order to realize the full resource utilization of ferronickel slag(FNS)in cement-based materials,this paper studied the influences of mechanical grinding activation on the physical and chemical properties and react...In order to realize the full resource utilization of ferronickel slag(FNS)in cement-based materials,this paper studied the influences of mechanical grinding activation on the physical and chemical properties and reactivity of ferrous extraction tailing of nickel slag(FETNS).Four grinding processes of 5,10,20 and 30 min were set up to evaluate the influence of grinding process on the physical and chemical properties of FETNS with the aid of BET,XRD,Rietveld analysis and particle size distribution.The cement-FETNS composite cementitious material was prepared by replacing cement with 0%,10%,15%,20%,25%and 30%FETNS.The influence of FETNS fineness and content on the properties of composite cementitious system were characterized by mechanical properties,reaction products,early hydration process and pore structure characteristics.The results show that the grinding process can effectively improve the pozzolanic activity of FETNS.The compressive strength of FETNS-M_(30)paste is higher than that of FETNS-M_(5) paste in the early and late stages,and the later strength is higher than that of the baseline group when the content of FETNS-M_(30)is 10%-25%.The pozzolanic activity of FETNS-M_(30)powder is significantly improved and higher than that of FETNS-M_(5) powder.Under the same content,the Ca/Si ratio of C-S-H gel in FETNS-M_(30)paste is small,and the degree of silicate polymerization is higher.When the FETNS-M_(30)content is 10%,the proportions of favorable pores d<50 nm(harmless pores and less-harmful pores)of FETNS-M_(5) paste and FETNS-M_(30)paste is 95.3%and 95.4%,respectively,indicating a denser pore structure of the FETNS-M_(30)paste.展开更多
This paper conducted experimental studies on the damping and mechanical properties of carbon nanotube-nanosilica-cement composite materials with different carbon nanotube contents. The damping and mechanical propertie...This paper conducted experimental studies on the damping and mechanical properties of carbon nanotube-nanosilica-cement composite materials with different carbon nanotube contents. The damping and mechanical properties enhancement mechanisms were analyzed and compared through the porosity structure test, XRD analysis, and scanning electron microscope observation. The results show that the introduction of nanosilica significantly improves the dispersion of carbon nanotubes in the cement matrix. At the same time, the addition of nanosilica not only effectively reduces the critical pore size and average pore size of the cement composite material, but also exhibits good synergistic effects with carbon nanotubes, which can significantly optimize the pore structure. Finally, a rationalization suggestion for the co-doping of nanosilica and carbon nanotubes was given to achieve a significant increase in the flexural strength, compressive strength and loss factor of cement-based materials.展开更多
Effects of calcined coal gangue （CG） aggregates treated by the surface thermal activation on the flowability and strength, and paste-CG aggregate interfaces of the cement-based material were investigated. The experi...Effects of calcined coal gangue （CG） aggregates treated by the surface thermal activation on the flowability and strength, and paste-CG aggregate interfaces of the cement-based material were investigated. The experimental results show that the compressive and flexural strength of the cement-based material with the calcined CG aggregates is much higher than that of the material with the natural CG aggregates, but the flowability of the material with calcined CG is significantly reduced with the calcined time. The strength of the material with the calcined CG aggregates only increases little with the calcined time at the same w/c ratio, but is reduced with the calcined time at the same flowability. The CG aggregates calcined by the surface thermal activation obviously overcomes the disadvantages of fully calcined CG.展开更多
The self-healing action of a permeable crystalline coating on the po rous mortar was investigated by two times impermeability test. Moreover, the sel f-healing mechanism of cement-based materials with the permeable cr...The self-healing action of a permeable crystalline coating on the po rous mortar was investigated by two times impermeability test. Moreover, the sel f-healing mechanism of cement-based materials with the permeable crystalline c oating was studied by SEM. The results indicate that the permeable crystalline c oating not only seals the pores and cracks in mortar during its curing process, but also heals the permeable pathway caused by first impermeability test or crac ks produced by freeze-thaw cycles. Therefore, cement-based materials can be im proved by the permeable crystalline coating for the self-healing function. SEM images prove that the self-healing function is realized by generating a great q uantity of non-soluble dendritic crystalline within the pores and cracks, which prevents the penetration of water and other liquids.展开更多
The influence of water content on the conductivity and piezoresistivity of cement-based material with carbon fiber （CF） and carbon black （CB） was investigated. The piezoresistivity of cement-based material with bo...The influence of water content on the conductivity and piezoresistivity of cement-based material with carbon fiber （CF） and carbon black （CB） was investigated. The piezoresistivity of cement-based material with both CF and CB was compared with that of cement-based material with CF only, and the changes in electrical resistivity of cement-based material with both CF and CB under static and loading conditions in different drying and soaking time were studied. It is found that the piezoresistivity of cement-based material with both CF and CB has better repeatability and linearity than that of cement-based material with CF only. The conductivity and the sensitivity of piezoresistive cement-based material with both CF and CB are enhanced as the water content in piezoresistive cement-based material increases.展开更多
The effects of specimen size and shape on development of water loss and shrinkage of mortar and concrete respectively were investigated. The experimental results showed that the effects of specimen size and shape on w...The effects of specimen size and shape on development of water loss and shrinkage of mortar and concrete respectively were investigated. The experimental results showed that the effects of specimen size and shape on water loss ratio were consistent with those on drying shrinkage strain. It is also indicated that drying shrinkage strain has obvious linear correlation with water loss ratios independent of specimen size and shape. The effects of specimen size and shape on the water loss ratio were embodied in established model of averaged relative humidity improved by considering effects of sequential hydration and calculated by finite difference method. Furthermore, the effects of specimen size and shape on drying shrinkage strain of concrete were experimentally deduced and applied to modify criterion EB-FIP1990. The comparison between experimental and calculated results shows that the modified EB-FIP1990 can be adopted to predict drying shrinkage strain of concrete with reasonable accuracy.展开更多
A self-made AMPS-modified polyacrylic acid superplasticizer and two others of the same type but with different molecular structures, which are commercially available, are used in this study to investigate the effect o...A self-made AMPS-modified polyacrylic acid superplasticizer and two others of the same type but with different molecular structures, which are commercially available, are used in this study to investigate the effect of a 2-acrylamide-2-methyl propylene sulfonic （AMPS）-modified polyacrylic acid superplasticizer on the properties of cement-based materials. In the experiments, initial fluidity, 1 and 2 h fluidity over time after admixtion, bleeding rate of the net cement mortar, and adsorption capacity and rate of cement particles are determined by adding different dosages of the three superplasticizers into the cement paste to characterize the dispersivity and the dispersion retention capability of each superplasticizer. Water-reducing rates of three kinds of mortars are simultaneously determined to characterize the water-reducing capacity of each superplasticizer, as well as the 3 and 28 d compressive strengths to characterize the compression resistance. Results show that water-reducing effect and fluidity better maintain the capability of the AMPS-modified polyacrylic acid superplasticizer than the two commercially available polyacrylic acid superplasticizers, and the compressive strengths after 3 and 28 d show significant growth. In conclusion, the effects of water reduction and strengthening of the AMPS-modified polyacrylic acid superplasticizer are evidently better than those of the two commercially available polyacrylic acid superplasticizers.展开更多
To investigate the transport characteristics of chloride ions in cement-based materials, the Mori-Tanaka (M-T) prediction scheme of the effective diffusion coefficient in composites containing single-phase and multi-p...To investigate the transport characteristics of chloride ions in cement-based materials, the Mori-Tanaka (M-T) prediction scheme of the effective diffusion coefficient in composites containing single-phase and multi-phase inclusions is systematically deduced based on the theory of composite mechanics and porous medium. The volume fraction, morphology and distribution of aggregates, as well as the interfacial transition zone (ITZ) are fully taken into consideration in this proposed model. The results show that the algorithm of M-T prediction scheme with high accuracy is relatively simple.展开更多
The hydration mechanism of low quality fly ash in cement-based materials was investigated. The hydration heat of the composite cementitious materials was determined by isothermal calorimetry, and the hydration product...The hydration mechanism of low quality fly ash in cement-based materials was investigated. The hydration heat of the composite cementitious materials was determined by isothermal calorimetry, and the hydration products, quantity, pore structure and morphology were measured by X-ray diffraction(XRD), thermalgravity-differential thermal analysis(TG-DTA), mercury intrusion porosimetry(MIP) and scanning electron microscopy(SEM), respectively. The results indicate that grinding could not only improve the physical properties of the low quality fly ash on particle effect, but also improve hydration properties of the cementitious system from various aspects compared with raw low quality fly ash(RLFA). At the early stage of hydration, the low quanlity fly ash acts as almost inert material; but then at the later stage, high chemical activity, especially for ground low quality fly ash(GLFA), could be observed. It can accelerate the formation of hydration products containing more chemical bonded water, resulting in higher degree of cement hydration, thus denser microstructure and more reasonable pore size distribution, but the hydration heat in total is reduced. It can also delay the induction period, but the accelerating period is shortened and there is little influence on the second exothermic peak.展开更多
To investigate the durability, especially the long-term stability of cement-based materials with very low w/b, the air permeability test, carbonation test, capillary absorption rate test and dilation potential test we...To investigate the durability, especially the long-term stability of cement-based materials with very low w/b, the air permeability test, carbonation test, capillary absorption rate test and dilation potential test were adopted under long-term heat treatment condition. Microstructure of these materials is also analyzed by scanning electronic microscopy （SEM） and mercury intrusion porosimeter （MIP） in order to further unveil its mechanism and interrelation between microstructure and its properties. The results indicate that in the area investigated, cement-based material with w/b 0.17, like RPC, possesses low porosity and excellent durability. Moreover, its porosity will further decrease under long-term heat treatment compared with normal heat treatment. Its long-term durability is much superior to that of other cement-based materials with w/b 0.25 or 0.35 as high strength concrete（HSC）.展开更多
The capillary absorption of water by unsaturated cement-based material is the main reason of degradation of the structures subjected to an aggressive environment since water often acts as the transporting medium for d...The capillary absorption of water by unsaturated cement-based material is the main reason of degradation of the structures subjected to an aggressive environment since water often acts as the transporting medium for damaging contaminants. It is well known that the capillarity coefficient and sorptivity are two important parameters to characterize the water absorption of porous materials. Generally, the former is used to describe the penetration depth or height of water transport, which must be measured by special and advanced equipment. In contrast, the sorptivity represents the relationship between cumulative volume of water uptake and the squareroot of the elapsed time, which can be easily measured by the gravimetric method in a normal laboratory condition. In the present study, an analytical method is developed to build up a bridge between these two parameters, with the purpose that the sorptivity or the gravimetric method can be used to predict the penetration depth of water absorption. Additionally, a new model to explain the dependence of sorptivity on initial water content of the material is developed in order to fit the in situ condition. The comparison of predicted results by the analytical method with experimental data or numerical calculation results, as well as some previous models, validates the feasibility of the methods presented in this paper.展开更多
The transmission and distribution of moisture in cement-based materials are of great significance to the properties and durability of materials. Traditional macro-humidity monitoring equipment in civil engineering can...The transmission and distribution of moisture in cement-based materials are of great significance to the properties and durability of materials. Traditional macro-humidity monitoring equipment in civil engineering cannot capture the microscale humidity inside cement-based materials in situ. In this paper, a method of using rhodamine 6G fluorescence to characterize the change in relative humidity in cement-based materials is proposed. Two kinds of moulding processes are designed, which are premixed and smeared after moulding, and the optimal preparation concentration is explored. The results showed that rhodamine 6G can reflect the relative humidity of cement-based materials in situ by its fluorescence intensity and had little effect on the hydration heat release and hydration products of cement-based materials;the fluorescence intensity was much higher when the internal relative humidity was 63% and 75%. The research results lead the application of polymer materials in the field of traditional building materials, help to explore the performance evolution law of cement-based materials in micro scale, and have important significance for the evolution from single discipline to interdisciplinary.展开更多
The development of strength and the form of attack of cement-based material made of limestone powder at low water-binder ratio under low-temperature sulfate environment were studied. The results indicate that when wat...The development of strength and the form of attack of cement-based material made of limestone powder at low water-binder ratio under low-temperature sulfate environment were studied. The results indicate that when water-binder ratio is lower than 0.40, the cement-based material with limestone powder has insignificant change in appearance after being soaked in 10% magnesium sulfate solution at low temperature for 120 d, and has significant change in appearance after being soaked at the age of 200 d. Expansion damage and exfoliation occur on the surface of concrete test cube at different levels. When limestone powder accounts for about 28 percent of cementitious material, with the decrease of water-binder ratio, the compressive strength loss has gradually decreased after the material is soaked in the magnesium sulfate solution at low temperature at the age of 200 d. After the specimen with the water-binder ratio of less than 0.4 and the limestone powder volume of greater than 20% is soaked in 10% magnesium sulfate solution at low temperature at the age of 200 d, gypsum attack-led destruction is caused to the concrete test cube, without thaumasite sulfate attack.展开更多
The mechanism of glutinous rice flour,a kind of natural admixture,on the hydration process,setting time,and microstructure of the Portland cement was investigated.The experimental results show that the glutinous rice ...The mechanism of glutinous rice flour,a kind of natural admixture,on the hydration process,setting time,and microstructure of the Portland cement was investigated.The experimental results show that the glutinous rice flour has an obvious setting retarding effect on cement pastes.The optimal dosage of the glutinous rice flour is 3wt%.In this case,the initial and final setting time of the paste are delayed by 140 and185 min,respectively.The flexural and compressive strengths of the hardened paste are increased by 0.35%and 0.07%after 56 d of curing.The glutinous rice flour hinders the mineral dissolution process and decreases the concentration of calcium ion at the initial stage of hydration due to the complexation effect,thereby hindering the nucleation and growth of CH and C-S-H phases and prolonging the hydration process.However,C-S-H phases combine with the glutinous rice flour to contribute the bonding effect together,which compacts the microstructure of hardened cement pastes at the later hydration stage of cement pastes.Thus,in-depth investigation on the utilization of glutinous rice flour as the admixture for the Portland cement is expected to be meaningful for the control of hydration exothermic rate and setting time.展开更多
Thaumasite form of sulfate attack（TSA）is a major concern in evaluating durability of concrete structures subjected to sulfate and carbonate ions.By means of Fourier transform infrared spectroscopy （FT-IR）,X-ray di...Thaumasite form of sulfate attack（TSA）is a major concern in evaluating durability of concrete structures subjected to sulfate and carbonate ions.By means of Fourier transform infrared spectroscopy （FT-IR）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,and energy dispersive spectrum（EDS） as well as Raman spectra of erosion substances,effect of fly ash on TSA resistance of Portland cement-based material were investigated.Immersed in magnesium sulfate solution with 33 800 ppm mass concentration of SO 4 2-at 5±2℃for 15 weeks,ratio of compressive strength loss decreased as binder replacement ratio of fly ash increased.Furthermore,when binder replacement of fly ash was 60%,compressive strength increased.When thaumasite came into being in samples with 0,15%binder replacement ratio of fly ash,ettringite and gypsum appeared in those with 30%,45%,60%binder replacement ratio of fly ash.Results mentioned above showed that fly ash can restrain formation of thaumasite and improve TSA resistance of Portland cement-based material sufficiently.展开更多
The influence of air-cooled blast furnace slag aggregates as replacement of natural aggregates on the water absorption of concrete and mortar was studied, and the mechanism was analyzed. The interface between aggregat...The influence of air-cooled blast furnace slag aggregates as replacement of natural aggregates on the water absorption of concrete and mortar was studied, and the mechanism was analyzed. The interface between aggregate and matrix in concrete was analyzed by using a micro-hardness tester, a laser confocal microscope and a scanning electron microscope with backscattered electron image mode. The pore structure of mortar matrixes under different curing conditions was investigated by mercury intrusion porosimetry. The results showed that when natural aggregates were replaced with air-cooled blast furnace slag aggregates in mortar or concrete, the content of the capillary pore in the mortar matrix was reduced and the interfacial structure between aggregate and matrix was improved, resulting in the lower water absorption of mortar or concrete. Compared to the concrete made with crushed limestone and natural river sand, the initial absorption coefficient, the secondary absorption coefficient and the water absorption capacity through the surface for 7 d of the concrete made from crushed air-cooled blast furnace slag and air-cooled blast furnace slag sand were reduced by 48.9%, 52.8%, and 46.5%, respectively.展开更多
The grinding characteristics of two or multi-component material of cli nker with limestone, blast furnace slag and fly ash were studied. Investigation was carried out on the particle size distribution, the Blaine fin...The grinding characteristics of two or multi-component material of cli nker with limestone, blast furnace slag and fly ash were studied. Investigation was carried out on the particle size distribution, the Blaine fineness and the s ieve residue of the separate and interground products. The relative contents of clinker and limestone in different size fractions of the interground product wer e examined, and the interaction of two components, which have different grindabi lities, was analyzed. The results show there exists a selective grinding effect during intergrinding, one component can help or hinder the grinding of the other . Making good use of this interaction appropriately not only enhances the grinda bilities of two or multi-component mixtures, which can promote the grinding pro cess of clinker with industrial wastes, but also improves their particle size di stribution and properties.展开更多
文摘Chloride ions(Cl^(-))have been shown to impact the long-lasting nature of reinforced concrete.However,Cl^(-)that are already bound inside the concrete will not lead to the deterioration of the concrete’s characteristics.The composition of the cement-based material,including the type of cement and auxiliary materials,greatly influences the ability of the material to bind Cl^(-),and varied components result in varying binding beha-vior of the Cl^(-).Simultaneously,the Cl^(-)binding process in concrete is influenced by both the internal and exterior surroundings,as well as the curing practices.These factors impact the hydration process of the cement and the internal pore structure of the concrete.Currently,mathematical theories and molecular dynamics simulations have increasingly been employed as the prevalent methods for examining the binding behaviors of Cl^(-)in concrete.These techniques are extensively utilized for predicting the lifespan and conducting microscopic studies of reinforced concrete in Cl^(-)settings.This work proposes recommendations for future research based on a summary of experimental and simulation investigations on Cl^(-)binding.Which will offer theoretical guidance for studying the binding of Cl^(-)in cement-based materials.
基金the financial support from Innovative Research Group Project of Natural Science Foundation of Hebei Province(No.E2022209093)Central Guidance Local Science and Technology Development Fund Project of Hebei Province(No.236Z3803G)+1 种基金Scientific and Technological Project of Tangshan(No.23130205E)Youth Teacher Pre Research Fund Project of the School of Metallurgy and Energy(No.YJY20244373).
文摘A slurry-phase carbonation technique was utilized,employing argon oxygen decarburization slag(AOD slag)as a source of calcium and MgCl_(2) as a regulator for the crystal morphology of acicular aragonite.Subsequently,the carbonated AOD slag,enriched with acicular aragonite,was employed in fabricating composite cementitious materials,followed by an analysis of their evolution in hydration heat,hydration products,and microscopic morphology.Additionally,it delved into the mechanism through which acicular aragonite enhances the stength of composite cementitious materials.Moreover,advanced simulation software for engineering and sciences(ABAQUS)was utilized to simulate the compressive performance of composite mortar with varying dosages of acicular aragonite.The findings demonstrate that the carbonated AOD slag,containing 83.4%acicular aragonite(with an average aspect ratio of 21.31),exhibited commendable compatibility with cement.Moderate integration of carbonated AOD slag facilitated the formation of calcium sulfoaluminate hydrate(AFt)phases.The acicular aragonite within the cementitious matrix showcased remarkable filling effects.As the dosage of carbonated AOD slag increased,flexural and compressive strengths of cement mortar initially rose before declining.Upon reaching a 6%cement inclusion of carbonated AOD slag,the various constituents of the cementitious material displayed optimal synergy.The numerical simulation results confirmed the experimental findings,demonstrating a favorable increase in compressive strength and flexural strength with the addition of acicular aragonite.The acicular aragonite strengthened the matrix by serving bridging and pull-out functions.
基金Project(2021YJ059)supported by the Research Project of China Academy of Railway Sciences。
文摘The study aims to investigate the carbonated water erosion mechanism of lining concrete in tunnels traversing karst environment and enhance its resistance.In this study,dynamic carbonated water erosion was simulated to assess erosion depth,microstructure,phase migrations,and pore structure in various tunnel lining cement-based materials.Additionally,Ca^(2+)leaching was analyzed,and impact of Ca/Si molar ratio in hydration products on erosion resistance was discussed by thermodynamic calculations.The results indicate that carbonated water erosion caused rough and porous surface on specimens,with reduced portlandite and CaCO_(3) content,increased porosity,and an enlargement of pore size.The thermodynamic calculations indicate that the erosion is spontaneous,driven by physical dissolution and chemical reactions dominated by Gibbs free energy.And the erosion reactions proceed more spontaneously and extensively when Ca/Si molar ratio in hydration products was higher.Therefore,cement-based materials with higher portlandite content exhibit weaker erosion resistance.Model-building concrete,with C-S-H gel and portlandite as primary hydration products,has greater erosion susceptibility than shotcrete with ettringite as main hydration product.Moreover,adding silicon-rich mineral admixtures can enhance the erosion resistance.This research offers theory and tech insights to boost cement-based material resistance against carbonated water erosion in karst tunnel engineering.
基金Funded by the Science and Technology Program of Gansu Province(Nos.25CXGA070,24JRRA213)the National Natural Science Foundation of China(Nos.52468036,52178216,U21A20150)。
文摘In order to realize the full resource utilization of ferronickel slag(FNS)in cement-based materials,this paper studied the influences of mechanical grinding activation on the physical and chemical properties and reactivity of ferrous extraction tailing of nickel slag(FETNS).Four grinding processes of 5,10,20 and 30 min were set up to evaluate the influence of grinding process on the physical and chemical properties of FETNS with the aid of BET,XRD,Rietveld analysis and particle size distribution.The cement-FETNS composite cementitious material was prepared by replacing cement with 0%,10%,15%,20%,25%and 30%FETNS.The influence of FETNS fineness and content on the properties of composite cementitious system were characterized by mechanical properties,reaction products,early hydration process and pore structure characteristics.The results show that the grinding process can effectively improve the pozzolanic activity of FETNS.The compressive strength of FETNS-M_(30)paste is higher than that of FETNS-M_(5) paste in the early and late stages,and the later strength is higher than that of the baseline group when the content of FETNS-M_(30)is 10%-25%.The pozzolanic activity of FETNS-M_(30)powder is significantly improved and higher than that of FETNS-M_(5) powder.Under the same content,the Ca/Si ratio of C-S-H gel in FETNS-M_(30)paste is small,and the degree of silicate polymerization is higher.When the FETNS-M_(30)content is 10%,the proportions of favorable pores d<50 nm(harmless pores and less-harmful pores)of FETNS-M_(5) paste and FETNS-M_(30)paste is 95.3%and 95.4%,respectively,indicating a denser pore structure of the FETNS-M_(30)paste.
文摘This paper conducted experimental studies on the damping and mechanical properties of carbon nanotube-nanosilica-cement composite materials with different carbon nanotube contents. The damping and mechanical properties enhancement mechanisms were analyzed and compared through the porosity structure test, XRD analysis, and scanning electron microscope observation. The results show that the introduction of nanosilica significantly improves the dispersion of carbon nanotubes in the cement matrix. At the same time, the addition of nanosilica not only effectively reduces the critical pore size and average pore size of the cement composite material, but also exhibits good synergistic effects with carbon nanotubes, which can significantly optimize the pore structure. Finally, a rationalization suggestion for the co-doping of nanosilica and carbon nanotubes was given to achieve a significant increase in the flexural strength, compressive strength and loss factor of cement-based materials.
基金Funded by the Major State Basic Research Development Program of China('973'Project,2001CB610705)
文摘Effects of calcined coal gangue （CG） aggregates treated by the surface thermal activation on the flowability and strength, and paste-CG aggregate interfaces of the cement-based material were investigated. The experimental results show that the compressive and flexural strength of the cement-based material with the calcined CG aggregates is much higher than that of the material with the natural CG aggregates, but the flowability of the material with calcined CG is significantly reduced with the calcined time. The strength of the material with the calcined CG aggregates only increases little with the calcined time at the same w/c ratio, but is reduced with the calcined time at the same flowability. The CG aggregates calcined by the surface thermal activation obviously overcomes the disadvantages of fully calcined CG.
基金Funded by the Scientific and Technological Project of Hubei Province(2004BCS005)
文摘The self-healing action of a permeable crystalline coating on the po rous mortar was investigated by two times impermeability test. Moreover, the sel f-healing mechanism of cement-based materials with the permeable crystalline c oating was studied by SEM. The results indicate that the permeable crystalline c oating not only seals the pores and cracks in mortar during its curing process, but also heals the permeable pathway caused by first impermeability test or crac ks produced by freeze-thaw cycles. Therefore, cement-based materials can be im proved by the permeable crystalline coating for the self-healing function. SEM images prove that the self-healing function is realized by generating a great q uantity of non-soluble dendritic crystalline within the pores and cracks, which prevents the penetration of water and other liquids.
基金Funded by the National Natural Science Foundation of China (No.50238040, 50538020)the Postdoctoral Science Foundation of China (No.20060390803)the High-Tech Research and Development Program of China (No. 2002AA335010)
文摘The influence of water content on the conductivity and piezoresistivity of cement-based material with carbon fiber （CF） and carbon black （CB） was investigated. The piezoresistivity of cement-based material with both CF and CB was compared with that of cement-based material with CF only, and the changes in electrical resistivity of cement-based material with both CF and CB under static and loading conditions in different drying and soaking time were studied. It is found that the piezoresistivity of cement-based material with both CF and CB has better repeatability and linearity than that of cement-based material with CF only. The conductivity and the sensitivity of piezoresistive cement-based material with both CF and CB are enhanced as the water content in piezoresistive cement-based material increases.
基金Funded by the National Basic Research Program of China(No.2009CB623200)Zhejiang Natural Science Foundation(No.LQ12E08002)+1 种基金Ningbo Natural Science Foundation(No.2012A610159)the School Disciplinary Projects(No.zj1113,XKL11D2081)
文摘The effects of specimen size and shape on development of water loss and shrinkage of mortar and concrete respectively were investigated. The experimental results showed that the effects of specimen size and shape on water loss ratio were consistent with those on drying shrinkage strain. It is also indicated that drying shrinkage strain has obvious linear correlation with water loss ratios independent of specimen size and shape. The effects of specimen size and shape on the water loss ratio were embodied in established model of averaged relative humidity improved by considering effects of sequential hydration and calculated by finite difference method. Furthermore, the effects of specimen size and shape on drying shrinkage strain of concrete were experimentally deduced and applied to modify criterion EB-FIP1990. The comparison between experimental and calculated results shows that the modified EB-FIP1990 can be adopted to predict drying shrinkage strain of concrete with reasonable accuracy.
基金Funded by the Fujian Education Department(Nos.JA11329,JA12412)Quanzhou(Fujian)Technology Research and Development Program(Nos.2013Z158,2013Z47,2010G7)
文摘A self-made AMPS-modified polyacrylic acid superplasticizer and two others of the same type but with different molecular structures, which are commercially available, are used in this study to investigate the effect of a 2-acrylamide-2-methyl propylene sulfonic （AMPS）-modified polyacrylic acid superplasticizer on the properties of cement-based materials. In the experiments, initial fluidity, 1 and 2 h fluidity over time after admixtion, bleeding rate of the net cement mortar, and adsorption capacity and rate of cement particles are determined by adding different dosages of the three superplasticizers into the cement paste to characterize the dispersivity and the dispersion retention capability of each superplasticizer. Water-reducing rates of three kinds of mortars are simultaneously determined to characterize the water-reducing capacity of each superplasticizer, as well as the 3 and 28 d compressive strengths to characterize the compression resistance. Results show that water-reducing effect and fluidity better maintain the capability of the AMPS-modified polyacrylic acid superplasticizer than the two commercially available polyacrylic acid superplasticizers, and the compressive strengths after 3 and 28 d show significant growth. In conclusion, the effects of water reduction and strengthening of the AMPS-modified polyacrylic acid superplasticizer are evidently better than those of the two commercially available polyacrylic acid superplasticizers.
基金Funded by the National Natural Science Foundations of China(Nos.51778378,51478278)。
文摘To investigate the transport characteristics of chloride ions in cement-based materials, the Mori-Tanaka (M-T) prediction scheme of the effective diffusion coefficient in composites containing single-phase and multi-phase inclusions is systematically deduced based on the theory of composite mechanics and porous medium. The volume fraction, morphology and distribution of aggregates, as well as the interfacial transition zone (ITZ) are fully taken into consideration in this proposed model. The results show that the algorithm of M-T prediction scheme with high accuracy is relatively simple.
基金Project(51208391) supported by the National Natural Science Foundation of China
文摘The hydration mechanism of low quality fly ash in cement-based materials was investigated. The hydration heat of the composite cementitious materials was determined by isothermal calorimetry, and the hydration products, quantity, pore structure and morphology were measured by X-ray diffraction(XRD), thermalgravity-differential thermal analysis(TG-DTA), mercury intrusion porosimetry(MIP) and scanning electron microscopy(SEM), respectively. The results indicate that grinding could not only improve the physical properties of the low quality fly ash on particle effect, but also improve hydration properties of the cementitious system from various aspects compared with raw low quality fly ash(RLFA). At the early stage of hydration, the low quanlity fly ash acts as almost inert material; but then at the later stage, high chemical activity, especially for ground low quality fly ash(GLFA), could be observed. It can accelerate the formation of hydration products containing more chemical bonded water, resulting in higher degree of cement hydration, thus denser microstructure and more reasonable pore size distribution, but the hydration heat in total is reduced. It can also delay the induction period, but the accelerating period is shortened and there is little influence on the second exothermic peak.
基金Funded by the National Natural Science Foundation of China(No.50708114)the Postgraduate Science Foundation of China(No.20060400883)
文摘To investigate the durability, especially the long-term stability of cement-based materials with very low w/b, the air permeability test, carbonation test, capillary absorption rate test and dilation potential test were adopted under long-term heat treatment condition. Microstructure of these materials is also analyzed by scanning electronic microscopy （SEM） and mercury intrusion porosimeter （MIP） in order to further unveil its mechanism and interrelation between microstructure and its properties. The results indicate that in the area investigated, cement-based material with w/b 0.17, like RPC, possesses low porosity and excellent durability. Moreover, its porosity will further decrease under long-term heat treatment compared with normal heat treatment. Its long-term durability is much superior to that of other cement-based materials with w/b 0.25 or 0.35 as high strength concrete（HSC）.
基金supported by the Key Programs of Ministry of Education of China(Grant No.109046)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Eduation Ministrythe Program of Innovative Research Team of Education of China(Grant No.IRT0518)
文摘The capillary absorption of water by unsaturated cement-based material is the main reason of degradation of the structures subjected to an aggressive environment since water often acts as the transporting medium for damaging contaminants. It is well known that the capillarity coefficient and sorptivity are two important parameters to characterize the water absorption of porous materials. Generally, the former is used to describe the penetration depth or height of water transport, which must be measured by special and advanced equipment. In contrast, the sorptivity represents the relationship between cumulative volume of water uptake and the squareroot of the elapsed time, which can be easily measured by the gravimetric method in a normal laboratory condition. In the present study, an analytical method is developed to build up a bridge between these two parameters, with the purpose that the sorptivity or the gravimetric method can be used to predict the penetration depth of water absorption. Additionally, a new model to explain the dependence of sorptivity on initial water content of the material is developed in order to fit the in situ condition. The comparison of predicted results by the analytical method with experimental data or numerical calculation results, as well as some previous models, validates the feasibility of the methods presented in this paper.
基金Project(2018YFD1101002) supported by the National Key R&D Program of ChinaProject(51308405) supported by the National Natural Science Foundation of China。
文摘The transmission and distribution of moisture in cement-based materials are of great significance to the properties and durability of materials. Traditional macro-humidity monitoring equipment in civil engineering cannot capture the microscale humidity inside cement-based materials in situ. In this paper, a method of using rhodamine 6G fluorescence to characterize the change in relative humidity in cement-based materials is proposed. Two kinds of moulding processes are designed, which are premixed and smeared after moulding, and the optimal preparation concentration is explored. The results showed that rhodamine 6G can reflect the relative humidity of cement-based materials in situ by its fluorescence intensity and had little effect on the hydration heat release and hydration products of cement-based materials;the fluorescence intensity was much higher when the internal relative humidity was 63% and 75%. The research results lead the application of polymer materials in the field of traditional building materials, help to explore the performance evolution law of cement-based materials in micro scale, and have important significance for the evolution from single discipline to interdisciplinary.
文摘The development of strength and the form of attack of cement-based material made of limestone powder at low water-binder ratio under low-temperature sulfate environment were studied. The results indicate that when water-binder ratio is lower than 0.40, the cement-based material with limestone powder has insignificant change in appearance after being soaked in 10% magnesium sulfate solution at low temperature for 120 d, and has significant change in appearance after being soaked at the age of 200 d. Expansion damage and exfoliation occur on the surface of concrete test cube at different levels. When limestone powder accounts for about 28 percent of cementitious material, with the decrease of water-binder ratio, the compressive strength loss has gradually decreased after the material is soaked in the magnesium sulfate solution at low temperature at the age of 200 d. After the specimen with the water-binder ratio of less than 0.4 and the limestone powder volume of greater than 20% is soaked in 10% magnesium sulfate solution at low temperature at the age of 200 d, gypsum attack-led destruction is caused to the concrete test cube, without thaumasite sulfate attack.
基金Funded by the Open Fund of Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province (JBGS008)the Research Lab Construction of Hainan University (ZY2019HN0904)the Opening Project of State Key Laboratory of Green Building Materials (2022GBM01)。
文摘The mechanism of glutinous rice flour,a kind of natural admixture,on the hydration process,setting time,and microstructure of the Portland cement was investigated.The experimental results show that the glutinous rice flour has an obvious setting retarding effect on cement pastes.The optimal dosage of the glutinous rice flour is 3wt%.In this case,the initial and final setting time of the paste are delayed by 140 and185 min,respectively.The flexural and compressive strengths of the hardened paste are increased by 0.35%and 0.07%after 56 d of curing.The glutinous rice flour hinders the mineral dissolution process and decreases the concentration of calcium ion at the initial stage of hydration due to the complexation effect,thereby hindering the nucleation and growth of CH and C-S-H phases and prolonging the hydration process.However,C-S-H phases combine with the glutinous rice flour to contribute the bonding effect together,which compacts the microstructure of hardened cement pastes at the later hydration stage of cement pastes.Thus,in-depth investigation on the utilization of glutinous rice flour as the admixture for the Portland cement is expected to be meaningful for the control of hydration exothermic rate and setting time.
基金Supported by the Scientific Research Foundation for the Talents of Hohai University(No.20090603)the Fundamental Research Funds for the Central Universities(No.2010B25514)the National Natural Science Foundation of China(No.50979032)
文摘Thaumasite form of sulfate attack（TSA）is a major concern in evaluating durability of concrete structures subjected to sulfate and carbonate ions.By means of Fourier transform infrared spectroscopy （FT-IR）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,and energy dispersive spectrum（EDS） as well as Raman spectra of erosion substances,effect of fly ash on TSA resistance of Portland cement-based material were investigated.Immersed in magnesium sulfate solution with 33 800 ppm mass concentration of SO 4 2-at 5±2℃for 15 weeks,ratio of compressive strength loss decreased as binder replacement ratio of fly ash increased.Furthermore,when binder replacement of fly ash was 60%,compressive strength increased.When thaumasite came into being in samples with 0,15%binder replacement ratio of fly ash,ettringite and gypsum appeared in those with 30%,45%,60%binder replacement ratio of fly ash.Results mentioned above showed that fly ash can restrain formation of thaumasite and improve TSA resistance of Portland cement-based material sufficiently.
基金Funded by the National Natural Science Foundation of China(Nos.51778003 and 51308004)the Project of Anhui Provincial Education Department for Sending Visiting Scholars to Research Abroad(No.gxfx ZD2016134)+1 种基金the Anhui Province Higher Education Revitalization Program Talent Project([2014]No.11)the National Key Research and Development Plan(No.2017YFB0310001)
文摘The influence of air-cooled blast furnace slag aggregates as replacement of natural aggregates on the water absorption of concrete and mortar was studied, and the mechanism was analyzed. The interface between aggregate and matrix in concrete was analyzed by using a micro-hardness tester, a laser confocal microscope and a scanning electron microscope with backscattered electron image mode. The pore structure of mortar matrixes under different curing conditions was investigated by mercury intrusion porosimetry. The results showed that when natural aggregates were replaced with air-cooled blast furnace slag aggregates in mortar or concrete, the content of the capillary pore in the mortar matrix was reduced and the interfacial structure between aggregate and matrix was improved, resulting in the lower water absorption of mortar or concrete. Compared to the concrete made with crushed limestone and natural river sand, the initial absorption coefficient, the secondary absorption coefficient and the water absorption capacity through the surface for 7 d of the concrete made from crushed air-cooled blast furnace slag and air-cooled blast furnace slag sand were reduced by 48.9%, 52.8%, and 46.5%, respectively.
基金Funded by Committee on Science and Technology Foundation of Guangdong (C11305)
文摘The grinding characteristics of two or multi-component material of cli nker with limestone, blast furnace slag and fly ash were studied. Investigation was carried out on the particle size distribution, the Blaine fineness and the s ieve residue of the separate and interground products. The relative contents of clinker and limestone in different size fractions of the interground product wer e examined, and the interaction of two components, which have different grindabi lities, was analyzed. The results show there exists a selective grinding effect during intergrinding, one component can help or hinder the grinding of the other . Making good use of this interaction appropriately not only enhances the grinda bilities of two or multi-component mixtures, which can promote the grinding pro cess of clinker with industrial wastes, but also improves their particle size di stribution and properties.
