The chloride penetration resistance of cement-based grout materials was improved by nano-silica emulsion.Specimens of mixtures containing different nano-silica particles or emulsions were exposed in sodium chloride so...The chloride penetration resistance of cement-based grout materials was improved by nano-silica emulsion.Specimens of mixtures containing different nano-silica particles or emulsions were exposed in sodium chloride solutions of specific concentrations with different test ages.Hardened properties of the mixes were assessed in terms of weight loss and compressive strength.X-ray diffraction(XRD)and scanning electron microscopy(SEM)of mixes were performed to analysis the phase evolution and microstructure.The results demonstrated that the introduction of nano-SiO_(2) emulsion significantly decreased the compressive strength loss and calcium hydroxide(CH)crystal content of hydration production,and then enhanced the resistance of cement-based grouting materials to chloride ion penetration.This improvement derives from the filling and pozzolanic effects of nano-SiO_(2) particles,which were incorporated via an emulsion and attributed to a well dispersion in grouting matrix.展开更多
Main performance of the cement grouting materials made up by Portland cement（PC） and sulphoaluminate cement（SAC） was investigated in this program, a kind of expanding agent（EA） which was mainly constituted by me...Main performance of the cement grouting materials made up by Portland cement（PC） and sulphoaluminate cement（SAC） was investigated in this program, a kind of expanding agent（EA） which was mainly constituted by metakaolin and alunite was utilized for the compensation of the shrinkage, the hydration products and micro structure of the grouting materials were researched by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The results showed that a high expansion rate of the grouting materials could be reached as the expanding agent mixed in 6% of PC mass; the addition of SAC in the S2（PC：SAC：EA=34：6：2.25） brought a further improvement of the expansion rate of the grouting materials, the analysis of XRD and SEM showed that due to the reaction of expanding agent and SAC in the grouting materials, more ettringite crystal was generated, which resulted in a higher early strength, the addition of SAC played an expansion and strength reinforcement role in the grouting materials.展开更多
The ongoing operation of subway systems makes existing tunnels vulnerable to deformations and structural damage caused by adjacent foundation pit construction.Such deformations-manifesting as horizontal displacement,h...The ongoing operation of subway systems makes existing tunnels vulnerable to deformations and structural damage caused by adjacent foundation pit construction.Such deformations-manifesting as horizontal displacement,heightened lateral convergence,and internal force redistribution-may significantly compromise subway operational safety.Grouting remediation has become a widely adopted solution for tunnel deformation control and structural reinforcement.Developing optimized grouting materials is crucial for improving remediation effectiveness,ensuring structural integrity,and maintaining uninterrupted subway operations.This investigation explores the substitution of fine mortar aggregates with 0.1 mm discarded rubber particles at varying concentrations(0%,3%,6%,9%,12%,and 15%).Experimental parameters included three water-cement ratios(0.65,0.70,and 0.75)with constant 4%WPU content.Mechanical properties including compressive strength,flexural strength,and compression-to-bending ratio were evaluated across specified curing periods.Material characterization employed Fourier Transform Infrared Spectroscopy(FTIR)spectroscopy for molecular analysis and Scanning Electron Microscopy(SEM)for microstructural examination.Results indicate optimal toughness at 0.70 water-cement ratio with 6%rubber content,meeting mechanical pumping specifications while maintaining structural performance.展开更多
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
The rapid development of urban rail transit has posed increasing construction and operational challenges for metro tunnels,often leading to structural damage.Grouting technology using cement-based materials is widely ...The rapid development of urban rail transit has posed increasing construction and operational challenges for metro tunnels,often leading to structural damage.Grouting technology using cement-based materials is widely applied to address issues such as seepage,leakage,and alignment correction in shield tunnels.This study investigates the additional stress induced by grouting in silty soil layers,using cement-based grouts with different water-to-cement ratios and polyurethane-modified cement-based materials.Results show that additional stress decreases with depth and is more influenced by horizontal distance from the grouting point.In staged grouting,the first injection phase contributes about 50%of the peak additional stress.A lower water-to-cement ratio(e.g.,0.6)increases additional stress but reduces grout flowability,while a higher ratio improves diffusion but increases the risk of grout loss.(≥1.0)The polyurethane-modified cement-based material enhances stress transfer performance,increasing peak additional stress by approximately 10%.These findings provide theoretical guidance for optimizing material selection and grouting design in metro tunnel repair within silty soil layers.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
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
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
Cement-based composite grouting materials were used to construct grouting cutoff wall for heavy metal contaminated soil in non-ferrous metal mining areas. Cement, fly ash, and slag as principal ingredients were mixed ...Cement-based composite grouting materials were used to construct grouting cutoff wall for heavy metal contaminated soil in non-ferrous metal mining areas. Cement, fly ash, and slag as principal ingredients were mixed with water glass in different ways to produce three composite grouting materials. In order to investigate the effect of water glass mixing ratio, Baume degree, fly ash and slag contents on the mechanical properties of the composite grouting materials, particularly their gel time and compressive strength, the beaker-to-beaker method of gel time test and unconfined compressive strength test were conducted. In addition, the phase composition and microstructure of the composite grouting materials were analyzed by the X-ray diffraction（XRD） and scanning electron microscope（SEM） techniques. The test results show that their gel time increases when water glass mixing ratio and Baume degree increase. The gel time increases dramatically when fly ash is added, but decreases slightly if fly ash is partly replaced by slag. When the mixing ratio of water glass is below 20%, their compressive strength increases with the increases of the ratio; when the ratio is above 20%, it significantly decreases. The compressive strength also tends to increase as Baume degree increases, and improves if fly ash and slag are added.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 effects of the component gradient distribution at interface and the fiber gradient distribution on the strength of cement-based materials were studied. The results show that the flexural strength and compressive s...The effects of the component gradient distribution at interface and the fiber gradient distribution on the strength of cement-based materials were studied. The results show that the flexural strength and compressive strength of the mortar and concrete with interface component and fiber gradient distributions are obviously improved. The strengthes of the fiber gradient distributed mortar and concrete (FGDM/C) are higher than those of fiber homogeneously distributed mortar and concrete (FHDM/C). To obtain the same strength, therefore, a smaller fiber volume content in FGDM/C is needed than that in FHDM/C. The results also show that the component gradient distribution of the concrete can be obtained by means of multi-layer vibrating formation.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
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
The pore structure and porosity of three kinds of mine grouting materials were characterized based on a thin-section analysis and low-field nuclear magnetic resonance (NMR) technique. The macroscopic pore interconnect...The pore structure and porosity of three kinds of mine grouting materials were characterized based on a thin-section analysis and low-field nuclear magnetic resonance (NMR) technique. The macroscopic pore interconnectivity was investigated using binary images captured from thin sections and a random walk pore spectral dimension (RWPSD) algorithm. The experimental results show that the microstructure of the grouting materials used consisted of interlayer pores, gel pores, capillary pores, circular air holes, and small fractures, and tailings can fill some gaps in the hydration product structure and dense hydration products. There is a positive correlation between pore interconnectivity and curing time. In addition, there is a relationship between pore interconnectivity and porosity. With increasing porosity and pore interconnectivity, a non-uniform pore structure occurs in mine grouting materials with an accelerator and results in reduced setting time and later strength.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 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
基金Funded by a Science and Technology Project from the Ministry of Housing and Urban-Rural Development of the People’s Republic of China(No.2019-K-047)Yangzhou Government-Yangzhou University Cooperative Platform Project for Science and Technology Innovation(No.YZ2020262)。
文摘The chloride penetration resistance of cement-based grout materials was improved by nano-silica emulsion.Specimens of mixtures containing different nano-silica particles or emulsions were exposed in sodium chloride solutions of specific concentrations with different test ages.Hardened properties of the mixes were assessed in terms of weight loss and compressive strength.X-ray diffraction(XRD)and scanning electron microscopy(SEM)of mixes were performed to analysis the phase evolution and microstructure.The results demonstrated that the introduction of nano-SiO_(2) emulsion significantly decreased the compressive strength loss and calcium hydroxide(CH)crystal content of hydration production,and then enhanced the resistance of cement-based grouting materials to chloride ion penetration.This improvement derives from the filling and pozzolanic effects of nano-SiO_(2) particles,which were incorporated via an emulsion and attributed to a well dispersion in grouting matrix.
基金Funded by the National Key Technology R&D Program in the12th Five Year Plan of China(No.2011BAE14B06)the National High Technology ResearchDevelopment Program of China(No.2015AA034701)
文摘Main performance of the cement grouting materials made up by Portland cement（PC） and sulphoaluminate cement（SAC） was investigated in this program, a kind of expanding agent（EA） which was mainly constituted by metakaolin and alunite was utilized for the compensation of the shrinkage, the hydration products and micro structure of the grouting materials were researched by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The results showed that a high expansion rate of the grouting materials could be reached as the expanding agent mixed in 6% of PC mass; the addition of SAC in the S2（PC：SAC：EA=34：6：2.25） brought a further improvement of the expansion rate of the grouting materials, the analysis of XRD and SEM showed that due to the reaction of expanding agent and SAC in the grouting materials, more ettringite crystal was generated, which resulted in a higher early strength, the addition of SAC played an expansion and strength reinforcement role in the grouting materials.
基金supported by the National Natural Science Foundation of China,Grant Nos.42477185,41602308the Zhejiang Provincial Natural Science Foundation of China,Grant No.LY20E080005+2 种基金the Zhejiang Province University Students Science and Technology Innovation Program,Grant No.0201310P28the PostGraduate Course Construction Project of Zhejiang University of Science and Technology,Grant No.2021yjskj05the Zhejiang University of Science and Technology Graduate Research and Innovation Fund,Grant No.2023yjskc10.
文摘The ongoing operation of subway systems makes existing tunnels vulnerable to deformations and structural damage caused by adjacent foundation pit construction.Such deformations-manifesting as horizontal displacement,heightened lateral convergence,and internal force redistribution-may significantly compromise subway operational safety.Grouting remediation has become a widely adopted solution for tunnel deformation control and structural reinforcement.Developing optimized grouting materials is crucial for improving remediation effectiveness,ensuring structural integrity,and maintaining uninterrupted subway operations.This investigation explores the substitution of fine mortar aggregates with 0.1 mm discarded rubber particles at varying concentrations(0%,3%,6%,9%,12%,and 15%).Experimental parameters included three water-cement ratios(0.65,0.70,and 0.75)with constant 4%WPU content.Mechanical properties including compressive strength,flexural strength,and compression-to-bending ratio were evaluated across specified curing periods.Material characterization employed Fourier Transform Infrared Spectroscopy(FTIR)spectroscopy for molecular analysis and Scanning Electron Microscopy(SEM)for microstructural examination.Results indicate optimal toughness at 0.70 water-cement ratio with 6%rubber content,meeting mechanical pumping specifications while maintaining structural performance.
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supported by the National Natural Science Foundation of China(No.42477185)Natural Science Foundation of Zhejiang Province(LQ24A020015)+1 种基金Research Achievement Award Cultivation Project of Zhejiang University of Science and Technology(2023JLYB001)the Postgraduate Course Construction Project of Zhejiang University of Science and Technology(2024yjskj05).
文摘The rapid development of urban rail transit has posed increasing construction and operational challenges for metro tunnels,often leading to structural damage.Grouting technology using cement-based materials is widely applied to address issues such as seepage,leakage,and alignment correction in shield tunnels.This study investigates the additional stress induced by grouting in silty soil layers,using cement-based grouts with different water-to-cement ratios and polyurethane-modified cement-based materials.Results show that additional stress decreases with depth and is more influenced by horizontal distance from the grouting point.In staged grouting,the first injection phase contributes about 50%of the peak additional stress.A lower water-to-cement ratio(e.g.,0.6)increases additional stress but reduces grout flowability,while a higher ratio improves diffusion but increases the risk of grout loss.(≥1.0)The polyurethane-modified cement-based material enhances stress transfer performance,increasing peak additional stress by approximately 10%.These findings provide theoretical guidance for optimizing material selection and grouting design in metro tunnel repair within silty soil layers.
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.
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Projects(41472278,41202220)supported by the National Natural Science Foundation of ChinaProject(20120022120003)supported by the Research Fund for the Doctoral Program of Higher Education,China+1 种基金Project(51900265647)supported by the Beijing Higher Education Young Elite Teacher Project,ChinaProject(2652012065)supported by the Fundamental Research Funds for the Central Universities,China
文摘Cement-based composite grouting materials were used to construct grouting cutoff wall for heavy metal contaminated soil in non-ferrous metal mining areas. Cement, fly ash, and slag as principal ingredients were mixed with water glass in different ways to produce three composite grouting materials. In order to investigate the effect of water glass mixing ratio, Baume degree, fly ash and slag contents on the mechanical properties of the composite grouting materials, particularly their gel time and compressive strength, the beaker-to-beaker method of gel time test and unconfined compressive strength test were conducted. In addition, the phase composition and microstructure of the composite grouting materials were analyzed by the X-ray diffraction（XRD） and scanning electron microscope（SEM） techniques. The test results show that their gel time increases when water glass mixing ratio and Baume degree increase. The gel time increases dramatically when fly ash is added, but decreases slightly if fly ash is partly replaced by slag. When the mixing ratio of water glass is below 20%, their compressive strength increases with the increases of the ratio; when the ratio is above 20%, it significantly decreases. The compressive strength also tends to increase as Baume degree increases, and improves if fly ash and slag are added.
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.
文摘The effects of the component gradient distribution at interface and the fiber gradient distribution on the strength of cement-based materials were studied. The results show that the flexural strength and compressive strength of the mortar and concrete with interface component and fiber gradient distributions are obviously improved. The strengthes of the fiber gradient distributed mortar and concrete (FGDM/C) are higher than those of fiber homogeneously distributed mortar and concrete (FHDM/C). To obtain the same strength, therefore, a smaller fiber volume content in FGDM/C is needed than that in FHDM/C. The results also show that the component gradient distribution of the concrete can be obtained by means of multi-layer vibrating formation.
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 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Project(41672298) supported by the National Natural Science Foundation of ChinaProject(2017YFC0602901) supported by the National Key Research and Development Program of China
文摘The pore structure and porosity of three kinds of mine grouting materials were characterized based on a thin-section analysis and low-field nuclear magnetic resonance (NMR) technique. The macroscopic pore interconnectivity was investigated using binary images captured from thin sections and a random walk pore spectral dimension (RWPSD) algorithm. The experimental results show that the microstructure of the grouting materials used consisted of interlayer pores, gel pores, capillary pores, circular air holes, and small fractures, and tailings can fill some gaps in the hydration product structure and dense hydration products. There is a positive correlation between pore interconnectivity and curing time. In addition, there is a relationship between pore interconnectivity and porosity. With increasing porosity and pore interconnectivity, a non-uniform pore structure occurs in mine grouting materials with an accelerator and results in reduced setting time and later strength.
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.
