In this paper,the durability of cement mortar prepared with a recycled-concrete fine powder(RFP)was examined;including the analysis of a variety of aspects,such as the carbonization,sulfate attack and chloride ion ero...In this paper,the durability of cement mortar prepared with a recycled-concrete fine powder(RFP)was examined;including the analysis of a variety of aspects,such as the carbonization,sulfate attack and chloride ion erosion resistance.The results indicate that the influence of RFP on these three aspects is different.The carbonization depth after 30 days and the chloride diffusion coefficient of mortar containing 10%RFP decreased by 13.3%and 28.19%.With a further increase in the RFP content,interconnected pores formed between the RFP particles,leading to an acceleration of the penetration rate of CO_(2)and Cl^(−).When the RFP content was less than 50%,the corrosion resistance coefficient of the compressive strength of the mortar was 0.84-1.05 after 90 days of sulfate attack.But the expansion and cracking of the mortar was effectively alleviated due to decrease of the gypsum production.Scanning electron microscope(SEM)analysis has confirmed that 10%RFP contributes to the formation of a dense microstructure in the cement mortar.展开更多
Cement-based materials are fundamental in the construction industry,and enhancing their properties is an ongoing challenge.The use of superabsorbent polymers(SAP)has gained significant attention as a possible way to i...Cement-based materials are fundamental in the construction industry,and enhancing their properties is an ongoing challenge.The use of superabsorbent polymers(SAP)has gained significant attention as a possible way to improve the performance of cement-based materials due to their unique water-absorption and retention properties.This study investigates the multifaceted impact of kaolin intercalation-modified superabsorbent polymers(K-SAP)on the properties of cement mortar.The results show that K-SAP significantly affects the cement mortar’s rheological behavior,with distinct phases of water absorption and release,leading to changes in workability over time.Furthermore,K-SAP alters the hydration kinetics,delaying the exothermic peak of hydration and subsequently modifying the heat release kinetics.Notably,K-SAP effectively maintains a higher internal relative humidity within the mortar,reducing the autogenous shrinkage behavior.Moreover,K-SAP can have a beneficial effect on pore structure and this can be ascribed to the internal curing effect of released water from K-SAP.展开更多
Cement is widely used in engineering applications,but it has both the characteristics of high brittleness and poor bending resistance.In this paper,the effects of different amounts ofgraphene oxide on the flexural str...Cement is widely used in engineering applications,but it has both the characteristics of high brittleness and poor bending resistance.In this paper,the effects of different amounts ofgraphene oxide on the flexural strength and compressive strength of cement mortar were studied by doping a certain amount of graphene oxide with cement mortar,and the strengthening mechanism of graphene oxide on cement mortar was obtained through microstructure detection.It is found that graphene oxide has a significant enhancement effect on the macroscopic mechanical properties of cement mortar,and graphene oxide provides nano-nucleation sites and growth templates for cement mortar,accelerates the hydration process,reduces the voids between hydration products,greatly increases the compactness,and improves the macroscopic properties of cement-based materials.展开更多
This study deals with the analysis of the detrimental effects of a“sulfate attack”on cement mortar for different dry-wet cycles.The mass loss,tensile strength,and gas permeability coefficient were determined and ana...This study deals with the analysis of the detrimental effects of a“sulfate attack”on cement mortar for different dry-wet cycles.The mass loss,tensile strength,and gas permeability coefficient were determined and analyzed under different exposure conditions.At the same time,nitrogen adsorption(NAD),scanning electron microscopy(SEM),and X-ray diffraction(XRD)techniques were used to analyze the corresponding variations in the microstructure and the corrosion products.The results show that certain properties of the cement mortar evolve differently according to the durations of the dry-wet cycles and that some damage is caused to the mortars in aqueous solution.The pores fill with corrosion products,increasing the mortar specimen mass and tensile strength while reducing the permeability coefficient and pore size distribution.As corrosion proceeds,the crystallization pressure of the corrosion products increases,resulting in a 16%reduction in tensile strength from the initial value and a 2.6-factor increase in the permeability coefficient,indicating sensitivity to sulfate attack damage.Furthermore,the main corrosion products generated in the experiment are gypsum and ettringite.Application of osmotic pressure and extension of the immersion time can accelerate the erosion process.展开更多
Since masonry structures are prone to collapse in earthquakes,a novel joint reinforcement method with a polypropylene band(PP-band)and cement mortar(CM)has been put forward.Compared with the common reinforcement metho...Since masonry structures are prone to collapse in earthquakes,a novel joint reinforcement method with a polypropylene band(PP-band)and cement mortar(CM)has been put forward.Compared with the common reinforcement methods,this method not only facilitates construction but also ensures lower reinforcement cost.To systematically explore the influence of joint reinforcement on the seismic performance of masonry walls,quasi-static tests were carried out on six specimens with different reinforcement forms.The test results show that the joint action of PP-band and CM can significantly improve the specimen′s brittle failure characteristics and enhance the integrity of the specimen after cracking.Compared with the specimen without reinforcement,each of the seismic performance indexes of the joint reinforced specimen had obvious improvement.The maximum increased rate about peak load and ductility of the joint reinforced specimen is 100.6%and 233.4%,respectively.展开更多
This paper describes a study on the corrosion behavior of steel reinforcement in CAC mortars via electrochemical methods including corrosion potential,electrochemical impedance,and linear polarization evaluation.Resul...This paper describes a study on the corrosion behavior of steel reinforcement in CAC mortars via electrochemical methods including corrosion potential,electrochemical impedance,and linear polarization evaluation.Results indicate that there is a non-linear relationship between the corrosion degree of steel reinforcement in CAC mortar and the concentration of NaCl solution.The electrochemical parameters of specimens immersed in 3%NaCl solution suddenly drop at 40 days,earlier than 60 days of the reference.And the charge transfer resistivity of the specimen has decreased by 11 orders of magnitude at 40 days,showing an evident corrosion on steel reinforcement.However,it is interesting to notice that the corrosion is delayed by high external chloride concentration.The specimens immersed in 9%and 15%NaCl solutions remain in a relatively stable state within 120 days with slight pitting.The great corrosion protection of CAC concrete to embedded steel bars enables its wide application in marine.展开更多
The aim of this study is to enhance the value and utilization of red mud generated in the Bayer process by preparing composite cement mortars.The effects of two different types of Bayer red mud with varying physical a...The aim of this study is to enhance the value and utilization of red mud generated in the Bayer process by preparing composite cement mortars.The effects of two different types of Bayer red mud with varying physical and chemical characteristics on the fluidity,mechanical strength,mineral composition,and microstructure of the composite cement mortar were systematically evaluated.The results showed that the optimal addition of red mud A was 10 wt%,while it was 20 wt% for red mud B.The mechanical properties of the composite cement mortar met the standards for P·O42.5 cement.Furthermore,the composite mortar with the addition of red mud B showed higher flexural and compressive strengths compared to the composite mortar with red mud A.This improvement is attributed to the smaller particle size of red mud B,which filled the micro-pores and increased the compactness of the cement stone,as well as its higher content of Na_(2)O,K_(2)O,and other free alkalis,which resulted in more obvious alkali activation,accelerating the hydration of the active minerals in the slurry.展开更多
The pozzolanic activity of coal gangue burned at different burning temperatures was investigated. The burned coal gangue was mixed with portland cement in different proportions ( 20% - 60% ). The pozzolanic activity...The pozzolanic activity of coal gangue burned at different burning temperatures was investigated. The burned coal gangue was mixed with portland cement in different proportions ( 20% - 60% ). The pozzolanic activity of coal gangue burned and the hydration products were examined, the compressive strengths of the pastes of the mixtures were tested, and the mechanism of the reaction was discussed. The experimental results slum, that the coal gangue burned at 750 ℃ has the optimum pozzolanic activity, and the burned coal ganguc with SiO2 and Al2 O3 is in an active form. When the coal gangue burned at 750℃ is mixed into portland cement, the content of calcium hydroxide in paste is significantly reduced, while the contents of hydrated calcium silk.ate and hydrated calcium aluminate are increased accordingly, hence resulting in the improvement of the microstructure of mortar. The compressive strength of cement paste decreases with increasing the content of burncd coal gangue. The decease in strength is small in the range of 20% - 30% coal gangue substitution and significant in 30%- 60% substitution.展开更多
To study the influence of multi-wall carbon nanotubes (MWCNTs) on the mechanical and microstructural properties of cementitious composites, 0.00, 0.02, 0.08, 0.10, and 0.20 wt% of multi-wall carbon nanotubes were ad...To study the influence of multi-wall carbon nanotubes (MWCNTs) on the mechanical and microstructural properties of cementitious composites, 0.00, 0.02, 0.08, 0.10, and 0.20 wt% of multi-wall carbon nanotubes were added into cement mortar, in which the cement-sand ratio was 1:1.5. The flexural and compressive strengths of cement mortar at the age of 3, 7, 28 and 90 d and the fracture performance at the age of 28 d were determined, its 2D micrograph was tested by means of SEM, and the 3D defects distribution was firstly determined with or without CNTs by means of XCT (X-ray computerized tomography). The results showed that 0.08 wt% of CNTs improved the compressive strength and flexural strength by 18% and 19~A, respectively, and a significant improvement of its fracture property was observed. Moreover lower addition of carbon nanotubes to cement mortars can improve its microstructure and decrease the defects significantly compared to the cement mortar without CNTs. With the increase of the content of CNTs, the mechanical properties of cement mortars presented to be declined largely due to the agglomeration of CNTs.展开更多
This research focused on using the waste rubber powder as a kind of regenerate resources to improve the mechanical properties of cement mortar.The two kinds of hybrid modified rubber powder TRP and ATRP were prepared ...This research focused on using the waste rubber powder as a kind of regenerate resources to improve the mechanical properties of cement mortar.The two kinds of hybrid modified rubber powder TRP and ATRP were prepared by sol-gel method and then used in cement mortar.The structures and properties of them were studied.It is shown that the nano Si-O-Si network is generated in TRP and ATRP networks and the hydrophilic group is grafted on the surface of ATRP.The mechanical properties of rubber-treated mortar(RTM) were tested and the microstructures of them were also studied.Compared to the mortars with unmodified rubber powders(RP),NaOH treated rubber powder(SRP) and coupling agent treated rubber powder(CRP),the RTM with ATRP has the highest compressive strength and flexural strength.The stress-strain curves shown that the peak of stress of RTM with ATRP is increased and indicated the higher compression deformation and toughness.It is found that the interfacial adhesion between the ATRP and cement mortar is increased distinctly by SEM,which results in enhanced ductility and mechanical properties of RTM with ATRP.展开更多
The epoxy resin polymer cement mortars with excellent performances were made up through modifying ordinary Portland cement with emulsified epoxy and micro fine slag.The microstructure of the epoxy resin polymer cemen...The epoxy resin polymer cement mortars with excellent performances were made up through modifying ordinary Portland cement with emulsified epoxy and micro fine slag.The microstructure of the epoxy resin polymer cement materials was studied and their hydration and hardening characteristics were discussed by means of modern analysis measures such as SEM,XRD and Hg intrusion micromeritics.The experimental results indicate that the series effects of water reducing,density,pozzolanicity,filling and solidification crosslinking through the action together with epoxy organism and micro fine slag endowed cement based materials with perfect performances.The main hydration products in the system are C S H gel and hydrated calcium aluminate.At later age,AFt can be in existence,and no Ca(OH) 2 is found.When epoxy resin is solidified,the organism is in a network structure.In the micro pore structure of hydrated cement with modified epoxy and fine slag,big harmful pores were fewer,more harmless abundant micro pores were and the possible pore radius was smaller than that of ordinary Portland cement.展开更多
In situ monitoring of the microstructure evolution of cement mortar in accelerated carbonation reaction for different carbonation ages was carried out by X-ray computed tomography (XCT). And the carbonation degrees ...In situ monitoring of the microstructure evolution of cement mortar in accelerated carbonation reaction for different carbonation ages was carried out by X-ray computed tomography (XCT). And the carbonation degrees of different time were measured by the volume fraction of uncarbonated and carbonated parts. Meanwhile, we presented a model for the carbonation of cement mortar by means of X-ray computed tomography (XCT). Based on the principles of chemical engineering processes, the reacted products become a solid inert ash layer. Finally, the model was validated with results of accelerated carbonation of cement mortar. The model is thus able to reasonably predict the carbonation ohenomena for accelerated conditions.展开更多
Mortar prisms were made with three different cementitious materials (with or without mineral admixture) plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, the mortars were submerg...Mortar prisms were made with three different cementitious materials (with or without mineral admixture) plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, the mortars were submerged in 2% magnesium sulfate solution at different temperatures (5℃, 20℃and alternate temperature between 5℃and 20℃) for a year. The appearance and strength development were measured on these immersed prisms at intervals, and samples selected from the surface of prisms were examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results show that the influence of temperature on the resistance to sulfate attack of mortar is related to the binder compositions. A higher temperature leads to a quicker strength loss and appearance deterioration of the mortar without mineral admixture. For blended cements, a higher temperature is favorable for the pozzolanic reaction of mineral admixture and the overall deterioration of mortar is reduced with the increasing temperature. When the mineral admixture has a lower reactivity, such influence of temperature on the resistance to sulfate attack of mortar containing admixtures becomes greater. At the three different solution temperatures, two blended cements show significantly improved resistances to sulfate attack. After 1 year of exposure to magnesium sulfate solutions, the formation of thaumasite was checked in the OPC mortars at both 5℃and 20℃. It is concluded that the thaumasite formation is not limited to structures at low temperature (less than 15℃).展开更多
Influences of polypropylene (PP) fiber and styrene-butadiene rubber (SBR) polymer latex on the strength performance, abrasion resistance of cement mortar were studied. The experimental results show that the flexur...Influences of polypropylene (PP) fiber and styrene-butadiene rubber (SBR) polymer latex on the strength performance, abrasion resistance of cement mortar were studied. The experimental results show that the flexural strength, brittleness index (σF/σC) and abrasion resistance can be improved significantly by the addition of PP fiber and SBR polymer latex. The relationship between the flexural strength and abrasion resistance was analyzed, showing a good linear relationship between them. The reinforced mechanism of PP fiber and SBR polymer latex on cement mortar was analyzed by some microscopic tests. The test results show that the addition of SBR polymer latex has no significant influence on the cement hydration after 7 d curing. Adding SBR polymer latex into cement mortar can form a polymer transition layer in the interfaces of PP fiber and cement hydrates, which improves the bonding properties between the PP fiber and cement mortar matrix effectively.展开更多
The deterioration mechanism of thaumasite towards cement or concrete structure and the deterioration pattern of in-situ construction caused by the formation of thaumasite were studied in this paper. To improve the TSA...The deterioration mechanism of thaumasite towards cement or concrete structure and the deterioration pattern of in-situ construction caused by the formation of thaumasite were studied in this paper. To improve the TSA (the thaumasite form of sulfate attack) resistance, the cement type, water to cement ratios, the mineral admixture and the circumstance factors should be taken into consideration.展开更多
A laboratory study was undertaken to investigate drying shrinkage and cracking sensitivity subjected to restrained shrinkage of mortar containing fly ash (FA), granulated blast-furnace slag (GBFS) and silica fume (SF)...A laboratory study was undertaken to investigate drying shrinkage and cracking sensitivity subjected to restrained shrinkage of mortar containing fly ash (FA), granulated blast-furnace slag (GBFS) and silica fume (SF). Six mortar mixtures including control Portland cement (PC) and FA, GBFS and SF mortar mixtures were prepared. FA replaced the cement on mass basis at the replacement ratios of 20% and 35%, GBFS replaced the cement at the replacement ratios of 40%, SF replaced the cement at the replacement ratios of 8% and the blended mixtures with 20% FA, 20% GBFS and 8% SF. Water-cementitious materials ratio and sand-cementitious materials ratio were 0.4 and 2.0 for all mixtures, respectively. The mixtures were cured at 65% relative humidity and 20℃. The drying shrinkage value, initial cracking time and cracking width of the mortar samples were measured. The results show that all the mortar mixture containing FA exhibited the decrease of drying shrinkage. Moreover, initial cracking time was markedly delayed, and the crack width of the initial crack was reduced. However, the incorporations of various ratios of GBFS and SF led to an increase of drying shrinkage, initial cracking time and cracking width as compared to control mixture.展开更多
An efficient and promising approach for effectively dispersing multi-walled carbon nanotubes(MWCNTs)in cementitious composites has been investigated.The naturally occurring organic extracts from species of indigenousl...An efficient and promising approach for effectively dispersing multi-walled carbon nanotubes(MWCNTs)in cementitious composites has been investigated.The naturally occurring organic extracts from species of indigenously known‘Keekar’trees scattered along tropical and sub-tropical regions;is found as an exceptional replacement to the non-natural commercial surfactants.In the initial phase of investigation,ideal surfactant’s content required for efficient dispersion of MWCNTs in solution was determined using ultra-violet spectroscopy.The experimental investigations were then extended to five different cement composite formulations containing 0.0,0.025,0.05,0.08 and 0.10%MWCNTs by weight of cement.It was observed that the natural surfactant produced efficient dispersion at much reduced cost(approx.14%)compared with the commercial alternate.The estimated weight efficiency factor f was found 6.5 times higher for the proposed sustainable replacement to the conventional along with remarkable increase of 23%in modulus of rupture on 0.08 wt%addition of MWCNTs.Besides strength enhancement,the dispersed MWCNTs also improved the first crack and ultimate fracture toughness by 51.5%and 35.9%,respectively.The field emission scanning electron microscopy of the cryofractured samples revealed efficient dispersion of MWCNTs in the matrix leading to the phenomenon of effective crack bridging and crack branching in the composite matrix.Furthermore,the proposed scheme significantly reduced the early age volumetric shrinkage by 39%.展开更多
Under dynamic loading, the constitutive relation of the cement mortar will be significantly affected by the transversal inertial effect of specimens with large diameters. In this paper, one-dimensional theoretical ana...Under dynamic loading, the constitutive relation of the cement mortar will be significantly affected by the transversal inertial effect of specimens with large diameters. In this paper, one-dimensional theoretical analysis is carried out to determine the transversal inertial effect on the relaxation/retardation time of the cement mortar under the harmonic wave. Relaxation time or retardation time is obtained by means of the wave velocity, attenuation coefficient and the frequency of the harmonic wave. Thus, the transversal inertial effect on the relaxation time from Maxwell model, as well as on retardation time from Voigt model is analyzed. The results show that the transversal inertial effect may lead to the increase of the relaxation time, but induce the decrease of the retardation time. Those should be taken into account when eliminating the transversal inertial effect in applications.展开更多
The aim of this study is to examine the performance of nano additives in two different sets of mortar specimens armed with reinforcing steel rebars. In particular, three sets of reinforced concrete cylinders with addi...The aim of this study is to examine the performance of nano additives in two different sets of mortar specimens armed with reinforcing steel rebars. In particular, three sets of reinforced concrete cylinders with additives of 0.1% wt of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have been exposed to a solution of 3.5% NaCl, and further examined for the impact of nano-modification on corrosion performance. The anti-corrosive performance of these additives was investigated through linear polarization technique (LPR), mass loss and mercury porosimetry technique (MIP). From the investigation results, it is found that the addition of CNTs/CNFs causes lower steel corrosion, whereas the pore structure of concrete with CNTs/CNFs can significantly reduce the mass loss rate and the relative permeability.展开更多
The SO4^(2-)concentration distributions in surface region of cement mortar immersed in sulfate solution at early stage were measured by layered sampling method combined with chemical analysis, and the diffusion coef...The SO4^(2-)concentration distributions in surface region of cement mortar immersed in sulfate solution at early stage were measured by layered sampling method combined with chemical analysis, and the diffusion coefficients of SO4^(2-)anions in surface region of mortar into internal area were calculated by means of instantaneous plane diffusion theory. The experimental results showed that the SO4^(2-)concentration gradually reduced when the diffusion depth increased in the surface region of mortar. Diffusion coefficient(D) was relevant with the concentration and kind of environmental sulfate solution, which reduced with immersion time at the beginning, and then rose slowly after a period of time. The calculation of initial diffusion coefficient(D0) and starting time of deterioration(t∞) caused by sulfate attack was further attempted based on the data of diffusion coefficient, and it was found that D0 and t∞ were all relevant with concentrations of sulfate and different kind of sulfate as well.展开更多
基金This work is supported by the Zhuhai Science and Technology Project(ZH22036203200015PWC)the Open Foundation of State Key Laboratory of Subtropical Building Science(2022ZB20).
文摘In this paper,the durability of cement mortar prepared with a recycled-concrete fine powder(RFP)was examined;including the analysis of a variety of aspects,such as the carbonization,sulfate attack and chloride ion erosion resistance.The results indicate that the influence of RFP on these three aspects is different.The carbonization depth after 30 days and the chloride diffusion coefficient of mortar containing 10%RFP decreased by 13.3%and 28.19%.With a further increase in the RFP content,interconnected pores formed between the RFP particles,leading to an acceleration of the penetration rate of CO_(2)and Cl^(−).When the RFP content was less than 50%,the corrosion resistance coefficient of the compressive strength of the mortar was 0.84-1.05 after 90 days of sulfate attack.But the expansion and cracking of the mortar was effectively alleviated due to decrease of the gypsum production.Scanning electron microscope(SEM)analysis has confirmed that 10%RFP contributes to the formation of a dense microstructure in the cement mortar.
基金the National Natural Science Foundation of China(52172017 and 51902095).
文摘Cement-based materials are fundamental in the construction industry,and enhancing their properties is an ongoing challenge.The use of superabsorbent polymers(SAP)has gained significant attention as a possible way to improve the performance of cement-based materials due to their unique water-absorption and retention properties.This study investigates the multifaceted impact of kaolin intercalation-modified superabsorbent polymers(K-SAP)on the properties of cement mortar.The results show that K-SAP significantly affects the cement mortar’s rheological behavior,with distinct phases of water absorption and release,leading to changes in workability over time.Furthermore,K-SAP alters the hydration kinetics,delaying the exothermic peak of hydration and subsequently modifying the heat release kinetics.Notably,K-SAP effectively maintains a higher internal relative humidity within the mortar,reducing the autogenous shrinkage behavior.Moreover,K-SAP can have a beneficial effect on pore structure and this can be ascribed to the internal curing effect of released water from K-SAP.
基金This work were supported by Natural Science Foundation of Zhejiang Province(LQ23E080003)a Doctoral program of Zhejiang University of science and technology(F701104L08)The Special Fund Project of Zhejiang University of Science and Technology's Basic Scientific Research Business Expenses in 2023(2023QN016).
文摘Cement is widely used in engineering applications,but it has both the characteristics of high brittleness and poor bending resistance.In this paper,the effects of different amounts ofgraphene oxide on the flexural strength and compressive strength of cement mortar were studied by doping a certain amount of graphene oxide with cement mortar,and the strengthening mechanism of graphene oxide on cement mortar was obtained through microstructure detection.It is found that graphene oxide has a significant enhancement effect on the macroscopic mechanical properties of cement mortar,and graphene oxide provides nano-nucleation sites and growth templates for cement mortar,accelerates the hydration process,reduces the voids between hydration products,greatly increases the compactness,and improves the macroscopic properties of cement-based materials.
基金This work is supported by the National Natural Science Foundation of China(No.51709097).
文摘This study deals with the analysis of the detrimental effects of a“sulfate attack”on cement mortar for different dry-wet cycles.The mass loss,tensile strength,and gas permeability coefficient were determined and analyzed under different exposure conditions.At the same time,nitrogen adsorption(NAD),scanning electron microscopy(SEM),and X-ray diffraction(XRD)techniques were used to analyze the corresponding variations in the microstructure and the corrosion products.The results show that certain properties of the cement mortar evolve differently according to the durations of the dry-wet cycles and that some damage is caused to the mortars in aqueous solution.The pores fill with corrosion products,increasing the mortar specimen mass and tensile strength while reducing the permeability coefficient and pore size distribution.As corrosion proceeds,the crystallization pressure of the corrosion products increases,resulting in a 16%reduction in tensile strength from the initial value and a 2.6-factor increase in the permeability coefficient,indicating sensitivity to sulfate attack damage.Furthermore,the main corrosion products generated in the experiment are gypsum and ettringite.Application of osmotic pressure and extension of the immersion time can accelerate the erosion process.
基金National Natural Science Foundation of China under Grant Nos.51968047 and 51608249the Key Research and Development Program of Jiangxi Province under Grant No.20161BBG70058。
文摘Since masonry structures are prone to collapse in earthquakes,a novel joint reinforcement method with a polypropylene band(PP-band)and cement mortar(CM)has been put forward.Compared with the common reinforcement methods,this method not only facilitates construction but also ensures lower reinforcement cost.To systematically explore the influence of joint reinforcement on the seismic performance of masonry walls,quasi-static tests were carried out on six specimens with different reinforcement forms.The test results show that the joint action of PP-band and CM can significantly improve the specimen′s brittle failure characteristics and enhance the integrity of the specimen after cracking.Compared with the specimen without reinforcement,each of the seismic performance indexes of the joint reinforced specimen had obvious improvement.The maximum increased rate about peak load and ductility of the joint reinforced specimen is 100.6%and 233.4%,respectively.
基金Funded by National Natural Science Foundation of China(Nos.51772212,51402216,51978505)。
文摘This paper describes a study on the corrosion behavior of steel reinforcement in CAC mortars via electrochemical methods including corrosion potential,electrochemical impedance,and linear polarization evaluation.Results indicate that there is a non-linear relationship between the corrosion degree of steel reinforcement in CAC mortar and the concentration of NaCl solution.The electrochemical parameters of specimens immersed in 3%NaCl solution suddenly drop at 40 days,earlier than 60 days of the reference.And the charge transfer resistivity of the specimen has decreased by 11 orders of magnitude at 40 days,showing an evident corrosion on steel reinforcement.However,it is interesting to notice that the corrosion is delayed by high external chloride concentration.The specimens immersed in 9%and 15%NaCl solutions remain in a relatively stable state within 120 days with slight pitting.The great corrosion protection of CAC concrete to embedded steel bars enables its wide application in marine.
基金the Guangxi Science and Technology Program(Guike AD21220052,AD22035126 and AB22035064)National Natural Science Foundation of China(52062009)Guangxi Key Laboratory of New Energy and Building Energy Saving(Guikeneng 22-J-21-19).
文摘The aim of this study is to enhance the value and utilization of red mud generated in the Bayer process by preparing composite cement mortars.The effects of two different types of Bayer red mud with varying physical and chemical characteristics on the fluidity,mechanical strength,mineral composition,and microstructure of the composite cement mortar were systematically evaluated.The results showed that the optimal addition of red mud A was 10 wt%,while it was 20 wt% for red mud B.The mechanical properties of the composite cement mortar met the standards for P·O42.5 cement.Furthermore,the composite mortar with the addition of red mud B showed higher flexural and compressive strengths compared to the composite mortar with red mud A.This improvement is attributed to the smaller particle size of red mud B,which filled the micro-pores and increased the compactness of the cement stone,as well as its higher content of Na_(2)O,K_(2)O,and other free alkalis,which resulted in more obvious alkali activation,accelerating the hydration of the active minerals in the slurry.
基金Funded by Social Development Plan in Science and Technologyof Jiangsu Province (No.BS2006033)
文摘The pozzolanic activity of coal gangue burned at different burning temperatures was investigated. The burned coal gangue was mixed with portland cement in different proportions ( 20% - 60% ). The pozzolanic activity of coal gangue burned and the hydration products were examined, the compressive strengths of the pastes of the mixtures were tested, and the mechanism of the reaction was discussed. The experimental results slum, that the coal gangue burned at 750 ℃ has the optimum pozzolanic activity, and the burned coal ganguc with SiO2 and Al2 O3 is in an active form. When the coal gangue burned at 750℃ is mixed into portland cement, the content of calcium hydroxide in paste is significantly reduced, while the contents of hydrated calcium silk.ate and hydrated calcium aluminate are increased accordingly, hence resulting in the improvement of the microstructure of mortar. The compressive strength of cement paste decreases with increasing the content of burncd coal gangue. The decease in strength is small in the range of 20% - 30% coal gangue substitution and significant in 30%- 60% substitution.
基金Funded by the National Basic Research Program of China(No.2009CB623200)the Program for Changjiang Scholars and Innovative Research Team in University of China(No.IRT13075)
文摘To study the influence of multi-wall carbon nanotubes (MWCNTs) on the mechanical and microstructural properties of cementitious composites, 0.00, 0.02, 0.08, 0.10, and 0.20 wt% of multi-wall carbon nanotubes were added into cement mortar, in which the cement-sand ratio was 1:1.5. The flexural and compressive strengths of cement mortar at the age of 3, 7, 28 and 90 d and the fracture performance at the age of 28 d were determined, its 2D micrograph was tested by means of SEM, and the 3D defects distribution was firstly determined with or without CNTs by means of XCT (X-ray computerized tomography). The results showed that 0.08 wt% of CNTs improved the compressive strength and flexural strength by 18% and 19~A, respectively, and a significant improvement of its fracture property was observed. Moreover lower addition of carbon nanotubes to cement mortars can improve its microstructure and decrease the defects significantly compared to the cement mortar without CNTs. With the increase of the content of CNTs, the mechanical properties of cement mortars presented to be declined largely due to the agglomeration of CNTs.
文摘This research focused on using the waste rubber powder as a kind of regenerate resources to improve the mechanical properties of cement mortar.The two kinds of hybrid modified rubber powder TRP and ATRP were prepared by sol-gel method and then used in cement mortar.The structures and properties of them were studied.It is shown that the nano Si-O-Si network is generated in TRP and ATRP networks and the hydrophilic group is grafted on the surface of ATRP.The mechanical properties of rubber-treated mortar(RTM) were tested and the microstructures of them were also studied.Compared to the mortars with unmodified rubber powders(RP),NaOH treated rubber powder(SRP) and coupling agent treated rubber powder(CRP),the RTM with ATRP has the highest compressive strength and flexural strength.The stress-strain curves shown that the peak of stress of RTM with ATRP is increased and indicated the higher compression deformation and toughness.It is found that the interfacial adhesion between the ATRP and cement mortar is increased distinctly by SEM,which results in enhanced ductility and mechanical properties of RTM with ATRP.
文摘The epoxy resin polymer cement mortars with excellent performances were made up through modifying ordinary Portland cement with emulsified epoxy and micro fine slag.The microstructure of the epoxy resin polymer cement materials was studied and their hydration and hardening characteristics were discussed by means of modern analysis measures such as SEM,XRD and Hg intrusion micromeritics.The experimental results indicate that the series effects of water reducing,density,pozzolanicity,filling and solidification crosslinking through the action together with epoxy organism and micro fine slag endowed cement based materials with perfect performances.The main hydration products in the system are C S H gel and hydrated calcium aluminate.At later age,AFt can be in existence,and no Ca(OH) 2 is found.When epoxy resin is solidified,the organism is in a network structure.In the micro pore structure of hydrated cement with modified epoxy and fine slag,big harmful pores were fewer,more harmless abundant micro pores were and the possible pore radius was smaller than that of ordinary Portland cement.
基金Funded by the National Basic Research Program of China(973Project)(Nos.2009CB623200 and 2011CB013800)the National Natural Science Foundation of China(No.51178103)the Scientific Research Foundation of the Graduate School of Southeast University(YBJJ1113)
文摘In situ monitoring of the microstructure evolution of cement mortar in accelerated carbonation reaction for different carbonation ages was carried out by X-ray computed tomography (XCT). And the carbonation degrees of different time were measured by the volume fraction of uncarbonated and carbonated parts. Meanwhile, we presented a model for the carbonation of cement mortar by means of X-ray computed tomography (XCT). Based on the principles of chemical engineering processes, the reacted products become a solid inert ash layer. Finally, the model was validated with results of accelerated carbonation of cement mortar. The model is thus able to reasonably predict the carbonation ohenomena for accelerated conditions.
基金Funded by the National Natural Science Foundation of China (No. 50408016) the "863" High-Tech Research and Development Program of China (No. 2005AA332010)
文摘Mortar prisms were made with three different cementitious materials (with or without mineral admixture) plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, the mortars were submerged in 2% magnesium sulfate solution at different temperatures (5℃, 20℃and alternate temperature between 5℃and 20℃) for a year. The appearance and strength development were measured on these immersed prisms at intervals, and samples selected from the surface of prisms were examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results show that the influence of temperature on the resistance to sulfate attack of mortar is related to the binder compositions. A higher temperature leads to a quicker strength loss and appearance deterioration of the mortar without mineral admixture. For blended cements, a higher temperature is favorable for the pozzolanic reaction of mineral admixture and the overall deterioration of mortar is reduced with the increasing temperature. When the mineral admixture has a lower reactivity, such influence of temperature on the resistance to sulfate attack of mortar containing admixtures becomes greater. At the three different solution temperatures, two blended cements show significantly improved resistances to sulfate attack. After 1 year of exposure to magnesium sulfate solutions, the formation of thaumasite was checked in the OPC mortars at both 5℃and 20℃. It is concluded that the thaumasite formation is not limited to structures at low temperature (less than 15℃).
基金Funded by the Science Project from Department of Communication of Hubei Province
文摘Influences of polypropylene (PP) fiber and styrene-butadiene rubber (SBR) polymer latex on the strength performance, abrasion resistance of cement mortar were studied. The experimental results show that the flexural strength, brittleness index (σF/σC) and abrasion resistance can be improved significantly by the addition of PP fiber and SBR polymer latex. The relationship between the flexural strength and abrasion resistance was analyzed, showing a good linear relationship between them. The reinforced mechanism of PP fiber and SBR polymer latex on cement mortar was analyzed by some microscopic tests. The test results show that the addition of SBR polymer latex has no significant influence on the cement hydration after 7 d curing. Adding SBR polymer latex into cement mortar can form a polymer transition layer in the interfaces of PP fiber and cement hydrates, which improves the bonding properties between the PP fiber and cement mortar matrix effectively.
文摘The deterioration mechanism of thaumasite towards cement or concrete structure and the deterioration pattern of in-situ construction caused by the formation of thaumasite were studied in this paper. To improve the TSA (the thaumasite form of sulfate attack) resistance, the cement type, water to cement ratios, the mineral admixture and the circumstance factors should be taken into consideration.
基金Funded by the 863 Program from Ministry of Science and Technology of China(2005AA332010) the Key Technologies R&D Program from Department of Science and Technology. Hubei Province (200410G0121)
文摘A laboratory study was undertaken to investigate drying shrinkage and cracking sensitivity subjected to restrained shrinkage of mortar containing fly ash (FA), granulated blast-furnace slag (GBFS) and silica fume (SF). Six mortar mixtures including control Portland cement (PC) and FA, GBFS and SF mortar mixtures were prepared. FA replaced the cement on mass basis at the replacement ratios of 20% and 35%, GBFS replaced the cement at the replacement ratios of 40%, SF replaced the cement at the replacement ratios of 8% and the blended mixtures with 20% FA, 20% GBFS and 8% SF. Water-cementitious materials ratio and sand-cementitious materials ratio were 0.4 and 2.0 for all mixtures, respectively. The mixtures were cured at 65% relative humidity and 20℃. The drying shrinkage value, initial cracking time and cracking width of the mortar samples were measured. The results show that all the mortar mixture containing FA exhibited the decrease of drying shrinkage. Moreover, initial cracking time was markedly delayed, and the crack width of the initial crack was reduced. However, the incorporations of various ratios of GBFS and SF led to an increase of drying shrinkage, initial cracking time and cracking width as compared to control mixture.
文摘An efficient and promising approach for effectively dispersing multi-walled carbon nanotubes(MWCNTs)in cementitious composites has been investigated.The naturally occurring organic extracts from species of indigenously known‘Keekar’trees scattered along tropical and sub-tropical regions;is found as an exceptional replacement to the non-natural commercial surfactants.In the initial phase of investigation,ideal surfactant’s content required for efficient dispersion of MWCNTs in solution was determined using ultra-violet spectroscopy.The experimental investigations were then extended to five different cement composite formulations containing 0.0,0.025,0.05,0.08 and 0.10%MWCNTs by weight of cement.It was observed that the natural surfactant produced efficient dispersion at much reduced cost(approx.14%)compared with the commercial alternate.The estimated weight efficiency factor f was found 6.5 times higher for the proposed sustainable replacement to the conventional along with remarkable increase of 23%in modulus of rupture on 0.08 wt%addition of MWCNTs.Besides strength enhancement,the dispersed MWCNTs also improved the first crack and ultimate fracture toughness by 51.5%and 35.9%,respectively.The field emission scanning electron microscopy of the cryofractured samples revealed efficient dispersion of MWCNTs in the matrix leading to the phenomenon of effective crack bridging and crack branching in the composite matrix.Furthermore,the proposed scheme significantly reduced the early age volumetric shrinkage by 39%.
基金the National Natural Science Foundation of China(No.10572064)K.C.Wong Magna Fund in Ningbo University,and the Natural Science Foundation of Zhejiang Province(No.Y107780)Ningbo University(No.XK0609017).
文摘Under dynamic loading, the constitutive relation of the cement mortar will be significantly affected by the transversal inertial effect of specimens with large diameters. In this paper, one-dimensional theoretical analysis is carried out to determine the transversal inertial effect on the relaxation/retardation time of the cement mortar under the harmonic wave. Relaxation time or retardation time is obtained by means of the wave velocity, attenuation coefficient and the frequency of the harmonic wave. Thus, the transversal inertial effect on the relaxation time from Maxwell model, as well as on retardation time from Voigt model is analyzed. The results show that the transversal inertial effect may lead to the increase of the relaxation time, but induce the decrease of the retardation time. Those should be taken into account when eliminating the transversal inertial effect in applications.
文摘The aim of this study is to examine the performance of nano additives in two different sets of mortar specimens armed with reinforcing steel rebars. In particular, three sets of reinforced concrete cylinders with additives of 0.1% wt of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have been exposed to a solution of 3.5% NaCl, and further examined for the impact of nano-modification on corrosion performance. The anti-corrosive performance of these additives was investigated through linear polarization technique (LPR), mass loss and mercury porosimetry technique (MIP). From the investigation results, it is found that the addition of CNTs/CNFs causes lower steel corrosion, whereas the pore structure of concrete with CNTs/CNFs can significantly reduce the mass loss rate and the relative permeability.
基金Funded by the Major State Basic Research Development Program of China(No.2011CB013800)
文摘The SO4^(2-)concentration distributions in surface region of cement mortar immersed in sulfate solution at early stage were measured by layered sampling method combined with chemical analysis, and the diffusion coefficients of SO4^(2-)anions in surface region of mortar into internal area were calculated by means of instantaneous plane diffusion theory. The experimental results showed that the SO4^(2-)concentration gradually reduced when the diffusion depth increased in the surface region of mortar. Diffusion coefficient(D) was relevant with the concentration and kind of environmental sulfate solution, which reduced with immersion time at the beginning, and then rose slowly after a period of time. The calculation of initial diffusion coefficient(D0) and starting time of deterioration(t∞) caused by sulfate attack was further attempted based on the data of diffusion coefficient, and it was found that D0 and t∞ were all relevant with concentrations of sulfate and different kind of sulfate as well.