Beach titanomagnetite(TTM)provides a cheap alternative source of Fe and Ti,but this ore is difficult to process to make suitable concentrates for the blast furnace.Recently studies showed that it is feasible to separa...Beach titanomagnetite(TTM)provides a cheap alternative source of Fe and Ti,but this ore is difficult to process to make suitable concentrates for the blast furnace.Recently studies showed that it is feasible to separate Fe and Ti by coal-based direct reduction.In this study,beach TTM was selected as the research object,the effects of reducing agents on reducing atmosphere in coal-based direct reduction of beach TTM were analyzed,and the role of volatiles was also studied.The results showed that when bitumite and coke were used as reducing agents of TTM,the CO produced from volatiles was involved in the reduction reaction,and the generated CO_(2) provided the raw material for the reaction of TTM.The reduction effect of bitumite was better than that of coke.The reason is that bitumite+TTM had a higher gas generation rate and produced a higher CO partial pressure,while coke+TTM had a lower gas generation rate and produced a lower CO partial pressure.When graphite was used as a reducing agent,there was a solid-solid reaction in the early stage in the reaction.With the continuous accumulation of CO_(2),the Boudouad reaction started and accelerated.Graphite+TTM also produced a higher CO partial pressure.展开更多
A process of purification of coal-based coke powder as anode the treatment of coke powder with dilute hydrofluoric acid solution, for Li-ion batteries was attempted. The process started with followed by united-acid-le...A process of purification of coal-based coke powder as anode the treatment of coke powder with dilute hydrofluoric acid solution, for Li-ion batteries was attempted. The process started with followed by united-acid-leaching using sulfuric acid and hydrochloric acid. The effects of altering the hydrofluoric acid addition, hydrofluoric acid concentration, contact time, temperature and acid type were investigated. A minimum ash content of 0.35% was obtained when proper conditions were applied. The electrochemical performance of purified coke powder shows greatly improved electrochemical performance. The as-purified coke powder presented an initial reversible capacity of 257.4 mAh/g and a retention rate of 95% after 50 cycles. The proposed purification process paves a way to prepare a promising anode material with good performance with low cost of coke powder for Li-ion batteries.展开更多
Solid wastes derived from metallurgical industries pose a significant threat to environment. The utilization and disposal of these solid wastes are the major concern in the world. Semi-coke generated in coal-based dir...Solid wastes derived from metallurgical industries pose a significant threat to environment. The utilization and disposal of these solid wastes are the major concern in the world. Semi-coke generated in coal-based direct reduction process of iron ore is a by-product and its suitable utilization is not available so far. In order to handle it properly, the characteristics of this by-product were comprehensively investigated. A series of analysis methods were used to demonstrate its mineral compositions, petrography and physico-chemical properties. The results reveal that the semi-coke has poor washability. The fixed carbon content of semi-coke reaches 76.11% and the gross calorific value is 28.10 MJ/kg, both of which are similar to those of traditional sinter coke breeze. Also, semi-coke ash possesses lower content of SiO2, Al2O3, S and higher content of CaO and MgO, which could improve the strength of sinter ore when partially substituting for coke breeze in sintering. Semi-coke features well-development porous structure and higher reaction activity, which predicts that the sintering speed could be elevated to some extent when employing it as a partial replacement of coke breeze, so the studies further suggest that the potential adverse effect of the high reactivity on sintering process could be weakened by adequately coarsening the semi-coke's particle size.展开更多
Microwave-curing and mechanical grinding of fly ash have both beenadopted as effective methods for improving the early-age strength of alkali-activated fly ash(AAFA)binders.This study combined these two approaches by ...Microwave-curing and mechanical grinding of fly ash have both beenadopted as effective methods for improving the early-age strength of alkali-activated fly ash(AAFA)binders.This study combined these two approaches by synthesizing AAFA using original,medium-fine,and ultrafine fly ash as precursors,and then specimens were cured with a five-stage temperature-controlled microwave.The compressive strength results indicate that the original AAFA develops the highest strength initially during microwave-curing,reaching 28 MPa at stage 2.Medium-fine AAFA exhibits the highest strength of 60 MPa when cured to stage 4-I,which is 26%higher than the peak strength of original AAFA.It is attributed to the significant rise in their specific surface area,which accelerates the dissolution of Si and Al from the precursor and facilitates the subsequent formation of N-A-S-H gels.Additionally,nanoscale zeolite crystals formed as secondary products fill the tiny gaps between amorphous products,thereby significantly improving their microstructure.In contrast,ultrafine fly ash,primarily composed of fragmented particles,necessitated a substantial amount of water,which adversely affects the absorption efficiency for microwave of AAFA specimens.Thus,ultrafine AAFA specimens consistently exhibit the lowest compressive strength.Specifically,at the end of curing,the compressive strength of these three specimens with microwave-curing is approximately 32%,59%,and 172%higher than that of the steam-cured sample,respectively.These findings demonstrate the compatibility of microwave-curing and fly ash refinement in enhancing the early compressive strength development of AAFA.展开更多
Traditional stabilization of backfilling material is done by using Portland cement. However, the high price of cement forced mining engineer s to seek cheaper binding materials. Fly ash, which is the indus- trial wast...Traditional stabilization of backfilling material is done by using Portland cement. However, the high price of cement forced mining engineer s to seek cheaper binding materials. Fly ash, which is the indus- trial wast e from thermal power plant, possess the potential activity of jellification, and can b e used in cemented fill as a partial substitute for cement to reduce the fill co s t. Tests were done during the past few years in Xinqiao Pyrite Mine and Phoenix Copper Mine to determine the technology parameters and the suitable content of f ly ash. Specimens with different cement/fly/ash tailings (sands) ratios were tes ted to obtain the strength values of the fill mass based on the analyses of both the chemical composition and physical and mechanical properties of fly ash . The compressive strength of specimens with a ratio of 1∶2∶8 (cement to fly ash to tailings ) can reach 2 MPa after 90 d curing, totally meeting the requiremen t of artificial pillar and reducing the fill cost by 20%-30%.展开更多
The main objective of this paper focuses on the changes that occur in the strength and microstructural properties of sodium silicate activated fly ash based geopolymer due to varying the sulfate salt and water content...The main objective of this paper focuses on the changes that occur in the strength and microstructural properties of sodium silicate activated fly ash based geopolymer due to varying the sulfate salt and water content.A series of tests including X-ray diffraction,Fourier transform infrared spectroscopy,scanning electron microscopy,physical adsorption and unconfined compressive strength were used to investigate this effect.The results indicate that the higher water content has an adverse effect on the alkali activation and microstructural properties of geopolymer,so the optimum mass ratio of sodium sulfate in alkali-activated geopolymer under different water-to-binder ratios shows a“peak shifting”phenomenon,i.e.,the higher the water-to-binder ratio,the higher the optimum mass ratio.Lower presence of sodium sulfate has no significant effect on the alkali-activated geopolymer systems;higher addition of sodium sulfate,however,could cause the symmetrical stretching vibration of Si—O and the symmetrical stretching vibration of Si—O—Si and Al—O—Si,and promote the formation of N-A-S-H gels.Furthermore,the cement effect of the gel and sodium sulfate aggregate could improve the integrity of pore structure obviously.The maximum strength of geopolymer curing at ambient temperature was 52 MPa.This study obtains the rule that the strength properties of alkali-activated geopolymers vary with the water-to-binder ratio and sodium sulfate content.The feasibility of geopolymer co-activated by sodium sulfate and sodium silicate was investigated,and reference for engineering application of alkali-activated geopolymer in salt-bearing areas was provided.展开更多
A novel microwave digestion and alkali fusion assisted hydrothermal method was proposed to synthesize zeolite from coal fly ash and the zeolite product was studied for removal of Cd(II)from aqueous solution through ba...A novel microwave digestion and alkali fusion assisted hydrothermal method was proposed to synthesize zeolite from coal fly ash and the zeolite product was studied for removal of Cd(II)from aqueous solution through batch experiments.The adsorbent was characterized by X-ray diffraction,scanning electron microscopy,Fourier transform infrared spectroscopy,surface area analyzer and zeta potential measurement.The results show that the synthetic zeolite was identified as faujasite.The optimum conditions for removal of Cd(II)are found to be:adsorbent dose of0.5g/L,pH6,contact time of90min and initial concentration of20mg/L,the removal rate of Cd(II)is98.55%.The experimental kinetic data agree well with the pseudo second-order equation;the Langmuir isotherm model is found to be more suitable to explicate the experimental equilibrium isotherm results than Freundlich,Dubinin-Radushkevich and Temkin models,and the maximum adsorption capacity of Cd(II)is found to be86.96mg/g.The thermodynamic parameters such asΔGΘ,ΔHΘandΔSΘwere evaluated and the results show that the adsorption of Cd(II)onto the as-synthesized zeolite is spontaneous,endothermic and feasible under studied conditions.展开更多
Chitosan-coated fly ash(CWF)was prepared by the acid leaching-coating method.Chitosan and fly ash were crosslinked in the solution of acetic acid and sulfuric acid.The microstructure of CWF was conducted by scanning e...Chitosan-coated fly ash(CWF)was prepared by the acid leaching-coating method.Chitosan and fly ash were crosslinked in the solution of acetic acid and sulfuric acid.The microstructure of CWF was conducted by scanning electron microscope(SEM)and X-ray diffraction(XRD).The removal of Cr(VI)from water by CWF was studied by adsorption experiments.The composite prepared by the experiment developed a pore structure and a crystal structure similar to SiO_(2) and chitosan chain-like coating was formed on the surface of fly ash.The new modified material has larger surface roughness,specific surface area and more adsorption channels.The Cr(VI)was enriched in modified materials by electrostatic adsorption between CrO_(4)^(2−)、CrO_(7)^(2−)and-NH_(3)^(+) group and surface acid functional groups.The movement of Cr(VI)in solution is a diffusion process from the main body of the liquid phase to the surface of the liquid film.展开更多
To improve the environmental benefits and solve the problems of large shrinkage and high brittleness, the partial replacement of calcined kaolin by fly ash as a raw material for geopolymer synthesis and the influences...To improve the environmental benefits and solve the problems of large shrinkage and high brittleness, the partial replacement of calcined kaolin by fly ash as a raw material for geopolymer synthesis and the influences of polypropylene (PP) fiber on the mechanical properties and volume stability were investigated. The results show that compressive strength of the geopolymer containing 33.3%(mass fraction) fly ash by steam curing at 80 ℃ for 6 d is improved by 35.5%. The 3-day compressive strength, flexural strength and impacting energy of geopolymers containing 0.05%PP fiber increase by 67.8%, 36.1% and 6.25%, while the shrinkage and modulus of compressibility decrease by 38.6% and 31.3%, respectively. The results of scanning electron microscopy (SEM) and the appearances of crack growths confirm that PP fiber can offer a bridging effect over the harmful pores and defects and change the expanding ways of cracks, resulting in a great improvement of strength and toughness.展开更多
Hydration shrinkage generated by cement hydration is the cause of autogenous shrinkage of high strength concrete. It may result in the volume change and even cracking of mortar and concrete. According to the data anal...Hydration shrinkage generated by cement hydration is the cause of autogenous shrinkage of high strength concrete. It may result in the volume change and even cracking of mortar and concrete. According to the data analysis in a series of experimental studies, the influence of ultra-fine fly ash on the hydration shrinkage of composite cementitious materials was investigated. It is found that ultra-fine fly ash can reduce the hydration shrinkage of cement paste effectively, and the more the ultra-fine fly ash, the less the hydration shrinkage. Compared with cement paste without the ultra-fine fly ash, the shrinkage ratio of cement paste reduces from 23.4% to 39.7% when the ultra-fine fly ash replaces cement from 20% to 50%. Moreover, the microscopic mechanism of the ultra-fine fly ash restraining the hydration shrinkage was also studied by scanning electron microscopy, X-ray diffraction and hydrated equations. The results show that the hydration shrinkage can be restrained to a certain degree because the ultra-fine fly ash does not participate in the hydration at the early stage and the secondary hydration products are different at the later stage.展开更多
The time-dependent rheological behaviors of alkali-activated cement(AAC)are expected to be precisely controlled,in order to meet the requirements of modern engineering practices.In this paper,the effects of activator,...The time-dependent rheological behaviors of alkali-activated cement(AAC)are expected to be precisely controlled,in order to meet the requirements of modern engineering practices.In this paper,the effects of activator,including the Na_(2)O concentration and SiO_(2)/Na_(2)O(S/N)molar ratio,on the rheological behavior of alkali-activated slag fly ash pastes were investigated.The small amplitude oscillatory shear(SAOS)and shear test were used to evaluate the structural build-up and flowability of pastes.Besides,zeta potential measurement,calorimetric test and thermogravimetric analysis(TGA)were carried out to reveal the physico-chemical mechanisms behind the rheological evolution of fresh pastes.It was found that high Na_(2)O concentration and low S/N molar ratio improved the flowability and structural build-up rate of paste.Moreover,the structural build-up of alkali-activated slag-fly ash pastes consists of two stages,which is controlled by the dissolution of solid reactants and formation of C-(A)-S-H gels,respectively.展开更多
基金Project(52104257)supported by the National Natural Science Foundation of China。
文摘Beach titanomagnetite(TTM)provides a cheap alternative source of Fe and Ti,but this ore is difficult to process to make suitable concentrates for the blast furnace.Recently studies showed that it is feasible to separate Fe and Ti by coal-based direct reduction.In this study,beach TTM was selected as the research object,the effects of reducing agents on reducing atmosphere in coal-based direct reduction of beach TTM were analyzed,and the role of volatiles was also studied.The results showed that when bitumite and coke were used as reducing agents of TTM,the CO produced from volatiles was involved in the reduction reaction,and the generated CO_(2) provided the raw material for the reaction of TTM.The reduction effect of bitumite was better than that of coke.The reason is that bitumite+TTM had a higher gas generation rate and produced a higher CO partial pressure,while coke+TTM had a lower gas generation rate and produced a lower CO partial pressure.When graphite was used as a reducing agent,there was a solid-solid reaction in the early stage in the reaction.With the continuous accumulation of CO_(2),the Boudouad reaction started and accelerated.Graphite+TTM also produced a higher CO partial pressure.
基金Projects(51274240,51204209) supported by the National Natural Science Foundation of ChinaProject(2012M521545) supported by the National Postdoctoral Science Foundation of China
文摘A process of purification of coal-based coke powder as anode the treatment of coke powder with dilute hydrofluoric acid solution, for Li-ion batteries was attempted. The process started with followed by united-acid-leaching using sulfuric acid and hydrochloric acid. The effects of altering the hydrofluoric acid addition, hydrofluoric acid concentration, contact time, temperature and acid type were investigated. A minimum ash content of 0.35% was obtained when proper conditions were applied. The electrochemical performance of purified coke powder shows greatly improved electrochemical performance. The as-purified coke powder presented an initial reversible capacity of 257.4 mAh/g and a retention rate of 95% after 50 cycles. The proposed purification process paves a way to prepare a promising anode material with good performance with low cost of coke powder for Li-ion batteries.
基金Project(2011GH561685)supported by the China Torch Program
文摘Solid wastes derived from metallurgical industries pose a significant threat to environment. The utilization and disposal of these solid wastes are the major concern in the world. Semi-coke generated in coal-based direct reduction process of iron ore is a by-product and its suitable utilization is not available so far. In order to handle it properly, the characteristics of this by-product were comprehensively investigated. A series of analysis methods were used to demonstrate its mineral compositions, petrography and physico-chemical properties. The results reveal that the semi-coke has poor washability. The fixed carbon content of semi-coke reaches 76.11% and the gross calorific value is 28.10 MJ/kg, both of which are similar to those of traditional sinter coke breeze. Also, semi-coke ash possesses lower content of SiO2, Al2O3, S and higher content of CaO and MgO, which could improve the strength of sinter ore when partially substituting for coke breeze in sintering. Semi-coke features well-development porous structure and higher reaction activity, which predicts that the sintering speed could be elevated to some extent when employing it as a partial replacement of coke breeze, so the studies further suggest that the potential adverse effect of the high reactivity on sintering process could be weakened by adequately coarsening the semi-coke's particle size.
文摘Microwave-curing and mechanical grinding of fly ash have both beenadopted as effective methods for improving the early-age strength of alkali-activated fly ash(AAFA)binders.This study combined these two approaches by synthesizing AAFA using original,medium-fine,and ultrafine fly ash as precursors,and then specimens were cured with a five-stage temperature-controlled microwave.The compressive strength results indicate that the original AAFA develops the highest strength initially during microwave-curing,reaching 28 MPa at stage 2.Medium-fine AAFA exhibits the highest strength of 60 MPa when cured to stage 4-I,which is 26%higher than the peak strength of original AAFA.It is attributed to the significant rise in their specific surface area,which accelerates the dissolution of Si and Al from the precursor and facilitates the subsequent formation of N-A-S-H gels.Additionally,nanoscale zeolite crystals formed as secondary products fill the tiny gaps between amorphous products,thereby significantly improving their microstructure.In contrast,ultrafine fly ash,primarily composed of fragmented particles,necessitated a substantial amount of water,which adversely affects the absorption efficiency for microwave of AAFA specimens.Thus,ultrafine AAFA specimens consistently exhibit the lowest compressive strength.Specifically,at the end of curing,the compressive strength of these three specimens with microwave-curing is approximately 32%,59%,and 172%higher than that of the steam-cured sample,respectively.These findings demonstrate the compatibility of microwave-curing and fly ash refinement in enhancing the early compressive strength development of AAFA.
文摘为探究Ash2l(absent,small,or homeotic 2-like,Ash2l)对小鼠大脑皮质神经祖细胞(neural progenitor cells,NPCs)的增殖能力和细胞周期的影响。本研究利用NPCs标志物PAX6和TBR2,检测NPCs数量和分布的改变情况。结果显示,Ash2l敲除导致NPCs数量显著减少(P<0.05),且分布紊乱。对E16.5小鼠进行在体30 min EdU标记实验,检测NPCs增殖能力,Ash2l敲除导致30 min EdU几乎无法进入NPCs(P<0.001)。结果表示,NPCs增殖能力受到严重的影响。用细胞周期M期标志物pH3,检测大脑皮质中处于M期的NPCs分布情况,同时提取了E16.5小鼠大脑皮质蛋白质,检测细胞周期蛋白A的表达量。Ash2l敲除的NPCs的M期细胞核分布紊乱,G_(2)期标志蛋白质细胞周期蛋白A表达量减少。利用EdU和BrdU双标记法,计算NPCs的S期长度。Ash2l敲除后的NPCs的S期长度缩短(P<0.05)。因此,Ash2l调控NPCs细胞周期进程,进而影响NPCs的增殖能力,敲除小鼠大脑皮质发育异常。本研究强调了表观遗传调控对胚胎期神经系统发育的重要作用,并对表型进行了深入探索。
文摘Traditional stabilization of backfilling material is done by using Portland cement. However, the high price of cement forced mining engineer s to seek cheaper binding materials. Fly ash, which is the indus- trial wast e from thermal power plant, possess the potential activity of jellification, and can b e used in cemented fill as a partial substitute for cement to reduce the fill co s t. Tests were done during the past few years in Xinqiao Pyrite Mine and Phoenix Copper Mine to determine the technology parameters and the suitable content of f ly ash. Specimens with different cement/fly/ash tailings (sands) ratios were tes ted to obtain the strength values of the fill mass based on the analyses of both the chemical composition and physical and mechanical properties of fly ash . The compressive strength of specimens with a ratio of 1∶2∶8 (cement to fly ash to tailings ) can reach 2 MPa after 90 d curing, totally meeting the requiremen t of artificial pillar and reducing the fill cost by 20%-30%.
基金Project(51878322)supported by the National Natural Science Foundation of ChinaProject(18YF1FA112)supported by Key Research and Development Program of Gansu Province,China。
文摘The main objective of this paper focuses on the changes that occur in the strength and microstructural properties of sodium silicate activated fly ash based geopolymer due to varying the sulfate salt and water content.A series of tests including X-ray diffraction,Fourier transform infrared spectroscopy,scanning electron microscopy,physical adsorption and unconfined compressive strength were used to investigate this effect.The results indicate that the higher water content has an adverse effect on the alkali activation and microstructural properties of geopolymer,so the optimum mass ratio of sodium sulfate in alkali-activated geopolymer under different water-to-binder ratios shows a“peak shifting”phenomenon,i.e.,the higher the water-to-binder ratio,the higher the optimum mass ratio.Lower presence of sodium sulfate has no significant effect on the alkali-activated geopolymer systems;higher addition of sodium sulfate,however,could cause the symmetrical stretching vibration of Si—O and the symmetrical stretching vibration of Si—O—Si and Al—O—Si,and promote the formation of N-A-S-H gels.Furthermore,the cement effect of the gel and sodium sulfate aggregate could improve the integrity of pore structure obviously.The maximum strength of geopolymer curing at ambient temperature was 52 MPa.This study obtains the rule that the strength properties of alkali-activated geopolymers vary with the water-to-binder ratio and sodium sulfate content.The feasibility of geopolymer co-activated by sodium sulfate and sodium silicate was investigated,and reference for engineering application of alkali-activated geopolymer in salt-bearing areas was provided.
基金Projects(2013BAC15B01,2013BAB07B03)supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of ChinaProject(Qian Ke He JZ[2014]2009)supported by the Key Foundation of Science and Technology of Guizhou Province,China
文摘A novel microwave digestion and alkali fusion assisted hydrothermal method was proposed to synthesize zeolite from coal fly ash and the zeolite product was studied for removal of Cd(II)from aqueous solution through batch experiments.The adsorbent was characterized by X-ray diffraction,scanning electron microscopy,Fourier transform infrared spectroscopy,surface area analyzer and zeta potential measurement.The results show that the synthetic zeolite was identified as faujasite.The optimum conditions for removal of Cd(II)are found to be:adsorbent dose of0.5g/L,pH6,contact time of90min and initial concentration of20mg/L,the removal rate of Cd(II)is98.55%.The experimental kinetic data agree well with the pseudo second-order equation;the Langmuir isotherm model is found to be more suitable to explicate the experimental equilibrium isotherm results than Freundlich,Dubinin-Radushkevich and Temkin models,and the maximum adsorption capacity of Cd(II)is found to be86.96mg/g.The thermodynamic parameters such asΔGΘ,ΔHΘandΔSΘwere evaluated and the results show that the adsorption of Cd(II)onto the as-synthesized zeolite is spontaneous,endothermic and feasible under studied conditions.
基金Project(41602310)supported by the National Natural Science Foundation of ChinaProject(2017M611044)supported by the China Postdoctoral Science Foundation。
文摘Chitosan-coated fly ash(CWF)was prepared by the acid leaching-coating method.Chitosan and fly ash were crosslinked in the solution of acetic acid and sulfuric acid.The microstructure of CWF was conducted by scanning electron microscope(SEM)and X-ray diffraction(XRD).The removal of Cr(VI)from water by CWF was studied by adsorption experiments.The composite prepared by the experiment developed a pore structure and a crystal structure similar to SiO_(2) and chitosan chain-like coating was formed on the surface of fly ash.The new modified material has larger surface roughness,specific surface area and more adsorption channels.The Cr(VI)was enriched in modified materials by electrostatic adsorption between CrO_(4)^(2−)、CrO_(7)^(2−)and-NH_(3)^(+) group and surface acid functional groups.The movement of Cr(VI)in solution is a diffusion process from the main body of the liquid phase to the surface of the liquid film.
基金Project(2006AA06Z225) supported by the National High-Tech Research and Development Program of China
文摘To improve the environmental benefits and solve the problems of large shrinkage and high brittleness, the partial replacement of calcined kaolin by fly ash as a raw material for geopolymer synthesis and the influences of polypropylene (PP) fiber on the mechanical properties and volume stability were investigated. The results show that compressive strength of the geopolymer containing 33.3%(mass fraction) fly ash by steam curing at 80 ℃ for 6 d is improved by 35.5%. The 3-day compressive strength, flexural strength and impacting energy of geopolymers containing 0.05%PP fiber increase by 67.8%, 36.1% and 6.25%, while the shrinkage and modulus of compressibility decrease by 38.6% and 31.3%, respectively. The results of scanning electron microscopy (SEM) and the appearances of crack growths confirm that PP fiber can offer a bridging effect over the harmful pores and defects and change the expanding ways of cracks, resulting in a great improvement of strength and toughness.
文摘Hydration shrinkage generated by cement hydration is the cause of autogenous shrinkage of high strength concrete. It may result in the volume change and even cracking of mortar and concrete. According to the data analysis in a series of experimental studies, the influence of ultra-fine fly ash on the hydration shrinkage of composite cementitious materials was investigated. It is found that ultra-fine fly ash can reduce the hydration shrinkage of cement paste effectively, and the more the ultra-fine fly ash, the less the hydration shrinkage. Compared with cement paste without the ultra-fine fly ash, the shrinkage ratio of cement paste reduces from 23.4% to 39.7% when the ultra-fine fly ash replaces cement from 20% to 50%. Moreover, the microscopic mechanism of the ultra-fine fly ash restraining the hydration shrinkage was also studied by scanning electron microscopy, X-ray diffraction and hydrated equations. The results show that the hydration shrinkage can be restrained to a certain degree because the ultra-fine fly ash does not participate in the hydration at the early stage and the secondary hydration products are different at the later stage.
基金Project(2017 YFB 0310100)supported by National Key R&D Program of ChinaProjects(51778629,51922109)supported by the National Natural Science Foundation of ChinaProjects(2020 zzts 617,2020 CX 011)supported by the Innovation-Driven Project of Central South University,China。
文摘The time-dependent rheological behaviors of alkali-activated cement(AAC)are expected to be precisely controlled,in order to meet the requirements of modern engineering practices.In this paper,the effects of activator,including the Na_(2)O concentration and SiO_(2)/Na_(2)O(S/N)molar ratio,on the rheological behavior of alkali-activated slag fly ash pastes were investigated.The small amplitude oscillatory shear(SAOS)and shear test were used to evaluate the structural build-up and flowability of pastes.Besides,zeta potential measurement,calorimetric test and thermogravimetric analysis(TGA)were carried out to reveal the physico-chemical mechanisms behind the rheological evolution of fresh pastes.It was found that high Na_(2)O concentration and low S/N molar ratio improved the flowability and structural build-up rate of paste.Moreover,the structural build-up of alkali-activated slag-fly ash pastes consists of two stages,which is controlled by the dissolution of solid reactants and formation of C-(A)-S-H gels,respectively.
