The pozzolanic activity of nano-SiO2 and silica fume was comparatirely stndied by X-ray diffraction ( XRD ) , differential scanning calorimetry (DSC), scanning electron micrascopy (SEM) and the compressive , bon...The pozzolanic activity of nano-SiO2 and silica fume was comparatirely stndied by X-ray diffraction ( XRD ) , differential scanning calorimetry (DSC), scanning electron micrascopy (SEM) and the compressive , bond and bending streugths of hardened paste and concrete were also measured. Results indicate that the compressive strength development of the paste made from Ca(OH)2 and nano-SiO2, the reaction rate of Ca( OH)2 with nano- SiO2 and the velocity of C-S-H gel formation from Ca ( OH)2 with nano-SiO2 showed marked increases over those of Ca( OH)2 with silica fume. Furthermore, the bond strength at the interface between aggregate and hardened cement paste, and the bending strength of concrete incorporated with 3% .NS increased more than those with SF, especially at early ages. To sum up, the pozzolanic activity of nano-SiO2 was much greater than that of silica fume. The results suggest that with a small amount of nano-SiO2, the Ca( OH)2 crystal at the interface between hardened cement paste and aggregate at early ages may be effectively absorbed in high performance concrete.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
The effect of calcination temperature on the pozzolanic activity of maize straw stem ash(MSSA)was evaluated.The MSSA samples calcined at temperature values of 500,700,and 850℃ were dissolved in portlandite solution f...The effect of calcination temperature on the pozzolanic activity of maize straw stem ash(MSSA)was evaluated.The MSSA samples calcined at temperature values of 500,700,and 850℃ were dissolved in portlandite solution for 6 h,thereby obtaining residual samples.The MSSA and MSSA residual samples were analyzed using Fourier transform infrared spectroscopy,X-ray powder diffraction scanning electron microscopy,and X-ray photoelectron spectroscopy to determine vibration bonds,minerals,microstructures,and Si 2p transformation behavior.The conductivity,pH value,and loss of conductivity with dissolving time of the MSSA-portlandite mixed solution were also determined.The main oxide composition of MSSA was silica and potassium oxide.The dissolution of the Si^(4+) content of MSSA at 500℃ was higher than those of the other calcination temperatures.The conductivity and loss of conductivity of MSSA at 700℃ were higher than those of the other calcination temperatures at a particular dissolving time due to the higher KCl content in MSSA at 700℃.C-S-H was easily identified in MSSA samples using X-ray powder diffraction,and small cubic and nearly spherical particles of C-S-H were found in the MSSA residual samples.In conclusion,the optimum calcination temperature of MSSA having the best pozzolanic activity is 500℃,but excessive agglomeration must be prevented.展开更多
Electrolytic manganese residue (EMR) is generated from electrolytic manganese metal (EMM) indus- try, and its disposal is currently a serious problem in China. The EMR were calcined in the interval 100-900 ℃ to e...Electrolytic manganese residue (EMR) is generated from electrolytic manganese metal (EMM) indus- try, and its disposal is currently a serious problem in China. The EMR were calcined in the interval 100-900 ℃ to enhance their pozzolanic activity and characterized by the differential thermal analysis-thermogravimetry (TG- DTA), X-ray diffraction (XRD), infra-red (IR) and chemical analysis techniques with the aim to correlate phase transitions and structural features with the pozzolanic activity of calcined EMR. From the phase analysis and compressive strength results, it is found that the EMR calcined within 700--800℃ had the best pozzolanic activity due to the decomposition of poorly-crystallized CaSO4 under the reducing ambient created by the decomposition of (NH4)2SO4. The appearance of reactive CaO mainly contributes to the good pozzolanic activity of EMR cal- cined within 700--800℃. The crystallinity of MnaO4 increases leading an unfavourable effect on the pozzolanic behaviour of EMR calcined at 900℃. The developed pozzolanic material containing 30% (mass fraction) EMR possesses compressive strength properties at a level similar to 42.5# normal Portland cement, in the range of 41.5--50.5 MPa. Besides, leaching results show that EMR blend cement pastes have excellent effect on the solidi- fication of heavy metals.展开更多
The results of investigation to assess the possibility of copper slag with high MgO to be used as a mineral admixture in concrete were reported in this study. The soundness of cement paste containing the slag has been...The results of investigation to assess the possibility of copper slag with high MgO to be used as a mineral admixture in concrete were reported in this study. The soundness of cement paste containing the slag has been examined by autoclave test. Pozzolanic activity of the slag was studied in comparison to fly ash. The slag was mixed calcium hydroxide and water,and the progress of the pozzolanic reaction was determined by X-ray diffraction,differential thermal analysis-thermogravimetry and scanning electron microscopy from 28 to 90 d. The experimental results showed that the autoclave expansion value of cement paste containing the slag was far below the expansion limit (0.8%). It can be conclude that the slag has little periclase content. The consumption of calcium hydroxide showed the slag exhibits high pozzolanic activity,which was higher than that of fly ash. Hence,use of the copper slag with high MgO but low periclase content as a mineral admixture in concrete seems feasible.展开更多
This paper presents a study of the potential use of iron mining tailings as artificial pozzolan (metakaolin) after their submission to thermal treatment via calcination in a flash furnace. The research consists of the...This paper presents a study of the potential use of iron mining tailings as artificial pozzolan (metakaolin) after their submission to thermal treatment via calcination in a flash furnace. The research consists of the characterization of the tailings before and after calcination, chemical, mineralogical, thermogravimetric, and mechanical strength analyses were conducted. The results were compared with those for commonly used pozzolans, metakaolin, and similarities were identified. The study of the morphology of the particles before and after calcination was conducted through analyses of images obtained by scanning electronic microscope. The pozzolanic activity of the fine mining tailings calcined with flash technology was evaluated in uniaxial compression trials, which showed excellent results.展开更多
The rice husk ash ( RHA) and silica ( Si02) nanoparticles are prepared from rice husk charcoal (RHC) by the methods of ventilated calcining and chemical precipitation, respectively, to remove the residual carbon...The rice husk ash ( RHA) and silica ( Si02) nanoparticles are prepared from rice husk charcoal (RHC) by the methods of ventilated calcining and chemical precipitation, respectively, to remove the residual carbon which is harmful to cement composites. The structures and morphologies of these products are investigated by the Fourier transform infrared spectroscopy, X-ray diffraction, scanning/ transmission electron microscopy and N2 adsorption- desorption analyzer. The results show that the as-produced RHA and Si02 nanoparticles exist in amorphous phase without residual carbon, and exhibit porous structures with specific surface areas of 170.19 and 248. 67 m2 /g , respectively. The micro particles of RHA are aggregated by numerous loosely packed Si02 gel particles with the diameter of 50 to 100 nm. The Si02 nanoparticles are well dispersed with the average size of about 30 nm. Both the RHA and Si02 nanoparticles can significantly reduce the conductivity of saturated Ca(OH)2 solution and increase the early strength of the cement composites. They also exhibit high pozzolanic activity, indicating that they can be used as ecological nano mineral admixtures.展开更多
Green and sustainable concrete has attracted significant attention from the construction industry and researchers since it was proposed.The ceramic waste materials are often directly buried in the ground or placed in ...Green and sustainable concrete has attracted significant attention from the construction industry and researchers since it was proposed.The ceramic waste materials are often directly buried in the ground or placed in an open dump,and the accumulation of ceramic waste contributes to environmental pollution,which makes the recycling of ceramic waste quite urgent.Owing to the pozzolanic activity,excellent mechanical properties and durability,industrial ceramic waste is considered as a suitable substitute for cement or natural aggregates to fabricate renewable concrete.In this paper,the pozzolanic activity of ceramic waste and the workability,mechanical performance,and durability of ceramic concrete are discussed.In addition,the most recent research results pertaining to ceramic concrete are reviewed.Ground ceramic powder improves the workability,compressive strength,resistance to chloride penetration,and carbonation resistance of concrete to a certain extent.Concrete containing ceramic as the aggregate has a lower mechanical performance than ordinary concrete.However,the resistance to chloride penetration,freeze-thaw resistance,and high-temperature resistance of ceramic concrete are remarkable.Ceramic concrete is environmentally friendly,requires fewer energy resources to manufacture than ordinary concrete,and has excellent engineering properties.However,further research is required for future engineering applications.展开更多
The demand for alternative cementitious materials is on the rise,as the cement causes huge energy consumption and produces greenhouse gas emission.Additionally,there is economic potential for the construction industry...The demand for alternative cementitious materials is on the rise,as the cement causes huge energy consumption and produces greenhouse gas emission.Additionally,there is economic potential for the construction industry to reuse wastes as supplementary building materials.The purpose of this study is to evaluate the potential of utilizing ferrochrome slag wastes in mortar as supplementary cementitious materials (SCMs),thereby achieving this double-sided goal.Thus,the mechanical and physical properties of ferrochrome slag wastes were investigated to be used as admixtures in concrete production.Three different cement mortar specimens were prepared by replacing cement with ferrochrome slag in ratios of 0,30%,and 60% by mass and flexural and compressive strengths of the specimens were determined at the ages of 7,28,56,90,and 180 days.Also,the effects of the ferrochrome slag replacement ratio on workability,setting time and volume expansion were revealed.Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were also investigated to study the microstructural properties of the specimens containing ferrochrome slag.Based on the results,it is concluded that ferrochrome slag wastes have pozzolanic activity,therefore reusing them as SCMs in the cement and concrete industry is convenient.展开更多
The role of metakaolin in the properties of Portland cement hydrated with ground water and sea water was described by magnetic susceptibility study. Cement pastes containing 0wt%, 10wt%, 20wt% and 30wt% replacement of...The role of metakaolin in the properties of Portland cement hydrated with ground water and sea water was described by magnetic susceptibility study. Cement pastes containing 0wt%, 10wt%, 20wt% and 30wt% replacement of metakaolin and in a water/cement (W/C) ratio of 0.4 were prepared. The susceptibility at different hydration periods was determined by Faraday Curie balance and it was related to the changes in setting time and compressive strength of admixtured cement. Compared with sea water-treated cement paste, the magnetic susceptibility of ground water-treated cement paste is higher in value. The observed result shows that, irrespective of water, the magnetic susceptibility increases with increasing metakaolin percentage replacement level in cement.展开更多
The overall aim was to investigate the effect of highly active rice husk ash (RHA) produced by an industrial furnace on some properties of concrete. The strength, pore volume and pore distribution of concrete and the ...The overall aim was to investigate the effect of highly active rice husk ash (RHA) produced by an industrial furnace on some properties of concrete. The strength, pore volume and pore distribution of concrete and the Ca(OH)-2 content in concrete were investigated by JIS A 1108 (Method of test for compressive strength of concrete), a mercury instrument porosimeter, and the thermogravimetric analysis, respectively. The results show that,with RHA replacement of cement,the compressive strength of concrete is increased evidently;the average pore radius of concrete is greatly decreased, especially the portion of the pores greater than 20nm in radius is decreased while the amount of smaller pores is increased, and the more the RHA replacement, the less the amount of Ca(OH)-2 in concrete. The latter two results are the main reasons for the strength enhancement of concrete.展开更多
In several countries, the residual RHA (rice husk ash) has been produced in rice processing industries or in thermoelectric plants that use rice husk to generate heat and/or electrical energy, usually without burnin...In several countries, the residual RHA (rice husk ash) has been produced in rice processing industries or in thermoelectric plants that use rice husk to generate heat and/or electrical energy, usually without burning process control. This causes a reduction in the amorphous silica content of residual RHA, which distinguishes them from the RHA produced according to controlled burning process, which is totally amorphous and considered a highly reactive pozzolan. In this paper, the hydration products and the porous structure of binders paste were studied by replacing, in weight of 5%, 10% and 20% of Portland cement OPC (ordinary Portland cement), by residual RHAs named A and B, which have high and low content of amorphous silica, respectively, using microstructure evaluation techniques as XRD (X-ray diffraction), TG (thermogravimetric) tests and MIP (mercury intrusion porosimetry). A reducing the size of the pores of the pastes was observed according to the increase of content replacement of RHA A and RHA B.展开更多
The cost of cement has made concrete production expensive such that the housing deficit in developing countries is on the rise despite all the efforts by governments and other stakeholders to produce affordable housin...The cost of cement has made concrete production expensive such that the housing deficit in developing countries is on the rise despite all the efforts by governments and other stakeholders to produce affordable housing units for the populace. Ashes of agricultural products such as rice husk, known as mineral admixtures may have pozzolanic characteristics which would be more beneficial to the housing industry in terms of strength gain and economy than being pollutants to the environment. Rice Husk Ash (RHA), because of its finely divided form and very high silica content and amorphousness, proved to be useful for strength gain of Rice Husk Ash Concrete (RHAC). Rice husk ash was manufactured by uncontrolled burning, ground, sieved and replaced with cement at 0%, 5%, 10%, 15%, 20% and 25% in mass for the mixes C20, C25, C30 and C35 where their compressive strengths were verified at 3, 7, 14, 21, 28, 56, 90 and 180 days. The X-ray diffraction pattern list indicated amorphous as well as diffused peak of about 8000 counts of SiO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> representing crystalline structures identified as cristobalite. A physical examination of the RHA showed very fine appearance, grey color and specific gravity of 2.06. The chemical analysis also revealed the existence of oxide content to be 55.8% representing 0.78% of Fe</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;">, 54% of SiO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> and 1.06% of Al</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> representing 20.23% lower than the minimum value of 70% required for pozzolans. Generally, the compressive strength values decreased as the RHA content in the mixes increased but when compared to the control concrete the optimum replacement percentage of Ordinary Portland Cement (OPC) with RHA at 5% showed an increase above the control concrete for C20 mix. The increase in the RHA in the mixes resulted in the high demand for water in all the mixes.展开更多
The high moisture content (80%) in the sewage dewatered sludge is the main obstacle to disposal and recycling. A chemical dewatering and stabilization/solidification (S/S) alternative for the sludge was developed,...The high moisture content (80%) in the sewage dewatered sludge is the main obstacle to disposal and recycling. A chemical dewatering and stabilization/solidification (S/S) alternative for the sludge was developed, using calcined aluminum salts (AS) as solidifier, and CaCl 2 , Na 2 SO 4 and CaSO 4 as accelerators, to enhance the mechanical compressibility making the landfill operation possible. The properties of the resultant matrixes were determined in terms of moisture contents, unconfined compressive strength, products of hydration, and toxicity characteristics. The results showed that AS exhibited a moderate pozzolanic activity, and the mortar AS 0 obtained with 5% AS and 10% CaSO 4 of AS by weight presented a moisture contents below 50%–60% and a compressive strength of (51.32 ± 2.9) kPa after 5–7 days of curing time, meeting the minimum requirement for sanitary landfill. The use of CaSO 4 obviously improved the S/S performance, causing higher strength level. X-ray diffraction, scanning electron microscopy and thermogravimetry- differential scanning calorimetry investigations revealed that a large amount of hydrates (viz., gismondine and CaCO 3 ) were present in solidified sludge, leading to the depletion of evaporable water and the enhancement of the strength. In addition, the toxicity characteristic leaching procedure (TCLP) and horizontal vibration (HJ 557-2009) leaching test were conducted to evaluate their environmental compatibility. It was found that the solidified products conformed to the toxicity characteristic criteria in China and could be safely disposed of in a sanitary landfill.展开更多
Alum sludge is a typical by-product of drinking water treatment processes.Most sludge is disposed of at landfill sites,and such a disposal method may cause significant environmental concern due to its vast amount.This...Alum sludge is a typical by-product of drinking water treatment processes.Most sludge is disposed of at landfill sites,and such a disposal method may cause significant environmental concern due to its vast amount.This paper assessed the feasibility of reusing sludge as a supplementary cementitious material,which could efficiently exhaust stockpiled sludge.Specifically,the pozzolanic reactivity of sludge at different temperatures,the reaction mechanism of the sludge-cement binder,and the resistance of sludge-derived mortar to microbially induced corrosion were investigated.The obtained results indicated that 800℃ was the optimal calcination temperature for sludge.Mortar containing sludge up to 30%by weight showed comparable physical properties at a curing age of 90 days.Mortar with 10%cement replaced by sludge can significantly improve the resistance to biogenic corrosion due to the formation of Al-bearing phases with high resistance to acidic media,e.g.,Ca_(4)Al_(2)O_(7)·xH_(2)O and strätlingite.展开更多
基金Funded bythe Center of Science Research, Zhejiang Universityof Technology of China
文摘The pozzolanic activity of nano-SiO2 and silica fume was comparatirely stndied by X-ray diffraction ( XRD ) , differential scanning calorimetry (DSC), scanning electron micrascopy (SEM) and the compressive , bond and bending streugths of hardened paste and concrete were also measured. Results indicate that the compressive strength development of the paste made from Ca(OH)2 and nano-SiO2, the reaction rate of Ca( OH)2 with nano- SiO2 and the velocity of C-S-H gel formation from Ca ( OH)2 with nano-SiO2 showed marked increases over those of Ca( OH)2 with silica fume. Furthermore, the bond strength at the interface between aggregate and hardened cement paste, and the bending strength of concrete incorporated with 3% .NS increased more than those with SF, especially at early ages. To sum up, the pozzolanic activity of nano-SiO2 was much greater than that of silica fume. The results suggest that with a small amount of nano-SiO2, the Ca( OH)2 crystal at the interface between hardened cement paste and aggregate at early ages may be effectively absorbed in high performance concrete.
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financially supported by the Distinguished Youth Funds of National Natural Science Foundation of China(No.51925402)the Ten Thousand Talent Program of China for Leading Scientists in Science,Technology and Innovation,the Shanxi Science and Technology Major Project Funds(No.20201102004)+3 种基金the Shanxi“1331 Project”Fundsthe Shanxi Province Key Laboratory Construction Project Fundsthe Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering(Nos.2021SX-TD001 and 2021SX-TD002)the Shanxi Province Postgraduate Education Innovation Project(No.2021Y191).
文摘The effect of calcination temperature on the pozzolanic activity of maize straw stem ash(MSSA)was evaluated.The MSSA samples calcined at temperature values of 500,700,and 850℃ were dissolved in portlandite solution for 6 h,thereby obtaining residual samples.The MSSA and MSSA residual samples were analyzed using Fourier transform infrared spectroscopy,X-ray powder diffraction scanning electron microscopy,and X-ray photoelectron spectroscopy to determine vibration bonds,minerals,microstructures,and Si 2p transformation behavior.The conductivity,pH value,and loss of conductivity with dissolving time of the MSSA-portlandite mixed solution were also determined.The main oxide composition of MSSA was silica and potassium oxide.The dissolution of the Si^(4+) content of MSSA at 500℃ was higher than those of the other calcination temperatures.The conductivity and loss of conductivity of MSSA at 700℃ were higher than those of the other calcination temperatures at a particular dissolving time due to the higher KCl content in MSSA at 700℃.C-S-H was easily identified in MSSA samples using X-ray powder diffraction,and small cubic and nearly spherical particles of C-S-H were found in the MSSA residual samples.In conclusion,the optimum calcination temperature of MSSA having the best pozzolanic activity is 500℃,but excessive agglomeration must be prevented.
基金the National Natural Science Foundation of China(Nos.51104008 and 51034008)China Postdoctoral Science Foundation Funded Project(No.20100480202)+1 种基金the Research Fund for the Doctoral Program of Higher Education of China (No.20100006120010)the Fundamental Research Funds for the Central Universities(No.FRF-TP-12- 026A)
文摘Electrolytic manganese residue (EMR) is generated from electrolytic manganese metal (EMM) indus- try, and its disposal is currently a serious problem in China. The EMR were calcined in the interval 100-900 ℃ to enhance their pozzolanic activity and characterized by the differential thermal analysis-thermogravimetry (TG- DTA), X-ray diffraction (XRD), infra-red (IR) and chemical analysis techniques with the aim to correlate phase transitions and structural features with the pozzolanic activity of calcined EMR. From the phase analysis and compressive strength results, it is found that the EMR calcined within 700--800℃ had the best pozzolanic activity due to the decomposition of poorly-crystallized CaSO4 under the reducing ambient created by the decomposition of (NH4)2SO4. The appearance of reactive CaO mainly contributes to the good pozzolanic activity of EMR cal- cined within 700--800℃. The crystallinity of MnaO4 increases leading an unfavourable effect on the pozzolanic behaviour of EMR calcined at 900℃. The developed pozzolanic material containing 30% (mass fraction) EMR possesses compressive strength properties at a level similar to 42.5# normal Portland cement, in the range of 41.5--50.5 MPa. Besides, leaching results show that EMR blend cement pastes have excellent effect on the solidi- fication of heavy metals.
文摘The results of investigation to assess the possibility of copper slag with high MgO to be used as a mineral admixture in concrete were reported in this study. The soundness of cement paste containing the slag has been examined by autoclave test. Pozzolanic activity of the slag was studied in comparison to fly ash. The slag was mixed calcium hydroxide and water,and the progress of the pozzolanic reaction was determined by X-ray diffraction,differential thermal analysis-thermogravimetry and scanning electron microscopy from 28 to 90 d. The experimental results showed that the autoclave expansion value of cement paste containing the slag was far below the expansion limit (0.8%). It can be conclude that the slag has little periclase content. The consumption of calcium hydroxide showed the slag exhibits high pozzolanic activity,which was higher than that of fly ash. Hence,use of the copper slag with high MgO but low periclase content as a mineral admixture in concrete seems feasible.
文摘This paper presents a study of the potential use of iron mining tailings as artificial pozzolan (metakaolin) after their submission to thermal treatment via calcination in a flash furnace. The research consists of the characterization of the tailings before and after calcination, chemical, mineralogical, thermogravimetric, and mechanical strength analyses were conducted. The results were compared with those for commonly used pozzolans, metakaolin, and similarities were identified. The study of the morphology of the particles before and after calcination was conducted through analyses of images obtained by scanning electronic microscope. The pozzolanic activity of the fine mining tailings calcined with flash technology was evaluated in uniaxial compression trials, which showed excellent results.
基金The Key Program of the National Natural Science Foundation of China(No.51438003)the National Basic Research Program of China(973 Program)(No.2015CB655105)
文摘The rice husk ash ( RHA) and silica ( Si02) nanoparticles are prepared from rice husk charcoal (RHC) by the methods of ventilated calcining and chemical precipitation, respectively, to remove the residual carbon which is harmful to cement composites. The structures and morphologies of these products are investigated by the Fourier transform infrared spectroscopy, X-ray diffraction, scanning/ transmission electron microscopy and N2 adsorption- desorption analyzer. The results show that the as-produced RHA and Si02 nanoparticles exist in amorphous phase without residual carbon, and exhibit porous structures with specific surface areas of 170.19 and 248. 67 m2 /g , respectively. The micro particles of RHA are aggregated by numerous loosely packed Si02 gel particles with the diameter of 50 to 100 nm. The Si02 nanoparticles are well dispersed with the average size of about 30 nm. Both the RHA and Si02 nanoparticles can significantly reduce the conductivity of saturated Ca(OH)2 solution and increase the early strength of the cement composites. They also exhibit high pozzolanic activity, indicating that they can be used as ecological nano mineral admixtures.
基金support received from Natural Science Foundation of Henan(Grant No.212300410018)National Natural Science Foundation of China(Grant No.U2040224)+1 种基金Program for Innovative Research Team(in Science and Technology)in University of Henan Province of China(Grant No.20IRTSTHN009)the Research and Develop Project of China Construction Seventh Engineering Division Co.,Ltd.(Grant No.CSCEC7b-2021-Z-11).
文摘Green and sustainable concrete has attracted significant attention from the construction industry and researchers since it was proposed.The ceramic waste materials are often directly buried in the ground or placed in an open dump,and the accumulation of ceramic waste contributes to environmental pollution,which makes the recycling of ceramic waste quite urgent.Owing to the pozzolanic activity,excellent mechanical properties and durability,industrial ceramic waste is considered as a suitable substitute for cement or natural aggregates to fabricate renewable concrete.In this paper,the pozzolanic activity of ceramic waste and the workability,mechanical performance,and durability of ceramic concrete are discussed.In addition,the most recent research results pertaining to ceramic concrete are reviewed.Ground ceramic powder improves the workability,compressive strength,resistance to chloride penetration,and carbonation resistance of concrete to a certain extent.Concrete containing ceramic as the aggregate has a lower mechanical performance than ordinary concrete.However,the resistance to chloride penetration,freeze-thaw resistance,and high-temperature resistance of ceramic concrete are remarkable.Ceramic concrete is environmentally friendly,requires fewer energy resources to manufacture than ordinary concrete,and has excellent engineering properties.However,further research is required for future engineering applications.
文摘The demand for alternative cementitious materials is on the rise,as the cement causes huge energy consumption and produces greenhouse gas emission.Additionally,there is economic potential for the construction industry to reuse wastes as supplementary building materials.The purpose of this study is to evaluate the potential of utilizing ferrochrome slag wastes in mortar as supplementary cementitious materials (SCMs),thereby achieving this double-sided goal.Thus,the mechanical and physical properties of ferrochrome slag wastes were investigated to be used as admixtures in concrete production.Three different cement mortar specimens were prepared by replacing cement with ferrochrome slag in ratios of 0,30%,and 60% by mass and flexural and compressive strengths of the specimens were determined at the ages of 7,28,56,90,and 180 days.Also,the effects of the ferrochrome slag replacement ratio on workability,setting time and volume expansion were revealed.Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were also investigated to study the microstructural properties of the specimens containing ferrochrome slag.Based on the results,it is concluded that ferrochrome slag wastes have pozzolanic activity,therefore reusing them as SCMs in the cement and concrete industry is convenient.
文摘The role of metakaolin in the properties of Portland cement hydrated with ground water and sea water was described by magnetic susceptibility study. Cement pastes containing 0wt%, 10wt%, 20wt% and 30wt% replacement of metakaolin and in a water/cement (W/C) ratio of 0.4 were prepared. The susceptibility at different hydration periods was determined by Faraday Curie balance and it was related to the changes in setting time and compressive strength of admixtured cement. Compared with sea water-treated cement paste, the magnetic susceptibility of ground water-treated cement paste is higher in value. The observed result shows that, irrespective of water, the magnetic susceptibility increases with increasing metakaolin percentage replacement level in cement.
文摘The overall aim was to investigate the effect of highly active rice husk ash (RHA) produced by an industrial furnace on some properties of concrete. The strength, pore volume and pore distribution of concrete and the Ca(OH)-2 content in concrete were investigated by JIS A 1108 (Method of test for compressive strength of concrete), a mercury instrument porosimeter, and the thermogravimetric analysis, respectively. The results show that,with RHA replacement of cement,the compressive strength of concrete is increased evidently;the average pore radius of concrete is greatly decreased, especially the portion of the pores greater than 20nm in radius is decreased while the amount of smaller pores is increased, and the more the RHA replacement, the less the amount of Ca(OH)-2 in concrete. The latter two results are the main reasons for the strength enhancement of concrete.
文摘In several countries, the residual RHA (rice husk ash) has been produced in rice processing industries or in thermoelectric plants that use rice husk to generate heat and/or electrical energy, usually without burning process control. This causes a reduction in the amorphous silica content of residual RHA, which distinguishes them from the RHA produced according to controlled burning process, which is totally amorphous and considered a highly reactive pozzolan. In this paper, the hydration products and the porous structure of binders paste were studied by replacing, in weight of 5%, 10% and 20% of Portland cement OPC (ordinary Portland cement), by residual RHAs named A and B, which have high and low content of amorphous silica, respectively, using microstructure evaluation techniques as XRD (X-ray diffraction), TG (thermogravimetric) tests and MIP (mercury intrusion porosimetry). A reducing the size of the pores of the pastes was observed according to the increase of content replacement of RHA A and RHA B.
文摘The cost of cement has made concrete production expensive such that the housing deficit in developing countries is on the rise despite all the efforts by governments and other stakeholders to produce affordable housing units for the populace. Ashes of agricultural products such as rice husk, known as mineral admixtures may have pozzolanic characteristics which would be more beneficial to the housing industry in terms of strength gain and economy than being pollutants to the environment. Rice Husk Ash (RHA), because of its finely divided form and very high silica content and amorphousness, proved to be useful for strength gain of Rice Husk Ash Concrete (RHAC). Rice husk ash was manufactured by uncontrolled burning, ground, sieved and replaced with cement at 0%, 5%, 10%, 15%, 20% and 25% in mass for the mixes C20, C25, C30 and C35 where their compressive strengths were verified at 3, 7, 14, 21, 28, 56, 90 and 180 days. The X-ray diffraction pattern list indicated amorphous as well as diffused peak of about 8000 counts of SiO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> representing crystalline structures identified as cristobalite. A physical examination of the RHA showed very fine appearance, grey color and specific gravity of 2.06. The chemical analysis also revealed the existence of oxide content to be 55.8% representing 0.78% of Fe</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;">, 54% of SiO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> and 1.06% of Al</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> representing 20.23% lower than the minimum value of 70% required for pozzolans. Generally, the compressive strength values decreased as the RHA content in the mixes increased but when compared to the control concrete the optimum replacement percentage of Ordinary Portland Cement (OPC) with RHA at 5% showed an increase above the control concrete for C20 mix. The increase in the RHA in the mixes resulted in the high demand for water in all the mixes.
基金supported by the Science and Technol- ogy Commission of Shanghai Municipality (No. 08DZ 1202802, 09DZ 1204105)
文摘The high moisture content (80%) in the sewage dewatered sludge is the main obstacle to disposal and recycling. A chemical dewatering and stabilization/solidification (S/S) alternative for the sludge was developed, using calcined aluminum salts (AS) as solidifier, and CaCl 2 , Na 2 SO 4 and CaSO 4 as accelerators, to enhance the mechanical compressibility making the landfill operation possible. The properties of the resultant matrixes were determined in terms of moisture contents, unconfined compressive strength, products of hydration, and toxicity characteristics. The results showed that AS exhibited a moderate pozzolanic activity, and the mortar AS 0 obtained with 5% AS and 10% CaSO 4 of AS by weight presented a moisture contents below 50%–60% and a compressive strength of (51.32 ± 2.9) kPa after 5–7 days of curing time, meeting the minimum requirement for sanitary landfill. The use of CaSO 4 obviously improved the S/S performance, causing higher strength level. X-ray diffraction, scanning electron microscopy and thermogravimetry- differential scanning calorimetry investigations revealed that a large amount of hydrates (viz., gismondine and CaCO 3 ) were present in solidified sludge, leading to the depletion of evaporable water and the enhancement of the strength. In addition, the toxicity characteristic leaching procedure (TCLP) and horizontal vibration (HJ 557-2009) leaching test were conducted to evaluate their environmental compatibility. It was found that the solidified products conformed to the toxicity characteristic criteria in China and could be safely disposed of in a sanitary landfill.
基金funded by ARC Research Hub for Nanoscience-based Construction Material Manufacturing,Grant No.IH150100006General Project of National Natural Science Foundation of China (No.51778523)SA Water for the research scholarship and financial support for this project.
文摘Alum sludge is a typical by-product of drinking water treatment processes.Most sludge is disposed of at landfill sites,and such a disposal method may cause significant environmental concern due to its vast amount.This paper assessed the feasibility of reusing sludge as a supplementary cementitious material,which could efficiently exhaust stockpiled sludge.Specifically,the pozzolanic reactivity of sludge at different temperatures,the reaction mechanism of the sludge-cement binder,and the resistance of sludge-derived mortar to microbially induced corrosion were investigated.The obtained results indicated that 800℃ was the optimal calcination temperature for sludge.Mortar containing sludge up to 30%by weight showed comparable physical properties at a curing age of 90 days.Mortar with 10%cement replaced by sludge can significantly improve the resistance to biogenic corrosion due to the formation of Al-bearing phases with high resistance to acidic media,e.g.,Ca_(4)Al_(2)O_(7)·xH_(2)O and strätlingite.