To guarantee the efficient and high-value reutilization of waste concrete from construction waste,the waste concrete was mechanically ground,and three degrees of fineness recycled concrete powder(RCP)were obtained by ...To guarantee the efficient and high-value reutilization of waste concrete from construction waste,the waste concrete was mechanically ground,and three degrees of fineness recycled concrete powder(RCP)were obtained by different grinding time.By analyzing the particle characteristics of RCP with different fineness,the filling-densification effect of cement-RCP cementitious material system was quantitatively investigated based on Andreasen,Fuller,and Aim-Goff models.In addition,the macroscopic mechanical properties of cement paste mixed with RCP were studied,and the influencing mechanisms of RCP on the microstructure of cement paste was revealed.Macroscopic research results show that the particle fineness of RCP after grinding is smaller than that of cement.When the RCP replaces 0%to 20%cement,the packing density based on the Aim-Goff model increases with the increase of RCP content,whereas the macro-mechanical properties first improve and then degrade with the increase of RCP content.Microscopic results show that at 5%RCP content,beneficial hydration products such as C-S-H and beneficial pore increase in cement-RCP paste;while at>15%content,beneficial products decrease and harmful substances such as Ca(OH)_(2)and harmful pore increases.These research findings suggest that the incorporation of RCP can make the cementitious system denser,and the appropriate RCP content can improve the macro-and microscopic properties of cement-based materials.展开更多
The use of recycled concrete and oyster shells as partial cement and aggregate replacements is ongoing research to solve this multifaceted problem of concrete waste in the construction industry as well as waste from o...The use of recycled concrete and oyster shells as partial cement and aggregate replacements is ongoing research to solve this multifaceted problem of concrete waste in the construction industry as well as waste from oyster shell farming. However, there is a lack of evidence on the possibility of producing a fully recycled composite consisting of recycled concrete and oyster shell without the need for new cement and natural aggregates. In this study, recycled concrete powder (RCP) and oyster shell were used to produce a green composite. Separate ground and combined ground (separate ground and co-ground) RCP and oyster shells are used to determine the effects of grinding approaches on the mechanical and chemical properties of the composite. The composite samples were molded via press molding by applying 30 MPa of pressure for 10 minutes. The results revealed that the composite prepared via the combined ground approach presented the highest flexural strength compared to the separate ground and unground samples. The FTIR and XRD characterization results revealed no chemical or phase alterations in the raw materials or the resulting composites before and after grinding. SEM analysis revealed that combined grinding reduced the particles’ size and improved the dispersion of the mixture, thereby increasing the strength.展开更多
Recycled concrete powder(RCP)is used more and more in cement-based materials,but its influence on the hydration process is still unclear.Therefore,this paper studied the influence of recycled concrete powder(RCP)on th...Recycled concrete powder(RCP)is used more and more in cement-based materials,but its influence on the hydration process is still unclear.Therefore,this paper studied the influence of recycled concrete powder(RCP)on the hydration process of cement and provides a theoretical basis for the hydration mechanism of cement composite materials.The hydration heat method was used to systematically analyze the thermal evolution process of cement paste with or without RCP.Hydration products were identified using X-ray diffraction(XRD)and thermal analysis(TG–DSC).The pore structure change of cement pastes was analyzed by mercury intrusion porosimetry(MIP)method.The mechanical properties of mortar were also evaluated.Four recycled concrete powder(RCP)dosages,such as 10%,20%,30%and 40%are considered.The results indicate that with the increase of RCP content,the hydration heat release rate and total heat release amount of paste decreased,but the second heat release peak of hydration reaction advanced;the proportion of harmful pores and more harmful pores increases,the total porosity and the most probable pore size also increase;the fluidity and mechanical strength of mortar decrease,but the crystal type of hydration products does not change.When the content of RCP is less than 20%,it has little effect on the mechanical strength of mortar.When fly ash and silica fume are mixed,the fluidity difference of mortar decreases,and when the content of fly ash is the highest,the fluidity of mortar is the highest,which is 15mm higher than that of the control group.When RCP content is 15%,fly ash and silica fume content is 15%(FA:SF=3:2),the hydration heat of the clean pulp is the highest among all the compounding ratios,and the hydration reaction is the most complete;the proportion of harmless pores increased by 9.672%,the proportion of harmful pores and more harmful pores decreased,and the compactness of material structure increased;the compressive strength and flexural strength of mortar reached 50.6 MPa and 9 MPa respectively,both exceeding those of control mortar.展开更多
Purpose–The efficient utilization of recycled concrete powder(RCP)has attracted much attention.To break through the limitation of single activation technology of RCP,this study investigates the effects of a mechanica...Purpose–The efficient utilization of recycled concrete powder(RCP)has attracted much attention.To break through the limitation of single activation technology of RCP,this study investigates the effects of a mechanical-microwave method on the reactivity of RCP.Design/methodology/approach–The mechanical properties,hydration products,and pore structure of RCP-incorporated mortar were evaluated.Findings–The results demonstrate that the combined activation reduces the median particle size of RCP and induces a low-frequency shift in the Si-O-T FT-IR characteristic peaks,signifying depolymerization of the silicate network and formation of highly reactive broken bond sites.Concurrently,decreased Si2p and Al2p binding energies in XPS spectra confirm enhanced surface reactivity.The 28-day strength activity index(SAI)of RCP mortar improved from 65.7(untreated)to 82.2%under optimal activation conditions(90-min ball milling followed by 10-min microwave irradiation),outperforming solely mechanical activation by 3.6–6.1%.Furthermore,combined activation increased chemically bound water content from 22.8 to 33.7%,accompanied by a low-wavenumber shift in FT-IR peaks of hydration products.The total porosity of RCP mortar decreased from 17.2 to 14.6%,indicating a denser pore structure.Originality/value–This study explores the feasibility and potential mechanism of mechanical-microwave activation of RCP,aiming to provide valuable insights for the sustainable development of materials.Using activated RCP in cement-based materials reduces the demand for cement and substantially cuts carbon emissions,thereby making a critical contribution to the construction industry’s green and low-carbon transition.展开更多
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
In order to make full use of waste recycled fine powder(RFP)in concrete and achieve the goal of carbon neutrality in the concrete industry,the durability of sulfate resistance is an important aspect of evaluating the ...In order to make full use of waste recycled fine powder(RFP)in concrete and achieve the goal of carbon neutrality in the concrete industry,the durability of sulfate resistance is an important aspect of evaluating the performance of recycled powder concrete(RPC).Therefore,the durability of RPC under partial sulfate immersion was studied to provide theoretical guidance for understanding the erosion mechanism of RPC.The compressive strength,mass loss,and microstructure change patterns of RPC under partial immersion of 5%Na2SO4 and MgSO4 solutions were analyzed by cubic compressive strength,mass loss rate,SEM-EDS,and XRD.The results showed that the surface crystalline matter of concrete in Na2SO4 solution was mainly white powders,and that of concrete in MgSO4 solution was mainly transparent paste,both of which had a little spalling on the outer surface of the concrete.The compressive strength and mass loss rate of concrete with 20%RFP was relatively good,indicating that concrete with 20%RFP had better durability against sulfate.The compressive strength of the lower part of the concrete partially immersed in Na2SO4 solution was higher than that of the upper part and the strength of the lower part of RPC-2 was 3.11%higher than the upper part at 180 d;The pattern was reversed in the MgSO4 solution,where the strength of the lower part of RPC-2 was 19.74%lower than the upper part at 180 d.Microscopic analysis showed that the hydration products of RPC were mainly gypsum and ettringite,while the RPC produced more hydration products with the promotion of magnesium ion in the MgSO4 solution.The higher the replacement rate of RFP,the more frequent the gypsum-type failures in the concrete.展开更多
Natural resource scarcity, CO2 emissions, and solid waste generated from the construction industry are major global environmental and developmental challenges, posing threats to the sustainability of terrestrial and a...Natural resource scarcity, CO2 emissions, and solid waste generated from the construction industry are major global environmental and developmental challenges, posing threats to the sustainability of terrestrial and aquatic ecosystems. In response to this multifaceted issue, recent studies focus on developing non-cement concrete, distinct from traditional cement-based compositions, by utilizing recycled concrete and wood waste molded at high temperature and pressure. Although wood hemicellulose shows adhesive properties and bonds particles at lower temperatures, it has not been studied in non-cement concrete. Hence, the present study focuses on developing green concrete using recycled concrete and hemicellulose, and further enhancing its strength with chitosan. The study used the press molding method with different pressing temperatures. The results, compared with conventional cement mortar and other wood components, revealed that hemicellulose-based green concrete exhibited superior bending strength compared to the other the components and even surpassed the strength of conventional cement mortar. Furthermore, an elevation in temperature to 60˚C resulted in enhanced strength, but a further increase to 160˚C led to delamination and thus a reduction in strength. Moreover, hemicellulose, when substituted by 50% of its weight with chitosan, further enhanced the strength of the concrete. The results also showed that hemicellulose has the potential to produce green concrete from abundant plants in a time interval of no more than ten minutes.展开更多
基金Funded by the National Natural Science Foundation of China Project(Nos.52108219 and U21A20150)the Lanzhou University of Technology Hongliu Outstanding Young Talent Program,China(No.04-062407)。
文摘To guarantee the efficient and high-value reutilization of waste concrete from construction waste,the waste concrete was mechanically ground,and three degrees of fineness recycled concrete powder(RCP)were obtained by different grinding time.By analyzing the particle characteristics of RCP with different fineness,the filling-densification effect of cement-RCP cementitious material system was quantitatively investigated based on Andreasen,Fuller,and Aim-Goff models.In addition,the macroscopic mechanical properties of cement paste mixed with RCP were studied,and the influencing mechanisms of RCP on the microstructure of cement paste was revealed.Macroscopic research results show that the particle fineness of RCP after grinding is smaller than that of cement.When the RCP replaces 0%to 20%cement,the packing density based on the Aim-Goff model increases with the increase of RCP content,whereas the macro-mechanical properties first improve and then degrade with the increase of RCP content.Microscopic results show that at 5%RCP content,beneficial hydration products such as C-S-H and beneficial pore increase in cement-RCP paste;while at>15%content,beneficial products decrease and harmful substances such as Ca(OH)_(2)and harmful pore increases.These research findings suggest that the incorporation of RCP can make the cementitious system denser,and the appropriate RCP content can improve the macro-and microscopic properties of cement-based materials.
文摘The use of recycled concrete and oyster shells as partial cement and aggregate replacements is ongoing research to solve this multifaceted problem of concrete waste in the construction industry as well as waste from oyster shell farming. However, there is a lack of evidence on the possibility of producing a fully recycled composite consisting of recycled concrete and oyster shell without the need for new cement and natural aggregates. In this study, recycled concrete powder (RCP) and oyster shell were used to produce a green composite. Separate ground and combined ground (separate ground and co-ground) RCP and oyster shells are used to determine the effects of grinding approaches on the mechanical and chemical properties of the composite. The composite samples were molded via press molding by applying 30 MPa of pressure for 10 minutes. The results revealed that the composite prepared via the combined ground approach presented the highest flexural strength compared to the separate ground and unground samples. The FTIR and XRD characterization results revealed no chemical or phase alterations in the raw materials or the resulting composites before and after grinding. SEM analysis revealed that combined grinding reduced the particles’ size and improved the dispersion of the mixture, thereby increasing the strength.
基金This research was supported by the National Natural Science Foundation of China(51668052)Qinghai Provincial Science and Technology Department Basic Research Project(2017-ZJ787)Qinghai Provincial Science and Technology Department Technology Basic Condition Platform Project(2018-ZJ-T01).
文摘Recycled concrete powder(RCP)is used more and more in cement-based materials,but its influence on the hydration process is still unclear.Therefore,this paper studied the influence of recycled concrete powder(RCP)on the hydration process of cement and provides a theoretical basis for the hydration mechanism of cement composite materials.The hydration heat method was used to systematically analyze the thermal evolution process of cement paste with or without RCP.Hydration products were identified using X-ray diffraction(XRD)and thermal analysis(TG–DSC).The pore structure change of cement pastes was analyzed by mercury intrusion porosimetry(MIP)method.The mechanical properties of mortar were also evaluated.Four recycled concrete powder(RCP)dosages,such as 10%,20%,30%and 40%are considered.The results indicate that with the increase of RCP content,the hydration heat release rate and total heat release amount of paste decreased,but the second heat release peak of hydration reaction advanced;the proportion of harmful pores and more harmful pores increases,the total porosity and the most probable pore size also increase;the fluidity and mechanical strength of mortar decrease,but the crystal type of hydration products does not change.When the content of RCP is less than 20%,it has little effect on the mechanical strength of mortar.When fly ash and silica fume are mixed,the fluidity difference of mortar decreases,and when the content of fly ash is the highest,the fluidity of mortar is the highest,which is 15mm higher than that of the control group.When RCP content is 15%,fly ash and silica fume content is 15%(FA:SF=3:2),the hydration heat of the clean pulp is the highest among all the compounding ratios,and the hydration reaction is the most complete;the proportion of harmless pores increased by 9.672%,the proportion of harmful pores and more harmful pores decreased,and the compactness of material structure increased;the compressive strength and flexural strength of mortar reached 50.6 MPa and 9 MPa respectively,both exceeding those of control mortar.
基金sponsored by Science and Technology Research and Development Plan of China National Railway Group Co.,Ltd.(L2022G009)National Natural Science Foundation of China(52438002)+1 种基金Research Project of China Academy of Railway Science Corporation Limited(2024YJ254)New Cornerstone Science Foundation through the XPLORER PRIZE.
文摘Purpose–The efficient utilization of recycled concrete powder(RCP)has attracted much attention.To break through the limitation of single activation technology of RCP,this study investigates the effects of a mechanical-microwave method on the reactivity of RCP.Design/methodology/approach–The mechanical properties,hydration products,and pore structure of RCP-incorporated mortar were evaluated.Findings–The results demonstrate that the combined activation reduces the median particle size of RCP and induces a low-frequency shift in the Si-O-T FT-IR characteristic peaks,signifying depolymerization of the silicate network and formation of highly reactive broken bond sites.Concurrently,decreased Si2p and Al2p binding energies in XPS spectra confirm enhanced surface reactivity.The 28-day strength activity index(SAI)of RCP mortar improved from 65.7(untreated)to 82.2%under optimal activation conditions(90-min ball milling followed by 10-min microwave irradiation),outperforming solely mechanical activation by 3.6–6.1%.Furthermore,combined activation increased chemically bound water content from 22.8 to 33.7%,accompanied by a low-wavenumber shift in FT-IR peaks of hydration products.The total porosity of RCP mortar decreased from 17.2 to 14.6%,indicating a denser pore structure.Originality/value–This study explores the feasibility and potential mechanism of mechanical-microwave activation of RCP,aiming to provide valuable insights for the sustainable development of materials.Using activated RCP in cement-based materials reduces the demand for cement and substantially cuts carbon emissions,thereby making a critical contribution to the construction industry’s green and low-carbon transition.
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(51668052)Qinghai Provincial Science and Technology Department Basic Research Project(2017-ZJ-787)Qinghai Provincial Science and Technology Department Technology Basic Condition platform Project(2018-ZJ-T01).
文摘In order to make full use of waste recycled fine powder(RFP)in concrete and achieve the goal of carbon neutrality in the concrete industry,the durability of sulfate resistance is an important aspect of evaluating the performance of recycled powder concrete(RPC).Therefore,the durability of RPC under partial sulfate immersion was studied to provide theoretical guidance for understanding the erosion mechanism of RPC.The compressive strength,mass loss,and microstructure change patterns of RPC under partial immersion of 5%Na2SO4 and MgSO4 solutions were analyzed by cubic compressive strength,mass loss rate,SEM-EDS,and XRD.The results showed that the surface crystalline matter of concrete in Na2SO4 solution was mainly white powders,and that of concrete in MgSO4 solution was mainly transparent paste,both of which had a little spalling on the outer surface of the concrete.The compressive strength and mass loss rate of concrete with 20%RFP was relatively good,indicating that concrete with 20%RFP had better durability against sulfate.The compressive strength of the lower part of the concrete partially immersed in Na2SO4 solution was higher than that of the upper part and the strength of the lower part of RPC-2 was 3.11%higher than the upper part at 180 d;The pattern was reversed in the MgSO4 solution,where the strength of the lower part of RPC-2 was 19.74%lower than the upper part at 180 d.Microscopic analysis showed that the hydration products of RPC were mainly gypsum and ettringite,while the RPC produced more hydration products with the promotion of magnesium ion in the MgSO4 solution.The higher the replacement rate of RFP,the more frequent the gypsum-type failures in the concrete.
文摘Natural resource scarcity, CO2 emissions, and solid waste generated from the construction industry are major global environmental and developmental challenges, posing threats to the sustainability of terrestrial and aquatic ecosystems. In response to this multifaceted issue, recent studies focus on developing non-cement concrete, distinct from traditional cement-based compositions, by utilizing recycled concrete and wood waste molded at high temperature and pressure. Although wood hemicellulose shows adhesive properties and bonds particles at lower temperatures, it has not been studied in non-cement concrete. Hence, the present study focuses on developing green concrete using recycled concrete and hemicellulose, and further enhancing its strength with chitosan. The study used the press molding method with different pressing temperatures. The results, compared with conventional cement mortar and other wood components, revealed that hemicellulose-based green concrete exhibited superior bending strength compared to the other the components and even surpassed the strength of conventional cement mortar. Furthermore, an elevation in temperature to 60˚C resulted in enhanced strength, but a further increase to 160˚C led to delamination and thus a reduction in strength. Moreover, hemicellulose, when substituted by 50% of its weight with chitosan, further enhanced the strength of the concrete. The results also showed that hemicellulose has the potential to produce green concrete from abundant plants in a time interval of no more than ten minutes.
