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
Among different teaching methods in second language teaching, there are five different core relations： the relations between language and speech, between oral and written language, between foreign and native language...Among different teaching methods in second language teaching, there are five different core relations： the relations between language and speech, between oral and written language, between foreign and native language, between integrity and individuality, between the use of foreign language and the development of intelligence. With a view on the entire structure of Chinese teaching and learning as a second language among American high school students and through scientifically conducting the five relations and subdividing the teaching purpose, contents, and objects, this paper will elaborate the strategy on selecting and combining different teaching methods in the whole Chinese teaching and learning process. The purpose of this paper is to greatly develop the effectiveness in teaching and learning Chinese as a second language through selecting appropriate strategies and integrating various advantages according to the teaching purpose, content, and the object.展开更多
Distributed fiber-optic sensing has become an indispensable tool for large-scale structural and environmentalmonitoring, where spectral interrogation of backscattering light enables high-precision quantitative measure...Distributed fiber-optic sensing has become an indispensable tool for large-scale structural and environmentalmonitoring, where spectral interrogation of backscattering light enables high-precision quantitative measurement ofexternal perturbations. Conventional spectral analysis methods, typically based on frequency-domain serialinterrogation or time-to-frequency mapping, face inherent trade-offs between measurement speed, dynamic strainmeasurement range, and system complexity. Here, we present a distributed frequency comb enabled spectrumcorrelationreflectometry as a universal spectral analysis framework that leverages optical frequency comb for parallelmulti-frequency interrogation, which is experimentally demonstrated in a phase-sensitive optical time-domainreflectometry (φ-OTDR) system. This method eliminates the need for large frequency scans, achieving more thantenfold improvement in measurement speed over the state-of-the-art spectral analysis methods. Compared to existingphase-demodulated φ-OTDR systems, this method enables vibration amplitude monitoring with a dynamic strainmeasurement range expanded by more than an order of magnitude, while intrinsically circumventing phaseunwrapping issues and interference fading. This work establishes a new paradigm for distributed spectral analysis,providing a flexible and robust platform for a wide range of sensing technologies, including Rayleigh and Brillouinbasedschemes, which may have significant impact for geophysics, seismology, civil engineering, and other fields.展开更多
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.
文摘Among different teaching methods in second language teaching, there are five different core relations： the relations between language and speech, between oral and written language, between foreign and native language, between integrity and individuality, between the use of foreign language and the development of intelligence. With a view on the entire structure of Chinese teaching and learning as a second language among American high school students and through scientifically conducting the five relations and subdividing the teaching purpose, contents, and objects, this paper will elaborate the strategy on selecting and combining different teaching methods in the whole Chinese teaching and learning process. The purpose of this paper is to greatly develop the effectiveness in teaching and learning Chinese as a second language through selecting appropriate strategies and integrating various advantages according to the teaching purpose, content, and the object.
基金supported by the National Key R&D Program of China(2023YFB2906303)Major Program(JD)of Hubei Province(2023BAA013)+1 种基金the National Natural Science Foundation of China(62105111,62225110)the Chilean National Agency for Research and Development(Fondecyt Regular 1241085,Fondequip EQM220113 and Basal AFB240002).
文摘Distributed fiber-optic sensing has become an indispensable tool for large-scale structural and environmentalmonitoring, where spectral interrogation of backscattering light enables high-precision quantitative measurement ofexternal perturbations. Conventional spectral analysis methods, typically based on frequency-domain serialinterrogation or time-to-frequency mapping, face inherent trade-offs between measurement speed, dynamic strainmeasurement range, and system complexity. Here, we present a distributed frequency comb enabled spectrumcorrelationreflectometry as a universal spectral analysis framework that leverages optical frequency comb for parallelmulti-frequency interrogation, which is experimentally demonstrated in a phase-sensitive optical time-domainreflectometry (φ-OTDR) system. This method eliminates the need for large frequency scans, achieving more thantenfold improvement in measurement speed over the state-of-the-art spectral analysis methods. Compared to existingphase-demodulated φ-OTDR systems, this method enables vibration amplitude monitoring with a dynamic strainmeasurement range expanded by more than an order of magnitude, while intrinsically circumventing phaseunwrapping issues and interference fading. This work establishes a new paradigm for distributed spectral analysis,providing a flexible and robust platform for a wide range of sensing technologies, including Rayleigh and Brillouinbasedschemes, which may have significant impact for geophysics, seismology, civil engineering, and other fields.
