The destruction of concrete building materials in severely cold regions of the north is more severely affected by freeze-thaw cycles,and the relationship between the mechanical properties and pore structure of concret...The destruction of concrete building materials in severely cold regions of the north is more severely affected by freeze-thaw cycles,and the relationship between the mechanical properties and pore structure of concrete with fine aggregate from municipal solid waste(MSW)incineration bottom ash after freeze-thaw cycles is analyzed under the degree of freeze-thaw hazard variation.In this paper,the gray correlation method is used to calculate the correlation between the relative dynamic elastic modulus,compressive strength,and microscopic porosity parameters to speculate on the most important factors affecting their changes.The GM(1,1)model was established based on the compressive strength of the waste incineration ash aggregate concrete,the relative error between the simulated and actual values in the model was less than 5%,and the accuracy of the model was level 1,indicating that the GM(1,1)model can well reflect the change in the compressive strength of the MSW incineration bottom ash aggregate concrete during freeze-thaw cycles.Using the gray correlation method,the correlation between the relative dynamic elastic modulus,compressive strength,air content,specific surface area,pore spacing coefficient,and pore average chord length was calculated,and the pore spacing coefficient and pore average chord length were determined to be highly correlated with each other.This determination can help analyze and infer the deterioration mechanism of concrete subject to freeze-thaw cycles.These results can provide a theoretical basis for guiding the engineering practice of concrete with fine aggregates of household bottom ash in the northern cold region.展开更多
A concrete gravity base structure may not be suitable for offshore weak soil because of its heavy weight. Therefore, a conceptual model for a concrete offshore wind turbine structure suitable for weak soils is propose...A concrete gravity base structure may not be suitable for offshore weak soil because of its heavy weight. Therefore, a conceptual model for a concrete offshore wind turbine structure suitable for weak soils is proposed. The proposed model is composed of a prestressed concrete(PSC) supported by a pile foundation. For a three-dimensional analysis of the large concrete structure, wave pressures based on the diffraction wave theory are developed using a three-dimensional solid finite element method. Static and dynamic analyses were performed to achieve the conceptual model of a PSC structure subjected to ocean environmental loads and a 5-MW turbine load on southwest coast in Korea. From the analysis, the maximum displacement and stresses of the proposed model did not exceed the allowable values from design standard, and the first mode of natural frequency of the structure was in a safe range to avoid resonance. The proposed model has enough structural stability to withstand external loads, and it is expected to be used in locations suitable for concrete gravity structures.展开更多
Based on behavior science and direct causes analysis of serious accidents in Chinese coal mines in recent 5 years, a conclusion that unsafe behaviors of coal mine staff were the direct causes of these serious accident...Based on behavior science and direct causes analysis of serious accidents in Chinese coal mines in recent 5 years, a conclusion that unsafe behaviors of coal mine staff were the direct causes of these serious accidents was drawn, accounting for 91.3%. If staff was divided into executor and manager, percentages of the executor＇s and manager＇s unsafe behaviors in direct causes of the accidents were 69% and 54%, respectively, with executor＇s unsafe behavior as direct causes and manager＇s unsafe behavior as essential reasons after thorough analysis of these accidents. Further, on the basis of dual structure theory analysis, three new understandings, including transformation, hierarchy classification and representativeness of behavior factors were il- lustrated. Behavior factors of executors and managers in Chinese coal mines were summarized and classified by new recogni- tion. Then, dual structure theory was applied in a coal mine in Hebei Province of China; weakening unsafe behaviors and strengthening safe factors can attain the purpose of motivating safer behaviors in the coal mine.展开更多
The thixotropic structural build-up is crucial in extrusion-based three-dimensional(3D)concrete printing.This paper uses a theoretical model to predict the evolution of static and dynamic yield stress for printed conc...The thixotropic structural build-up is crucial in extrusion-based three-dimensional(3D)concrete printing.This paper uses a theoretical model to predict the evolution of static and dynamic yield stress for printed concrete.The model employs a structural kinetics framework to create a time-independent constitutive link between shear stress and shear rate.The model considers flocculation,deflocculation,and chemical hydration to anticipate structural buildability.The reversible and irreversible contributions that occur throughout the build-up,breakdown,and hydration are defined based on the proposed structural parameters.Additionally,detailed parametric studies are conducted to evaluate the impact of model parameters.It is revealed that the proposed model is in good agreement with the experimental results,and it effectively characterizes the structural build-up of 3D printable concrete.展开更多
基金supported by the National Natural Science Foundation of China Project 51868058,52068058Inner Mongolia Natural Science Foundation 2018MS05011Inner Mongolia“Grassland Talent”CYYC5039.
文摘The destruction of concrete building materials in severely cold regions of the north is more severely affected by freeze-thaw cycles,and the relationship between the mechanical properties and pore structure of concrete with fine aggregate from municipal solid waste(MSW)incineration bottom ash after freeze-thaw cycles is analyzed under the degree of freeze-thaw hazard variation.In this paper,the gray correlation method is used to calculate the correlation between the relative dynamic elastic modulus,compressive strength,and microscopic porosity parameters to speculate on the most important factors affecting their changes.The GM(1,1)model was established based on the compressive strength of the waste incineration ash aggregate concrete,the relative error between the simulated and actual values in the model was less than 5%,and the accuracy of the model was level 1,indicating that the GM(1,1)model can well reflect the change in the compressive strength of the MSW incineration bottom ash aggregate concrete during freeze-thaw cycles.Using the gray correlation method,the correlation between the relative dynamic elastic modulus,compressive strength,air content,specific surface area,pore spacing coefficient,and pore average chord length was calculated,and the pore spacing coefficient and pore average chord length were determined to be highly correlated with each other.This determination can help analyze and infer the deterioration mechanism of concrete subject to freeze-thaw cycles.These results can provide a theoretical basis for guiding the engineering practice of concrete with fine aggregates of household bottom ash in the northern cold region.
基金supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP) and Ministry of Trade,Industry & Energy(MOTIE) of the Republic of Korea(No.20153030023830)
文摘A concrete gravity base structure may not be suitable for offshore weak soil because of its heavy weight. Therefore, a conceptual model for a concrete offshore wind turbine structure suitable for weak soils is proposed. The proposed model is composed of a prestressed concrete(PSC) supported by a pile foundation. For a three-dimensional analysis of the large concrete structure, wave pressures based on the diffraction wave theory are developed using a three-dimensional solid finite element method. Static and dynamic analyses were performed to achieve the conceptual model of a PSC structure subjected to ocean environmental loads and a 5-MW turbine load on southwest coast in Korea. From the analysis, the maximum displacement and stresses of the proposed model did not exceed the allowable values from design standard, and the first mode of natural frequency of the structure was in a safe range to avoid resonance. The proposed model has enough structural stability to withstand external loads, and it is expected to be used in locations suitable for concrete gravity structures.
文摘Based on behavior science and direct causes analysis of serious accidents in Chinese coal mines in recent 5 years, a conclusion that unsafe behaviors of coal mine staff were the direct causes of these serious accidents was drawn, accounting for 91.3%. If staff was divided into executor and manager, percentages of the executor＇s and manager＇s unsafe behaviors in direct causes of the accidents were 69% and 54%, respectively, with executor＇s unsafe behavior as direct causes and manager＇s unsafe behavior as essential reasons after thorough analysis of these accidents. Further, on the basis of dual structure theory analysis, three new understandings, including transformation, hierarchy classification and representativeness of behavior factors were il- lustrated. Behavior factors of executors and managers in Chinese coal mines were summarized and classified by new recogni- tion. Then, dual structure theory was applied in a coal mine in Hebei Province of China; weakening unsafe behaviors and strengthening safe factors can attain the purpose of motivating safer behaviors in the coal mine.
基金A grant from CSIR,New Delhi,generously funds this studypartially supported by the City University of Hong Kong,China(No.9610661).
文摘The thixotropic structural build-up is crucial in extrusion-based three-dimensional(3D)concrete printing.This paper uses a theoretical model to predict the evolution of static and dynamic yield stress for printed concrete.The model employs a structural kinetics framework to create a time-independent constitutive link between shear stress and shear rate.The model considers flocculation,deflocculation,and chemical hydration to anticipate structural buildability.The reversible and irreversible contributions that occur throughout the build-up,breakdown,and hydration are defined based on the proposed structural parameters.Additionally,detailed parametric studies are conducted to evaluate the impact of model parameters.It is revealed that the proposed model is in good agreement with the experimental results,and it effectively characterizes the structural build-up of 3D printable concrete.
