The evolution law of mechanical properties and damage characteristics of early-age flexible formwork filling concrete have a decisive influence on the stability control of surrounding rock of large deformation roadway...The evolution law of mechanical properties and damage characteristics of early-age flexible formwork filling concrete have a decisive influence on the stability control of surrounding rock of large deformation roadway. This study obtained the mechanical evolution characteristics of flexible formwork concrete filling body by using the standard ratio of engineering site and laboratory system test, clarified the time-space coupling mechanism of acoustic emission characteristic parameters and stress field evolution in the process of damage accumulation, and established a multi-parameter damage constitutive model of early-age concrete considering aging characteristics in combining with the theory of damage mechanics. The results show that:(1) Under the same curing age, the compressive strength of the filling body is significantly negatively correlated with the water-cement ratio, and the correlation decreases with the increase of the curing age, showing obvious strain softening behavior in the post-peak stage;(2) During the loading process, the concrete filling body presents a typical' three-stage' acoustic emission response characteristics, that is, the rising period of the initial micro-fracture accumulation, the active period of the main fracture development and the attenuation period after the failure;(3) At a certain curing age, with the increase of water-cement ratio, the total number of acoustic emission b-value signal points generated by the specimen during the test gradually decreases, and the b-value curve changes, and the minimum value appears near the peak stress point;and(4) The pre-peak and post-peak complete damage constitutive equations are established, which can accurately predict the mechanical response of concrete backfill under different curing times and water-cement ratios. The research results provide a basis for selecting the support time and support parameters for large deformation roadway.展开更多
Fabric,as a flexible formwork for concrete,gives builders,engineers,and architects the ability to form virtually any shape.This technique produces a superb concrete surface quality that requires no further touch up or...Fabric,as a flexible formwork for concrete,gives builders,engineers,and architects the ability to form virtually any shape.This technique produces a superb concrete surface quality that requires no further touch up or finishing.Woven polyolefin fabrics are recommended for this application.The texture of this fabric allows water from concrete mix to bleed,and therefore reduces the water-cement ratio of the mix.Due to the reduction in the water-cement ratio,a higher compressive strength in fabric-formed concrete is achieved,which is also suggested by earlier studies.The current research study was conducted to investigate and document the changes in concrete strength and overall quality due to these woven polyolefin fabrics.Use of fabric formwork will result in a decrease in construction cost,construction waste,and greenhouse gas emissions.Two sets of tests were conducted in this research study:a comparison of the compressive strength of fabric-formed versus PVC-formed concrete cylinders,and a comparison of the behaviour of the fabric-formed columns versus cardboard-formed reinforced concrete columns.Variables in this research were limited to two types of fabric that included one with coarse and one with a more refined texture,and two types of concrete that included ordinary and flyash concrete.The laboratory results revealed that the effects of fabric formwork on concrete quality in a large member are limited mostly to the surface zone and the core of the concrete remains the same as a conventionally formed concrete.Even though fabric-formed cylinder tests showed an average of a 15%increase in compressive strength of the concrete samples,the compressive strength of the reinforced columns did not dramatically change when compared to the companion cardboard formed control columns.This research confirmed that fabric formwork is a structurally safe alterna-tive for forming reinforced concrete columns.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 52004289 and U22A20165)the fundamental Research Funds for the Central Universities (Nos. 2022XJNY01 and BBJ2024001)。
文摘The evolution law of mechanical properties and damage characteristics of early-age flexible formwork filling concrete have a decisive influence on the stability control of surrounding rock of large deformation roadway. This study obtained the mechanical evolution characteristics of flexible formwork concrete filling body by using the standard ratio of engineering site and laboratory system test, clarified the time-space coupling mechanism of acoustic emission characteristic parameters and stress field evolution in the process of damage accumulation, and established a multi-parameter damage constitutive model of early-age concrete considering aging characteristics in combining with the theory of damage mechanics. The results show that:(1) Under the same curing age, the compressive strength of the filling body is significantly negatively correlated with the water-cement ratio, and the correlation decreases with the increase of the curing age, showing obvious strain softening behavior in the post-peak stage;(2) During the loading process, the concrete filling body presents a typical' three-stage' acoustic emission response characteristics, that is, the rising period of the initial micro-fracture accumulation, the active period of the main fracture development and the attenuation period after the failure;(3) At a certain curing age, with the increase of water-cement ratio, the total number of acoustic emission b-value signal points generated by the specimen during the test gradually decreases, and the b-value curve changes, and the minimum value appears near the peak stress point;and(4) The pre-peak and post-peak complete damage constitutive equations are established, which can accurately predict the mechanical response of concrete backfill under different curing times and water-cement ratios. The research results provide a basis for selecting the support time and support parameters for large deformation roadway.
文摘Fabric,as a flexible formwork for concrete,gives builders,engineers,and architects the ability to form virtually any shape.This technique produces a superb concrete surface quality that requires no further touch up or finishing.Woven polyolefin fabrics are recommended for this application.The texture of this fabric allows water from concrete mix to bleed,and therefore reduces the water-cement ratio of the mix.Due to the reduction in the water-cement ratio,a higher compressive strength in fabric-formed concrete is achieved,which is also suggested by earlier studies.The current research study was conducted to investigate and document the changes in concrete strength and overall quality due to these woven polyolefin fabrics.Use of fabric formwork will result in a decrease in construction cost,construction waste,and greenhouse gas emissions.Two sets of tests were conducted in this research study:a comparison of the compressive strength of fabric-formed versus PVC-formed concrete cylinders,and a comparison of the behaviour of the fabric-formed columns versus cardboard-formed reinforced concrete columns.Variables in this research were limited to two types of fabric that included one with coarse and one with a more refined texture,and two types of concrete that included ordinary and flyash concrete.The laboratory results revealed that the effects of fabric formwork on concrete quality in a large member are limited mostly to the surface zone and the core of the concrete remains the same as a conventionally formed concrete.Even though fabric-formed cylinder tests showed an average of a 15%increase in compressive strength of the concrete samples,the compressive strength of the reinforced columns did not dramatically change when compared to the companion cardboard formed control columns.This research confirmed that fabric formwork is a structurally safe alterna-tive for forming reinforced concrete columns.
