Improving the knowledge of rheological and tribological characteristics of fresh concrete is important to contribute to the progress of construction sites and the final quality of the work. The objective of this study...Improving the knowledge of rheological and tribological characteristics of fresh concrete is important to contribute to the progress of construction sites and the final quality of the work. The objective of this study is to identify the effect of a superplasticizer based on polycarboxylic ether on the tribological behavior of fresh concrete at the concrete/formwork and concrete/oil/formwork interfaces. Friction tests on fresh concrete were carried out using a plan/plan tribometer. In order to study the behavior of the superplasticizer close to the formwork, three concretes with 30% of paste and different dosage of superplasticizer were formulated. The results show that the increase of the dosage of superplasticizer reduces the friction stress. The properties of the superplasticizer generate a deflocculating action of concrete grains and lead to a stabilisation of the soap-oil micellae present in the vicinity of the formwork. Thus, the efficiency of superplasticizer depends on the quantity of fines, on the quantity of soap formed and so, on the release agent formulation.展开更多
A CaCO_(3)coating with good anticorrosion and adhesion performance was fabricated via ultrasound-assisted chemical conversion on AZ41 magnesium alloy,with a water-bath treated coating as a control.The coating formed o...A CaCO_(3)coating with good anticorrosion and adhesion performance was fabricated via ultrasound-assisted chemical conversion on AZ41 magnesium alloy,with a water-bath treated coating as a control.The coating formed on AZ41 mainly consists of an outer CaCO_(3)layer and an inner(Ca,Mg)CO_(3)layer.Surface characterizations were carried out to obtain the morphology and the chemical composition,mechanical tests were also adopted to assess the hardness and the adhesion of the coating prepared.Afterwards,the long-term corrosion resistance was investigated via electrochemical methods in the chloride-containing Portland cement system.Results show that the ultrasound-assisted coating exhibits higher mechanical properties.In addition,the corrosion resistance of the ultrasound-assisted coating is also higher than that of the bare AZ41 alloy and the water-bath treated coating.This could be due to the formation of a much more compact CaCO_(3)coating on AZ41 Mg alloy,which is mainly benefit from the assistance of the ultrasound.Ultrasound accelerates the nucleation of CaCO_(3)crystals and assists the removal of hydrogen bubbles.Additionally,corrosion mechanism was suggested and discussed for the CaCO_(3)coating.展开更多
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
文摘Improving the knowledge of rheological and tribological characteristics of fresh concrete is important to contribute to the progress of construction sites and the final quality of the work. The objective of this study is to identify the effect of a superplasticizer based on polycarboxylic ether on the tribological behavior of fresh concrete at the concrete/formwork and concrete/oil/formwork interfaces. Friction tests on fresh concrete were carried out using a plan/plan tribometer. In order to study the behavior of the superplasticizer close to the formwork, three concretes with 30% of paste and different dosage of superplasticizer were formulated. The results show that the increase of the dosage of superplasticizer reduces the friction stress. The properties of the superplasticizer generate a deflocculating action of concrete grains and lead to a stabilisation of the soap-oil micellae present in the vicinity of the formwork. Thus, the efficiency of superplasticizer depends on the quantity of fines, on the quantity of soap formed and so, on the release agent formulation.
基金the National Key Research and Development Program of China(Grant No.2021YFB3701100)the Natural Science Foundation Commission of China(Grant Nos.U20A20234and 51874062)+1 种基金Chongqing Foundation and Advanced Research Project(Grant No.cstc2019jcyj-zdxmX 0010)the Science and Technology Major Project of Shanxi Province(Grant No.20191102008)。
文摘A CaCO_(3)coating with good anticorrosion and adhesion performance was fabricated via ultrasound-assisted chemical conversion on AZ41 magnesium alloy,with a water-bath treated coating as a control.The coating formed on AZ41 mainly consists of an outer CaCO_(3)layer and an inner(Ca,Mg)CO_(3)layer.Surface characterizations were carried out to obtain the morphology and the chemical composition,mechanical tests were also adopted to assess the hardness and the adhesion of the coating prepared.Afterwards,the long-term corrosion resistance was investigated via electrochemical methods in the chloride-containing Portland cement system.Results show that the ultrasound-assisted coating exhibits higher mechanical properties.In addition,the corrosion resistance of the ultrasound-assisted coating is also higher than that of the bare AZ41 alloy and the water-bath treated coating.This could be due to the formation of a much more compact CaCO_(3)coating on AZ41 Mg alloy,which is mainly benefit from the assistance of the ultrasound.Ultrasound accelerates the nucleation of CaCO_(3)crystals and assists the removal of hydrogen bubbles.Additionally,corrosion mechanism was suggested and discussed for the CaCO_(3)coating.
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.
