The advanced temperature and stress test machine was introduced to determine the early cracking tendency of concrete with inclusion of light-burnt MgO under full restraint by tracking the development of thermal,physic...The advanced temperature and stress test machine was introduced to determine the early cracking tendency of concrete with inclusion of light-burnt MgO under full restraint by tracking the development of thermal,physical and deformation properties.Results showed that light-burnt MgO being incorporated ranging between 4 wt% and 6 wt% of cementitious materials was beneficial to increase the maximum compressive stress and cracking stress of concrete by 0.37 MPa and 0.2 MPa on average respectively.The second zero stress temperature was reduced by 11.4 ℃ and the maximum temperature was slightly reduced while cracking thermal impact was significantly enhanced from 59.8 ℃ to 66.2 ℃.Sensitive anti-cracking coefficient F was forwarded to assess the early cracking tendency of concrete and the inclusion of 4 wt% light-burnt MgO with activity of 109 s ranked the best in crack resistance.展开更多
The effects of different contents of a MgO expansive agent and phosphorus slag on the mechanical properties,shrinkage behavior,and the heat of hydration of concrete were studied.The slump flow,setting time,dry shrinka...The effects of different contents of a MgO expansive agent and phosphorus slag on the mechanical properties,shrinkage behavior,and the heat of hydration of concrete were studied.The slump flow,setting time,dry shrinkage,and hydration heat were used as sensitive parameters to assess the response of the considered specimens.As shown by the results,in general,with an increase in the phosphorus slag content,the hydration heat of concrete decreases for all ages,but the early strength displays a downward trend and the dry shrinkage rate increases.The 90-d strength and dry shrinkage of concrete could be improved with a phosphorus residue content between 0%-20%,with the best performances in terms of mechanical properties and shrinkage characteristics being achieved for a content of 20 kg/m^(3).On the basis of these results,it can be concluded that appropriate amounts of phosphorus slag and MgO expansive agent can be used to improve the compressive strength of concrete in the later stage by reducing the hydration heat and dry shrinkage rate,respectively.展开更多
To investigate the assumptions proposed in this paper,the evolution law governing the strength and expansion performance of MgO and nano-MgO micro-expansive concrete in the environment of mineral powder was firstly ob...To investigate the assumptions proposed in this paper,the evolution law governing the strength and expansion performance of MgO and nano-MgO micro-expansive concrete in the environment of mineral powder was firstly observed in this study.Secondly,SEM,XRD,and TG-DSC microscopic tests were conducted to reveal the effects of the active mineral-powder admixture on the hydration degree and expansion performance of MgO and nano-MgO in HPC.Our experimental results successfully verified our hypothesis,which indicated that the expansion performance of macro-MgO and nano-MgO was indeed depressed by the addition of active mineral power admixtures,even though the mechanical property of concrete composites was effectively improved.Furthermore,the hydration test also demonstrated the negative interference on the mineral powders,which was induced by the expansion agents.It is found the amounts of hydrates tend to decrease because the mineral powder ratio reaches and exceeds 40%.Moreover,it is also concluded the effect of expansion agents is governed by the alkalinity cement paste,especially for the nano-MgO.In other words,the expansion performance of nano-MgO will vary more obviously with the hydration process,than MgO.The results of this study provide that effective experimental and theoretical data support the hydration-inhibition mechanism of magnesium expansive agents.展开更多
In this paper, concrete with limestone coarse aggregate was studied due to frost action in saline and nonsaline environments. The main focus is to explain the damaging formula of concrete with poor quality of limeston...In this paper, concrete with limestone coarse aggregate was studied due to frost action in saline and nonsaline environments. The main focus is to explain the damaging formula of concrete with poor quality of limestone aggregate in frost actions. All investigated concretes fulfill the recommendations of the European standard EN 206, Concrete--Specification, Performance, Production and Conformity limiting values for composition and properties of concrete （maximum W/C （water/cement） ratio, minimal class of compressive strength, minimal mass of cement and minimal percentage of entrained air）. The damaging formula of the frost resistant concrete is studied through scaling test of concrete during freeze/thaw process, frost resistant test of coarse limestone aggregate and chemical analysis of limestone. Experiments results showed that there is a correlation between CaO/MgO ratio and Al2O3 of limestone and frost resistance of concrete, using chemical composition for determining potential ACR （alkali-carbonate reactivity） will indicate higher risk of damaging effect of concrete.展开更多
In recent years, energy-retrofitting is becoming an imperative aim for existing buildings worldwide and increased interest has focused on the development of nanoparticle blended concretes with adequate mechanical...In recent years, energy-retrofitting is becoming an imperative aim for existing buildings worldwide and increased interest has focused on the development of nanoparticle blended concretes with adequate mechanical properties and durability performance, through the optimization of concrete permeability and the incorporation of the proper nanoparticle type in the concrete matrix. In order to investigate the potential use of nanocomposites as dense barriers against the permeation of liquids into the concrete, three types of nanoparticles including Zinc Oxide (ZnO), Magnesium Oxide (MgO), and composite nanoparticles were used in the present study as partial replacement of cement. Besides, the effect of adding these nanoparticles on both pore structure and mechanical strengths of the concrete at different ages was determined, and scanning electron microscopy (SEM) images were then used to illustrate the uniformity dispersion of nanoparticles in cement paste. It was demonstrated that the addition of a small number of nanoparticles effectively enhances the mechanical properties of concrete and consequently reduces the extent of the water permeation front. Finally, the behavioral models using Genetic Algorithm (GA) programming were developed to describe the time-dependent behavioral characteristics of nanoparticle blended concrete samples in various compressive and tensile stress states at different ages.展开更多
基金Funded by National Natural Science Foundation of China(No.50539010)China Central Non-profit Research Funds of MWR(Nos.200901066,YWF0907)
文摘The advanced temperature and stress test machine was introduced to determine the early cracking tendency of concrete with inclusion of light-burnt MgO under full restraint by tracking the development of thermal,physical and deformation properties.Results showed that light-burnt MgO being incorporated ranging between 4 wt% and 6 wt% of cementitious materials was beneficial to increase the maximum compressive stress and cracking stress of concrete by 0.37 MPa and 0.2 MPa on average respectively.The second zero stress temperature was reduced by 11.4 ℃ and the maximum temperature was slightly reduced while cracking thermal impact was significantly enhanced from 59.8 ℃ to 66.2 ℃.Sensitive anti-cracking coefficient F was forwarded to assess the early cracking tendency of concrete and the inclusion of 4 wt% light-burnt MgO with activity of 109 s ranked the best in crack resistance.
基金supported by CSCEC Technology Research and Development Plan(CSCEC-2020-Z-39).
文摘The effects of different contents of a MgO expansive agent and phosphorus slag on the mechanical properties,shrinkage behavior,and the heat of hydration of concrete were studied.The slump flow,setting time,dry shrinkage,and hydration heat were used as sensitive parameters to assess the response of the considered specimens.As shown by the results,in general,with an increase in the phosphorus slag content,the hydration heat of concrete decreases for all ages,but the early strength displays a downward trend and the dry shrinkage rate increases.The 90-d strength and dry shrinkage of concrete could be improved with a phosphorus residue content between 0%-20%,with the best performances in terms of mechanical properties and shrinkage characteristics being achieved for a content of 20 kg/m^(3).On the basis of these results,it can be concluded that appropriate amounts of phosphorus slag and MgO expansive agent can be used to improve the compressive strength of concrete in the later stage by reducing the hydration heat and dry shrinkage rate,respectively.
基金Funded by the National Natural Science Foundation of China(No.51578325)。
文摘To investigate the assumptions proposed in this paper,the evolution law governing the strength and expansion performance of MgO and nano-MgO micro-expansive concrete in the environment of mineral powder was firstly observed in this study.Secondly,SEM,XRD,and TG-DSC microscopic tests were conducted to reveal the effects of the active mineral-powder admixture on the hydration degree and expansion performance of MgO and nano-MgO in HPC.Our experimental results successfully verified our hypothesis,which indicated that the expansion performance of macro-MgO and nano-MgO was indeed depressed by the addition of active mineral power admixtures,even though the mechanical property of concrete composites was effectively improved.Furthermore,the hydration test also demonstrated the negative interference on the mineral powders,which was induced by the expansion agents.It is found the amounts of hydrates tend to decrease because the mineral powder ratio reaches and exceeds 40%.Moreover,it is also concluded the effect of expansion agents is governed by the alkalinity cement paste,especially for the nano-MgO.In other words,the expansion performance of nano-MgO will vary more obviously with the hydration process,than MgO.The results of this study provide that effective experimental and theoretical data support the hydration-inhibition mechanism of magnesium expansive agents.
文摘In this paper, concrete with limestone coarse aggregate was studied due to frost action in saline and nonsaline environments. The main focus is to explain the damaging formula of concrete with poor quality of limestone aggregate in frost actions. All investigated concretes fulfill the recommendations of the European standard EN 206, Concrete--Specification, Performance, Production and Conformity limiting values for composition and properties of concrete （maximum W/C （water/cement） ratio, minimal class of compressive strength, minimal mass of cement and minimal percentage of entrained air）. The damaging formula of the frost resistant concrete is studied through scaling test of concrete during freeze/thaw process, frost resistant test of coarse limestone aggregate and chemical analysis of limestone. Experiments results showed that there is a correlation between CaO/MgO ratio and Al2O3 of limestone and frost resistance of concrete, using chemical composition for determining potential ACR （alkali-carbonate reactivity） will indicate higher risk of damaging effect of concrete.
文摘In recent years, energy-retrofitting is becoming an imperative aim for existing buildings worldwide and increased interest has focused on the development of nanoparticle blended concretes with adequate mechanical properties and durability performance, through the optimization of concrete permeability and the incorporation of the proper nanoparticle type in the concrete matrix. In order to investigate the potential use of nanocomposites as dense barriers against the permeation of liquids into the concrete, three types of nanoparticles including Zinc Oxide (ZnO), Magnesium Oxide (MgO), and composite nanoparticles were used in the present study as partial replacement of cement. Besides, the effect of adding these nanoparticles on both pore structure and mechanical strengths of the concrete at different ages was determined, and scanning electron microscopy (SEM) images were then used to illustrate the uniformity dispersion of nanoparticles in cement paste. It was demonstrated that the addition of a small number of nanoparticles effectively enhances the mechanical properties of concrete and consequently reduces the extent of the water permeation front. Finally, the behavioral models using Genetic Algorithm (GA) programming were developed to describe the time-dependent behavioral characteristics of nanoparticle blended concrete samples in various compressive and tensile stress states at different ages.
