The effects of the water-cement ratio and the molding temperature on the hydration heat of cement were investigated with semi-adiabatic calorimetry.The specimens were prepared with water-cement ratios of 0.31,0.38,and...The effects of the water-cement ratio and the molding temperature on the hydration heat of cement were investigated with semi-adiabatic calorimetry.The specimens were prepared with water-cement ratios of 0.31,0.38,and 0.45,and the molding temperature was specified at 10 and 20℃.The experimental results show that,as the water-binder ratio increases,the value of the second temperature peak on the temperature curve of the cement paste decreases,and the age at which the peak appears is delayed.The higher the water-cement ratio,the higher the hydration heat release in the early period of cement hydration,but this trend reverses in the late period.There are intersection points of the total hydration heat curve of the cement pastes under the influence of the water-cement ratio,and this law can be observed at both molding temperatures.With the increase in the molding temperature,the age of the second temperature peak on the temperature curve of the cement paste will advance,but the temperature peak will decrease.The higher the molding temperature,the earlier the acceleration period of the cement hydration began,and the larger the hydration heat of the cement in the early stage,but the smaller the total heat in the late period.A subsection function calculation model of the hydration heat,which was based on the existing models,was proposed in order to predict the heat of the hydration of the concrete.展开更多
By means of low-field nuclear magnetic resonance(LF-NMR),the transverse relaxation time(T_(2))signals of physically bound water in cement paste were monitored to indicate water content change and characterize the earl...By means of low-field nuclear magnetic resonance(LF-NMR),the transverse relaxation time(T_(2))signals of physically bound water in cement paste were monitored to indicate water content change and characterize the early-age hydration process.With the curves of the T_(2)signals and hydration time obtained,the hydration process could be divided into four typical periods using the null points of the second derivative curve,and the influences of water-cement ratio(w/c)and hydration heat regulating materials(HHRM)on hydration process were analyzed.The experimental results showed that the hydration rate of pure cement paste in accelerated period presented a positive correlation with w/c.Compared to pure cement paste,the addition of HHRM extended all four periods,and led to a much faster hydration rate in initial period as well as a slower rate in accelerated period.Finally,according to the LFNMR test results,the early-age hydration model of cementitious materials was proposed considering w/c and HHRM content.展开更多
The purpose of this study is to reveal the service performance of recycled aggregate concrete(RAC)components for different values of water-cement ratio and replacement rate of recycled coarse aggregate(RCA).Generally,...The purpose of this study is to reveal the service performance of recycled aggregate concrete(RAC)components for different values of water-cement ratio and replacement rate of recycled coarse aggregate(RCA).Generally,the concrete strength decreases with the increase of the replacement rate of RCA,in order to meet the strength requirements when changing the replacement rate of RCA,it is necessary to change the water-cement ratio at the same time.Therefore,the axial compressive strengths of prism with 25 mix proportions,the short-term mechanical properties and long-term deformation properties of reinforced concrete beams were tested respectively by changing water-cement ratio and RCA replacement rate.The bearing capacity and the strain nephogram of samples under different loads were obtained using the Digital Image Correlation(DIC)method,and a self-made gravity loading experimental device was used for long-term deformation investigation.Results showed that the damage pattern of RAC was the same as that of natural aggregate concrete(NAC),but the brittleness was more pronounced.The brittleness of concrete before failure can be reduced more effectively by adjusting the replacement rate of RCA than by adjusting the water-cement ratio.The water-cement ratio has an evident influence on the axial compressive strength and early creep of concrete,while the replacement rate of RCA has a remarkable effect on the long-term deformation of the concrete beams.展开更多
基金the National Natural Science Foundation of China(Nos.52368032 and 51808272)the China Postdoctoral Science Foundation(No.2023M741455)+1 种基金the Tianyou Youth Talent Lift Program of Lanzhou Jiaotong UniversityGansu Province Youth Talent Support Project(No.GXH20210611-10)。
文摘The effects of the water-cement ratio and the molding temperature on the hydration heat of cement were investigated with semi-adiabatic calorimetry.The specimens were prepared with water-cement ratios of 0.31,0.38,and 0.45,and the molding temperature was specified at 10 and 20℃.The experimental results show that,as the water-binder ratio increases,the value of the second temperature peak on the temperature curve of the cement paste decreases,and the age at which the peak appears is delayed.The higher the water-cement ratio,the higher the hydration heat release in the early period of cement hydration,but this trend reverses in the late period.There are intersection points of the total hydration heat curve of the cement pastes under the influence of the water-cement ratio,and this law can be observed at both molding temperatures.With the increase in the molding temperature,the age of the second temperature peak on the temperature curve of the cement paste will advance,but the temperature peak will decrease.The higher the molding temperature,the earlier the acceleration period of the cement hydration began,and the larger the hydration heat of the cement in the early stage,but the smaller the total heat in the late period.A subsection function calculation model of the hydration heat,which was based on the existing models,was proposed in order to predict the heat of the hydration of the concrete.
基金Funded by National Natural Science Foundation of China(Nos.U1965105,51878245)National Key R&D Program of China(No.2021YFF0500802)。
文摘By means of low-field nuclear magnetic resonance(LF-NMR),the transverse relaxation time(T_(2))signals of physically bound water in cement paste were monitored to indicate water content change and characterize the early-age hydration process.With the curves of the T_(2)signals and hydration time obtained,the hydration process could be divided into four typical periods using the null points of the second derivative curve,and the influences of water-cement ratio(w/c)and hydration heat regulating materials(HHRM)on hydration process were analyzed.The experimental results showed that the hydration rate of pure cement paste in accelerated period presented a positive correlation with w/c.Compared to pure cement paste,the addition of HHRM extended all four periods,and led to a much faster hydration rate in initial period as well as a slower rate in accelerated period.Finally,according to the LFNMR test results,the early-age hydration model of cementitious materials was proposed considering w/c and HHRM content.
基金the National Natural Science Foundation of China(Grant Nos.52168015,51768005)Natural Science Foundation of Guangxi Province(No.2018GXNSFAA281333).
文摘The purpose of this study is to reveal the service performance of recycled aggregate concrete(RAC)components for different values of water-cement ratio and replacement rate of recycled coarse aggregate(RCA).Generally,the concrete strength decreases with the increase of the replacement rate of RCA,in order to meet the strength requirements when changing the replacement rate of RCA,it is necessary to change the water-cement ratio at the same time.Therefore,the axial compressive strengths of prism with 25 mix proportions,the short-term mechanical properties and long-term deformation properties of reinforced concrete beams were tested respectively by changing water-cement ratio and RCA replacement rate.The bearing capacity and the strain nephogram of samples under different loads were obtained using the Digital Image Correlation(DIC)method,and a self-made gravity loading experimental device was used for long-term deformation investigation.Results showed that the damage pattern of RAC was the same as that of natural aggregate concrete(NAC),but the brittleness was more pronounced.The brittleness of concrete before failure can be reduced more effectively by adjusting the replacement rate of RCA than by adjusting the water-cement ratio.The water-cement ratio has an evident influence on the axial compressive strength and early creep of concrete,while the replacement rate of RCA has a remarkable effect on the long-term deformation of the concrete beams.
