Study On Calculation Model Of Basic Thermal Parameters Of UHPC-CA

Compared with the traditional coarse aggregate-free UHPC（Ultra-high performance concrete）,not only the mechanical properties and durability of UHPC-CA（Ultra-high performance concrete with coarse aggregate）are particularly excellent,but also Its advantages include low cost,low energy consumption,high stiffness and low risk of shrinkage cracking.It is very suitable for some engineering fields with high requirements for durability and strength of materials,such as long-span bridges and industrial buildings.In this paper,the thermophysical parameters of UHPC-CA are measured by experiments.The influencing factors of thermophysical parameters of UHPC-CA are analyzed,and the prediction model is established.The following important conclusions are obtained:（1）Based on the standard specimens,the thermal conductivity of UHPC-CA is3.05～3.32 W/（m·℃）,the specific heat capacity is 2.14～2.40 kJ/（kg·℃）,and the linear expansion coefficient is 8.20×10^-6～11.47×10^-6℃^-1.The thermal conductivity of UHPC without coarse aggregate is 2.69～3.05 W/（m·℃）,the specific heat capacity is 2.14～2.33kJ/（kg·℃）,and the linear expansion coefficient is 10.76×10^-6～12.23×10^-6℃^-1.（2）It is found that the thermal conductivity,specific heat capacity and thermal diffusion coefficient have a strong correlation with the compressive strength and apparent density of the specimen.The greater the compressive strength,the greater the thermal conductivity,specific heat capacity and diffusion coefficient.The larger the apparent density,the greater the thermal conductivity,specific heat capacity and diffusion coefficient.（3）UHPC-CA was divided into four units:cementitious material hydration,quartz sand,steel fiber and coarse aggregate.In the test range,based on the series-parallel model,the prediction model of basic thermal physical parameters of UHPC-CA was established with the content of hydration products,quartz sand,steel fiber,coarse aggregate,water-cement ratio,gas content and ITZ interface thermal resistance reduction coefficient as independent variables.（4）Based on the prediction model,it is found that the thermal conductivity decreases first and then increases with the increase of water-binder ratio.The water-binder ratio at the turning point is 0.177,and the thermal conductivity of the paste sample is 0.93 W/（m·℃）.The thermal conductivity increases with the increase of quartz sand,steel fiber and coarse aggregate content in the range of 1.75～3.32 W/（m·℃）。（5）The specific heat capacity increases first and then decreases with the increase of water-binder ratio,and the water-binder ratio at the turning point is 0.155.At this time,the specific heat capacity of the paste specimen is 2.58 kJ/（kg·℃）,and it decreases with the increase of the content of quartz sand,ranging from 2.15 to 2.59 kJ/（kg·℃）.There is little change with the content of steel fiber,and increases with the increase of the content of coarse aggregate.（6）The linear expansion coefficient increases first and then decreases with the increase of temperature.70℃is the turning point,and the peak value is about11.9×10^-6～18.9×10^-6℃^-1.（7）The air content and moisture content of UHPC-CA are lower than those of ordinary concrete,and its thermal conductivity is higher than that of UHPC without coarse aggregate,and the thermal conductivity of UHPC without coarse bone is higher than that of ordinary concrete.