Experimental Study On Thermal Conductivity Of Hydraulic Concrete Considering The Influence Of Temperature And Humidity

Thermal conductivity of concrete is an important thermal parameter for temperature control and crack prevention of concrete dams,and its value usually changes with the thermal properties of the concrete constituent materials and changes in temperature and humidity.Most of the concrete dams have relatively small changes in ambient temperature.The thermal conductivity of concrete is usually regarded as a constant,ignoring the influence of temperature and humidity.However,in northern China,the daily temperature variation at the location of the concrete dam can reach 35°C.Under this extreme temperature change condition,the influence of temperature and humidity on the thermal conductivity of concrete cannot be ignored.Based on the basic theory of heat conduction,this paper proposes a least-squares finite element method to test the non-constant thermal conductivity of hydraulic concrete,and conducts a research on the thermal conductivity of hydraulic concrete under the influence of temperature and humidity.The main research work is as follows:(1)Using a combination of experiment and numerical back calculation,a method for testing the non-constant thermal conductivity of hydraulic concrete based on the least-squares finite element method is proposed.The method mainly includes two parts: the test system and the numerical back calculation program.The test system imposes temperature interference on the concrete,and obtains the data of the temperature change of each measuring point inside the concrete with time.The numerical back calculation program is based on the principle of least squares finite element method.It can use test data as input parameters to calculate the thermal conductivity of concrete at different temperatures.(2)Carried out an experimental study on the influence of temperature and humidity(saturation)on the thermal conductivity of concrete constituent materials.The thermal conductivity of coarse aggregate and cement mortar was tested with a transient plane heat source thermal conductivity tester.The results show that the thermal conductivity of coarse aggregate decreases with increasing temperature,the thermal conductivity of cement mortar is greatly affected by temperature and saturation,and its thermal conductivity increases with increasing temperature and humidity.(3)Conducted experimental research on the thermal conductivity of hydraulic concrete.Using the proposed non-constant thermal conductivity test method,the influence of aggregate volume fraction on the thermal conductivity of hydraulic concrete was studied.The test results show that the thermal conductivity of hydraulic concrete increases with the increase of the aggregate volume fraction.By simulating the service environment of large-volume concrete under severe temperature fluctuation conditions,the thermal conductivity of its thermal conductivity with temperature changes was tested.The results show that its thermal conductivity first decreases and then increases with the increase of temperature.(4)The thermal conductivity model of hydraulic concrete considering the influence of temperature and humidity was established.Consider hydraulic concrete as a multi-phase composite material composed of aggregate,mortar,water,air and other substances.According to Wiener series-parallel theory,a hydraulic concrete thermal conductivity model is derived.The model parameters are solved using the thermal conductivity test results of the concrete constituent materials,and the correctness of the model is verified by the mass concrete thermal conductivity test results,and then analyzed The thermal conductivity of hydraulic concrete varies with various influencing factors.