Study On Thermal Expansion Coefficient Of Cement Concrete Based On The Theory Of Multiphase Inclusion

Cement concrete, as a kind of important construction engineering material, has been widely used in buildings, bridges, water conservancy and other field. At present, the cement concrete pavement also has a wide range of applications in highway construction in our country, but the cracks of cement concrete pavement which caused by the temperature, has seriously restricted the application and development of the cement road. Thermal expansion coefficient is one of the important thermophysical parameters influencing the temperature stress, the study on thermal expansion coefficient helps to reduce the temperature stress in the cement concrete pavement slab, decrease the temperature cracks of cement concrete pavement slab, thus to improve the service life of the cement concrete pavement. So, to explore a kind of economic, applicable, high accuracy prediction method of the thermal expansion coefficient is of great theoretical and practical significance.This paper regarded cement concrete as a composite material which constituted with polyphase components materials. The cement concrete model in meso-scale was established, based on the theory of micromechanics, the explicit expression of concrete materials thermal expansion coefficient was deduced, then through the test to verify the accuracy of model and the calculated result, the last, on the basis of the theoretical model to explore the main factors influencing the thermal expansion coefficient of cement concrete.The main contents and results are as follows:First, in order to find a appropriate mesoscopic mechanics model,analyzed the advantages,disadvantages and applicability of different kinds of mesoscopic mechanics model, choosed generalized self-consistent model which considered the interaction between inclusions, to established the cement concrete mesoscopic mechanics model under the assumption of ellipse and rectangular aggregate shape respectively,which was different from common circular aggregate assumption.According to the theory of mesoscopic mechanics, derived the expression that utilized the properties of concrete mesoscopic composition material to express macroscopic effective thermal expansion coefficient under the two kinds of aggregate shape assumption.Secondly, tested the thermal expansion coefficient of cement concrete.In order to research the goodness of fit between the theoretical calculation value and experimental results in several aspects, made different types of concrete specimens including different water cement ratio, different gradations and different aggregate types.Developed the experiment scheme to test thermal expansion coefficient of cement concrete, testing apparatus was the low temperature triaxial test device which has been disposed according to the test demand, using temperature sensor and displacement sensor to automatically acquire the temperature around the specimen and the highly direction deformation of cement concrete under different temperature, taking the measure of linear fitting algorithm,that applied to the temperature data and the rate of linear expansion to get the thermal expansion coefficient of concrete. For the convenience of calculation, using MATLAB to establish the user operation interface of concrete thermal expansion coefficient calculation.In order to analysis the shape of aggregate, acquiring the picture of aggregate which has been used in the test by means of taking photo or scan,then using the image analysis software to analyze the aggregate shape, got each aggregate shape data. Determing aggregate shape parameters, mechanical parameters and thermal physical property parameters of input, then get the theoretical calculation value of thermal expansion coefficient of different cement concrete, Making comparisons between the theoretical calculation value and the test results, the results show that the model with ellipse and square two aggregate shape assumption, can accurately predict the thermal expansion coefficient of concrete material, the relative error can be controlled within 15%.Finally, exploring the factors affecting the thermal expansion coefficient of cement concrete material.Based on the theoretical model, analyzed the effect of different components of material properties on the thermal expansion coefficient by changing the input parameters of theoretical calculation formula, respectively from the mixed phase, matrix and the equivalent inclusion phase three aspects. The results show that thermal expansion coefficient of cement concrete material increases with the increase of the thermal expansion coefficient of aggregate and mortar, when the aggregate volume fraction and the elastic modulus increase, the thermal expansion coefficient of cement concrete decreases.Finally through the analysis of the influence factors, putting forward the measures for decreasing the thermal expansion coefficient from the aspect of material.