Capillary Water Absorption Properties Of Coal Gangue Concrete Under Freeze-Thaw Cycles

Coal gangue is the solid waste that is discharged during coal production.It has serious environmental pollution and threaten the human life and health.Therefore,using the abandoned waste coal gangue in concrete to produce coal gangue concrete,a green building materials,can turn waste into treasure and also can bring important economic,social and environmental benefits.Considering the origin,physicochemical properties,development and application of coal gangue,this paper mainly studies the frost resistance durability of concrete,which plays a decisive role in the service life of coal gangue concrete.Learning the water transportation in concrete is vitally important to study its frost resistance because the speed of water transport inside the material matrix directly affects the deterioration rate of the concrete under freeze-thaw cycles.The main mode of water migration in most of the in-service concrete structural matrices under engineering practice is capillary water absorption.Therefore,the present study takes coal gangue concrete and steel fiber reinforced coal gangue concrete as the research object.The capillary water absorption performance of coal gangue concrete and steel fiber reinforced coal gangue concrete under freeze-thaw environment was studied through a combination of experimental research and theoretical analysis.The research results are of great significance to the evaluation of frost resistance of coal gangue concrete and steel fiber reinforced coal gangue concrete in severe cold regions.The specific work and conclusions are as follows:(1)The concrete's freeze-thaw damage mechanism,fiber reinforcement theory,capillary water absorption principle and its theoretical equations are briefly introduced,and the main parameters involved in the capillary water absorption process are presented.Raw materials,methods and instruments used in this paper are introduced in detail;(2)Freeze-thaw test,sorptivity test and mechanical properties test of coal gangue concrete and steel fiber reinforced coal gangue concrete were carried out.To calculate the Relative Elastic Modulus under different freeze-thaw numbers by measuring the ultrasonic sounds of two types of concrete under freeze-thaw circumstance.And then,determining the number of freeze-thaw cycles for the water absorption test.(3)The capillary water absorption properties of coal gangue concrete and steel fiber reinforced coal gangue concrete under freeze-thaw conditions were studied experimentally.The effects of coal gangue substitution rate,steel fiber volume fraction and the number of freeze-thaw cycles on the capillary water absorption performance were analyzed.Through the analysis and calculation of the test data,the cumulative water absorption of the two types of concrete was obtained,and the curve of cumulative water absorption versus time was plotted.The initial sorptivity,secondary rate of water absorption and late rate of water absorption of coal gangue concrete and steel fiber reinforced coal gangue concrete were obtained through the linear fitting of the staged cumulative water absorption curve,and the variation of sorptivity with freeze-thaw cycles was plotted.The initial sorptivity prediction models of coal gangue concrete and steel fiber reinforced coal gangue concrete in freeze-thaw environment were established according to the initial rate of water absorption to characterize the water absorption properties of the two concretes,which provides a theoretical reference for the study of frost resistance of coal gangue concrete and steel fiber reinforced coal gangue concrete in server cold regions.