Program On Fractal Geometry Of Cement Mortar's Microcharacters With Time Effect Of Weathering

Cement mortar is widely used in geotechnical bolt support in construction engineering,and plays the role of main structure and transfer stress in large project.In massive buildings such as tunnels and dams,the geological environment of cement mortar is complex and affected by many factors such as humidity and stress,however,the life of large projects is decades or even hundreds of years,so it is very important to carry out the research on the characteristics of cement mortar.At present,there are few studies on the meso damage law of cement mortar under different weathering effects.Cement mortar is a kind of heterogeneous material,and the cement mortar is a three phase material consisting of aggregate,cement slurry and interface transition zone.The essence of destruction is the process of the generation,expansion and evolution of internal cracks.Cement mortar contains a large number of microscopic and mesoscopic defects(damage),which are important factors affecting the mechanical properties of cement mortar.The main factors of weathering resistance of cement mortar include temperature,humidity,time effect and stress environment.Environmental and climatic conditions,such as environmental humidity,relative humidity and high stress,are one of the main factors that affect the durability of cement mortar.The effects of climate and environment on the macro level and the meso level of cement mortar are studied in this paper.In this paper,uniaxial compression tests and graded loading creep tests on specimens with different water contents were performed.Graded loading creep tests were performed on specimens that had experienced different temperature histories.In this way,the stress and strain of the joints at different times during the entire test process are obtained,and macroscopic pictures of the cement mortar's fracture surfaces are collected.The fracture surface of the cement mortar specimen was observed by reflection polarizing microscope to obtain fracture information of the test piece.The obtained images are divided into fractal processing,and the obtained images are transformed into grayscale images,and then the grayscale images are converted into binary images that the computer can recognize by using software recognition.The fractal dimension of the fracture surface is calculated by the box counting method under the ImageJ software.The conclusion is following:(1)The fractal geometry of the fracture surface of the cement mortar specimen is studied,and the fractal characteristics of the cement mortar material can be obtained.The fractal dimension can be used to quantitatively describe the complexity of the fracture surface morphology of the cement mortar.(2)The calculated fractal dimensions of the three groups are all in 1.4-1.9,which can be found to have good self similarity with the fracture surface of cement mortar after the different magnifications.(3)With the influence of different water content,the fractal calculation is made for fracture surface destroyed by the uniaxial compression test and grading loading creep test.There is a good linear correlation between the fractal dimension and the moisture content calculated at macro level or meso level.In macro level and four different magnification times,the fractal dimension increases along with the increase of moisture content of cement mortar specimens.It is verified that the increase of the moisture content of the test specimen leads to the reduction of the brittleness of the cement mortar.The long time stress will lead to the development of the micro cracks in the specimen,which leads to the increase of the complexity of the fracture surface of the specimen,thus the fractal dimension increases with the increase of water content.(4)Through the different temperature baking,the cement mortar specimens are graded loading creep test,and the fractured surface is calculated by fractal calculation.The fractal dimension has a good linear correlation with the baking temperature.The calculated fractal dimension is negatively correlated with the temperature,indicating that fractal dimension of the cement mortar decreases with the increase of temperature by roasting.(5)this test verifies that the increase of moisture in the cement mortar specimen will lead to the continuation of the hydration reaction of cement mortar.The new hydration products fill the original gap and lead to the formation of the cracks at the more microscopic level,which makes the cement mortar more complex under the external force,thus making the fracture surface complex.