| High-strength and high-performance concrete has been widely used in modern engineering construction.However,due to its high density and low permeability,the high-strength and high-performance concrete has serious internal microstructure damage under sudden fire and high temperature,and it is prone to burst,causing its macroscopic mechanical properties to show a significant decline.The model reconstruction and simulation analysis of the degradation evolution of high-strength high-performance concrete internal microstructure high-temperature damage are carried out to reveal the relationship between macroscopic performance damage and internal microstructure degradation of high-performance concrete under high temperature fire,in order to be high-strength high-performance concrete.The theory of fire resistance and the post-disaster repair and reinforcement provide theoretical and experimental basis.This paper relies on the National Natural Science Foundation of China-Microstructure-based high-performance concrete fire degradation mechanism and damage assessment theory research(fund number 51287325),C60 and C80 not scanned with 0.2% polypropylene fiber scanned by CT technology The X-ray CT image of the microstructure of the high-performance concrete specimen is processed by the image processing software.The reconstructed concrete is reconstructed by the 3D reconstruction software based on the processed CT image to obtain high-performance concrete under different temperature conditions.The meso-microstructure three-dimensional model is used to analyze the relationship and regularity of damage degradation evolution of concrete micro-structure under various temperatures.The main research contents are as follows.1.Three-dimensional reconstruction of meso-microstructure model of high-strength and high-performance concrete(1)The image processing software is used to binarize the CT image,and the background color and the hole color are distinguished.Based on different materials showing different gray values,the mask command in the 3D reconstruction software is used to create two masks for the hole crack and the concrete matrix.Three-dimensional models of concrete under different temperature conditions were reconstructed based on different masks.(2)Extracting holes and cracks in the CT image using image processing software.Independent pores at normal temperature,pores under high temperature conditions and cracks between pores were obtained and reconstructed in three dimensions using reconstruction software.2.High-temperature damage analysis of three-dimensional reconstruction of meso-microstructure model of high-strength and high-performance concrete(1)Qualitative analysis of C60 and C80 high performance concrete based on 3D reconstruction modelWhen C60 and C80 are not blended with fiber-reinforced concrete,the primary pores are continuously increasing with the increase of the working temperature,and new pores are sprouted.Since the pore volume is relatively small,the pore change is not large as a whole,but compared with the concrete model at normal temperature and 600?,the pores and cracks can be clearly seen,many small pores have been penetrated,the number of pores is obviously increased,and the outer surface of concrete also appears.(2)Quantitative analysis of C60 and C80 high performance concrete based on 3D reconstruction model(1)C80 high performance concrete high temperature microstructure damageThe porosity of C80 high performance concrete without fiber blending before 300? does not change much,and it starts to increase after 300?.The higher the temperature,the more obvious the porosity increases.The increase of porosity of C80 HPC is greater than that of C80 PPHPC.Compared with the normal temperature,C80 HPC increases more at 500? and 600? porosity,40% and 74%,respectively,and can define 500? ~ 600? as the threshold temperature of C80 HPC.For C80 PPHPC,the increase in porosity at 400?,500? and 600? increased more,respectively 39.25%,55.45%,and the temperature segment with severe microstructural damage was 400? ~ 600?,which is its threshold temperature.Prior to 400?,the pore surface area increase of C80 HPC was greater than that of C80 PPHPC,and the opposite was true after 400?.Under different temperature conditions,the proportion of pores with C80 without fiber blending in the range of 1~5?m is the largest.The proportion of pores with a pore diameter of 1 to 5 ?m in C80 HPC at room temperature(20?)to 600? was 48.7%,51.3%,50.4%,49.7%,47.6% and 43.9%,respectively.The proportion of pores having a pore diameter of 1 to 5?m in C80 PPHPC at room temperature(20?)to 600? was 59.3%,57.3%,55.9%,54.1%,51% and 46.8%,respectively.The number of small holes in C80 PPHPC is more than the number of C80 HPC.(2)C60 high performance concrete high temperature microstructure damageThe pore volume increase of C60 high performance concrete increases with the increase of the working temperature,and the pore volume increase of C60 HPC is obviously larger than that of C60 PPHPC.Compared with the normal temperature,the porosity of C60 HPC increased at 200? and 600?,respectively,28.8%,20.7%.The porosity of C60 PPHPC increased at 500?,which was 30.49%.The porosity of C60 high performance concrete without blending with fiber-doped specimens did not change much before 400?,and began to increase after 400?,and the porosity of C60 PPHPC increased much faster than C60 HPC.Prior to 400?,the pore surface area of C60 HPC increased more than C60PPHPC;the opposite was true at 400?.After the C60 high-performance concrete is applied at different temperatures,the pore size distribution is the largest,and the pore size ranges from 1 to 5?m.The proportion of pores with a pore diameter of 1 to 5?m in C60 HPC at normal temperature(20?)to 600? is 53.18%,54.2%,58%,53.69%,54.2% and 50.88%,respectively.The proportion of pores with a pore diameter of 1 to 5 ?m in C60 PPHPC at room temperature(20?)to 600? was 58.02%,65.9%,57.25%,56.2%,51.86% and 48.23%,respectively.With the increase of the working temperature,the number of pores in the pore size range of 1~5?m without fiber blending increased first and then decreased.The proportion of C60 PPHPC before 400? was greater than that of C60 HPC,and the opposite was true after 400?.(3)Comparative analysis of high temperature microstructure damage of C80 and C60 high performance concreteFor plain concrete,the porosity of C80 HPC changes much more than C60 HPC after 300?;but for fiber concrete,the change of porosity of C80 PPHPC after 400? is smaller than that of C60 PPHPC.Due to the large primary pores of C60 PPHPC,the degree of deterioration of concrete is aggravated.The proportion of P60 PPHPC and C80 PPHPC with a distribution of 1~5?m is increasing from 300? to 500?,and it is decreasing after 500?.It shows that with the increase of the action temperature,new fine pores are constantly decreasing.The increase of small pores develops into larger pores when the temperature reaches 500?.(3)Evolution analysis of CT model of internal cavity cracks in high performance concreteAs the applied temperature increases,fine cracks are formed between the original holes in the concrete until the two penetrate.The defect volume growth rate of plain concrete(C60HPC,C80HPC)showed an increasing trend before 400?;it decreased at 500?,and the maximum increase was reached at 600?.The fiber-filled concrete(C60PPHPC,C80PPHPC)has a decrease in defect volume at 300?,indicating that fiber melting slows the generation of cracks and the penetration of holes.The defect surface area of C60 and C80 high performance concrete changes almost uniformly in each temperature range,and it increases with the increase of temperature,and the difference between the two is small. |
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