Damage Analysis And Siulation Of Meso-scale Recycled Aggregate Concrete Mixed With Glazed Hollow Beads After High Temperature Based On X-CT Scanning Technique

Building fire is one of the most destructive and harmful disasters in today’s society.The occurrence of fire often leads to the damage and deterioration of the micro-meso-structure of concrete materials,which is reflected in the decomposition of hydrates,the coarsening of pore structure,thermal cracking,and the cracking induced by the increase of water vapor pressure,which in turn lead to the decline of the macroscopic mechanical properties and durability of materials,and is accompanied by huge economic losses and casualties.The meso-regulatory function of the lightweight,high-strength,internally porous,and highly thermally stable glazed hollow beads(GHB)can improve the high-temperature resistance of concrete.Based on the recycled aggregate concrete mixed with glazed hollow beads(RATIC)residual compressive strength test and CT scanning experiment of the research group in the early stage,this study will further study the damage and deterioration mechanism of RATIC under high temperature and the mechanical property degradation criterion after high temperature by CT image analysis and mesoscopic simulation,which aims to provide a feasible solution to improve the high temperature deterioration resistance of concrete.The main research contents and conclusions are as follows:(1)Based on CT image analysis results,a thermal damage model of RATIC after high temperature is established considering the cross-scale relationship among concrete residual compressive strength,temperature and fractal dimension.The CT images of RATIC after high temperature are preprocessed,and an improved image segmentation method based on adaptive threshold method and region growing method is proposed,and the extracted images of pores and cracks of RATICspecimens at room temperature and after high temperature are obtained.Firstly,the pore and crack were quantitatively analyzed,and the relationship between pore characteristics and crack characteristics and residual compressive strength was carried out,respectively.The research shows that although the pore characteristics and crack characteristics can reflect the degradation trend of concrete residual compressive strength to a certain extent.Then,the influence of pores and cracks was comprehensively considered,and the mesoscopic damage of RATIC after high temperature was quantitatively characterized based on the box dimension fractal dimension,and a thermal damage model of RATIC after high temperature is established considering the cross-scale relationship among concrete residual compressive strength,temperature and fractal dimension,and the model was proved to have good accuracy by analysing the predicted value and experimental value of residual compressive strength by contrast.(2)The real aggregate model and random aggregate model of RATIC are established.Based on the CT image of RATIC at room temperature,the binarized image of each mesoscopic component in RATIC was obtained by image segmentation method,and the MATLAB software was used to identify the boundary of the binarized image and obtain the real coordinate information.After storing the coordinate information,a RATIC numerical model based on the real structure was established in ABAQUS using an external Python script.In addition,based on the Monte-Carlo method,a modeling method of the RATIC two-dimensional random aggregate model is proposed,which can consider the initial defects and the RCA replacement rate.The aggregate gradation and delivery rate of the random aggregate model generated by this method meet the requirements,and this model have good applicability.(3)By analyzing the temperature field and temperature stress in RATIC under high temperature,the damage and deterioration pattern in RATIC under high temperature were clarified.Based on the real aggregate model and random aggregate model,the temperature field distribution and temperature stress distribution inside RATIC under high temperature were explored using the same temperature loading curve as the test,and the temperature stress was quantitatively analyzed.Based on CT images,The process of initiation,development and coalescence of internal microcracks in RATIC with different GHB contents and RCA replacement rates with temperature change were studied.In addition,the differences of high temperature damage simulations of different RATIC numerical models were analyzed by contrast.The results show that the residual compressive strength of concrete after high temperature can be reflected by the internal temperature stress,and both the real aggregate model and the random aggregate model can well simulate the mesoscopic deterioration performance of RATIC under high temperature.(4)Based on the random aggregate model,the effect of RCA replacement rates,GHB contents and porosities on the mechanical property of RATIC after high temperature was explored.The research shows that with the increase of temperature,the damage distribution of all RATIC specimens after high temperature shows a gradually intensifying trend under load,and the damage distribution of RATIC specimens is intensified after 500 ℃ compared with that of before 400 ℃,and the addition of GHBs can moderate the damage distribution of RATIC after 400 °C to a certain extent.At the same fire temperature,the damage distribution of RATIC also showed a trend of increasing gradually with the increase of porosity.In addition,the damage distribution under the simulated conditions is in good agreement with the experimental failure pattern,and the error between the simulated and experimental values of strength is small.Therefore,the meso-scale simulation can better explore the damage and deterioration performance of RATIC after high temperature under load.