Study On Dynamic Evolution Characteristics Of Pore-crack And Mechanism Of Enhancing And Toughening Of BFPMC Under Load

Basalt fiber polymer modified concrete(BFPMC)is developed on the basis of basalt fiber reinforced concrete.By adding basalt fiber and polymer emulsion to concrete,the strength and toughness and other properties of concrete can be effectively enhanced,and the defect of concrete can be effectively improved.In this paper,the mechanical properties of BFPMC were tested.The effect of basalt fiber and VAE emulsion on macro performance of concrete,such as compressive strength and flexural strength,were studied.At the same time,the failure process of BFPMC was described by the compressive load-displacement curve.Based on the ratio of flexural strength and compressive strength,the influence of fiber content and VAE emulsion content on the toughness of concrete was obtained.With the help of the high-precision X-ray industrial CT scanning system,the image processing and three-dimensional reconstruction technology were used to construct the mesostructure model.The effect of basalt fiber and VAE emulsion on meso pore structure of concrete,such as pore type,shape,volume and coordination number,were analyzed.In this way,the mechanism of the interaction between basalt fiber and VAE emulsion in meso scale was explained.At last,the industrial CT scanning system equipped with the loading device was used to scan BFPMC under loading.After scanning,the CT images in different scanning points were obtained.The crack and pore structure of each scanning point was reconstructed based on CT images.The development process of BFPMC pores and cracks structure were studied in mesc scale,and the development rule of internal cracks and pores of BFPMC was obtained.The main work and research results are as follow:(1)The compressive strength and flexural strength of BFPMC with different fiber content and VAE emulsion content were tested.The results show that the compressive strength and flexural strength were changed to varying degrees with the addition of basalt fiber and VAE emulsion.Through analysising the change of the ratio of flexural strength and compressive strength and the compressive load-displacement curve,it is concluded that the deformation capacity of concrete will change in varying degrees due to the addition of the two materials,and the change effect is related to the content of the two materials.Taking into account the above test results,when the basalt fiber content is3 kg/m~3 and the VAE emulsion dosage is 6%,the compressive strength,flexural strength and deformation capacity are highest,and the ratio of flexural strength and compressive strength is higher than ordinary concrete.(2)Basing on the CT scanning technology,image processing technology and related theoretical basis,the BFPMC meso pore structure was reconstructed,and the pore structure characteristic parameters were quantitatively characterized.The results show that the addition of basalt fiber and VAE emulsion in concrete can reduce porosity,pore average size and concrete heterogeneity.At the same time,adding basalt fiber and VAE emulsion to concrete will also reduce the size difference of internal pores in concrete,but increase the number of pores,increase the proportion of irregular pores in concrete,and enhance the connectivity of pores.(3)The in-situ loading scanning of BFPMC was completed based on the CT scanning system and loading device equipped inside the CT scanning system.Based on the CT scanning images,the three-dimensional models of the internal cracks and pores of BFPMC in each scanning point were established respectively,and the distribution of the internal cracks and pores of BFPMC was observed.The characterization of crcak and pore structure characteristic parameters show that BFPMC has obvious crack resistance.When BFPMC is under load,there are great differences between the internal cracks and pores development stages.When the pores are obviously compressed due to load,the cracks are in the initiation and development stage.At this time,the cracks first appear in the center of the specimen,the crack trend is flat,and the plane inclination of the cracks is small,close to the vertical direction.With the increase of load,the crack develops rapidly in the specimen,which shows that the parameters such as crack volume and surface area increase rapidly.Compared with the degree of crack development,the pore develops slowly in this stage.When the load reaches a certain value,with the increase of load,the crack development slows down,and BFPMC shows obvious crack resistance,which is reflected in the decrease of the growth rate of crack volume,surface area and other parameters.Finally,the crack penetrates inside the specimen,resulting in the crush of the specimen.At this time,the bending degree of the crack surface is the largest,and the corresponding three-dimensional fractal dimension reaches the maximum.There are 67 pictures,18 tables and 86 references.