Microscopic pore structure characteristics and strengthening mechanism of fiber polymer flexible concrete
In view of the defective problems such as low strength,brittleness,and poor tough-ness exhibited by traditional concrete in down hole practical applications,the mechanical prop-erties of concrete can be improved by adding polymers and fibers to form composite materials.The mechanical strength,toughness,pore structure and fiber distribution of the composites were studied by Computed Tomography(CT)and Scanning Electron Microscope(SEM).It has been shown that when basalt fibers(BF)and vinyl acetate-ethylene copolymer(VAE poly-mers)are added to concrete,BF reduces the size and number of original pores in concrete by filling pores.VAE polymer obtains a polymer film through a series of hydration reactions,which is attached to the surface of BF and matrix aggregate,thereby increasing the bonding performance and achieving the effect of strengthening and toughening.Under single-size BF ad-mixture conditions,the best effect on concrete mechanical property enhancement was observed at fiber admixture of 3.0 kg/m3,VAE polymer dosage of about 3％and BF length of about 9 mm.On the basis of the preliminary test by adjusting the mixing ratio of three sizes of BF in concrete,the design of multi-size BF mixing,compared with the preliminary test,the overall mechanical properties of the foundation test has been improved.Using digital image processing technology to adjust the gray value of the slices,the matrix with the same density is accurately differentiated from the fibers,and a clear grayscale map of the internal structure is obtained,thus realizing the visualization of the fibers.The fine structure study with the help of CT scan-ning results and SEM images shows that the number of pores inside the concrete decreases and then increases with the increase of BF admixture for the same BF size,compared to the small porosity and less number of BF in the specimen under the multi-size BF mix.The results of the study can be useful for the study of large deformation support of soft rock tunnel and the evo-lution of fine-scale pore structure of concrete composites.
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