Influence of ultra-high-rise pumping on microstructure and multi-scale mechanical properties of concrete based on X-ray CT and 3D mesoscopic numerical simulation

Abstract

At present, it is unclear how the microstructure and multi-scale mechanical properties of concrete change after ultra-high-rise pumping. To this end, this study applied BSE image analysis method and nanoindentation test to investigate the influence of ultra-high-rise pumping on the porosity, thickness and elastic modulus of interface transition zone (ITZ) in concrete, firstly. The results showed when increasing the pumping height, the elastic modulus and uniaxial compressive strength of concrete and mortar increased slightly, the thickness and porosity of ITZ decreased, and the elastic modulus of ITZ increased. Secondly, based on the porosity test results of ITZ and paste, the volume fractions of pores, mortar and equivalent body (aggregate + ITZ) in concrete with different pumping heights were determined, and then a 3D model of concrete was established based on the X-ray Computed Tomography test results. Thirdly, according to the mechanical properties of the mortar before and after ultra-high-rise pumping, the constitutive relationship of the mortar in the ultra-high-rise pumping concrete was modified, and the mechanical parameters of the equivalent body in the model considered different pumping heights were calculated by the homogenization method. Finally, the uniaxial compression of ultra-high-rise pumping concrete was accurately simulated using the finite element method. On this basis, according to the relationship between pumping measurement index (PMI) and the performance of ultra-high-rise pumping concrete, the uniaxial compressive stress–strain curve of ultra-high-rise pumping concrete was precisely predicted.