The Influence of Fly Ash Contents on Mechanical Properties and Energy Response of Concrete at a High Strain Rate

The dynamic uniaxial impact compression test was carried out by the Hopkinson pressure bar test system to test the dynamic mechanical properties of concrete with different fly ash contents ( $P=0$ , 10%, 20%, 30%, 40%, and 50%) under 0.3 MPa air pressure. The influences of fly ash content variation on the mechanical characteristics, ductility characteristics (which were calculated according to the concrete ductility formula), energy dissipation characteristics, and surface specific energy variation characteristics (which were calculated by converting the fragments into spheres) of concrete were analyzed, respectively, and the influences of fly ash content variation on the fragment distribution and fractal features of concrete were obtained by statistical analysis. In addition, the application of concrete with the change of fly ash contents in rock burst mine was studied. The results showed that the dynamic peak stress, residual stress, ductility characteristics, fragments distribution, fractal dimension, transmitted energy, dissipated energy, and surface specific energy change significantly with the increase of fly ash contents under dynamic uniaxial impact compression. By analyzing the relationship between surface specific energy and concrete fragment distribution, it could be found that the energy dissipated by stress waves in concrete can be estimated by using the particle size distribution of the field fragments.

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