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

Abstract

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.

Study on the Influence of Sample Size on the Mechanical and Integrity Characteristics of Coal Measure Sandstone under High Strain Rate

“…Figure 5 was the original waveform diagram of the impact load test, from which it could be seen that the incident wave, reflected wave, and transmitted wave have a good rising edge, meeting the one-dimensional propagation characteristics of the stress wave. According to the one-dimensional stress wave propagation hypothesis, the strain of the member under one-dimensional stress wave is ε(t), and the overall displacement of the bar is l, which can be expressed as follows [31,32]:…”

“…where l is the overall displacement of the bar, C S is the propagation speed of the stress wave in the bar, which is 5450 m/s, t is time, which is seconds, and the overall displacement l 1 of the incident bar during the propagation of the stress wave in the incident bar can be obtained by using Formula (1) [31,32]:…”

“…Combined with the overall displacement of the incident rod and the transmission rod, the average strain of the sample can be obtained [31,32]:…”

“…Combined with Formulas (1), ( 2), (3), and (4), the original waveform in the SHPB test was processed, that is, the three-wave method, and the formulas of strain rate, strain, and stress [31,32] were obtained as follows:…”