Analysis of fractal and energy characteristics of low-temperature concrete under an impact load

Abstract

In this study, impact compression tests on low-temperature concrete were conducted using a split Hopkinson pressure bar. The impacts of low temperatures on the strength, fractal, and energy characteristics of concrete were analyzed. The damage evolution mechanism of the microcrack density was discussed based on microscopic damage theory and microscopic tests. The results demonstrated that the impact fractal dimension and energy dissipation density of low-temperature concrete were positively correlated with the strain rate. The strain rate sensitivity of the impact fractal dimension was significantly affected by low temperature at low strain rates; however, low temperature had little effect at high strain rates. The pore water transformed into ice at negative temperatures, the fracture energy of the concrete increased, and the energy dissipation density increased. More than 50 % of the capillary and free water inside the concrete was frozen at −10 °C; approximately 30 % of the capillary and free water and 65 % of bound water did not freeze when the temperature was −30 °C. The macropores did not collapse under the action of ice filling at high strain rates; however, microcracks were generated around them. With a decreasing temperature, the threshold stress for microcrack propagation increased, crack propagation required more energy, and the microcrack density decreased.