Abstract
Polypropylene (PP) concrete, a kind of high-performance fiber-reinforced concrete, is widely used in large concrete structures. Studies on the dynamic mechanical properties of polypropylene concrete under temperature–impact load can provide a theoretical basis for research on the structural stability of concrete structures during fires, explosions, and other disasters. The purpose of this paper was to study the dynamic mechanical properties of polypropylene concrete under real-time high-temperature conditions and to establish a dynamic damage constitutive model for polypropylene concrete under real-time high-temperature conditions. In this paper, Split Hopkinson Pressure Bar (SHPB) equipment was used to test the dynamic mechanical properties of polypropylene concrete with different high strain rates under different real-time high temperatures (room temperature, 100 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, and 800 °C). A modified “Z-W-T” model was used to determine the recursion of the dynamic damage constitutive model of polypropylene concrete under different temperature–impact loads, and the model was compared with the experimental data. The results show that the thermal conditions influenced the chemical composition and microstructure of the polypropylene fiber concrete, which was why the high temperatures had a strong influence on the dynamic mechanical properties of polypropylene concrete. When the heating temperature exceeded 300 °C, although the polypropylene concrete specimen was still able to maintain a certain strength, the dynamic mechanical properties showed a deterioration trend as the temperature increased. The comparation between the experimental data and the fitting curve of the dynamic damage constitutive model showed that the dynamic stress–strain curves could be well matched with the fitting curves of the dynamic damage constitutive model, meaning that this model could describe the dynamic mechanical properties of polypropylene concrete under different real-time high temperatures well.
Highlights
In recent years, a new tendency to add different kinds of materials [1,2], such as carbon nano-fibers [3,4], steel fibers [5], and polypropylene fibers [6], to concrete to improve its mechanical properties has been observed
Polypropylene fiber-reinforced concrete has less of a risk of cracking when exposed to high temperatures, a benefit from the internal steam pressure caused by the fusion temperature of the polypropylene fiber (170 ◦C) [7]
Studying the dynamic mechanical properties and dynamic damage evolution relationship of concrete materials under high temperatures is of great significance to improve the fire resistance and explosion resistance of concrete structures, allowing the structure’s security requirements as well as national defense requirements to be satisfied
Summary
A new tendency to add different kinds of materials [1,2], such as carbon nano-fibers [3,4], steel fibers [5], and polypropylene fibers [6], to concrete to improve its mechanical properties has been observed. The dynamic mechanical properties and dynamic damage evolution models of polypropylene fibers affected by thermal conditions are receiving increased attention, most concrete specimens are heated and naturally cooled to room temperature during specimen treatment processes in the present research. Other studies have shown that the mechanical properties of concrete material were obviously affected by the strain rate especially and they were sensitive at high strain rates [26].The strain rate of polypropylene concrete under the impact load 102 s−1 [30] resulted in a short observation time; in this case, the low-frequency Maxwell element could not be relaxed, showing linear springs characteristics, whereas the Maxwell element with a relaxation time of θ2 described the viscoelastic mechanical behavior of the material under high strain rate conditions. Where σa represents effective stress, σr represents the nominal stress, and D represents the damage variable
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