Dynamic Mechanical Properties and Mechanisms of Ordinary Concrete after High Temperature

Abstract

Concrete structures are at risk of fire and explosion effects during service. This paper mainly conducted static and dynamic mechanical test research of concrete after high temperature. Five different target temperatures and two cooling methods (air cooled with furnace and water cooled by immersion in water) were set to investigate its effects. Hydraulic servo machine and split Hopkinson pressure bar (SHPB) were used to obtain static and dynamic mechanical behavior, failure patterns, and mechanical characteristic parameters of concrete. The research results indicated that the compressive strength of concrete at 800°C was reduced by 77% and 67% under air-cooled and water-cooled methods, respectively. When the temperature was below 600°C, the compressive strength of water-cooled concrete was lower than that of the air-cooled specimen. The failure patterns of the concrete vary from a small amount of aggregate crushing at low strain rates to a large amount of coarse aggregate crushing at high strain rates. The increase in temperature weakens the dynamic increase factor (DIF) of concrete and causes a significant strain-softening phenomenon in the concrete stress–strain curve. By utilizing scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and X-ray computed tomography (X-CT) techniques, the microstructural features of concrete were obtained. The deterioration and enhancement mechanisms of the mechanical properties of concrete under high temperature and strain rates were studied by combining the results with static and dynamic mechanical properties analyses. Meanwhile, a dynamic constitutive model for concrete considering high-temperature influencing factors is established.