SHPB Test and Microstructure Analysis on Ready-Mixed Concrete in Uniaxial Load and Passive Confining Pressure States

Abstract

Ready-mixed concrete has been used as a support in mine roadways, where the impact load of blasting excavation can cause damage to the concrete support of the roadway. However, limited studies are available on the effect of water content, storage period, and impact pressure on dynamic mechanical properties of ready-mixed concrete in uniaxial load and passive confining pressure states. To investigate the effect of water contents (0%, 1.0%, 1.5%, and 2.0% by mass of dry sand), storage periods (0 d, 3 d, 7 d, 15 d, 20 d, and 30 d), and impact pressures (0.6 MPa and 0.9 MPa) on dynamic mechanical properties of ready-mixed concrete in uniaxial load and passive confining pressure states, the dynamic compression test using split Hopkinson pressure bar (SHPB) has been carried out. In addition, the microscopic test based on the scanning electron microscope (SEM) is conducted to analyze the effect of water content and storage period on the microstructure of ready-mixed concrete. The experimental results show that under the conditions of uniaxial load and passive confining pressure, the dynamic compressive strength of ready-mixed concrete decreases with the increase of water content and storage period but increases with the increase of impact pressure. At the same impact pressure, the dynamic compressive strength in passive confining pressure state is larger than that in uniaxial load state. The dynamic stress-strain curves of ready-mixed concrete in uniaxial load and passive confining pressure states can be divided into three stages: elastic stage, plastic stage, and failure stage. The peak strain increases with increasing impact pressure, and the peak strain in passive confining pressure state is more than that in uniaxial load state. The degree of damage for ready-mixed concrete specimens increases with the increase of the storage period and water content; however, the damage of specimens in passive confining pressure state is less than that of specimens in uniaxial load state. Meanwhile, an analysis to the microstructural mechanism of water content and storage period inside of ready-mixed concrete has been performed.