Dynamic Evolution of Concrete Strength Grades: Insights Across Different Ages and Strain Rates

This paper investigated the dynamic response of plain concrete with three different strength grades, namely C30, C40, and C50, at an early age (3, 7, 14, and 28 days, respectively). Significant patterns were uncovered using a 75-mm-diameter split Hopkinson pressure bar (SHPB) apparatus. Initially, pronounced viscoelastic behaviour was observed in the concrete’s early stages, characterised by a sharp stress-strain curve both before and after reaching its peak. As the concrete matures, stress concentration within the stress-strain curve becomes more pronounced. Additionally, exponential growth in dynamic strength with higher strain rates was observed, while the strain rate index decreased with age. Improving concrete quality was found to reduce the sensitivity of dynamic strength to strain rate. A viscoelastic damage constitutive model was formulated based on experimental analysis to describe the mechanical response effectively. The evolution of concrete properties over time was accurately captured by fitting model parameters to the experimental data. The theoretical stress-strain curves derived from this damage model closely matched experimental curves across various ages.