The Coupled Influence of Size and Strain Rate on the Failure Mechanism and Model Prediction of Fly Ash Concrete

Abstract

This study investigates the mechanical behavior and failure characteristics of fly ash concrete under quasi-static to low-to-medium strain rate loading. Uniaxial compression tests were conducted on three specimen sizes under four strain rate conditions (totaling 12 working conditions), analyzing damage evolution and failure patterns across different scales and loading rates. Results indicate that at lower strain rates, uniformly distributed cracks formed on specimen surfaces, with damage concentrated at coarse aggregate-mortar interfaces. In contrast, higher strain rates induced brittle failure characterized by crack propagation along the loading direction and coarse aggregate fracture - particularly evident in smaller specimens. As strain rates increased, the compressive strength of small, medium, and large specimens rose by 48.18%, 38.19%, and 29.07% respectively, demonstrating diminishing strength enhancement and reduced strain rate sensitivity with larger dimensions. Based on Weibull and log-normal statistical models, this study introduces a coupling coefficient accounting for size and strain rate effects, establishing a novel dynamic strength model capable of predicting stress-strain responses within target strain rate ranges. The model provides theoretical support for optimizing fly Ash cement-based materials and offers valuable references for durability assessment in hydraulic and civil engineering structures.