Effect of age and stress on creep damage characteristics of alkali-activated slag concrete

Abstract Concrete exhibits creep deformation and damage under elevated stress, potentially leading to failure. This study experimentally investigates the short-term creep damage behavior and early-stage mechanisms of alkali-activated slag (AAS) concrete under sustained compressive loading. Mechanical properties, creep coefficients, and nominal Poisson’s ratios were evaluated for specimens across various stress levels and loading ages. Furthermore, ultrasonic nondestructive testing and microstructural analyses were employed to examine microcrack evolution. Results indicate that creep-related damage initiates when applied stress exceeds 40% of the compressive strength, accelerating markedly at 70%. Consequently, creep-damaged specimens exhibited reduced compressive strength and elastic modulus, alongside a significantly increased nominal Poisson’s ratio. Microstructural evidence revealed that medium-to-high stress exposure causes localized degradation of the cementitious matrix and aggregate–paste interface, promoting internal microcrack initiation and propagation. As these findings primarily reflect early-age short-term mechanisms, extrapolating them to long-term behavior warrants caution.