Effect of Fiber Dosage and Age on Creep Failure of Alkali-Activated Slag Concrete Under High Stress Sustained Loading

Abstract

Alkali-activated slag (AAS) has emerged as a sustainable alternative to Ordinary Portland Cement (OPC), offering a viable pathway for mitigating global environmental footprints. However, its widespread structural application is often hindered by pronounced time-dependent creep deformation, particularly nonlinear creep under high sustained stress, which precipitates progressive internal damage and potential structural failure. While fiber reinforcement is recognized for enhancing concrete ductility, its specific role in modulating the high-stress creep behavior of AAS systems remains insufficiently explored. This study experimentally investigates the creep failure characteristics of Polypropylene (PP) fiber-reinforced AAS concrete, scrutinizing the coupled effects of fiber dosage, loading age, and stress intensity. Failure mechanisms were characterized via a multi-scale analysis incorporating failure patterns, creep coefficients, apparent lateral strain ratios, ultrasonic non-destructive testing, and crack morphology. Results indicate that fiber reinforcement fundamentally modifies the creep failure kinetics. Specifically, fibers actively constrain lateral expansion, reducing the apparent lateral strain ratio by up to 34% at failure, thereby transitioning the failure mode from brittle fracture to a pseudo-ductile yielding. The efficiency of the fibers is highly age-dependent. While improvements are marginal at 1 day, at 28 days under a critical 0.95 f c stress level, a 1.0% fiber dosage yielded a 156% increase in creep lifetime. These findings demonstrate that fiber inclusion provides a critical safety margin and mechanical redundancy for AAS concrete subjected to sustained high loads.