Creep Damage Characteristics of Fiber-Reinforced Alkali-Activated Slag Concrete: Effect of Age and Stress

This study investigates the effects of fiber reinforcement, stress levels, and curing age on the creep behavior of alkali-activated slag (AAS) concrete. Through comprehensive cyclic loading tests, we demonstrate that fiber reinforcement significantly reduces irreversible creep strain by 1.2-5.3% under high-stress conditions (0.7fc), with optimal performance at 1.0% fiber content. Quantitative analysis reveals that fiber-reinforced specimens exhibit 10.0% higher elastic modulus and maintain 83% of peak strength after creep damage, compared to 86% strength retention in non-fiber specimens. Ultrasonic testing confirmed that fibers effectively mitigate internal damage under high stress, limiting wave propagation time increases to 47-62% versus 66% in plain AAS concrete. This research quantifies the pronounced age sensitivity of creep behavior, with 7-day specimens exhibiting 28% higher creep strain than 28-day specimens under 0.8fc stress, corresponding to irreversible strain ratios of 21.3% and 18.4%, respectively. A 102% increase in Poisson's ratio at high stress levels provides direct evidence of fiber-controlled volumetric expansion during microcracking. These findings establish that strategic fiber incorporation fundamentally alters the creep damage mechanisms in AAS concrete, providing critical quantitative thresholds for engineering applications subjected to sustained loading. The results offer practical guidance for optimizing fiber-reinforced AAS concrete in infrastructure requiring long-term dimensional stability.