Numerical Analysis of Cyclic Loading and Fatigue Behavior of Alkali-Activated Concrete Beams

Alkali-activated concretes (AAC) are emerging as sustainable alternatives to Portland cement concrete (PCC) due to their substantially lower carbon emissions; however, their fatigue behaviour requires further investigation. This study numerically evaluates the monotonic and fatigue performance of fly ash-based AAC in comparison with PCC of comparable strength. Three-point bending under monotonic loading is first simulated using ABAQUS/CAE. A two-dimensional notched beam specimen of size 262.5 mm × 75 mm with a centrally located bottom notch of 15 mm × 3 mm is modelled. Two strength grades of AAC and corresponding PCC mixes are analysed. Ultimate load, mid-span deflection, and crack mouth opening displacement are obtained from history outputs. The monotonic response is then used to define constant-amplitude cyclic loading for fatigue analysis, with load ranges of 20-80% and 25-95% of the ultimate load. Structural responses under cyclic loading are examined and compared. Since finite element modelling cannot directly capture the complete fatigue life of quasi-brittle materials, fatigue resistance is approximated using the number of cycles associated with the initial rapid deformation stage, assumed to represent 10% of the total fatigue life. From the observed results, AAC performed higher fatigue strength with respect to the PCC, highlighting its potential for sustainable constructions.