‘Onion-peel’ cracking and spalling in coupled meso-mechanical analysis of External Sulfate Attack in concrete using zero-thickness interface elements

External Sulfate Attack (ESA) is a chemical degradation process that may affect concrete structures exposed to sulfate-rich environments. The ingress of sulfate ions causes chemical reactions leading to the formation of secondary ettringite, with significant volume expansion and subsequent characteristic cracking. The model proposed combines a diffusion-reaction model with a meso-mechanical model in which the larger aggregates are represented explicitly and pre-inserted fracture-based zero-thickness interface elements represent potential cracks. In the model, opening cracks also become preferential diffusion paths for sulfate penetration, which brings in chemical-mechanical coupling in a staggered scheme. By exploiting improved calculation capabilities, significant extensions of previous 2D results and new 3D calculations have been obtained. The new results demonstrate the model's effectiveness in realistically replicating “onion-peel” cracking and spalling patterns observed in experiments, as well as to sulfate ion penetration profiles.