Enhancing cement mortar longevity using self-healing agents derived from CAC and FGD gypsum

One of the most persistent challenges in cementitious materials is the formation and propagation of cracks. While many self-healing approaches have been explored, most depend on costly or complex encapsulated agents with limited reactivity and questionable sustainability. This study addresses these limitations by introducing a novel, low-cost self-healing additive made from aggregate composed of Calcium Aluminate Cement (CAC) and Flue Gas Desulfurization (FGD) gypsum, two readily available industrial by-products with potential for both structural enhancement and autonomous crack repair. The aggregate was synthesized without surface treatment and characterized using XRD, TGA, and FTIR to evaluate its physical, chemical, and morphological properties. Three different aggregate size ranges were incorporated into mortar mixes and assessed for workability, mechanical performance (including flexural strength, compressive strength, and dynamic modulus), and self-healing capacity through capillary absorption, Crack Mouth Healing percentage (CMH %), and FTIR analysis of healing products. The aggregate replaced fine aggregate by weight in each mix, while the Mix 3 composition (1.18–2.34 mm aggregate) delivering the most favorable results by increasing compressive strength by 19%, achieving 58.15% surface crack closure, and reducing sorptivity by 47.03% compared to the cracked reference. FTIR confirmed the formation of calcite, ettringite, and AH₃ within healed cracks. Overall, this study demonstrates the dual functionality of CAC-FGD aggregate as both durable and sustainable self-healing agents. Activated by water ingress, a scalable and environmentally responsible strategy for extending the service life of cement-based infrastructure is provided. A practical and sustainable approach to improving the durability and longevity of concrete structures through autonomous self-healing technology is offered by this research. Overall, this study demonstrates the dual-functionality of CAC-FGD pellets as both durable and sustainable self-healing agents. Activated by water ingress, they provide a scalable and environmentally responsible strategy for extending the service life of cement-based infrastructure. This research offers civil engineers a practical and sustainable approach to improving the durability and longevity of concrete structures through autonomous self-healing technology.