Internal strengthening of cement mortar using sustainable functional aggregate with a controlled-release effect

Inspired by the concept of controlled drug release in pharmaceuticals, this study introduces a novel type of functional aggregate designed to enhance the durability of cementitious materials through the controlled release of internal strengthening agents. The effects of functional aggregate incorporation on the fresh and hardened properties, as well as on the durability-related performance of cement mortar, were systematically investigated. The results demonstrated that the prepared functional aggregates exhibited excellent compatibility with the cementitious matrix. Notably, the incorporation of functional aggregates led to a 36.8% reduction in the chloride ion diffusion coefficient and a 6% decrease in water absorption, confirming their effectiveness in improving the durability of cementitious materials. Microstructural analyses revealed that the delayed release of sodium silicate promoted secondary reactions with portlandite, resulting in the formation of a dense alkali calcium silicate hydrate (C-S-H) gel surrounding the functional aggregates. This densified interfacial region significantly enhanced the impermeability and overall durability of the cementitious matrix. The findings of this study provide new insights into the design and fabrication of engineered aggregates with tunable performance, highlighting the potential of using sustainable recycled materials to develop high-durability concrete systems.