Coralline Red Algae as a Bio‐Active Additive for Self‐Healing Cement: Crack Closure and Mg‐Calcite‐Like Mineral Precipitation

Abstract

The construction sector faces growing pressure to reduce its environmental impact and integrate carbon capture and storage (CCS) into material design. Cement production accounts for nearly 8% of global CO ₂ emissions, highlighting the urgent need for durable, low‐carbon solutions. Extending the lifespan of concrete through self‐healing mineralization not only reduces the frequency of repairs but also contributes to carbon capture, making biogenic processes, such as microbially induced calcium carbonate precipitation (MICP), a promising approach for sustainable construction. However, most microbial systems face challenges related to survival, nutrient demand, and long‐term stability in highly alkaline environments. We propose calcifying algae as a living performance additive for self‐healing binder mixtures. These photosynthetic counterparts to established bacterial systems, such as Bacillus spp., are capable of autonomous CaCO ₃ formation without nutrient supply or encapsulation, enabling continuous carbon capture and storage over the lifetime of buildings or bridges. We dosed Portland cement with 0–5 bwof % (by weight of cement), and specimens were evaluated under exposure to natural elements and accelerated aging cycles. Visible crack closure occurred within 57 days at 0.5 bwof %, with higher dosages correlating with reduced crack formation. Microscopic analysis confirmed CaCO ₃ deposition and matrix densification, indicating enhanced healing and durability. Mechanical and rheological performance tests showed no loss of early or late strength.