Evaluation of crack healing potential of cement mortar incorporated with blue-green microalgae

Microbial induced calcite (CaCO3) precipitation (MICP) is a biochemical process that induces calcite precipitation. MICP is considered a solution for remediation of concrete cracks using bio-mineralization. This study aims to use microalgae as an agent in the healing of micro-cracks. Microalgae were used in cement mortar to induce the formation of calcium carbonate to seal the cracks. Two microalgae species, namely Synechococcus elongatus (Syn. elongatus) and Spirulina platensis (S. platensis), were tested for their characteristics and then incorporated into the cement mortar. The specimens were cured under two different conditions, namely ambient and water curing. Next, the mechanical properties and crack healing of the cement mortar were examined. The cement mortars that were cured for 28 days in the air and water were subjected to a compressive load of 70% of its maximum threshold load, to induce micro-cracks. Subsequently, the specimens with pre-induced cracks were cured under ambient and water to check for the ability to seal cracks through bio-mineralization. The effect of replacing cement with 4, 8 and 12% of both species of microalgae were investigated. The results demonstrate that the mortars cured in water have a higher strength compared to the mortars cured in air. The investigation results also reveal that the mortars with S. platensis showed better strength and crack healing compared to mortars with Syn. elongatus. The water cured specimens with 12% S. platensis developed a compressive strength of 72% of the control specimen (100%), compared with 12% Syn. elongatus that exhibited only 36%. The healing potential was evident as the micro-camera images showed the narrowing of the induced cracks on the surface of the mortar after 14 days of water curing. Furthermore, the residual compressive strength of the biotically healed specimens showed 35% of the strength regain with 12% S. platensis as a cement replacement. The formation of crystalline calcium carbonate precipitates in the specimens with S. platensis and Syn. elongatus exhibits an increase in the derivatives of calcium ions; the enhancement in the strength of mortar due to the calcium carbonate (crystal) formation, which seals the surface of the crack, was supported by the SEM-EDS and XRD analysis. It was also found that the integration of microalgae into the cement had the effect of self-healing and could potentially improve the future direction of crack healing.

Automated summary

Microbial induced calcite precipitation (MICP) is a biochemical process used for remediation of concrete cracks by inducing calcite precipitation. This study investigates the use of microalgae for healing micro-cracks in cement mortar, with results showing that water-cured specimens have higher strength compared to those cured in air. Additionally, Spirulina platensis was found to have better strength and crack healing properties compared to Synechococcus elongatus, with the 12% S. platensis specimens showing a compressive strength of 72% compared to only 36% for 12% Syn. elongatus.