Development of a functionally graded bacteria capsule for self-healing concrete

This paper reported the development of a novel functionally graded reactive magnesia cement-based bacteria spores (RMC-B) capsule for self-healing concrete. The capsule had a gradient structure with a dense shell and a porous and low alkaline core to better protect and to enhance the viability of the bacteria spores. With the addition of the capsule, the strength of the matrix can be maintained while engaging self-healing of cracks. Results showed that the inclusion of the RMC-B capsules did not negatively impact the hydration and the fresh properties of the PC paste and enhanced the 28-day compressive strength of the hardened PC paste by 18%. Specimens with the RMC-B capsules exhibited strong crack healing performance as evidenced by the closure of cracks of few hundred microns and reduction of transport properties due to the dense formation of layered rhombohedral calcite along the entire crack from the surface to the interior.