Do microbes categorically heal the cracks in concrete or only seal the cracks - this study aims to answer, based on a few experimental findings, highlighting the self-healing concepts in cement-based materials. Alkaliphilic spore-forming Bacillus cohnii microbes (105-1010 cells/ml) are used in the cement-concrete (bio-concrete) in addition to varying nutrient amounts. The healing in the form of regaining its structural efficiency is evaluated by its mechanical (compressive, flexural) strength and durability properties. Bio-mineralized calcium carbonate seals 37% of 20–50 nm dimensioned pores and 87% of 50–200 nm dimensioned pores resulting in 43–48% total voids reduction within 28 days of the healing period. Microbes only degrade the nutrients to precipitate healing agents (calcium carbonate) without affecting the C–S–H structure in concrete. Statistical analysis reveals that calcite deposition mostly influences the strength of self-healed bio-concrete whereas experimental findings show 5.8–6.3 wt% calcium carbonate deposition augments the 40–60% compressive strength of bio-concrete compared to reference concrete. The complete-to-60% sealing of cracks of 0.02–2 mm width is examined using visual inspection of concrete skins. Microbes reduce porosity, sealing cracks intensifies mechanical strength, and the durability of the concrete validates self-healing rather than only sealing the cracks.