Evidence date · 2022-07-01 · Research note 2 of 3
1 2 3
See current Track status →
Since the previous research note · Earlier expectation not tested
Track continuity
Since the previous research note: Could changing bacterial functions help supply microbes for self-healing concrete?
Previous expectation: Adjusting mineral-making functions in suitable bacteria might eventually support lasting crack repair and reduce maintenance of concrete structures.
What this study adds: The July 2022 study reports bacterial mortar with improved strength and reduced permeability, alongside recovery in reloaded reinforced laminates. The supplied evidence does not establish use or testing of the engineered functions or transfer tools behind the earlier expectation.
What changed in this study
A stronger mortar is not automatically a self-healing mortar. Strength tests show how well a material bears a load, while healing requires evidence that damaged material can recover useful properties. A July 2022 study examined both questions using mortar containing Bacillus pasteurii or Bacillus sphaericus.
What the bacterial mortar tests measured
The researchers added the bacteria at reported levels of 0.25% and 0.5% of cement weight. They compared the treated mixtures with control mortar containing no bacteria. The study assessed water uptake, capillary permeability, permeable void volume, compressive strength and flexural strength. It also examined the material with microscopy, elemental analysis and thermal analysis.
These measurements address related but different aspects of durability. Water uptake and capillary permeability indicate how readily water can move into the mortar, while permeable void volume describes the connected space available for that movement. Compressive strength concerns resistance to being squeezed. Flexural strength concerns resistance to bending. Neither strength measurement, on its own, tests whether a damaged specimen can restore its performance.
How calcite changed the material’s water pathways
Microbially induced calcite precipitation, or MICP, refers here to bacteria-associated formation of calcite, a calcium carbonate mineral. The study’s microscopy and elemental analysis supported a denser treated material with fewer voids. Thermal analysis also supported higher calcite amounts and greater crystallinity in the treated samples.
The material observations matched separate water-transport measurements. All treated samples reportedly had lower water uptake, lower capillary permeability and lower volume of permeable voids than the bacteria-free controls. Together, those results suggest that the treated mortar offered less connected space for water to enter and move through it. They support improved resistance to water penetration, while the strength and reloading tests address other performance questions.
Strength gains appeared at different test ages
After 28 days of curing, the treated samples showed reported compressive-strength increases of 28–50% compared with the control. At 120 days, flexural strength was reported as 19.29–65.94% higher. The two ranges should be read alongside their different properties and test ages: compression and bending are not interchangeable measures.
The abstract does not identify which bacterial species or addition level produced each value. The ranges therefore show the scale of the reported changes across the tested treatments, not a ranking of the best organism or dose. They also describe initial material performance, rather than recovery after damage.
Reloading offered a separate test of recovery
The study also assessed bacterial reinforced laminates under load. These specimens reportedly showed less deformation than the controls. When the bacterial laminates were reloaded after 28, 90 and 120 days, the authors reported restoration of their physical and mechanical properties and performance, interpreting the result as evidence of healing.
That recovery evidence is important because it addresses a different question from whether the original mortar was stronger. At the same time, the supplied study summary does not provide crack dimensions, the detailed damage-and-reloading sequence, numerical recovery completeness or evidence from repeated damage cycles. It therefore supports the authors’ healing interpretation without showing how completely, consistently or durably the material would recover under broader structural conditions.
What bacterial repair could mean for concrete maintenance
Cementitious materials that resist water entry and recover useful performance after small cracks could eventually reduce repair demands for building and infrastructure owners. The potential benefit follows a clear path: bacterial mineral formation may make pore spaces less open to water, while the reloading results suggest that some useful properties can return after damage.
That prospect remains conditional. The laboratory effects would need to remain effective under service conditions and repeated damage before they could be linked to longer service life or lower maintenance needs. In this study, maintenance savings were a possible consequence of the material behavior, not a measured outcome.
Key Sources
- Primary source: Microbially-Induced-Calcite-Precipitation (MICP): A biotechnological approach to enhance the durability of concrete using Bacillus pasteurii and Bacillus sphaericus
DOI or Journal Page · Peer-Reviewed Paper · 2022-07-01