Bio-Concrete Self-Healing: Bacterial Calcite Precipitation

Feedstock & Environment

Bacterial spore density 10⁶ /mL

Calcium lactate feedstock 20 g/L

Temperature 30 °C

Crack moisture 70 %

⚠ Below ~25% moisture the encapsulated spores stay dormant — urease needs an aqueous film to hydrolyse urea. No healing occurs.

Healing State

Days elapsed

0.0

Crack healed

0 %

CaCO₃ rate

0 mg/L·d

Crack width left

0.50 mm

How it works

Bio-concrete embeds dormant spores of alkaliphilic, urease-positive bacteria (e.g. Sporosarcina pasteurii) together with a calcium-lactate nutrient in microcapsules. When a crack lets water in, the spores germinate and drive microbially induced calcite precipitation (MICP):

CO(NH₂)₂ + 2H₂O --urease-->  2NH₄⁺ + CO₃²⁻
Ca²⁺ + CO₃²⁻  -->  CaCO₃(s)  (calcite, fills the crack)

The precipitation rate follows saturating Michaelis–Menten kinetics in the calcium-lactate substrate, a bell-shaped thermal response (bacteria are most active near 30 °C and shut down toward the extremes), and a hard moisture gate — no aqueous film, no ureolysis:

rate = Vmax · [S]/(Km+[S]) · exp(−(T−30)²/2σ²) · moistureGate
dose(t) = ∫ rate dt,   healed = clamp(dose / doseToSeal, 0, 1)
width(t) = width₀ · (1 − healed)

The 3D view shows the two crack faces of a concrete slab; as dose accumulates, cream-coloured calcite crystals nucleate and grow across the gap in the order they were seeded, and the crack visually narrows as width(t) shrinks — matching how real self-healing concrete seals hairline cracks (typically ≤0.5–0.8 mm) over a few weeks of wet-dry cycling, without any manual repair. This is one concrete branch of the same CO₂-mineralisation chemistry used in curing kilns and carbon-mineralization reactors: here the CO₃²⁻ comes from bacterial metabolism rather than injected CO₂ gas.

Spore density / lactate — more spores and more feedstock raise the ceiling on precipitation rate (spores scale activity, lactate saturates it via Km).
Temperature — activity peaks near 30 °C and falls off toward both hot and cold extremes.
Moisture — must exceed ~25% to activate ureolysis at all, and reaches full rate above ~70%.

Concrete slab Precipitated CaCO₃ (calcite)

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