Core Technology: The "Crack Diagnosis and Treatment" Mechanism of Microbial Capsules
The heart of this smart material lies in its "pre-embedded biological repair system." Technical teams encapsulate specially acclimated Bacillus subtilis and calcium lactate nutrients in biodegradable sodium alginate capsules (2-3mm in diameter), then mix them into concrete with 20-50mm cobblestone aggregates at a 3% volume ratio. Cobblestones, as natural high-strength aggregates (compressive strength ≥120MPa), provide the concrete's basic mechanical support; microbial capsules, like "dormant repair soldiers," distribute evenly in the aggregate gaps.
When the concrete develops cracks (width ≤0.5mm) due to load or temperature changes, rainwater or maintenance water seeps into the cracks and triggers capsule degradation, releasing Bacillus subtilis and calcium lactate. With moisture and oxygen, the bacteria rapidly reproduce and metabolize to produce calcium carbonate (calcite), forming a crystalline filling layer in the crack within 3-7 days. This biomineralized product, with a compressive strength of 35MPa, matches the strength of the parent concrete, achieving "autonomous crack closure." Lab data shows the system achieves 100% repair rate for micro-cracks (0.1-0.3mm wide) and over 90% for 0.3-0.5mm cracks.
Engineering Validation: Qingdao Cross-Sea Bridge's "Self-Healing" Practice
The maintenance project of Qingdao Jiaozhou Bay Cross-Sea Bridge marked the first large-scale application of this technology. This 36.48km cross-sea project, with traditional concrete sections, developed 237 visible cracks after 10 years of service due to seawater erosion and vehicle loads, requiring over 20 million yuan annually for manual repairs. In 2022, its approach bridge sections were renovated using self-healing cobblestone concrete, covering 12,000㎡.
Post-renovation monitoring data shows: after 2 years of tide and temperature test, the renovated section developed only 19 new cracks, 17 of which (89%) self-healed within a month, achieving an overall crack repair rate of 92%. Structural bearing capacity tests indicated the repaired concrete's elastic modulus recovered to 95% of its original state, far exceeding the 80% recovery rate of traditional repair materials. Based on this trend, the bridge section's lifespan is projected to extend from the designed 50 years to 100 years, with no need for large-scale manual repairs throughout its life.
Cost Comparison: Economic Revolution from a Full-Lifecycle Perspective
Although self-healing cobblestone concrete costs 15% more than ordinary cobblestone concrete (approximately ¥480/m³ vs ¥417/m³), its full-lifecycle cost advantage is significant. Taking Qingdao Cross-Sea Bridge as an example, traditional concrete sections require large-scale crack repairs every 10 years, with cumulative maintenance costs reaching ¥600/㎡; with self-healing materials, only 3 basic maintenance operations are needed over 100 years, reducing maintenance costs to ¥240/㎡-a 60% decrease.
For new projects, the economics are even more striking: a 10,000-ton port dam using this material increases initial construction costs by approximately ¥800,000 but saves over ¥5 million in maintenance costs by reducing 8 major overhauls. Currently, the technology is included in the Guidelines for Application of New Materials in Highway Engineering and has been promoted in 12 large domestic infrastructure projects, becoming a benchmark for intelligent construction.