Low-carbon concrete crack repair strategies based on soybean urease induced calcium carbonate precipitation technology

Concrete cracking is a common issue that compromises structural integrity and reduces service life. With increasing emphasis on sustainability and carbon neutrality in the construction industry, effective crack repair is essential—not only to restore structural performance but also to reduce the need for reconstruction, thereby lowering cement consumption and associated carbon emissions. However, traditional chemical-based repair methods may pose risks to human health and the environment. This study investigates the application of soybean urease-induced calcium carbonate precipitation (SICP), a cost-effective biomineralization technique, for concrete crack repair. The effects of different crack widths (0.1–2.0 mm) and repair strategies (immersion, injection, and sand-filling methods) on crack healing performance were experimentally evaluated. Ultrasonic transmission time and unconfined compressive strength (UCS) tests were conducted to assess the recovery of mechanical properties. Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were used to characterize the calcium carbonate crystals formed within the cracks. Results showed that SICP treatment reduced ultrasonic transit time and partially restored mechanical strength. Repair effectiveness decreased with increasing crack width across all methods. The sand-filling method yielded superior results for wider cracks (1.0–2.0 mm), while the injection method was more effective for narrower ones (0.1–0.5 mm). Microstructural analyses confirmed the formation of calcium carbonate, with distinct differences in crystal morphology and distribution depending on the repair technique. This study provides valuable insights into the selection of appropriate repair methods for cracks of different widths, contributing to the development of efficient crack repair strategies.