Prof. Farnam (CAEE, Drexel University), Prof. Sales (CAEE, Drexel University), Prof. Schauer (MSE, Drexel University), and Prof. Najafi received a $555K grant from the National Science Foundation (NSF). This three-year research program entitled “Engineering Multifunctional Microbial Polymeric Fiber (BioFiber) for Concrete Self-Healing” takes a collaborative and multidisciplinary approach to establish a robust autonomic self-healing paradigm in concrete to improve its durability and resilience. The program focuses on designing multifunctional microbial fiber-reinforced concrete (BioFRC) with two major functionalities: reduced potential of crack growth and autonomic self-healing capability after occurrence of micro-cracks. Accordingly, the design strategy of BioFRC must fulfill two main mechanisms: first, harmonizing mechanical interaction among concrete fracture, fiber fracture and fiber bridging, and second, balancing the extent of microbial calcium carbonate precipitation (MCCP) with crack volume creation. We aim to tackle and couple these two mechanisms by engineering novel polymeric composite fibers (BioFibers) that consist of (1) an inner hydrogel-based fibrous core loaded with microbial spores with desirable mechanical/interfacial properties, porosity, and swelling potential, and (2) an outer melamine-based shell with desirable mechanical/interfacial properties, impermeability, and rigidity.
The harmonized mechanical interaction in BioFRC will be tailored using experimental and numerical work by (i) tuning concrete-shell-core fracture processes in which concrete fracture leads to strain rupture of the shell activating MCCP and (ii) by balancing load bearing and energy absorption roles of fiber bridging. By integrating polymer and microbiology principles, the balance between MCCP activity/kinetics with crack volume creation will be established by (i) tailoring core processing-composition-structure to tune core porosity/swelling capacity for microbe incorporation/distribution, and (ii) predictively engineering microbial activity in BioFRC before/after cracking considering the effects of supplies of bacterial spores, urea, water, oxygen and nutrients. The phase-field numerical method will be used to predict the fracture process in fiber, matrix, and interface. The findings will be used to design BioFRC whose competence will be tested by understanding the sealing/healing mechanisms of BioFRC using fracture mechanics principles, Ohtsu’s 3D image analysis, and the intrinsic mass transport law of porous fractured materials.