CAREER: Consecutive Assembly-and-Mineralization Processed Calcium-Silicate-Hydrate Nacre with High Specific Flexural Strength and Fracture Toughness

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This Faculty Early Career Development (CAREER) program will address the challenge to transform calcium-silicate-hydrate (CSH) - the ingredient of cement that is primarily responsible for its strength - and achieve unprecedented mechanical properties. CSH has high strength under compression, but is significantly weaker under bending and has low fracture toughness. The irregular and random nature of the nanostructure of CSH is responsible for its brittle nature. This research will innovate new CSH nanostructures that are inspired by the unique architecture of nacre, which is ultra-lightweight and recognized as one of the strongest biomaterials. The growth of natural nacre will be mimicked to synthesize CSH with polymers and organics to form highly ordered nacre-like architectures. This research will create novel cement-based materials with crack resistance as high as that of natural nacre, which will tremendously enhance the resilience, sustainability, and durability of civil engineering structures (such as prefabricated walls and panels of buildings, linings of tunnels or pipelines, and permanent formwork of bridges), energy infrastructure (such as solar panels, offshore wind farms), aerospace structures and others. The education and outreach activities of this project will engage and create opportunities for K-12 students and underrepresented minorities in STEM disciplines to learn about biomimetic materials and structures in engineering. The goal of this research is to demonstrate the hypothesis that CSH nacre architecture can be synthesized to achieve high specific flexural strength and fracture toughness through a consecutive assembly-and-mineralization process mimicking the growth of natural nacre. The main objectives of this research are to: (i) develop methods to synthesize and control growth of CSH mesocrystals; (ii) develop a consecutive assembly-mineralization process for scalable fabrication of CSH nacre; (iii) characterize mechanical properties of the synthetic CSH nacre; and (iv) establish links for the fabrication process, microstructure, and mechanical properties to optimize the CSH nacre. To this end, a scaffold will first be fabricated by freeze casting and followed by nucleation and growth of CSH mesocrystals on the scaffold through controlled mineralization; then, laminated CSH nacre will be synthesized through organic phase infiltration and hot-pressing. The CSH nacre will be tested and optimized by experiments, modeling, and machine learning.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.