Novel Greening, Processing Route, and Bio-Inspired Hierarchical Structuring of Engineered Cementitious Composites for Sustainable Infrastructure

Abstract

Strain-hardening cementitious composites (SHCCs) are a family of cementitious materials that preserve the advantages of concrete as a construction material, while eliminating many of concrete’s shortcomings. While concrete is weak and brittle in tension, SHCCs exhibit a degree of tensile ductility under extreme loading and material toughness hundreds of times that of concrete, providing enhanced durability and resilience for cementitious infrastructure. This research covers three materials design projects aimed at expanding the capabilities of the SHCC family, offering their durability and resilience benefits to new infrastructure use cases and enhancing those qualities in others.

First, the use of natural plant fibers, rather than synthetic polymer fibers, as the sole reinforcement in SHCC materials is explored as a route for material greening. Strategies to overcome the design challenges associated with the use of natural fibers are reported and a curauá fiber reinforced strain-hardening cementitious composite is introduced.

Second, the concept and micromechanical design considerations of strain-hardening cementitious composites are applied to cementitious materials designed for building-scale 3D printing. Automated additive manufacturing techniques, such as 3D printing, are poised to revolutionize the construction industry, offering benefits in time and cost efficiency and human safety. However, the full potential of building-scale 3D printing has been hampered by the required insertion of ancillary reinforcement, antithetical to the bottom-up, freeform 3D printing paradigm. By using SHCC materials as the primary printing material, these limitations could be removed, improving design freedoms, efficiency, and the inherent durability and resiliency of the printed structure. Compositional and processing strategies to achieve printability in SHCC materials (and cementitious materials in general) are investigated and reported. Proof-of-concept printable SHCC materials are demonstrated, and their mechanical performance is characterized.

Third, enhanced mechanical property profiles of SHCC materials are pursued, as inspired by the structure and deformation mechanisms of a natural composite material found in seashells. Despite being composed 95% of a brittle chalk-like material, nacre exhibits remarkable tensile strength, tensile ductility, and toughness. Strategies of adapting nacre’s hierarchical structural organization and associated deformation mechanisms to a large size scale and with materials relevant to infrastructural applications are explored and evaluated. SHCCs serve as an efficient means to achieve this structure and these mechanisms due to their characteristic tensile behaviors. These nacre-inspired composite design strategies are pursued as means to improve the holistic mechanical property profiles of SHCCs. Applied to the highest strength versions of SHCCs, these bio-inspired design strategies offer benefits to seismic, blast, and impact resistant infrastructure applications.

This research seeks broad impact by addressing the sustainability of infrastructure through material greening and improved durability and resilience of the fundamental building block of most modern infrastructure: cementitious materials. Parametric studies are used to design novel versions of SHCCs with new and useful characteristics, all while deliberately engineering the fiber, matrix, and interfacial properties to generate strain-hardening behavior. In addition to addressing specific compositional or performance targets, resulting in three novel types of functional SHCCs, each design project produces results and implications related to the others.