Enhancing the Mechanical Properties of Engineered Cementitious Composites through 3D printed Auxetic and Non-Auxetic Reinforcement

Abstract

Currently concrete is one of the most used building materials in the world. Despite its ability to withstand compressive loads, concrete has a low tensile strength, making it prone to cracking when pulled apart. Therefore, reinforcement is required to withstand the tensile stresses. This is generally achieved by applying steel rebars into the tension zone of the concrete structure. In recent years, there has been a growing trend of incorporating fibers into concrete mixtures to develop cement-based materials with properties resembling steel, such as Engineered Cementitious Composites (ECC).
This thesis explores innovative approaches to improve the mechanical properties of ECC by employing 3D-printed auxetic and non-auxetic reinforcements. Auxetic materials display a distinctive characteristic where, upon vertical stretching, they exhibit lateral expansion, and upon vertical compression, they undergo lateral contraction. In other words, when subjected to tensile loading, auxetic materials expand horizontally, and when subjected to compressive loading, they contract horizontally.
The main research question revolves around the possibility of enhancing the deformation capacity of ECC through these innovative reinforcements. To address this question, numerical simulations, experimental tests, and comprehensive analyses were conducted.
The study begin with the creation of ECC samples reinforced with 3D printed polymeric meshes, exploring different angles, volumes, and sizes of reinforcements using two distinct 3D printing materials, namely Acrylonitrile Butadiene Styrene (ABS) and Thermoplastic Poly-urethane (TPU). The mechanical characteristics of the composite materials were assessed by uniaxial tensile testing, and their response to stress was thoroughly examined.
The results conclusively demonstrate that the incorporation of 3D printed auxetic and non-auxetic reinforcements significantly increases the deformation capacity of ECC. The auxetic designs have improved deformation and flexibility, which makes them perfect for applications that value ductility and strain capacity. In contrast, non-auxetic designs, in particular honeycomb structures, exhibit higher stiffness and load-bearing capacities, making them appropriate for situations that demand structural rigidity and resistance to deformation.
Moreover, the study highlights the crucial role played by the choice of 3D printing material in influencing the strength and strain capacity of the reinforcement. ABS exhibits superior load-bearing capacity due to its high stiffness, while TPU showcases exceptional strain capacity, owing to its elastic and flexible properties. The investigation of many factors, including angles, volumes, and sizes, highlights their substantial influence on the mechanical characteristics of the ECC reinforcement. These characteristics can be changed to allow for alternatives between stiffness, load-bearing capacity, and strain capacity, which can be used to optimize the design of reinforcement for a variety of applications.
In conclusion, this thesis makes a contribution to the developing topic of "designer construction materials," where the properties of cementitious composites can be tailored and optimized through innovative reinforcement strategies. Future constructions that are durable, flexible, and sustainable will be made possible by the combination of 3D printing technology with ECC. This thesis encourages researchers to go further, where imagination and creativity meet concrete, creating a world where materials work with us to create a physical environment that is more resilient.