Behaviour of Nacre Inspired ECC Structures under Different Mechanical Loading Conditions

Abstract

Engineered Cementitious Composite (ECC) is a high-performance cementitious material with notable mechanical properties. It is recommended for bridges, high-rise buildings, and industrial facilities that experience a wide range of loads. While ECC exhibits significant bendability and energy absorption capability, it is vulnerable to impact loads. Biomimetic design, inspired by nacre, offers a solution to enhance the structure’s resilience. This thesis investigates the behaviour of nacre inspired designs in improving the structural behaviour and resilience of metre-scale ECC structures under various mechanical loading conditions. A high-strength ECC was developed with polyethylene (PE) and steel fibre and its mechanical properties were comprehensively studied in compression, tension, and bending. Test results indicated that the PE fibre lengths had a significant effect on the quasi-static force-displacement curves. However, under low-velocity impact (3.5 m/s to 4.5 m/s) no such effect was observed. Further, monolithic ECC beams were brittle. Nacre's features were introduced into the design of ECC beams to improve the mechanical response. Four designs were cast and tested under three-point bending, including a monolithic beam and three bioinspired designs mimicking nacre's body structure. Results demonstrated that the nacre inspired designs exhibited significantly higher ductility, energy absorption, and resistance to impact loads compared to monolithic beams. Nacre's features were also integrated into panel structures. Quasi-static punch tests on these panels showed that bioinspired designs exhibited superior structural performance including increased ductility, energy absorption capacity and flexural compliance compared to monolithic panels. High-velocity impact tests (620 m/s to 640 m/s) on ECC panels using a 16 mm spherical steel projectile revealed that monolithic panels experienced a catastrophic failure. In contrast, bioinspired panels demonstrated local bulging, resulting in significantly less damage on their front and back surfaces, despite having a similar penetration resistance. Finite element models were developed using Abaqus to simulate the behaviour of ECC panels. The models incorporated material and geometric nonlinearity, layered configurations with hyperelastic adhesives, fibre mesh, and cohesive interactions. The models were validated through comparison to experimental results, including force-displacement curves and failure modes. The models agreed well with the experimental results. This thesis has developed a high-strength ECC material by incorporating a hybrid combination of PE, steel fibres, and fly ash. The incorporation of fly ash offers sustainability and holds promise for utilization in various infrastructure undertakings. Furthermore, nacre-inspired designs have demonstrated improved mechanical properties, including heightened ductility and enhanced energy absorption. Moreover, when subjected to high-velocity impacts, these nacre-inspired structures exhibited minimal damage, signifying their ease of maintenance and reduced risk of debris-related hazards.