Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Civil and Environmental Engineering | en_US |
| dc.contributor.advisor | Teng, Jin-guang (CEE) | en_US |
| dc.contributor.advisor | Yu, Tao (CEE) | en_US |
| dc.creator | Li, Ruilong | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/14432 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Behaviour and modelling of early-age 3D-printed concrete | en_US |
| dcterms.abstract | The advent of extrusion-based 3D concrete printing technology marks a paradigm shift in construction methodologies, opening avenues for automated construction, on-demand customisation, and the ambitious goal of extraterrestrial constructions. At the heart of this technology is the printing stage, during which soft, fresh concrete is deposited layer-by-layer to form a temporarily weak structure that gradually hardens as concrete cures over several days. Existing modelling approaches for fresh concrete structures have yet to produce reliable predictive models, as significant discrepancies persist between experimental results and predictions. These inconsistencies stem from a lack of understanding of the mechanical behaviour of fresh 3D-printed concrete (3DPC). | en_US |
| dcterms.abstract | To address these knowledge gaps, this thesis aims to develop a comprehensive understanding of the mechanical behaviour of early-age 3DPC and its implications for fresh concrete structures during construction. The research programme integrates three key components: experimental studies, theoretical developments, and numerical simulations to achieve this objective. | en_US |
| dcterms.abstract | Through a series of pioneering experimental studies, the mechanical behaviour of fresh 3DPC was systematically characterised. The material behaviour under biaxial compression, arguably the most pertinent stress condition for printed material during construction, was investigated. This comprehensive experimental study spanned concrete ages ranging from a few minutes to six hours and included biaxial stress ratios of 0 (uniaxial compression), 0.33, 0.5, 0.7, and 1 (equibiaxial compression). It addressed a significant gap in existing literature, which had primarily focused on uniaxial compression and shear testing. Moreover, innovative uniaxial compression tests were designed to investigate the material's elasticity, viscous behaviour (e.g., creep, stress relaxation), and healing properties. In particular, the cyclic compression tests revealed that the actual elastic modulus of fresh 3DPC is 5 to 20 times higher than previously reported values. Multi-step creep-recovery experiments established the predominantly nonlinear and non-recoverable nature of creep deformation, whilst material healing tests provided groundbreaking evidence that equivalent plastic strain can decrease due to ongoing hydration - a phenomenon that fundamentally challenges conventional plasticity theory. | en_US |
| dcterms.abstract | Analysis of the biaxial compression test data demonstrated that the widely used von Mises and Mohr-Coulomb criteria inadequately represent the strength behaviour of fresh 3DPC. In response, two complementary strength models were developed: a simplified model for rapid assessment of biaxial-to-uniaxial strength ratios at different ages, and a comprehensive multi-axial strength model. To capture the complete stress-strain response, an elastoplastic model was developed, capable of accurately simulating the uniaxial and biaxial compressive behaviour of fresh 3DPC across different ages. The framework was further enhanced through viscoplasticity theory to incorporate material creep effects, enabling the accurate simulation of nonlinear creep behaviour that conventional linear viscoelastic approaches failed to capture. | en_US |
| dcterms.abstract | Finally, a series of finite element (FE) simulations connected the enhanced material-level knowledge to the structural-level response of printed structures during construction. FE models incorporating the proposed elastoplastic model outperformed existing numerical models, revealing two distinct instability failure mechanisms: elastic buckling and plastic buckling - both previously misidentified due to the adoption of inappropriate material models. Moreover, the research highlighted the critical role of complex interactions between material ageing, creep, and printing speed on the mechanics of printed structures. This work not only provides deeper insights into the structural responses during concrete printing but also establishes a reliable framework for toolpath and printing parameter optimisation, advancing both the theoretical understanding and practical applications of 3D concrete printing technology. | en_US |
| dcterms.extent | xxxiv, 346 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2026 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.accessRights | open access | en_US |
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