| Author: | Lu, Jianxin |
| Title: | High-performance lightweight concrete with ultra high-performance binder |
| Advisors: | Poon, Chi Sun (CEE) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Lightweight concrete Concrete construction Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | 341 pages : color illustrations |
| Language: | English |
| Abstract: | Modular integrated construction (MiC) is perceived as an innovative construction worldwide for addressing the shortage of manpower, increased costs of construction, and declining productivity in the construction industry. However, conventional concrete materials similar to those used for on-site construction are normally used in the MiC, which poses challenges for requiring stronger hoist cranes and special logistics. Furthermore, Hong Kong releases over 60% of its CO2 for building operations, so that improving energy performance of buildings is being the particular area of interest. Lightweight concrete (LWC) would be a good energy-efficient element for promoting low-carbon buildings due to its good thermal insulation. However, traditional LWC produced by chemical and physical foaming usually achieves low strength, typically applied in non-load bearing members. Therefore, the principal objective of this research is to develop high-performance lightweight concrete (HPLC) for enhancing the lifting capacity, reducing the transportation cost and improve energy performance of the precast construction. To enhance the mechanical properties and durability of lightweight concrete, three strategies have been attempted: use of good-quality binder matrix, selection of proper lightweight materials, and addition of fibers. Among, improving the quality of the mortar matrix is the key point in the production of HPLC considering the weakest component of lightweight materials in the matrix. In this thesis, an ultra high-performance cementitious composite (UHPC) was used as a binder to leverage its very high strength and superior durability. Based on a literature review that identified the existing knowledge gaps, this thesis presents a systematic study on mix design and characteristics of this UHPC-based HPLC to enhance its functional and durability performance. To reduce the density of the HPLC, the UHPC was first combined with different types of aluminosilicate lightweight aggregates (LWA). By virtue of the physical-chemical interactions of LWA, the synergetic use of UHPC and pre-wetted shale LWA was able to produce an HPLC with high structural efficiency, good thermal insulation, low autogenous shrinkage and permeability. To further improve the sustainability and performance of HPLC, different lightweight aluminosilicate microspheres were incorporated in a green UHPC, which was prepared with a large volume of waste glass. The developed HPLC exhibited a low density and excellent mechanical properties. Such superior performance of HPLC was ascribed to the high pozzolanic reactivity of glass powder and its promotion on cement hydration, the low thermal conductivity of glass, the chemical reactivity of microspheres as well as their hollow nature for impeding heat transfer. Compared to the fly ash-based lightweight microspheres, micro-sized hollow glass microspheres were more efficient in improving the performance of HPLC. Hence, a new concept of ultra high-performance lightweight concrete (UHP-LWC) with high structural efficiency was proposed by introducing the high strength glass microspheres. The UHP-LWC could achieve a compressive strength of higher than 120 MPa and a density down to around 1800 kg/m3. By using glass microspheres with a high stiff shell, the fundamental properties of the UHP-LWC including thermal insulation, sound absorption, resistance to water ingress and electrical resistivity were improved significantly. Sequentially, this thesis presents a design method for producing UHP-LWC using a mathematical approach. The statistical optimization via Central Composite Design was proved to be an effective method to produce the UHP-LWC. The designed UHP-LWC showed comparable or even superior functional and durability properties than normal-weight UHPC and high-performance cement mortar. The use of specified lightweight materials played prominent roles in ensuring the mechanical properties and great durability of UHP-LWC. The highly dense structure which causes the risk of explosive spalling is one of the major limitations of using UHPC and UHP-LWC, thus a strategy to improve its structural efficiency and lower the risk of explosive spalling was proposed. The UHP-LWC was cured at different curing regimes to maximize its structural efficiency and prevent its spalling after exposure to high temperature. The combination of lightweight materials and dry heat curing was effective in reducing the density (<1800 kg/m3) and enhancing the compressive strength (>150 MPa) of the UHP-LWC. By means of minimizing the amount of internal free water, the heat curing approach contributed to avoiding the explosive spalling and significantly improving the structural efficiency of the UHP-LWC. The thesis concluded that the synergetic use of UHPC and proper lightweight materials was able to produce desirable HPLC with high structural efficiency, good thermal insulation, and excellent durability. Such HPLC would be a promising material for applications in long-span lightweight structures and buildings. |
| Rights: | All rights reserved |
| Access: | open access |
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