| Author: | Yang, Ning |
| Title: | Development of multiple functional geopolymer coating for performance upgrading of civil engineering structure |
| Advisors: | Dai, Jian-guo (CEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Inorganic polymers Coatings Protective coatings Corrosion and anti-corrosives Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xix, 177 pages : color illustrations |
| Language: | English |
| Abstract: | The increasing number of aged civil engineering structures has become a significant concern. Surface coating is a cost-effective technology to prevent their deterioration and extend their service life. While coatings with various functions have been developed in recent years to improve the durability and upgrade the performance of civil engineering structures, the matrices of most of commercially available coatings are typically polymeric and may encounter significant aging problems (e.g., UV degradation) when exposed to outdoor environments or elevated temperatures. In addition, these polymeric coatings are organic materials derived from non-renewable fossil resources, and they release volatile organic compounds (VOCs) during their applications that impact adversely the environment and the human’s health. Against this background, inorganic geopolymer coatings have emerged as an alternative to traditional polymeric coatings in various civil engineering applications for low carbon and improved durability. In recent years, it is noted that the surface coating can also be functionalized with high solar reflectance and heat emittance to provide passive radiative cooling for buildings and infrastructures without energy input, providing a promising solution for the promotion of energy conservation and carbon neutrality. Geopolymer binder is a kind of alkali activated aluminosilicate precursor material and exhibits a significantly low carbon footprint compared to conventional Portland cement binder. This thesis therefore focuses on the development of geopolymer-based multifunctional coatings for improved durability and sustainability of civil engineering structures, including: (1) in-situ reduced graphene oxide (RGO) modified geopolymer coating for improved corrosion resistance; (2) alkali-activated geopolymer (AAGP)-based and phosphate-activated geopolymer (PAGP)-based radiative cooling coatings for energy-saving purpose; (3) hydrophobic modified AAGP radiative cooling coatings; and (4) red mud-based geopolymer (RMGP) pavement radiative cooling coating. The developed RGO-modified geopolymer coating was found to exhibit excellent corrosion-prevention performance when implemented on carbon steel. The coating with an optimum GO content of 0.1% by weight of binder increased the corrosion resistance by more than two orders of magnitude compared to the bare carbon steel electrode. The developed AAGP radiative cooling coating achieved a high long wave emissivity of 0.9491 and a solar reflectance of 97.6%, respectively, while the developed PAGP achieved a high long wave emissivity of 0.9634 and a solar reflectance of 94.71%, owing to the addition of different functional additives and the hierarchical air pores formed in the geopolymer matrix. The optimized AAGP and PAGP cooling coatings could achieve a maximum sub-ambient cooling effect up to 8.9 °C and 3.8 °C, respectively, under direct sunlight in Hong Kong’s climate. To improve the water resistance and better maintain the optical properties of the geopolymer radiative cooling coating, four types of hydrophobic agents, including sodium methyl silicate (SMS), polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE), and triethoxyoctylsilane (TEOS) were used to modify the AAGP for comparison. The solar reflectance, hydrophobicity, and other material characteristics of the modified coatings were measured and analyzed. The test results show that SMS-AAGP (5%), PDMS (50cP)-AAGP (10%), PTFE-AAGP (one-layer) and TEOS-AAGP (60°C) achieved excellent optical performance and impressive hydrophobic performance. After 6-month outdoor exposure, the TEOS-AAGP (60°C) and SMS-AAGP (5%) cooling coating exhibited the best overall performance in terms of the optical, hydrophobic and adhesive properties. This has paved the way to the practical applications of multifunctional geopolymer radiative cooling coatings in building applications. Furthermore, to enable practical applications of the geopolymer radiative cooling coating in pedestrian pavement, a RMGP cooling coating was also successfully developed with a moderate visible reflectance (0.52748) and higher NIR reflectance (0.75364), as well as a high long wave emissivity of 0.9455, enabling a cool red color with CIE value of L*=74.56, a*=9.55, b*=11.98, and a maximum surface temperature reduction of 15.9℃ compared to the uncoated counterpart. In summary, a series of geopolymer-based coatings with different functions, especially the radiative cooling capacity, have been successfully developed through the thesis work and demonstrated their application scenarios. The knowledge generated through the thesis work provides a solid foundation for the widespread and practical applications of low-carbon, waterproofing, and energy saving geopolymer coatings for the improved sustainability of civil engineering structures. |
| Rights: | All rights reserved |
| Access: | open access |
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