Development of Multiple Functional Geopolymer Coating for Performance Upgrading of Concrete Building Structures

A rising number of aged buildings in Hong Kong result from deterioration caused by steel corrosion, concrete spalling etc, which has become an increasingly important issue. In addition, the hot weather in Hong Kong requires huge energy consumption to cool the indoor building environment for human comfort. It is said that the air conditioning inside buildings accounts for one-third of the total local electricity consumption in Hong Kong, generating significant energy and environmental burden. The durability and thermal performance of an RC building relies heavily on the performance of the building envelope, which significantly influences the service life, the indoor living environment, and the energy consumption of the building. Therefore, its proper maintenance is of critical importance. Among the many existing maintenance technologies, surface coating is a most cost-effect means which can isolate the building envelope from various external hostile environments such as water, UV radiations, carbon dioxide and chlorides. The surface coating can be also incorporated with heat insulation or reflective functions to reduce the thermal gradient between the indoor and outdoor environment in the building envelope, so that energy needed to maintain the human comfort in the building can be saved. This project aims to develop an innovative multiple functional geopolymer coating for improving the sustainability of concrete building envelope. The system will be featured with the waterproofing, self-cleaning and passive cooling functions. In particular, it is featured with two distinguished characteristics: (1) Ability of sub-ambient daytime radiative cooling (SDRC), which is a breakthrough technology emerging very recently and can reduce the building surface temperature well below the air temperature under direct sunlight. As a result, the amount of energy required for cooling the buildings can be significantly reduced. (2) Use of inorganic geopolymer matrix, which is a cement-free, low-carbon and environmental friendly material and formed by alkali-activation of aluminosilicate sources. Compared to existing polymeric coatings, the geopolymer matrix exhibits superior fire and weathering resistance (e.g., UV resistance), which are important for building applications. The project consists of five research tasks covering design of coating mix-proportion, improvement of optical properties, hydrophobic treatment, durability assessment and cooling effect analysis. Upon the success of the project, a cost-effective method will be established for the service life extension and energy efficiency improvement of existing concrete building, leading to a comprehensive solution for the improvement of building sustainability, in Hong Kong, the Greater Bay Area and the rest of China.