In Hong Kong, a huge quantity of construction and demolition (C&D) wastes and waste glass is produced every day representing a large fraction of the total solid waste stream. The disposal of these wastes has become a severe social and environmental problem in the territory. Government sources have indicated that there are acute shortages of both public filling area (reclamation sites) and landfill space in Hong Kong. Hong Kong's three mega landfills are expected to be full within 5-6 years. The possibility of reducing and recycling these wastes is thus of prime importance. Hong Kong also faces a serious air pollution problem. In particular, the densely populated urban area in the city which houses many tall buildings hinder and prevent the circulation of air at the street level.

The Hong Kong Polytechnic University has been conducting research on methods to recycle waste and tackle the air pollution problem. The Eco-block effectively uses construction and demolition waste and recycled waste glass as major constituents in the production of concrete blocks. The Eco-block has undergone three generations of development and the latest generation has successfully combined the use of recycled materials and a small quantity of photo-catalyst for paving block production. The block is able to remove low concentrations of air pollutants such as nitrogen oxides via a photo-catalytical reaction. This technology utilizes sun-light as the energy source, and requires no additional driving energy, minimal maintenance actions and can work throughout the year. It not only reduces the disposal of wastes, but also conserves the use of natural resources in the production of eco-friendly construction materials.

In practice, the technology uses a mechanized molding method for producing the concrete paving blocks. Using such a method, the mixed materials are molded under a combined vibrating and compacting action so that the requirement for maintaining a workable mix is not so important as that in normal concretes. Only a minimal amount of water is needed to make the mixture fluid enough to be fed into the molding machine.

A series of stringent tests have been conducted on the blocks to test their compressive strength, transverse strength, drying shrinkage, skid resistance and other durability properties. The test results showed that using this technique, the concrete paving blocks made are just as good as those made with virgin materials in the market.
Experiment results show that at least 20% of nitrogen oxides can be effectively removed by the blocks under laboratory conditions.

Indeed, the Eco-blocks have already been put into uses at a number of different sites in Hong Kong including recreation grounds, the eco-park, university and school campuses, public pavements and a number of private and public housing estates.

This developed recycling technology has been commercially transferred to local manufacturers. But the lack of knowledge about the availability and performance of the recycled material in the local construction industry is still hindering the wider use of the material in Hong Kong.









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