Trial Production and Performance Monitoring of Paving Blocks Made with Recycled Construction and Demolition Materials  

Project Title: Trial Production and Performance Monitoring of Paving Blocks Made with Recycled Construction and Demolition Materials

Applicant: The Hong Kong Polytechnic University (Prof. Poon Chi-sun)

Total Approved Grant: $135,708

Duration: 25/3/2002 to 25/6/2003

Project Status/Remarks: completed

Scope: To apply a technology in using a mechanized moulding method for producing paving blocks from recycled aggregates instead of natural aggregates and to promote the practical use of such paving blocks. The paving blocks produced from recycled aggregates will be able to comply with the requirements of BS6717 and the General Specifications for Civil Engineering Works of the Government. A number of government departments and public organizations (e.g. Highways Department, Architectural Services Department, Housing Department and KCRC) have agreed to use the paving blocks produced with recycled aggregates on a trial basis so that the performance of the blocks can be monitored and compared with those made with virgin materials.

Summary of the Findings/Outcomes:

The study has demonstrated that both recycled fine and coarse aggregates can be used to replace virgin materials to produce grade 30 concrete paving blocks. In general, the performance of the recycled aggregate pavers after almost 1 year of monitoring was similar to that of the natural ones.

An extension of this work to produce Grade 45 pavers is being carried out under a further funding of ECF 2/2002. Methods to lower the rate of water absorption will also be tried.

At the same time, using an internal funding, the PolyU is also conducting research on producing air pollutant removing concrete bricks and paving blocks using recycled aggregates. The paving block is consisted of a concrete base layer made from cement and recycled aggregates, and a thin surface layer made of cement, recycled aggregates, other industrial wastes, and a small amount of titanium dioxide. When the surface of the block is irradiated by sunlight, active oxygen is created on the surface of the block, which oxidizes NOx in the air into nitrate. The resultant nitric acid can be washed away by rain. Preliminary results are encouraging. Although the long-term pollutant removal ability of the surface layer has not yet been tested, it is anticipated that the performance will not deteriorate as much in comparison to similar products on the market due to its relatively dense surface layer as compared to the much larger open void texture used by other commercial products. This may be one of the ways forward to further develop a technology that can combat the C&D waste and air pollution problems in Hong Kong at the same time.