Re ECF Project: 2011-48

Project Title: Feasibility of utilizing sewage sludge incinerator ash for concrete blocks production

Applicant: Prof. C.S. Poon, Department of Civil and Structural Engineering, The Hong Kong Polytechnic University

Total Approved Grant: $792,040 (ECF & WWGF: 50/50)

Duration: 10/6/2013 to 9/6/2016

Project Status/Remarks: Completed

The project aims to assess, through a comprehensive laboratory and pilot plant study, the feasibility of using sludge incineration ash derived from the future Sludge Treatment Facility in Hong Kong as alternative construction materials such as in concrete blocks.

Summary of the Findings/Outcomes:
Although the volume of sewage sludge can be largely reduced after thermal treatment (incineration), the sewage sludge incinerator ash (SSA) still needs to be disposed of at landfills. This project aimed to investigate the feasibility of reusing and recycling SSA as a supplementary cementitious material for concrete blocks production. The study included laboratory studies followed by a plant trial. Laboratory studies were carried out on wet (paste and mortar) and dry (block) mixes with SSA obtained from EPD’s Sludge Treatment Facility to replace ordinary Portland cement (OPC) at levels of up to 20% by weight. The findings indicated that although cement hydration was accelerated with the incorporation of SSA, compared with pulverized fly ash, the SSA itself showed lower pozzolanic activity. SSA does contain heavy metals but the leaching of which is low and it can be further reduced by its incorporation in the cement based system. Replacing OPC by SSA generally reduced the strength of the concrete products produced but this can be compensated with use of appropriate mix design method. The pilot plant trial using the mix proportions developed showed 10% SSA can be used to replace 10% OPC to produce eco-glass paving blocks meeting the specified strength requirements. One conference paper and one journal paper were published.