MODIFATION OF FINE-GRAINED DREDGED SEDIMENTS BY HEATING TO HIGH TEMPERATURES: PROGRESS REPORT

April 2005

Prepared by Morris,PH; Smith,J; Wong,LT; University of Queensland. School of Engineering

This report describes part of an ongoing investigation into the feasibility of modifying fine-grained dredged sediments for beneficial engineering uses by heating them to high temperatures. Earlier research conducted at The University of Queensland into the optimum temperature for this showed that it lies between 800°C and 1100°C. The work reported here was aimed at reducing this range, and confirming the suitability of the artificial aggregates produced for use in geotechnical engineering applications.
 
Dredged sediment was collected from Pond S2 in the Port of Brisbane reclamation area at Fisherman Islands, and its particle size distribution, Atterberg limits, specific gravity, and organic content were determined in the laboratory. The as-sampled sediment was similar but not identical to that tested in the earlier research, which was also collected from Pond S2. Both lay comfortably within the range of other dredged sediments tested earlier in the investigation.
 
The Pond S2 sediment was heated to either 900°C or 1050°C, and subsequently crushed and sieved to produce artificial aggregates with particle size distributions conforming to the Queensland Department of Main Roads standard specification for road base. The aggregates were subjected to laboratory testing to determine whether they met the remaining Department of Main Roads requirements for road base, were resistant to weathering, and suitable for use in other geotechnical engineering  applications. In the earlier research, the sediment was heated to either 800°C or 1100°C and the aggregates produced were subjected to similar testing. Aggregate produced by crushing and sieving common bricks was also tested for comparison.

The artificial aggregates met the Department of Main Roads' requirements for intermediate and low grades of road base, but not for high grades. The optimum temperature for converting dredged sediments to road base lies between 1050°C, or possibly 1000°C, and 1100°C. Lower grade road base can be produced at lower temperatures. The performance of the crushed bricks showed that it is unlikely that the engineering properties of the artificial aggregates can be improved significantly by modifying the heating process. However, it might be possible to improve them by applying high pressure as well as heat. Both the artificial aggregates and the crushed brick were suitable for use in a variety of geotechnical engineering applications.
 
The present investigation did not address the emission of harmful gases as the sediments were heated, or the mobility of residual salinity or heavy metal or other contaminants in the artificial aggregates. It is recommended that further research be conducted in these areas. Alternative applications of artificial aggregates produced by heating dredged sediments, for example, as aggregate in concrete, and the potential for improving the quality and hence the value of the aggregates by applying high pressure as well as heat to the sediments should also be investigated.