DOI: 10.5593/SGEM2014/B32/S13.014


C.M. Chan
Wednesday 1 October 2014 by Libadmin2014

References: 14th International Multidisciplinary Scientific GeoConference SGEM 2014, www.sgem.org, SGEM2014 Conference Proceedings, ISBN 978-619-7105-14-8 / ISSN 1314-2704, June 19-25, 2014, Book 3, Vol. 2, 99-106 pp

Dredging is a necessary maintenance measure to keep the operational depths of ports and waterways adequate for navigation of waterborne transport. Due to natural sedimentation mechanism, as well as re-routing of the natural course of near-shore water pathways as a result of manmade shoreline alterations, dredging has seen a marked increase in terms of frequency and amount of sediments displaced. The materials dredged are generally considered wastes to be disposed of either at designated locations in open waters or contained landfills inland. Both disposal methods incur costs, labour, time and more importantly, the risks of depositing contaminants along the transportation route. It is therefore favourable for the conveyance and disposal of the dredged materials to be minimized or eliminated, if possible. One potential solution towards that is by reusing the material, with sufficient pre-treatment nonetheless, as any other good geomaterials in construction, particularly along the coastline to avoid long distance hauling. The present work involved examination of a typical dredged marine sample retrieved from a local port area, and the identification of its fundamental physico-chemical properties. Pre-treatment was achieved via solidification, where known dosages of hydraulic binders, i.e. cement and fly ash, were admixed with the dredged soil at a certain mixing water content. Cement is arguably the most common hydraulic binder used in the civil engineering world, while fly ash, a byproduct of coal combustion in power plants, was added to explore the possibility of cement substitution. A relatively small binder dosage was used in this study, i.e. 10 %, with various combinations of cement : fly ash ratios in the attempt to establish the solidification pattern and effects. The test specimens were left to cure up to a month, with measurements taken at intervals of 3, 7, and 28 days in the current study for an understanding of the time effect for maturity of the solidification process. A nondestructive bender element test was conducted together with the conventional unconfined compression test on the specimens to monitor the modified strength and stiffness with time and different binder ratios. The findings were interesting: while prolonged curing contributed to the maturity and improved performance of the solidified dredged soil, excessive cement addition seemed to impede the strength and stiffness gain despite the longer curing period. In conclusion, the study sheds some light on the potential of reviving dredged soil, otherwise destined for disposal as a waste, to a useful second life by solidification. Of course, this is but a preliminary exploratory work, which requires further test programmes to ascertain the long term performance, both in terms of engineering properties and environmental impact. Yet, this could very likely be the right step forward for a more sustainable handling of the increasing dredged materials worldwide.

Keywords: dredged materials, strength, stiffness, reuse, solidification, cement, fly ash

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