Substituting spent copper slag as a replacement for sand as fill material in land reclamation projects

Abstract

The lack of waste landfill used for waste disposal and the increasing cost of fill materials used for land reclamation projects in Singapore has led to the study on the suitability of using spent copper slag, a by-product of removing rust and marine deposit on ships, as the primary fill material for construction and land reclamation in Singapore.

The spent copper slag will undergo several laboratory tests to determine its physical, geotechnical properties, heavy metal toxicity concentration and compressive strength.

The physical and geotechnical properties of both spent copper slag and sand is found to be similar. The particle size of spent copper slag was found to be 0.61mm with well graded particle size distribution. It has a specific gravity of 3.27 and a pH value of 8.1. The physical and geotechnical properties documented in the experiments were found to display similar attributes when compared to sand.

A batch leaching test is conducted to determine the concentration of heavy metals found in the material at pH 5.0. The result of the Toxicity Characteristics Leaching Procedure (TCLP) shows the concentration found in the heavy metals falls within the maximum regulatory levels as referred by the US EPA. Another batch leaching is conducted at different pH ranging from pH 3.0 to pH 8.0. This is to further understand the difference in heavy metal concentration at different pH values. The experimented results show the significant increase of heavy metal concentration at decreasing pH. However, the highest concentration of heavy metal still falls within the regulatory levels as referred by the US EPA.

A compression test is conducted to determine the compressive strength of spent copper slag concrete mixture and spent copper slag and marine clay concrete mixture. The compression test results show the peak compressive strength of spent copper slag sample at 42.9 N/mm2(50% - 75% copper slag percentage), whereas the compressive strength of spent copper slag and marine clay sample is10.5 N/mm2( 75% - 100% copper slag percentage).

In conclusion, spent copper slag could be used as a replacement for sand as fill materials in land reclamation project.