The Engineering Properties of Dredged Marine Soil Solidified with Activated Steel Slag

Abstract

Dredging is the operation of removing material from one part of the water environment and relocating it to another. Generally, the purpose of dredging is to relocate underwater sediments and soils for the offshore construction, maintenance of waterways and reclamation. Dredging produces a very large amount of dislodged materials known as dredged soils, which are commonly considered a waste. Generally, dredged soil is dumped into open sea and causes environmental problems. On the other hand, steel slag is an industrial waste resulting from the process of steelmaking. However, for the last 3 decades, almost 35 % of the steel slag produced was dumped in landfills. As such, this study is about the mixing of a dredged marine soil with activated steel slag, with the aim of determining the effectiveness of the slag in solidifying the soil. The dredged soil was collected from Marina Melaka and categorized as a high plasticity silt (MH). It has a natural moisture content of 130. 7 %, specific gravity 2.53, liquid limit 66 % and plastic limit 51.6 %. The steel slag was first ground to particles smaller than 2 mm for mixing with the soil. It was activated with 4, 6, 8, 10 and 12 mol of natrium hydroxide (NaOH), with only the optimum molarity resulting in maximum improvement of the soil being used throughout the study. 3 predetermined ratios of clay: activated steel slag were examined, i.e. 3:7, 5:5 and 7:3, and the soil-slag specimens were left to cure for 3, 7, 14 and 28 days. The solidified specimens were subjected to the unconfined compressive strength (UCS) test, the vane shear test as well as the bender element test at the respective ages. It was found that greater strength and stiffness improvement were produced by higher steel slag content. Longer curing periods resulted in more significant improvement of the engineering properties too. The steel slag addition also helped reduce moisture in the originally wet soil. Overall it can be concluded that activated steel slag from Malaysian steel-making industry can be potentially used to solidify the otherwise waste dredged marine soils for reuse as a sound geomaterial.