Effect of Soil Organic Matters in Dredged Soils to Utilization of their Mixtures Made with a Steel Slag.

Kanako Toda,Satoshi Nishimura,Tsutomu Sato,Michihiro Aimoto,Yuzoh Akashi,Ryosuke Kikuchi,Takeshi Kokado,Tsubasa Otake

doi:10.3390/ma13235450

Abstract

Dredged soils have been used as construction materials by alkaline activation with steel slag (steel slag-dredged soil mixtures) at harbors. Such mixtures develop strength chiefly by calcium silicate hydrate (C-S-H) formation by the pozzolanic reaction. However, the strength of such mixtures is unpredictable, and in some cases, mixtures have been too soft for the intended engineering application. An identification of strength development indicators would accelerate evaluation processes for strength development to facilitate and promote the utilization of such materials. This paper focuses on the relationship between the characteristics of soil organic matters in dredged soils and the strength development of the mixtures by a comparison of eight dredged soils collected from eight different Japanese harbors. The characteristics of the soil organic matters were identified to determine as indicators of mixtures with weak strength development, i.e., enriched sulfur content in extracted soil organic matter (humic acid) fraction, and the N/C ratio of humic acid similar to land humic acid standards. Increases in the validated fraction of dredged soils and steel slag by replacing fractions disadvantageous to construction resources would contribute to reduce waste production, which would lower the environmental impact of the use, aiming to achieve sustainable utilization of such materials.

Highlights

The excavation of soil sediments in water ways for shipping safety produces significant volumes of dredged soils (e.g., [1,2,3])
Dredged soils with enriched sulfur content in the humic acid fraction, and/or N/C ratio of extracted humic acids similar to that of land humic acids, resulted in the formation of soft mixtures. These characteristics could be used as indicators of dredged soils that form soft mixtures, together with the inorganic amorphous silica content in the dredged soils
The total organic carbon (TOC) and humic acid content in dredged soils are not suggested as indicators of soft mixture formation

Summary

Introduction

The excavation of soil sediments in water ways for shipping safety produces significant volumes of dredged soils (e.g., [1,2,3]). The concretion of dredged soils by mixing alkaline activators [5,6,7,8,9] makes them useful as construction materials and offers the potential to promote their utilization. Steel slag is a by-product in the iron-making process, and it has the ability to develop the strength with dredged soils by mixing and curing at room temperature [10,11,12]. It is a kind of alkaline activator of dredged soils. Steel slag-dredged soil mixtures are utilized in engineering works close to the seashore because of the ease of material transport and application

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