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

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

転炉系製鋼スラグを用いた浚渫窪地埋め戻し時の海洋環境改善予測

金沢大学理工研究域機械工学系There are many borrow pits, caused by the sand mining at the bottom of the coastal sea in Japan. Borrow pits have been identified as a source of oxygen-deficient water killing benthic fauna by hydrogen sulfide. And, much nutrients such as nitrogen or phosphorus tend to release from the bottom of borrow pits, which is attributed to red tide. From these reasons, it has become more important to restore borrow pits for marine environment improvement. But, a large amount of earth and sand materials are needed to restore borrow pits. Then, we have examined the restoring borrow pits process by ”slag mixture material” mixing the steelmaking slag that is the by-product of the steel industry with the dredged material generated by the sea route maintenance. In this study, firstly, by the experiment using ”slag mixture material”, we examined the sulfide generation control effect and the microalgae generation control effect by phosphorus release control. Then, by the developed ”biogeochemical model” based on the experiment, we predicted the improvement effect when ”slag mixture material” are applied to a borrow pit of Osaki area in Mikawa Bay. As a result of that, ”slag mixture material” decreased 92% of the reduction material release such as hydrogen sulfide. And. compared with dredged material, ”slag mixture material” decreased 26% of the reduction material release. The prediction shows the ”slag mixture material” bring larger improvement effects. The restoring borrow pits process by ”slag mixture material” mixing the steelmaking slag is more effective for marine environment improvement