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.

In Japan, volcanic fine soil as well as highly organic soil are categorized as 'problematic soil'. Since the engineering properties of these problematic soils greatly differ from those of textbook-type geomaterials, these soils are often improved in the engineering practice by mixing them with cement, for instance. It has been reported that some natural agents included in the problematic soils such as allophane and organic substance often impede cement solidification reaction. It has also been reported that the inhibition of the solidification reaction may be avoided by adding steelmaking slag comprising free lime. However, laboratory investigation into the effects of content of these agents on the cement solidification reaction is scarce. In this paper, the mechanical as well as chemical properties of various problematic soils are examined by using a single indicator, i.e., the content of alkali adsorption capacity. First, a fairly good relationship between the amount of allophane/organic substance and the alkali adsorption capacity was found for of several problematic soils tested. Second, it was manifested that the unconfined compression strength of cement/steel-slag mixed soil was much higher than that of comparative strength of cement mixed soil. The tendency was more pronounced as the alkali adsorption capacity increased.

No abstract

No abstract