Effects of primary curing and subsequent disturbances on strength development of steel slag-treated marine clay

Steel slag-treated marine clay (SSTC) is a novel geomaterial used for recycling steel slag. This article reports the effects of the primary curing (the time delay between mixing and fill work) and the subsequent disturbances (the processes of remolding, handling, and placement) on the strength development of the geomaterial. The results of a series of experiments point to the possibility of improving the initial strength of SSTC for maritime fill work. Laboratory tests were performed to investigate the changes in and the recovery of the geomaterial strength brought about by one to three days of primary curing and the subsequent disturbances during various secondary curing times. In the field tests, three embankments, using SSTC that had previously undergone one or two days of primary curing, were constructed in seawater with an actual construction machine. The test results indicated that the initial strength of SSTC previously treated with one, two, or three days of primary curing increased to approximately 14 kN/m2. The loss in strength that occurred at the primary stage of curing was recovered at a later stage of curing, namely, after 28 days, and the strength of the SSTC in the three embankments was 52-70% of the sample that was cured without primary disturbance. Larger amounts of disturbances were applied to the SSTC in the field tests than in the laboratory tests. The field tests produced submerged embankments, 1.8 m in height, with average slopes of 1:2.1-1:2.9, by undergoing one to two days of primary curing. The strength of the SSTC in all the embankments recovered significantly with time after construction, and the unconfined compressive strength of the SSTC exceeded 200 kN/m2 at 100 days, which is deemed sufficient for the construction of embankments. Overall, it was confirmed that the one-day primary curing and the sea-bottom fill method presented better results than the two-day primary curing and the sea-surface fill method, considering the gradient of the slope and the strength-recovery characteristics of the SSTC. (c) 2021 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).