Stiffness and strength mobilisation in steel-slag-mixed dredged clays in early curing

Abstract

The presence of portlandite (Ca(OH)2) in steel slag leads to potential hydration capacity, and this can be exploited to improve the engineering properties of high-water-content dredged clays. The strength and stiffness mobilisation characteristics of four dredged clays from Japan mixed with two steel slags were continuously investigated from early hours to 28 d of curing in this study, by using direct shear apparatus and bender elements, which allowed testing of mixed specimens from the initial, soft, uncemented states. The stiffness and strength increase rates in the second, main stage of evolution in the clay–slag mixtures were found to be loosely correlated to the amount of amorphous silica. The correlation was also influenced by the amount of portlandite in the slags. The results can be used to screen out clays that are hard to solidify in the medium term, based on quick on-site measurement of the amorphous silica content. For quality control in practice, the strength–stiffness relationship was critically examined as a means to assess the strength using non-destructive stiffness probes. Close observation revealed that to represent a wide range of curing time and mixing conditions by a single line, as proposed in existing studies, could be misleading. A new interpretation for the relationship is proposed.