Engineering and Design Considerations for Steel Furnace Slag Aggregates in Concrete Pavements

Abstract

The use of steel furnace slag (SFS) aggregates is limited in the United States and abroad, primarily because of the inherent expansion potential of the material, which results from the hydration of the free calcium and magnesium oxides present from the slagging process. When used in concrete, the literature presents contradictory findings, such as that the strength can increase or decrease with the addition of SFS aggregates. Microstructural investigations of the SFS aggregates as well as the interfacial transition zone (ITZ) in mortars revealed that the mechanical properties are strongly dependent on the SFS type and source. Certain SFS types can develop with a porous interior and/or a porous outer layer of different composition, both of which act as weaknesses in the bulk concrete. Depending on the SFS type, the ITZ may also be more porous, which can lead to further weakening of the concrete. Given the potential deleterious expansion of SFS, there are rapid screening protocols, which can quantify both the free lime content (complexometric titration) and expansion potential (autoclave index test) of the SFS. While the literature currently presents limits for the SFS to be used as a base material, no limits are defined for the use of SFS in bound applications, despite the fact that low expansion SFS aggregates are being used in several countries for certain applications.