Expansive and concrete properties of SFS-FRAP aggregates

Steel furnace slag (SFS) is an industrial by-product that is used as an abrasion-resistant aggregate in asphalt pavement surfaces. However, SFS has found limited application in concrete pavements because of its potential for expansion from hydration of the free calcium and magnesium oxides present in the slag. This study investigated the application of asphalt-coated SFS aggregates, i.e., coarse fractionated reclaimed asphalt pavement (FRAP), as an aggregate in concrete. Autoclave expansion testing of SFS FRAP samples and chemical analyses revealed that the SFS FRAP contains residual free calcium oxide and therefore has the potential to expand, although the presence of the asphalt coating reduced the overall expansion magnitude. The performance of SFS FRAP in concrete at 20% and 50% replacements was similar to concrete with unexpansive dolomite FRAP in terms of strength and fracture properties, though the SFS FRAP may cause higher shrinkage strains and reduced freeze/thaw durability. Therefore, application of SFS FRAP with low autoclave expansion, but available free oxides should be limited for use in concrete but may be suitable for nonstructural applications or temporary roads. With further standardized expansion testing, SFS FRAP may be suitable for use as an unbound foundation material or again as an aggregate in a bound asphalt layer.