# A Review of the Influence of Steel Furnace Slag Type on the Properties of Cementitious Composites
## 5 Requirements for SFS Characterization
### Expansion Potential  
Given the volumetric expansion when free CaO and free MgO hydrate, SFS aggregates can exhibit significant expansion, as has been demonstrated in a number of failure case studies (e.g., [295; 296; 297; 298; 299; 300]). While the primary expansion issues are attributed to the hydration of free CaO and free MgO, additional expansion effects have been argued to be attributable to the conversion of \(\beta\)-dicalcium silicate to \(\gamma\)-dicalcium silicate, oxidation of FeO to Fe\({}_{3}\)O\({}_{4}\), carbonation of oxide or hydroxide phases, hydration of silicate or sulfide phases, and/or rust formation from metallic inclusions [294]. Additional hydration products have also been identified, such as calcium monocarbonaluminate, calcite, hexagonal calcium aluminate hydrates, hydrogarnet, and calcium silicate hydrate [39; 114; 251; 123], although it is unclear if and how much these additional hydration products contribute to expansion. Based on the expansion potential, it is recommended that granular SFS undergo some form of an expansion test, a number of which have been proposed in the literature, some examples of which include the following:  
* _Autoclave expansion test (unbound SFS)_. This rapid expansion test of unbound SFS aggregates uses the ASTM C151 autoclave procedure (steam at 300 psi (2.1 MPa) and 420 \({}^{\circ}\)F (215 \({}^{\circ}\)C) for 3 h) [9; 258; 279; 301]. The SFS sample is compacted in a steel mold and exposed to the autoclave conditions with an applied surcharge. The height of the surcharge before and after autoclaving is measured to calculate a percent expansion. While this expansion value does not necessarily correlate well to field performance or free CaO content, it is a very rapid test method that can be used as an index test. In addition, autoclaving conditions can be used to study the hydration reactions in SFS [302; 303]. * _Autoclave expansion test (bound SFS)_. Inspired by the ASTM C151 autoclave test also, some researchers have used an autoclave to study the expansion of cementitious pastes, mortars, or concretes with SFS [56; 89; 126; 242; 304]. The concept of this test is to accelerate the expansive reaction(s) in the SFS, so it is also useful as an index test or as a test to simulate rapid weathering. * _Expansion force test_. [PERSON] [136] developed this test for unbound SFS coarse aggregates as a method to compute the expansion force generated by a single SFS aggregate bound in a rigid matrix such as concrete. In this test, compacted unbound SFS aggregates are compacted in a cylindrical mold and submerged in water at 74 \({}^{\circ}\)C (165 \({}^{\circ}\)F), and a load cell is used to monitor the force exerted by \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**SFS Type**} & **EGN Value from** & **Ca(OH)\({}_{2}\) Content** & **Stoichiometric CaO** & **Estimated Free** \\  & **Titration (\%)** & **from TGA (\%)** & **Content in Ca(OH)\({}_{2}\) (\%)** & **CaO Content (\%)** \\ \hline BOF 1 & 4.4 & 1.3 & 1.0 & 3.4 \\ EAF 1 & 0.1 & 0.0 & 0.0 & 0.1 \\ LMF 1 & 0.5 & 0.2 & 0.1 & 0.4 \\ LMF 2 & 3.5 & 1.3 & 1.0 & 2.5 \\ SFS 1 * & 4.0 & 1.4 & 1.1 & 2.9 \\ SFS 2 * & 3.7 & 1.1 & 0.8 & 2.9 \\ SFS 3 * & 5.1 & 1.1 & 0.9 & 4.2 \\ \hline \hline \end{tabular}  
* Unknown SFS type but suspected to be BOF.  
\end{table} 
Table 7: Estimated total free CaO contents based on titration and TGA [9; 222; 279]. the expanding aggregate. From these data, the tensile stresses induced by a single expanding SFS particle can be computed, which can be used to assess the \"usability criteria\" of the SFS aggregates to be used in bound applications [5]. * _Disruption ratio test_. This test also uses autoclave conditions but determines the percentage of SFS aggregates that cracked or powdered after autoclaving [136]. This test can be used as a rapid indexing test for volumetric stability of SFS aggregates.