# A Review of the Influence of Steel Furnace Slag Type on the Properties of Cementitious Composites
## 6 Recommendations  
Because of different production processes, fluxing agents, steel chemistries, and so forth, the properties of SFS can vary greatly. Therefore, to qualify a given SFS stock  
Figure 1: Compositional BSE micrographs at the edge of a (**a**) BOF slag and (**b**) EAF slag particle. The BOF slag particle exhibited a surface composition that was compositionally different from the interior of the particle, whereas the EAF slag particle appeared to have similar surface and interior compositions. concrete or other bound applications, it is recommended that the following tests be performed at a minimum, listed in order of suggested importance:  
1. _Free CaO_. The hydration of CaO yields a volume expansion of 92% and reacts quicker than free MgO. Initial or early-age expansion can be expected to be attributable to free CaO. Therefore, estimating the free CaO content is a rapid method to quickly assess an expansion potential. The common method to evaluate free CaO content is with ethylene glycol extraction and complexometric titration, which can also be coupled with TGA to provide a more precise quantification of free CaO and Ca(OH)\({}_{2}\). 2. _Expansion test_. The most concerning effect of using SFS in bound applications is expansion that can result in structural failure. A number of accelerated and long-term expansion tests have been proposed in the literature, so the data are insufficient to recommend a specific test method. The allowable expansion depends on the specific application of SFS, so no limits are recommended. For the routine utilization of SFS, one recommendation is to select a specific expansion test and develop a testing history to empirically determine what limit(s) is permissible for a given application. Accelerated expansion tests can also be used to rapidly screen a given SFS stock, such as to track weathering progress. 3. _Mineral composition_. Qualitative XRD can be used to quickly identify the presence of crystalline phases that can be involved in deleterious reactions. Quantitative XRD can be used to determine the relative amounts of crystalline and amorphous phases. Due to fluorescence issues with Cu K\(\alpha\) radiation and iron-bearing phases, an appropriate anode should be considered, such as Co K\(\alpha\) radiation. 4. _Concrete mechanical properties_. In conjunction with the above recommended tests, the mechanical properties of concrete with SFS aggregates should be tested to confirm whether or not the design minimum properties are met. Given that the SFS aggregates can have a varied effect on concrete mechanical properties, as demonstrated in Table 2, testing the concrete mechanical properties can quickly screen a given SFS stock for appropriateness as an aggregate. 5. _Chemical composition_. The elemental composition of the SFS should be assessed, particularly if heavy metals are of concern. However, this composition is arguably not as useful as the other tests since it does not provide any information on expansion potential (e.g., there is no distinction between Ca in free CaO and bound in a mineral phase). In addition to the above tests, further recommended testing can be conducted if needed. These secondary tests include the following, listed in order of suggested importance:  
1. _Concrete durability properties_. Given that the SFS aggregates can have a varied effect on concrete durability properties, as demonstrated in Table 2, various tests can be performed to assess and predict the performance of the concrete. The specific tests should be selected based on the expected environmental conditions of the in-service concrete. If SFS expansion may be an issue, based on the results of the recommended primary tests above, then both early-age and long-term durability properties should be assessed to consider hydration of free CaO and free MgO, respectively. 2. _Microstructural characterization_.