# Experimental Study on the Workability and Stability of Steel Slag Self-Compacting Concrete
## Materials and Methods
### Mix Proportion  
Considering the influence of steel slag sand on the workability of concrete, the volume percentage of steel slag (VPS) replacing natural sand was used as a variable parameter to design the mix proportion of concrete. The volume replacement rate of steel slag used in mix proportion were 0.0%, 20%, 40%, 60%, 80% and 100% respectively. In the experiment, the influence of steel slag on the workability of SSCC was investigated keeping concrete mix proportion unchanged by changing the amount of steel slag in each group of concrete specimen. The codes of different groups relating to the mix proportion of concrete were explained according to the substitution rate of steel slag to natural san, as shown in Table 8.  
After the analysis, calculation and adjustment of the preliminary experiments, mix proportion of the reference group (S\({}_{0}\)SCC) of SSCC was determined as shown in Table 9. Then, the mix proportion of each group of SSCC can be preliminarily designed according to the different VPS as shown in Table 8.  
In the workability experiment of fresh SSCC prepared with the reference mix proportion, the workability of SSCC declined with the gradual increase of the steel slag sand amount (substitution rate). When the amount of steel slag sand was more than 20%, the fresh SCC mixture made it difficult to achieve the design goal of workability.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Group** & **Code** & **Name** \\ \hline A & S\({}_{0}\)SCC & Ordinary self-compacting concrete \\ \hline B & S\({}_{20}\)SCC & Self-compacting concrete with equal volume of steel slag sand instead of 20\% natural fine aggregate \\ \hline C & S\({}_{40}\)SCC & Self-compacting concrete with equal volume of steel slag sand instead of 40\% natural fine aggregate \\ \hline D & S\({}_{60}\)SCC & Self-compacting concrete with equal volume of steel slag sand instead of 60\% natural fine aggregate \\ \hline E & S\({}_{80}\)SCC & Self-compacting concrete with equal volume of steel slag sand instead of 80\% natural fine aggregate \\ F & S\({}_{100}\)SCC & Self-compacting concrete with equal volume of steel slag sand instead of 100\% natural fine aggregate \\ \hline \hline \end{tabular}
\end{table}
Table 8: Substitution of steel slag mixture in different groups.  
The reason is that the water absorption of steel slag sand is larger than that of natural sand and the particle surface is rough, so the free water in the mixture is relatively lower under the same water consumption, which makes the flow performance of the concrete worse. The void fraction of accumulated steel slag sand particles is bigger, and needs more cement slurry to wrap particles' surface and fill the gap between and particles, so that when the content of steel slag sand was 100%, the anti segregation performance of concrete mixture decreased obviously, and the mixture almost fell into scattered particles.  
Therefore, based on the preliminary experiment and cause analysis of the influence of the VPS on the S\({}_{0}\)SCC, guided by the predetermined workability design goal, the mix proportion of SSCC with ideal workability under different VPS was finally obtained after constantly changing the proportion of raw materials in SCC. In adjusting mix proportion, the water-binder ratio (W/B) remained unchanged as much as possible. Being trial mixed mainly by adjusting the amount of superplasticizer, the volume of cement slurry and the slurry-aggregate ratio of the mixture, the basic workability of the SSCC with different VPS was tested and analyzed. It should be pointed out that when design mix proportion was S\({}_{100}\)SCC, which is due to the large water demand of the mixture, it was difficult to meet the workability goal if keeping unchanged the original mix proportion (W/B = 0.40). Therefore, the water binder ratio of the S\({}_{100}\)SCC groups was adjusted to 0.42. The mix proportion of SSCC which satisfied the workability design goal after adjustment i shown as Table 9.