# Experimental Study on the Workability and Stability of Steel Slag Self-Compacting Concrete
## Materials and Methods
### Raw Materials
#### 2.1.4 Aggregates  
Natural gravel particles with grading of 5-16 mm were used as coarse aggregate. Some basic properties of coarse aggregate were listed in Table 5.  
Steel slag sands, which were accumulated a long time for aging, and natural river sand were used as fine aggregates. According to Chinese standard GB/T 14684-2011 [29], the physical properties of both natural and steel slag aggregates were measured and are given in Table 6; a sieve analysis was conducted and the results are shown in Figure 1. The chemical composition of steel slag is presented in Table 7. The X-ray diffraction (XRD) analysis results are shown in Figure 2a.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Admixture** & **Solid** & **PH Value/\%** & **Alkali** & **Water** & **Dosage Range/wt** \\
**State** & **Content/wt \%** & **Content/wt \%** & **Reducing** & **\% (Proportion to** \\  & & & **Rate/\%** & **Binder)** \\ \hline Liquid & 2.04 & 0.75 & \(\leq\)2.0 & 30\% & 0.8–1.5 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Basic performance parameters of the polycarboxylic high-performance superplasticizer (JMPCA).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Fineness/(m\({}^{2}\)/kg)** & **Setting Time/min** & **Compressive Strength/MPa** & **Flexural Strength/MPa** \\ \cline{2-5}  & **Initial** & **Final** & **3d** & **28d** & **3d** & **28d** \\ \hline \(\geq\)350 & \(\geq\)60 & \(\leq\)280 & 24.5 & 49.0 & 4.8 & 8.4 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Basic properties of cement.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Admixture** & **Cushing Index** & **Needle and** & **Nud Content/wt \%** & **Water Content/wt** \\
**Density/(kg/m\({}^{3}\))** & **Crushing Index** & **Flake/wt \%** & **Nud Content/wt \%** & **\%** \\ \hline
2678 & 11.8\% & 6.3\% & 0.2\% & 0.6\% \\ \hline \hline \end{tabular}
\end{table}
Table 5: Physical properties of coarse aggregates.  
As the surface of steel slag sand is rough and porous, which has better water absorption than natural sand, it will have a greater impact on the workability of SSCC. Therefore, it is necessary to measure the water absorption of steel slag sand before the experiment. We took 1200 g of dried steel  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type of Fine** & **Apparent** & **Fineness Modulus** & **Nud Content/wt \%** &
\begin{tabular}{c} **Water** \\ **Content/wt \%** \\ \end{tabular} \\ \hline Natural river sand & 2580 & 2.4 & 1.2 & 2.8 \\ Steel slag sand & 3590 & 3.9 & - & 1.2 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Physical properties of fine aggregates.  
Figure 1: Grading of fine aggregates according to sieving analysis test.  
Figure 2: X-ray diffraction (XRD) and water absorption experimental results of steel slag used as fine aggregates in self compaction concrete: (**a**) XRD test results; (**b**) water absorption.  
slag sand as a sample for the test and measured water absorption of the sample. The test results are shown in Figure 2b.  
According to Table 7 and Figure 2a, the steel slag used is basically composed of crystalline minerals, and the content of amorphous material is very low. The main mineral components of the steel slag aggregate were calcium silicate, Ca(OH)\({}_{2}\), f-CaO, RO phase (RO phase is a broad solid solution formed by melting FeO, MgO, and other divalent metal oxides such as MnO) and CaCO\({}_{3}\). Because the steel slag has been stored in the open air for a long time, some f-CaO has reacted with water to form Ca(OH)\({}_{2}\), and some has carbonated to CaCO\({}_{3}\). The decrease of f-CaO reduces the expansion effect when being used in concrete, which is beneficial to the volume stability of SSCC.  
From Figure 2b, it can be seen that the water absorption rate of steel slag sand increases rapidly in the first 4 h. Therefore, it has a great influence on the workability of SSCC, especially the fluidity and anti segregation performance of a fresh concrete mixture. It is necessary to control the time interval from mixing to pouring the concrete mixture.