# An Experimental Study on Alkali Silica Reaction of Concrete Specim Using Steel Slag as Aggregate
## 3 Results and Discussion
### Evaluation Expansion Properties of Concrete with Steel Slag
#### 3.3.3 Evaluation of Crack Number and Crack Width in Concrete Specimens Due to ASR  
We evaluated the number of cracks and their width to investigate the crack patterns due to ASR. Table 6 shows the number of cracks, the crack width, the maximum crack length, and the total crack length in the surface of the concrete specimens. The cracks in concrete specimen were retraced on the Auto CAD program for calculating the crack width, maximum crack length, and total crack length. The maximum and total crack lengths increased with the increase in the duration of the test period, regardless of the type of binder. Moreover, the expansion in the concrete specimens was 0.04% higher, and the maximum crack length exceeded 100 mm after 14 days.  
In the specimens with OPC, the number of cracks, the crack width, and the length of the cracks increased with the increase in the duration of the test period. The crack width after 14 days is higher than the allowable maximum crack width specified by ACI 224R. Currently, there is no design code for the crack limit width caused by ASR when designing the concrete structures.  
Moreover, using steel slag as the coarse aggregate in concrete significantly affects ASR. Consequently, for concrete specimens using steel slag as the coarse aggregate, we must determine a method that provides improved resistance against ASR.  
In contrast, in the concrete specimens with mineral admixture, the number of cracks, crack area, and crack width are decreased after 14 days as the expansion reduced. It appears that the number of cracks after 7 days were lower than the number of cracks at crack initiation. Essentially, as the cracks are developed and connected to each other, the number of cracks reduced, however, maximum crack length and total crack length is continuously increased.  
While the ASR expansion was within the permitted limit defined by ASTM C 1293 [24], the maximum and total crack lengths in the specimens with BFS30 were longer than those in the specimens with FA20. However, this trend was reversed when the expansion exceeded the permitted limit. Despite the fact that the expansion rate of the concrete with FA20 was lower than that of the concrete with BFS30, the BFS30 reduced the maximum and total crack lengths after 14 days more efficiently than the FA20. This implies that the crack length is directly affected by mineral admixtures. Therefore, to accurately predict the level of deterioration due to ASR, we must not only evaluate the expansion rate but also develop indicators such as the crack pattern.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Specimen ID** & \begin{tabular}{c} **Test Period** \\ **(days)** \\ \end{tabular} & \begin{tabular}{c} **Number of** \\ **Cracks** \\ \end{tabular} & \begin{tabular}{c} **Crack Width** \\ **(mm)** \\ \end{tabular} & \
\begin{tabular}{c} **Maximum Crack Length** \\ **(mm)** \\ \end{tabular} &
\begin{tabular}{c} **Total Crack Length** \\ **(mm)** \\ \end{tabular} \\ \hline \multirow{3}{*}{OPC} & 2 & 7 & 0.2 & 11.59 & 63.95 \\  & 7 & 21 & 0.25 & 96.18 & 699.23 \\  & 14 & 37 & 0.4 & 173.06 & 1444.75 \\ \hline \multirow{3}{*}{FA20} & 3 & 19 & 0.05 & 15.57 & 158.12 \\  & 7 & 12 & 0.2 & 47.75 & 333.30 \\  & 14 & 17 & 0.3 & 160.35 & 1031.31 \\ \hline \multirow{3}{*}{BFS30} & 5 & 14 & 0.05 & 21.98 & 131.39 \\  & 7 & 10 & 0.15 & 71.19 & 399.13 \\ \cline{1-1}  & 14 & 17 & 0.3 & 104.16 & 694.78 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Crack properties of concrete specimens (length, width, etc.).