## 2 Derivation of Appropriate Mixing Ratio for SFRM
### Workabiliy Tests  
Plastering work requires fresh mortar to have adhesion enough to prevent flowing down on the vertical face of masonry walls. However, workability represented in the form of a specific slump or flow appropriate for plastering work of fresh mortar is not clearly prescribed in Korean Industrial Standards (KS) and Korean Construction Specifications (KCS) such as KS F 4716 [24], KS F 2262 [25], KCS 41 16 01 [26] and KCS 41 16 02 [15], which only provide testing methods for hardened mortar or specifications for plastering work. Instead, recommended values of flow were found from the literature survey. [PERSON] (2009) [27] suggested an appropriate flow range of lightweight mortar mixed with gypsum, of which fire resistance performance was tested, from 170 to 210 mm. [PERSON] (2010) [28] suggested a flow of 180 mm suitable for constructability in a study of diverse mortar for interior finishing plaster. In this study, the target flow of SFRM was determined to be 180 mm in light of preceding research. Flow table tests for various mixing ratios of SFRM were carried out in accordance with KS L 5111 [29]. Measured flow values are plotted with respect to the fiber volume fraction in Figure 2. The flow value obtained for S/C20-W/C25-AD01 containing superplasticizer, and S/C20-W/C50 and S/C20-W/C50 with a relatively high water-cement ratio exceeded the target, 180 mm, by 20 mm or higher. The fiber volume fraction does not have clear influence on the flow for those specimens. However, flow values for other specimens are lower than 200 mm and tend to decrease slowly as the fiber volume fraction increases. The three groups of specimens corresponding to S/C20-W/C40, S/C15-W/C35, and S/C10-W/C32 had flow values that were adequately close to the target, 180 mm. \begin{table}
\begin{tabular}{c c} \hline
**Type** & **Amorphous Steel Fiber** \\ \hline Specific gravity & 7.25 \\ \hline Tensile strength (MPa) & 1400 \\ \hline Fiber thickness (\(\upmu\)m) & 24 \\ \hline Fiber length (mm) & 15 \\ \hline Fiber width (mm) & 1 \\ \hline Slenderness & 83 \\ \hline Equivalent diameter (mm) & 0.18 \\ \hline Shape & Flat and straight \\ \hline \end{tabular}
\end{table} 
Table 3: Properties of amorphous steel fiber [23]. Figure 2: Flow of SFRM. The adhesion of SFRM to bricks was tested using a procedure proposed by the authors, since test methods and acceptance criteria for the adhesion of fresh mortar are not specified in the Korean or international standards investigated by authors, as mentioned above. The test method is to check the deflection of the plastered SFRM in 1 min after a trial plastering of SFRM with a thickness of 2.5 mm as shown in Figure 3, and the measured flow values and overlayable thickness are summarized in Table 4. The trial plastering and measurement of the deflection was conducted repeatedly and recorded. The adhesion of SFRM for each trial plastering was evaluated as good, normal, and poor for a deflection of 0, 2, and 5 mm, respectively. The maximum plastered thickness for which accumulated total deflection was restrained under 2 mm are summarized as the overlayable thickness in Table 4. The overlayable thickness for SFRM tends to decrease gradually as the fiber volume ratio increases. The S/C20-W/C25-AD01 specimen containing superplasticizer and the S/C20-W/C50 with a relatively high water-cement ratio show relatively low overlayable thickness that does not exceed 7.5 mm. The low overlayable thickness may lengthen the construction periods because subsequent plastering shall be conducted on previous overlay, which hardened sufficiently. On the other hand, the two mixing ratios of S/C20-W/C45 and S/C10-W/C32 showed good adhesion performance with all the overlayable thickness higher than or equal to 10 mm in Table 4. Based on the adhesion test result, the thickness of the SFRM for a single trial of plastering was decided to be 10 mm for the production of strengthened masonry prism specimens