# A Study on Reactive Ultra-Fine Fly Ash and Sulfoaluminate Cement in Self-Leveling Mortar
## 2 Materials and Methods  
### Materials  
In this study, we used Type I Portland cement with a specific gravity of 3.15 and a surface area of 331 m\({}^{2}\)/kg. SAC had a specific gravity of 2.876, and its surface area, tested with BET, was 16,376 cm\({}^{2}\)/g. PUFA had a specific gravity of 2.2, with a BET surface area of 36,694 cm\({}^{2}\)/g; at 7 days, its activity index was 110.29%, and at 28 days, the activity index increased to 128.84%. Figure 1 shows an SEM image of PUFA, displaying a spherical structure that is similar to that of conventional fly ash. Therefore, the ball bearing effect [24], which increases the flowability of mortar and concrete, of PUFA is similar to that of conventional fly ash. Figure 2 presents the XRD pattern of PUFA (the QXRD analysis indicates a crystallinity of 7.4% and an amorphous content of 92.6%), which indicates that PUFA has an amorphous structure that is similar to those of silica fume and metkaoolin. The XRD diffractometer is a product of Riaku Miniflex, and the specification of the apparatus is a maximum of 40 kV/15 mA. The amorphous phase of PUFA implies better chemical activity; that is, the pozzolanic reaction of PUFA occurs faster than for conventional fly ash. In addition, the small size of PUFA also increases the chemical activity. Although there exist numerous studies focusing on the use of conventional fly ash for making mortar or concrete, how to use PUFA appropriately with other raw materials and the corresponding engineering properties still requires to be investigated in depth. Figure 1: PUFA high-magnification SEM image. The fine aggregate had a specific gravity of 2.63, a water absorption of 2.51%, and a fineness modulus of 2.97. The sieve analysis of the fine aggregate is tabulated in Table 1. To achieve consistent workability meeting the specification requirements, a high-performance polycarbonate superplasticizer was added. The superplasticizer had a specific gravity of 1.05, and its usage ranged from 0.3% to 2.0% of cement weight. The chemical composition of Type I Portland cement, SAC, and PUFA is shown in Table 2.  
In the following, the reasons why SAC and PUFA were used are explained. In this study, SAC was chosen for its early strength development and ability to reduce drying shrinkage. However, SAC has a lower specific weight than Type I Portland cement, leading to segregation as SAC floats to the surface of mortar. To prevent this, PUFA or conventional fly ash can be used to improve the consistency of mortar. However, considering that SAC, although it can provide strength at an early age, shows worse strength at a late age, some \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sieve No.** & **Individual Retained (\%)** & **Cumulative Retained (\%)** \\ \hline \#4 & 1.2 & 1.2 \\ \hline \#8 & 25.4 & 26.6 \\ \hline \#16 & 23.6 & 50.2 \\ \hline \#30 & 15.9 & 66.1 \\ \hline \#50 & 11.9 & 78.0 \\ \hline \#100 & 6.9 & 84.9 \\ \hline Bottom & 15.1 & – \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Sieve analysis of fine aggregates. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Type I** & **SAC** & **Reactive Ultra-Fine Fly Ash** \\ \hline SiO\({}_{2}\) & 21.04 & 0.368 & 68.58 \\ \hline Al\({}_{2}\)O\({}_{3}\) & 5.46 & 43.14 & 18.95 \\ \hline Fe\({}_{2}\)O\({}_{3}\) & 2.98 & 1.588 & 0.04 \\ \hline CaO & 63.56 & 39.839 & 0.13 \\ \hline MgO & 2.52 & - & 0.22 \\ \hline SO\({}_{3}\) & 2.01 & - & 0.55 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Chemical composition of materials (%). Figure 2: X-ray diffraction pattern showing the amorphous structure of PUFA. pozzolanic material as a supplementary cementitious material is necessary to compensate for the strength loss. It is well known that conventional fly ash contributes little to strength development, which is instead fostered by pozzolanic material with higher strength activity. Silica fume, or metakaolin, is a possible candidate.