## 2 Materials and Experimental Program
All samples were cured in a humidity chamber at 23 \({}^{\circ}\)C with greater than 99% relative humidity for all curing periods. The flows of fresh cement paste samples were tested by using a flow table in accordance with the ASTM C1437 [25]. Each fresh paste was placed in a mold with a bottom inner diameter (= base diameter) of 100 mm, a top inner diameter of 70 mm, and a height of 50 mm. After the mold was lifted away, the flow table was dropped 25 times in 15 s; then, the diameter of a spread paste was measured 4 times, and their average diameter was determined. Flow value was obtained by (average diameter-inner base diameter)/inner base diameter \(\times\) 100. The compressive strength tests were conducted with a universal testing machine (1500 HDX; Instron, Norwood, MA, USA) at 1 day, 7 days, and 28 days of curing for all samples. For TG, XRD, and chloride binding tests, fractured pieces were collected after strength testing and ground. To cease any further reaction and remove any remaining water, all prepared samples were stored in isopropanol and dried in a vacuum desiccator according to a method previously described in the literature [26]. For the SEM testing, the hardened samples were sliced into 2 mm-thick pieces and mounted using an epoxy resin; then the mounted samples were polished with an EcoMet 250 Grinder-Polisher (Buehler, Lake Bluff, IL, USA). The XRD patterns of the hardened paste samples were collected using the same instrument and conditions used for the XRD of the CSA cement, at 1 day, 7 days, and 28 days. The XRD patterns were examined with the International Center for Diffraction Data (ICDD) PDF-2 database and the Inorganic Crystal Structure Database (ICSD) [27]. The TG tests were conducted at 1 day and 28 days of curing using a simultaneous thermal analyzer (SDT Q600, TA Instruments, New Castle, DE, USA) from room temperature to 1000 \({}^{\circ}\)C with a heating rate of 10 \({}^{\circ}\)C/min in an N\({}_{2}\) condition using an alumina pan. The chloride binding tests were carried out to measure the contents of free and bound chlorides in hardened pastes at 28 days of curing. The Korean Standard (KS) F 2714 [28], which is similar to the American Society of Testing and Materials (ASTM) C1218, was used to measure the acid-soluble total chloride contents. In addition, the KS F 2715 [29], which is similar to the ASTM C1152, was used to obtain the water-soluble free chloride contents. Backscattered electron (BSE) images were taken only for the CG and ROG samples because (1) the ROG mixture in Table 4 was selected to be used for brick production at the end of this study based on the results of strength testing, XRD, TG/DTG, and chloride binding, and (2) comparing the microstructure between CG and ROG might provide useful insights into the influence of the RO reject water. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Group**} & \multirow{2}{*}{**Label**} & \multicolumn{3}{c}{**Binder**} & \multicolumn{3}{c}{**Water**} & \multirow{2}{*}{**w/b**} \\ \cline{3-3} \cline{5-7}  & & **CSA** & & & & \\ \hline \multirow{4}{*}{Without gypsum} & C & 100 & - & 50 & - & - \\  & SW & 100 & - & - & 50 & - \\ \cline{1-1}  & RO & 100 & - & - & - & 50 \\ \cline{1-1}  & CG & 85.04 & 14.96 & 50 & - & - \\ \cline{1-1}  & SWG & 85.04 & 14.96 & - & 50 & - \\ \cline{1-1}  & ROG & 85.04 & 14.96 & - & - & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mixture proportions of paste samples (wt%). The BSE images were obtained using ultra-high-resolution field emission scanning electron microscopy (FE-SEM, Hitachi S-4800, Tokyo, Japan) with energy dispersive spectroscopy (EDS). Triplicate brick samples were produced using mortar with water, binder, and sand in a weight ratio of 0.6:1.0:3.0, respectively as in Table 5. Mixture proportion of bricks (kg/m3).. ROG in Table 4 was selected as a binder mixture proportion for brick production, and this will be discussed in the results and discussion sections of this study. The dimensions of the brick were 190 mm \(\times\) 90 mm \(\times\) 57 mm.