## 2 Materials and Methods
### Experimental Program
#### 2.2.2 Test Procedures  
1. Compressive strength: The test was performed with reference to the Chinese national standard GB/T17671-1999 [22]. 2. The capillary water absorption coefficient test was carried out according to ASTM C1585 [23]. The specimens were first dried in an oven at 40 \({}^{\circ}\)C for 7 days, then placed in a drying dish at 20 \({}^{\circ}\)C for 48 h to achieve a uniform distribution of relative humidity inside the specimens and, finally, sealed around with aluminum foil tape (exposing the bottom surface). The 40 mm \(\times\) 40 mm surface was immersed in water to a height of 3-5 mm and the mass of the specimen was weighed at 1, 3, 5, 8, 12, 16, 20, 25, 30, 35, 40, 45, 50, 55 and 60 min (after which, the mass of the specimen was basically stable). Then, the water absorption rate coefficient was calculated according to the following formula: \[i=a+St^{0.5}\] where \(i\) is the volume of water absorbed per unit area (mm\({}^{3}\)/mm\({}^{2}\)); \(S\) is a material constant called the sorptivity (mm/min\({}^{0.5}\)); \(a\) is a constant (mm); and \(t\) is the time elapsed (min). 3. Isothermal calorimetry: A hydration heat test was performed using an I-CAL4000/8000 isothermal calorimeter from Calmetrix, MA, USA. The test should be conducted in a 25 \({}^{\circ}\)C environment, and the instrument should be run for 24 h before the experiment to ensure the stability of the instrument. The water and alkali activator needed for the experiment also needed to be put into the apparatus in advance so that their temperature was kept at 25 \({}^{\circ}\)C. For the test, the total water-cement ratio was maintained at 0.4 and the effect of the incorporation of sodium stearate on the heat of the hydration of the alkali-activated slag-red mud-steel slag was determined. After weighing the cementitious material proportionally, the material was quickly mixed, homogenized and immediately placed in the test channel, and the test time was updated to start the test. The instrument recorded data every minute for 72 h.
4. Resistivity test: The CCR-3 induction resistivity of China Zhongheng Gang ke was used for the test. The mold was installed in advance, the stirred paste was poured into the mold, the paste in the mold was gently shaken up and down several times by hand on the standoffs and, finally, the mold was sealed well. The temperature was kept at around 20 \({}^{\circ}\)C during the test. 5. FTIR analyses: To determine the chemical groups in the reaction products, an FTIR analysis was performed using the KBr particle method. The 28-day paste samples were dried in an oven (temperature: 40 \({}^{\circ}\)C) for 3 days, and then the samples were crushed and ground into a powder. The tests were performed using a Thermo Nexus 470 Fourier-transform infrared spectrometer (FTIR) from Nicolet, USA. The tests were acquired using a resolution of 8 cm\({}^{-1}\) and a 64-scan program to obtain the IR spectral data in the wavelength range of 400 to 4000 cm\({}^{-1}\). 6. X-ray diffraction (XRD): Prior to testing, 28-day-old paste samples were dried in a drying oven at 40 \({}^{\circ}\)C and ground to a powder with a mortar that was able to pass through a 200-mesh square-hole sieve; then, the sample under the sieve was collected for X-ray diffraction testing and analysis. The crystalline phases in the samples were \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Group** & **NaOH/g** & **Sodium Silicate/g** & **Sand/g** & **Water/g** & **Slag/g** & **Red Mud/g** & **Steel Slag/g** & **NaSt/g** \\ \hline AASRSS/Control & 15.55 & 118.25 & 1350 & 114.38 & 180 & 180 & 90 & – \\ AASRSS/0.5\% & 15.55 & 118.25 & 1350 & 114.38 & 180 & 180 & 90 & 2.25 \\ AASRSS/1.5\% & 15.55 & 118.25 & 1350 & 114.38 & 180 & 180 & 90 & 6.75 \\ \hline \end{tabular}
\end{table} 
Table 2: AASRSS mortar mixture proportions (per group). identified using a PANantical X'Per PRO diffractometer with a 40 kV voltage, a 40 mA current and a scanning speed of 2\({}^{\circ}\)/min. The scanning range was 5\({}^{\circ}\) to 80\({}^{\circ}\) (20). 7.