## 3 Materials and Methods
### Test Method  
(1) Dry shrinkage test: The dry shrinkage test was conducted in accordance with the Test Method for Dry Shrinkage of Cement Mortar in China (JC/T 603-2004), and the mix proportions are shown in Table 2. The modified sodium silicate solution with the appropriate modulus and alkali equivalent was prepared 24 h in advance, then the \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Mix ID** & **a W/b B** & **RP** & **Slag** & **c W** & **NaOH** & **Na2 SiO3** \\ \hline RP-S0-M1.3N6 & 0.35 & 500.00 & 0.00 & 107.95 & 23.09 & 142.42 \\ RP-S15-M1.3N6 & 0.35 & 425.00 & 75.00 & 107.95 & 23.09 & 142.42 \\ RP-S30-M1.3N6 & 0.35 & 350.00 & 150.00 & 107.95 & 23.09 & 142.42 \\ RP-S45-M1.3N6 & 0.35 & 275.00 & 225.00 & 107.95 & 23.09 & 142.42 \\ \hline RP-S30-M0.9N6 & 0.35 & 350.00 & 150.00 & 132.75 & 27.90 & 98.60 \\ RP-S30-M1.1N6 & 0.35 & 350.00 & 150.00 & 120.35 & 25.49 & 120.51 \\ RP-S30-M1.5N6 & 0.35 & 350.00 & 150.00 & 95.55 & 20.69 & 164.33 \\ RP-S30-M1.7N6 & 0.35 & 350.00 & 150.00 & 83.15 & 18.28 & 186.24 \\ \hline RP-S30-M1.3N3 & 0.35 & 350.00 & 150.00 & 141.48 & 11.54 & 71.21 \\ RP-S30-M1.3N9 & 0.35 & 350.00 & 150.00 & 74.43 & 34.63 & 213.63 \\ RP-S30-M1.3N12 & 0.35 & 350.00 & 150.00 & 40.91 & 46.18 & 284.84 \\ RP-S30-M1.3N15 & 0.35 & 350.00 & 150.00 & 7.38 & 57.72 & 356.06 \\ \hline \end{tabular}  
* W (Water content) = water content of Na2 SiO3 solution + \({}^{\star}\) W. \({}^{\mathrm{b}}\) B = RP + S + solid content of Na2 SiO3 solution.
* W—additional water.  
\end{table} 
Table 2: The mixture proportions of RPSG. Figure 4: The particle size distribution of RP. modified sodium silicate solution was mixed with RP and slag and poured into the cement mortar mixer. After stirring on low speed for 3 min, a scraper was used to scrape up the slurry from the bottom of the mortar mixing pot and stir manually for 2 min, then stirring continued on high speed for 3 min. The mixed slurry was rapidly poured into a 25 mm \(\times\) 25 mm \(\times\) 280 mm mold with embedded metal nails at both ends. After 20 s of vibrating, it was cured with plastic film at room temperature for 48 h, then stripped and transferred to 20 \(\pm\) 2 \({}^{\circ}\)C and 50 \(\pm\) 5% relative humidity for 28 days of dry shrinkage curing. BC-300 cement length meter was used to measure the size change, and the length was measured once every 24 h. Each group contained 3 specimens, and the average value of the results was analyzed. (2) Capillary porosity test: According to Table 2, the rectangular specimens with 40 mm \(\times\) 40 mm \(\times\) 40 mm were wrapped by film under standard conditions for 28 days, and then crushed into pieces. The capillary porosity of the pieces was determined using the saturated water method [45]. (3) Rapid efflorescence test: The specimen preparation method was the same as that of the capillary porosity test. The specimens were wrapped in plastic film and maintained for 28 days under standard conditions, then placed in plastic containers with an appropriate amount of tap water so that the bottom of the specimen was immersed in water for approximately 5 mm. A camera was used to record the images of the specimens over time. The temperature and relative humidity during the experiment were 25 \({}^{\circ}\)C and 55%, respectively. During the test, the proper amount of water was added to the plastic container every 5 h to maintain a fixed water level at the bottom of the specimen. After 7 days, the addition of water to the container was stopped, and the water in the container underwent complete evaporation. The white crystals and broken epidermis on the surface of the specimens were scraped out with a spatula and then weighed. (4) PH value test: The specimens were crushed into granules from 28 days of film curing. Solid particles with a size range of 0.6-1.18 mm were selected, and then immersed in purified water. The pH value of the immersion solution was measured every 10 min for the first hour.