## 2 Materials and Methods
### Experimental Program
#### 2.2.2 Test Procedures  
1. Density and specific surface area test: The density test of raw materials refers to the Chinese National Standard GB/T 208-2014 Cement Density Determination Method [12]. The specific surface area test refers to the Chinese National Standard GB/T 8074-2008 Cement-Specific Surface Area Determination Method: Burr's Method [13].
2. Mechanical performance test: Referring to Chinese National Standard GB/T 17671-1999 Test Method For Cementitious Sand Strength (ISO Method) [14], the flexural strength and compressive strength of mortar specimens were tested at 3 d, 7 d, and 28 d.
3. Isothermal calorimetry: The hydration process of the slurry was monitored using isothermal calorimetry (TAM Air Thermometric, I-CAL4000/8000 made by Calmetrix Corporation, Boston, MA, USA, set at 25 \({}^{\circ}\)C). Manual stirring was performed, using a disposable spoon for 1 min to achieve the desired homogeneity. After stirring, the spoon was left in the sample cup to minimize the sample mass loss. Measurements were performed every minute for 72 h.
4. XRD analysis: The block samples of 3 d and 28 d were dried in a vacuum-drying oven at 40 \(\pm\) 5 \({}^{\circ}\)C and then ground through 200 square mesh hole sieves with agate mortar powder. Next, a certain amount was taken with a medicine spoon, pressed into a mold, and tested using an X-ray diffractometer (PANalytical's XPert Pro X-ray). The test diffraction angle was 5-80\({}^{\circ}\), the dwell time was 0.5 s, and the scanning speed was 0.02\({}^{\circ}\)/min to identify the crystalline phase of the sample.
5. TG-DTG analysis: The 28 d lump samples were dried in a vacuum oven at 40 \({}^{\circ}\)C \(\pm\) 5 \({}^{\circ}\)C and then ground through 200 square mesh hole sieves with agate mortar powder. Next, a certain amount was spooned into a crucible and tested using a thermogravimetric analyzer (Q 5000 IR) with an air atmosphere and a heating rate of 10 \({}^{\circ}\)C/min for the analysis of the hydration products of the samples.
6. Pore structure analysis: After the block sample at 28 d was cut with a precision cutter about a size of 1 cm \(\times\) 1 cm \(\times\) 1 cm or so, the sample was dried in a vacuum drying oven at 40 \({}^{\circ}\)C \(\pm\) 5 \({}^{\circ}\)C to obtain the final product. The pore structure of the  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & **OPC** & **SS** & **RM** & **EMR** & \
\begin{tabular}{c} **Sand–Binder** \\ **Ratio** \\ \end{tabular} &
\begin{tabular}{c} **Water–Binder** \\ **Ratio** \\ \end{tabular} \\ \hline A0 & 70 & 30 & 0 & 0 & & \\ A1 & 70 & 15 & 15 & 0 & & \\ A2 & 70 & 15 & 12 & 3 & & \\ A3 & 70 & 15 & 9 & 6 & 1:3 & 0.5 \\ A4 & 70 & 15 & 6 & 9 & & \\ A5 & 70 & 15 & 3 & 12 & & \\ A6 & 70 & 15 & 0 & 15 & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Experimental proportioning (wt%).  
mortar specimen was tested and analyzed by a high-performance automatic mercury pressure instrument.
7. Calculation method of activity index: Referring to Chinese National Standard GB/T 51003-2014 Technical Specifications For The Application Of Mineral Dopants, [15], the activity index of composite mortar was calculated according to the following formula, using pure cement group as the reference group. \[A=\frac{R_{t}}{R_{0}}\times 100\] where \(A\)--activity index (%); \(R_{t}\)--compressive strength of the examined sand at the corresponding age, in MPa; \(R_{0}\)--compressive strength of contrasting colluvium at the corresponding age, in MPa.