*2.3. Test Methods*

### (1) Mechanical property

The compressive strength of concrete was tested in accordance with Chinese standard GB/T 50,081 (standard for test methods of mechanical properties of ordinary concrete). Cube specimens of 100 mm × 100 mm × 100 mm were used to measure the compressive strength of concrete for 7 d, 28 d, 90 d and 360 d after curing to a specific age in a standard curing room (20 ◦C and 95 RH%).

### (2) Chloride permeability

After curing to a specific age in a standard curing room (20 ◦C and 95 RH%), the 100 mm × 100 mm × 100 mm cube specimens were cut into 100 mm × 100 mm × 50 mm specimens. The chloride permeability of concrete at 28 d and 360 d was measured according to ASTM C1202 (standard test method for chloride ion permeability resistance of concrete). The instrument model is CABR-RCP9. After installing the test block, 0.3 mol/L NaOH solution and 3 wt.% NaCl solution were prepared immediately (ensuring the accuracy of solution concentration), followed by injecting NaOH solution at the positive extreme and NaCl solution at the negative extreme without any liquid leakage. The measurement time was 6 h, and the electric flux of each group of concrete was recorded.

### (3) Sulphate-corrosion Resistance

The sulphate-corrosion resistance of 100 mm × 100 mm × 100 mm cube specimens was tested by the dry/wet cycle method [14]. Each sample was dried in an oven at 80 ± 5 ◦C for 6 h, cooled it for 2 h, and then soaked in Na2SO<sup>4</sup> solution with concentration of 5%. This process is one cycle (i.e., one dry wet cycle is completed in one day). At the same time, the samples with the same ratio were placed in the standard curing room for curing. After 120 and 150 cycles, the compressive strength of the specimens in the standard curing

room was measured as S1 and the compressive strength of concrete after the dry wet cycle was measured as S2. The strength loss rate was calculated according to the following Equation (2):

$$
\eta = (\text{S1} - \text{S2}) / \text{S1} \times 100\% \tag{2}
$$

### (4) Connected porosity

The connected porosity of concrete was measured by the "water saturation drying" method [15]. A piece of 10 cm × 10 cm × 2 cm concrete sheet was cut and prepared, the volume V of the test piece was measured by a drainage method, and the mass m<sup>1</sup> of the test piece after vacuum water saturation was measured. The test piece was dried in an oven at 80 ◦C for 14 d, and the mass m<sup>2</sup> after drying was measured. The connected porosity was calculated according to the following Equation (3):

$$\mathbf{P} = (\mathbf{m}\_1 - \mathbf{m}\_2) / \rho \mathbf{V} \tag{3}$$

where ρ is the density of water.

### (5) Hydration heat release

The Calmetrix 8000 HPC isothermal calorimeter was used to determine the hydration heat release of the sample slurry [16]. The test method meets the requirements of ASTM C1702-2015. The temperature was set at 25 ◦C to determine the heat release rate and total heat release of C, L-11 and L-22 within 72 h.

### (6) Adiabatic temperature rise

Concrete (C, L-11 and L-22) prepared according to the mix proportion was put into the concrete adiabatic temperature rise instrument to measure its adiabatic temperature rise. The amount of concrete used for each test was 40~45 L. The temperature control error was less than ±0.1 ◦C, and the minimum temperature resolution was 0.02 ◦C. The automatic data acquisition system collected data every 5 min, and guaranteed the concrete center temperature to be 0.1 ◦C higher than the concrete outer wall temperature during the measurement process.

### (7) Shrinkage property

The shrinkage deformation of concrete (C, L-11 and L-22) was measured by contact method. 100 <sup>×</sup> <sup>100</sup> <sup>×</sup> 400 mm<sup>3</sup> concrete specimen was molded. After demolding, the specimen was cured at room temperature for 7 days, and it was covered with plastic film to prevent moisture loss. After curing for 7 days, the plastic film was removed, then the deformation length was measured by a length comparator with a dial indicator (accuracy 0.001 mm) and calibrated before each measurement. The results were the mean of three groups of concrete.

### **3. Results and Discussion**

### *3.1. Compressive Strength*

Figure 1 shows the compressive strength (a) 7 d (b) 28 d (c) 90 d (d) 360 d of concrete mixed with different content of PLC. The compressive strength of the control sample (C) was ~35 MPa at the age of 7 days. When 20% cement was replaced by PLC, the compressive strength of L-1 decreased to ~30 MPa. However, when reducing the water/binder ratio from 0.425 to 0.418, the compressive strength of L-11 increased from ~30 MPa to ~35 MPa. When 33% cement was replaced by PLC, the compressive strength of L-2 further reduced to ~25 MPa. By comparison, when lowing the water/binder ratio from 0.405 to 0.39, the compressive strength of L-22 increased from ~25 MPa to ~35 MPa accordingly, indicating that reduction of water can make up for the loss of the early strength of concrete caused by adding PLC to a certain extent. However, at the age of 90 days and 360 days, the compressive strength of concrete mixed with 20% and 33% PLC was all around 50 MPa, indicating that the addition of PLC does not affect the long-term strength of concrete. When

the water/binder ratio decreased by 0.1–0.15, the long-term strength of concrete increased by ~10%, compared with the control sample. When the water/binder ratio decreased by 0.1–0.15, the long-term strength of concrete increased by ~10%, compared with the control sample.

MPa. When 33% cement was replaced by PLC, the compressive strength of L-2 further reduced to ~25 MPa. By comparison, when lowing the water/binder ratio from 0.405 to 0.39, the compressive strength of L-22 increased from ~25 MPa to ~35 MPa accordingly, indicating that reduction of water can make up for the loss of the early strength of concrete caused by adding PLC to a certain extent. However, at the age of 90 days and 360 days, the compressive strength of concrete mixed with 20% and 33% PLC was all around 50 MPa, indicating that the addition of PLC does not affect the long-term strength of concrete.

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**Figure 1.** Compressive strength of concrete mixed with PLC: (**a**) 7d (**b**) 28d (**c**) 90d (**d**) 360d. **Figure 1.** Compressive strength of concrete mixed with PLC: (**a**) 7 d (**b**) 28 d (**c**) 90 d (**d**) 360 d.

### *3.2. Chloride Permeability, Sulfate Attack and Connected Porosity 3.2. Chloride Permeability, Sulfate Attack and Connected Porosity*

Figure 2 shows the chloride permeability (a) 28d (b) 360d of concrete mixed with different content of PLC. At the age of 28 days, the chloride permeability of the control sample (C), L-1, L-11 and L-22 was in the "low" grade, whereas the chloride permeability of L-2 (i.e., the content of PLC was 33%, and the water/binder ratio was 0.405) was in the "medium" grade. At the age of 360 days, the chloride permeability of L-11 (i.e., the content of PLC was 20%, the water/binder ratio was 0.418) and L-22 (i.e., the content of PLC was 33%, the water to binder ratio was 0.39) decreased to the "very low" grade. However, the chloride permeability of the control sample (C) and L-1 was still in the "low" grade. Figure 2 shows the chloride permeability (a) 28 d (b) 360 d of concrete mixed with different content of PLC. At the age of 28 days, the chloride permeability of the control sample (C), L-1, L-11 and L-22 was in the "low" grade, whereas the chloride permeability of L-2 (i.e., the content of PLC was 33%, and the water/binder ratio was 0.405) was in the "medium" grade. At the age of 360 days, the chloride permeability of L-11 (i.e., the content of PLC was 20%, the water/binder ratio was 0.418) and L-22 (i.e., the content of PLC was 33%, the water to binder ratio was 0.39) decreased to the "very low" grade. However, the chloride permeability of the control sample (C) and L-1 was still in the "low" grade. *Crystals* **2021**, *11*, x FOR PEER REVIEW 6 of 11

**Figure 2.** Chloride ion permeability of concrete mixed with PLC: (**a**) 28d (**b**) 360d. **Figure 2.** Chloride ion permeability of concrete mixed with PLC: (**a**) 28 d (**b**) 360 d.

Figure 3 shows the strength loss rate of concrete mixed with different content of PLC after sulfate immersion (a) 120 cycles (b) 150 cycles. The strength loss rate of the control sample (C) after 120 cycles was 17.5%, and its strength loss rate after 150 cycles was as high as 30.5%. The strength loss rates of L-11 and L-22 after 120 cycles were only one Figure 3 shows the strength loss rate of concrete mixed with different content of PLC after sulfate immersion (a) 120 cycles (b) 150 cycles. The strength loss rate of the control sample (C) after 120 cycles was 17.5%, and its strength loss rate after 150 cycles was as high as 30.5%. The strength loss rates of L-11 and L-22 after 120 cycles were only one quarter

quarter of that of the control sample, that is, 3.8% and 3.6%, respectively. After 150 cycles,

of the strength loss rate of the control sample. This trend shows that PLC can effectively

**Figure 3.** Strength loss rate of concrete mixed with different content of PLC after sulfate immersion:

Figure 4 shows the connected porosity (a) 28d (b) 360d of concrete mixed with different content of PLC. The trend of chloride permeability can be explained by the trend of the connected porosity, that is, the lower the connected porosity, the better the chlorideattack resistance. At the age of 28 days, the connected porosity of the control sample (C) was 10.98. After adding 20% and 33% PLC, the connected porosity of L-1 and L-2 decreased to 10.56 and 10.85, respectively. The connected porosity of L-11 and L-22 decreased to 10.13 and 10.26, respectively, after a 0.1–0.15 reduction in water/binder ratio. Similarly, at the age of 360 days, the connected porosity of the samples showed the same trend, indicating that adding PLC or reducing the water/binder mass ratio can reduce the connected porosity of concrete, and the effect is the most positive when they are both per-

improve the sulfate resistance of concrete.

(**a**) 120 cycles (**b**) 150 cycles.

formed at the same time.

of that of the control sample, that is, 3.8% and 3.6%, respectively. After 150 cycles, the strength loss rates of L-11 and L-22 were 18.5% and 19%, respectively, which was 60% of the strength loss rate of the control sample. This trend shows that PLC can effectively improve the sulfate resistance of concrete. high as 30.5%. The strength loss rates of L-11 and L-22 after 120 cycles were only one quarter of that of the control sample, that is, 3.8% and 3.6%, respectively. After 150 cycles, the strength loss rates of L-11 and L-22 were 18.5% and 19%, respectively, which was 60% of the strength loss rate of the control sample. This trend shows that PLC can effectively improve the sulfate resistance of concrete.

Figure 3 shows the strength loss rate of concrete mixed with different content of PLC after sulfate immersion (a) 120 cycles (b) 150 cycles. The strength loss rate of the control sample (C) after 120 cycles was 17.5%, and its strength loss rate after 150 cycles was as

**Figure 2.** Chloride ion permeability of concrete mixed with PLC: (**a**) 28d (**b**) 360d.

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**Figure 3.** Strength loss rate of concrete mixed with different content of PLC after sulfate immersion: (**a**) 120 cycles (**b**) 150 cycles. **Figure 3.** Strength loss rate of concrete mixed with different content of PLC after sulfate immersion: (**a**) 120 cycles (**b**) 150 cycles.

Figure 4 shows the connected porosity (a) 28d (b) 360d of concrete mixed with different content of PLC. The trend of chloride permeability can be explained by the trend of the connected porosity, that is, the lower the connected porosity, the better the chlorideattack resistance. At the age of 28 days, the connected porosity of the control sample (C) was 10.98. After adding 20% and 33% PLC, the connected porosity of L-1 and L-2 decreased to 10.56 and 10.85, respectively. The connected porosity of L-11 and L-22 decreased to 10.13 and 10.26, respectively, after a 0.1–0.15 reduction in water/binder ratio. Similarly, at the age of 360 days, the connected porosity of the samples showed the same trend, indicating that adding PLC or reducing the water/binder mass ratio can reduce the connected porosity of concrete, and the effect is the most positive when they are both performed at the same time. Figure 4 shows the connected porosity (a) 28 d (b) 360 d of concrete mixed with different content of PLC. The trend of chloride permeability can be explained by the trend of the connected porosity, that is, the lower the connected porosity, the better the chlorideattack resistance. At the age of 28 days, the connected porosity of the control sample (C) was 10.98. After adding 20% and 33% PLC, the connected porosity of L-1 and L-2 decreased to 10.56 and 10.85, respectively. The connected porosity of L-11 and L-22 decreased to 10.13 and 10.26, respectively, after a 0.1–0.15 reduction in water/binder ratio. Similarly, at the age of 360 days, the connected porosity of the samples showed the same trend, indicating that adding PLC or reducing the water/binder mass ratio can reduce the connected porosity of concrete, and the effect is the most positive when they are both performed at the same time. *Crystals* **2021**, *11*, x FOR PEER REVIEW 7 of 11

**Figure 4.** Connected porosity (**a**) 28d (**b**) 360d of concrete mixed with different content of PLC. **Figure 4.** Connected porosity (**a**) 28 d (**b**) 360 d of concrete mixed with different content of PLC.

### *3.3. Hydration Heat and Adiabatic Temperature Rise 3.3. Hydration Heat and Adiabatic Temperature Rise*

Figure 5 shows the (a) heat evolution and (b) total heat release of cement paste mixed with PLC. It can be seen from Figure 5a that the second exothermic peak of L-11 (i.e., the content of PLC was 20%, and the water/binder ratio was 0.418) was slightly earlier than that of the control sample, indicating that 20% of PLC can promote the reactivity of cement. However, the second exothermic peak of L-22 (i.e., the content of PLC was 33%, and the water/binder ratio was 0.39) was delayed, indicating that when the content of PLC is above certain threshold, the cement hydration will be weakened. It can be seen from figure Figure 5 shows the (a) heat evolution and (b) total heat release of cement paste mixed with PLC. It can be seen from Figure 5a that the second exothermic peak of L-11 (i.e., the content of PLC was 20%, and the water/binder ratio was 0.418) was slightly earlier than that of the control sample, indicating that 20% of PLC can promote the reactivity of cement. However, the second exothermic peak of L-22 (i.e., the content of PLC was 33%, and the water/binder ratio was 0.39) was delayed, indicating that when the content of PLC is above certain threshold, the cement hydration will be weakened. It can be

5b that the total heat release of L-11 and L-22 decreased by 12% and 25%, respectively,

also be seen from Figure 6 that the adiabatic temperature rises of L-11 and L-22 were 60 °C and 55 °C, respectively, lower than that of the control sample (65 °C), which is con-

 **Figure 5.** (**a**) Heat release rate (**b**) total heat release of cement paste mixed with PLC.

sistent with the results of hydration heat release.

seen from Figure 5b that the total heat release of L-11 and L-22 decreased by 12% and 25%, respectively, indicating that PLC can significantly reduce the heat release of cement hydration. It can also be seen from Figure 6 that the adiabatic temperature rises of L-11 and L-22 were 60 ◦C and 55 ◦C, respectively, lower than that of the control sample (65 ◦C), which is consistent with the results of hydration heat release. 5b that the total heat release of L-11 and L-22 decreased by 12% and 25%, respectively, indicating that PLC can significantly reduce the heat release of cement hydration. It can also be seen from Figure 6 that the adiabatic temperature rises of L-11 and L-22 were 60 °C and 55 °C, respectively, lower than that of the control sample (65 °C), which is consistent with the results of hydration heat release.

**Figure 4.** Connected porosity (**a**) 28d (**b**) 360d of concrete mixed with different content of PLC.

Figure 5 shows the (a) heat evolution and (b) total heat release of cement paste mixed with PLC. It can be seen from Figure 5a that the second exothermic peak of L-11 (i.e., the content of PLC was 20%, and the water/binder ratio was 0.418) was slightly earlier than that of the control sample, indicating that 20% of PLC can promote the reactivity of cement. However, the second exothermic peak of L-22 (i.e., the content of PLC was 33%, and the water/binder ratio was 0.39) was delayed, indicating that when the content of PLC is above certain threshold, the cement hydration will be weakened. It can be seen from figure

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*3.3. Hydration Heat and Adiabatic Temperature Rise* 

**Figure 5. Figure 5.**( ( **aa**) Heat release rate ( ) Heat release rate ( **b b** ) total heat release of cement paste mixed with PLC. ) total heat release of cement paste mixed with PLC.

**Figure 6.** Adiabatic temperature rise of concrete mixed with PLC. **Figure 6.** Adiabatic temperature rise of concrete mixed with PLC.

### *3.4. Drying Shrinkage 3.4. Drying Shrinkage*

Figure 7 shows the drying shrinkage of concrete mixed with PLC. The drying shrinkage of both the control group and concrete mixed with PLC developed rapidly in the early stage. There is no obvious difference in the drying shrinkage curve between 1–50 days and their values were all around 350. From 50–150 days, the drying shrinkage (380) of concrete mixed with 33% PLC was less than that of the control group (420), and from 150– 360 days, the drying shrinkage tended to be stable. The drying shrinkage rates of the control group C, L-11 (i.e., the content of PLC was 20%, and the water/binder ratio was 0.418) and L-22 (i.e., the content of PLC was 33%, and the water/binder ratio was 0.39) were 420, 400 and 380, respectively. Figure 7 shows the drying shrinkage of concrete mixed with PLC. The drying shrinkage of both the control group and concrete mixed with PLC developed rapidly in the early stage. There is no obvious difference in the drying shrinkage curve between 1–50 days and their values were all around 350. From 50–150 days, the drying shrinkage (380) of concrete mixed with 33% PLC was less than that of the control group (420), and from 150–360 days, the drying shrinkage tended to be stable. The drying shrinkage rates of the control group C, L-11 (i.e., the content of PLC was 20%, and the water/binder ratio was 0.418) and L-22 (i.e., the content of PLC was 33%, and the water/binder ratio was 0.39) were 420, 400 and 380, respectively.

### *3.5. Reaction Mechanism*

*3.5. Reaction Mechanism* 

Figure 8 shows the reaction mechanism of PLC in concrete. When no PLC is added, as described in Equations (4)–(6), the reaction in concrete mainly produces C-A-S-H gel, ettringite and calcium hydroxide, among which calcium hydroxide is unfavorable for strength and durability. When the PLC is added, as described in Equations (7)–(10), the main reactions of PS in concrete are the pozzolanic reaction effect and filling effect. PS contains large amount of glass, which can react with calcium hydroxide produced by the hydration of cement to form C-A-S-H gel. These gels increase the compactness of concrete.

Figure 8 shows the reaction mechanism of PLC in concrete. When no PLC is added, as described in equation (4)–(6), the reaction in concrete mainly produces C-A-S-H gel, ettringite and calcium hydroxide, among which calcium hydroxide is unfavorable for strength and durability. When the PLC is added, as described in equation (7)–(10), the main reactions of PS in concrete are the pozzolanic reaction effect and filling effect. PS contains large amount of glass, which can react with calcium hydroxide produced by the hydration of cement to form C-A-S-H gel. These gels increase the compactness of concrete.

**Figure 7.** Drying shrinkage of concrete mixed with PLC.

At the same time, the reduction in the content of calcium hydroxide can enhance the sulfate resistance of concrete. The main functions of limestone in concrete are nucleation effect and filling effect. Due to the heterogeneous nucleation of cement hydration, the surface of LS particles can become the attachment point of the crystal nucleus, which make the low-energy crystal nucleus and nucleation matrix (particle surface of LS) a replacement of the high-energy crystal nucleus and liquid interface. This reduces the nucleation barrier, promotes the hydration of cement and accelerates the strength development of concrete. Meanwhile, both PS and LS have the filling effect. This is because the fineness of PS and LS is less than that of cement, which can supplement the fine particles missing in cement and form continuous gradation in cementitious materials, filling the pores in concrete. These filling effects can improve the pore size distribution of concrete and reduce the connected porosity of concrete so as to improve the durability of concrete. **Figure 6.** Adiabatic temperature rise of concrete mixed with PLC. *3.4. Drying Shrinkage*  Figure 7 shows the drying shrinkage of concrete mixed with PLC. The drying shrinkage of both the control group and concrete mixed with PLC developed rapidly in the early stage. There is no obvious difference in the drying shrinkage curve between 1–50 days and their values were all around 350. From 50–150 days, the drying shrinkage (380) of concrete mixed with 33% PLC was less than that of the control group (420), and from 150– 360 days, the drying shrinkage tended to be stable. The drying shrinkage rates of the control group C, L-11 (i.e., the content of PLC was 20%, and the water/binder ratio was 0.418) and L-22 (i.e., the content of PLC was 33%, and the water/binder ratio was 0.39) were 420, 400 and 380, respectively. *Crystals* **2021**, *11*, x FOR PEER REVIEW 9 of 11 At the same time, the reduction in the content of calcium hydroxide can enhance the sulfate resistance of concrete. The main functions of limestone in concrete are nucleation effect and filling effect. Due to the heterogeneous nucleation of cement hydration, the surface of LS particles can become the attachment point of the crystal nucleus, which make the low-energy crystal nucleus and nucleation matrix (particle surface of LS) a replacement of the high-energy crystal nucleus and liquid interface. This reduces the nucleation barrier, promotes the hydration of cement and accelerates the strength development of concrete. Meanwhile, both PS and LS have the filling effect. This is because the fineness of PS and LS is less than that of cement, which can supplement the fine particles missing in

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**Figure 7.** Drying shrinkage of concrete mixed with PLC. **Figure 7.** Drying shrinkage of concrete mixed with PLC. C3A + CŜH + H2O→AFt (10)

**Figure 8.** The reaction mechanism of PLC in concrete. **Figure 8.** The reaction mechanism of PLC in concrete.

**4. Conclusions**  Without PS and LS:

ment.

Phosphorus slag (PS) and limestone (LS) composite (PLC) were prepared with a mass ratio of 1:1. The effects of the content of PLC and the water/binder ratio on the mechanical C3S + H2O→C-S-H + Ca(OH)<sup>2</sup> (4)

properties, durability and dry shrinkage of concrete were studied via compressive C2S + H2O→C-S-H + Ca(OH)<sup>2</sup> (5)

mal calorimeter, adiabatic temperature rise instrument and shrinkage deformation instru-

strength, electric flux, sulfate dry/wet cycle method, saturated drainage method, isother-C3A + CSH + H ˆ <sup>2</sup>O→AFt (6)

With PS and LS:

$$\text{C}\_3\text{S} + \text{H}\_2\text{O} + \text{LS} \rightarrow \text{C-S-H (LS nucleation)} + \text{Ca(OH)}\_2\tag{7}$$

$$\text{C}\_2\text{S} + \text{H}\_2\text{O} + \text{LS} \rightarrow \text{C-S-H} \text{ (LS nucleation)} + \text{Ca(OH)}\_2\tag{8}$$

$$\text{SiO}\_2\cdot\text{Al}\_2\text{O}\_3\text{(PS)} + \text{Ca(OH)}\_2 + \text{LS} \rightarrow \text{C-A-S-H (LS nucleation)}\tag{9}$$

$$\rm C\_3A + C\_2^\sharp H + H\_2O \to AFt \tag{10}$$

### **4. Conclusions**

Phosphorus slag (PS) and limestone (LS) composite (PLC) were prepared with a mass ratio of 1:1. The effects of the content of PLC and the water/binder ratio on the mechanical properties, durability and dry shrinkage of concrete were studied via compressive strength, electric flux, sulfate dry/wet cycle method, saturated drainage method, isothermal calorimeter, adiabatic temperature rise instrument and shrinkage deformation instrument.

(1) The adiabatic temperature rises of L-11 and L-22 are 60 ◦C and 55 ◦C, respectively, lower than that of the control sample C (65 ◦C). The addition of PLC does not affect the long-term strength of concrete. When the water/binder ratio decreases by 0.1–0.15, the long-term strength of concrete with PLC increases by about 10% compared with the control sample.

(2) At the age of 360 days, the chloride permeability of L-11 (i.e., the content of PLC was 20%, the water/binder ratio was 0.418) and L-22 (i.e., the content of PLC was 33%, the water/binder ratio was 0.39) decreases to the "very low" grade. After 150 cycles, the strength loss rates of L-11 and L-22 are about 18.5% and 19%, respectively, which is 60% of the strength loss rate of the control sample, indicating that PLC can effectively improve the sulfate resistance of concrete.

(3) The drying shrinkage of samples C, L-11 and L-22 are 420, 400 and 380, respectively. The addition of PLC can reduce the drying shrinkage. The obtained results provide theoretical and technical support for the application of PLC in mass concrete and corrosionresistant concrete.

**Author Contributions:** Conceptualization, K.L. and Y.C.; methodology, K.L.; software, Y.C.; validation, K.L. and Y.C.; formal analysis, K.L.; investigation, K.L.; resources, Y.C.; data curation, Y.C.; writing—original draft preparation, K.L.; writing—review and editing, Y.C.; visualization, Y.C.; supervision, Y.C.; project administration, Y.C.; funding acquisition, Y.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Natural Science Foundation of China, grant number 51822807.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All the data supporting reported results can be found in this manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.

### **References**

