**Figure 1.**
Appearance of crumb rubber and basalt fiber: (**a**) crumb rubber; (**b**) basalt fiber.

**Figure 1.**
Appearance of crumb rubber and basalt fiber: (**a**) crumb rubber; (**b**) basalt fiber.

**Figure 2.**
Aggregate gradation of PAM.

**Figure 2.**
Aggregate gradation of PAM.

**Figure 3.**
Normal probability plot of VA.

**Figure 3.**
Normal probability plot of VA.

**Figure 4.**
Predictions and actual values of VA.

**Figure 4.**
Predictions and actual values of VA.

**Figure 5.**
3D surface plots between VA and factors: (**a**) Influence of A, B at C = 0.40; (**b**) influence of A, C at B = 10.0; (**c**) influence of B, C at A = 4.5.

**Figure 5.**
3D surface plots between VA and factors: (**a**) Influence of A, B at C = 0.40; (**b**) influence of A, C at B = 10.0; (**c**) influence of B, C at A = 4.5.

**Figure 6.**
Normal probability plot of MS.

**Figure 6.**
Normal probability plot of MS.

**Figure 7.**
Predictions and actual values of MS.

**Figure 7.**
Predictions and actual values of MS.

**Figure 8.**
3D surface plots between MS and factors: (**a**) Influence of A, B at C = 0.40; (**b**) influence of A, C at B = 10.0; (**c**) influence of B, C at A = 4.5.

**Figure 8.**
3D surface plots between MS and factors: (**a**) Influence of A, B at C = 0.40; (**b**) influence of A, C at B = 10.0; (**c**) influence of B, C at A = 4.5.

**Figure 9.**
Normal probability plot of FV.

**Figure 9.**
Normal probability plot of FV.

**Figure 10.**
Predictions and actual values FV.

**Figure 10.**
Predictions and actual values FV.

**Figure 11.**
3D surface plots between FV and factors: (**a**) Influence of A, B at C = 0.40; (**b**) influence of A, C at B = 10.0; (**c**) influence of B, C at A = 4.5.

**Figure 11.**
3D surface plots between FV and factors: (**a**) Influence of A, B at C = 0.40; (**b**) influence of A, C at B = 10.0; (**c**) influence of B, C at A = 4.5.

**Figure 12.**
Normal probability plot of MQ.

**Figure 12.**
Normal probability plot of MQ.

**Figure 13.**
Predictions and actual values of MQ.

**Figure 13.**
Predictions and actual values of MQ.

**Figure 14.**
3D surface plots between MQ and factors: (**a**) Influence of A, B at C = 0.40; (**b**) influence of A, C at B = 10.0; (**c**) influence of B, C at A = 4.5.

**Figure 14.**
3D surface plots between MQ and factors: (**a**) Influence of A, B at C = 0.40; (**b**) influence of A, C at B = 10.0; (**c**) influence of B, C at A = 4.5.

**Figure 15.**
Normal probability plot of CPL.

**Figure 15.**
Normal probability plot of CPL.

**Figure 16.**
Predictions and actual values CPL.

**Figure 16.**
Predictions and actual values CPL.

**Figure 17.**
3D surface plots between CPL and factors: (**a**) Influence of A, B at C = 0.40; (**b**) influence of A, C at B = 10.0; (**c**) influence of B, C at A = 4.5.

**Figure 17.**
3D surface plots between CPL and factors: (**a**) Influence of A, B at C = 0.40; (**b**) influence of A, C at B = 10.0; (**c**) influence of B, C at A = 4.5.

**Figure 18.**
Pavement performance test results: (**a**) Low-temperature cracking resistance; (**b**) moisture stability.

**Figure 18.**
Pavement performance test results: (**a**) Low-temperature cracking resistance; (**b**) moisture stability.

**Table 1.**
Properties of SBS-modified bitumen.

**Table 1.**
Properties of SBS-modified bitumen.

Properties | Results | Chinese Standard |
---|

Penetration (25 °C, 0.1 mm) | 65.2 | 60–80 |

Softening point (°C) | 64.2 | ≥55 |

Ductility (5 °C, cm) | 34.5 | ≥30 |

Flash point (°C) | 264 | ≥230 |

Elastic recovery (25 °C, %) | 91.7 | ≥65 |

**Table 2.**
Properties of aggregates and filler.

**Table 2.**
Properties of aggregates and filler.

Index | Apparent Specific Density (g/cm^{3}) | Los Angeles Abrasion (%) | Crushed Stone Value (%) |
---|

Coarse aggregate | 3.527 | 12.9 | 13.9 |

Fine aggregate | 3.389 | − | − |

Filler | 2.722 | − | − |

**Table 3.**
Physical properties of crumb rubber.

**Table 3.**
Physical properties of crumb rubber.

Properties | Results | Technical Criterion |
---|

Apparent density (g/cm^{3}) | 1.18 | 1.1–1.3 |

Metal content (%) | 0.038 | <0.05 |

Moisture content (%) | 0.32 | <1 |

Fiber content (%) | 0.43 | <1 |

Ash content (%) | 4.5 | ≤8 |

**Table 4.**
Physical properties of basalt fiber.

**Table 4.**
Physical properties of basalt fiber.

Index | Diameter | Length | Specific Gravity | Tensile Strength |
---|

Units | μm | mm | g/cm^{3} | MPa |

Value | 13 | 6 | 2.63 | 2320 |

**Table 5.**
Experimental results of 19 groups.

**Table 5.**
Experimental results of 19 groups.

Test Serial Number | Independent Variables | Responses |
---|

A | B | C | VA | MS | FV | MQ | CPL |
---|

(%) | (%) | (%) | (%) | (kN) | (mm) | (kN/mm) | (%) |
---|

1 | 4.5 | 10 | 0.25 | 20.42 | 7.64 | 3.90 | 1.959 | 14.42 |

2 | 4 | 8 | 0.25 | 20.64 | 7.35 | 3.33 | 2.207 | 15.02 |

3 | 4.5 | 8 | 0.4 | 19.87 | 8.04 | 3.50 | 2.297 | 9.85 |

4 | 4.5 | 10 | 0.55 | 20.91 | 7.65 | 3.16 | 2.421 | 13.59 |

5 | 4 | 8 | 0.55 | 21.68 | 7.59 | 3.15 | 2.410 | 28.97 |

6 | 5 | 12 | 0.55 | 18.36 | 7.30 | 3.53 | 2.068 | 4.03 |

7 | 5 | 12 | 0.25 | 18.02 | 7.07 | 4.56 | 1.550 | 4.35 |

8 | 4.5 | 10 | 0.4 | 20.12 | 8.28 | 3.26 | 2.540 | 12.18 |

9 | 4.5 | 10 | 0.4 | 20.20 | 8.21 | 3.38 | 2.429 | 10.65 |

10 | 4 | 12 | 0.25 | 21.10 | 7.22 | 3.25 | 2.222 | 16.99 |

11 | 5 | 8 | 0.55 | 19.34 | 7.38 | 4.14 | 1.783 | 8.27 |

12 | 5 | 10 | 0.4 | 18.78 | 7.87 | 4.25 | 1.852 | 5.29 |

13 | 4.5 | 12 | 0.4 | 19.57 | 7.95 | 3.21 | 2.477 | 9.74 |

14 | 4.5 | 10 | 0.4 | 20.29 | 8.18 | 3.31 | 2.471 | 10.36 |

15 | 4.5 | 10 | 0.4 | 20.45 | 8.30 | 3.42 | 2.427 | 10.78 |

16 | 5 | 8 | 0.25 | 20.03 | 7.24 | 4.42 | 1.638 | 6.07 |

17 | 4 | 10 | 0.4 | 21.73 | 7.93 | 3.25 | 2.440 | 17.14 |

18 | 4.5 | 10 | 0.4 | 19.95 | 8.32 | 3.28 | 2.537 | 12.35 |

19 | 4 | 12 | 0.55 | 21.17 | 7.49 | 3.00 | 2.497 | 21.78 |

**Table 6.**
The ANOVA results of the VA model.

**Table 6.**
The ANOVA results of the VA model.

| Quadratic Sum | DF | Mean Square | R^{2} | Adj. R^{2} | F Value | p Value | Significant |
---|

Model | 17.53 | 9 | 1.95 | 0.9463 | 0.8926 | 17.63 | 0.0001 | √ |

Residual error | 0.99 | 9 | 0.11 | | | | | |

Lack of fit | 0.86 | 5 | 0.17 | | | 4.9 | 0.0743 | × |

Pure error | 0.14 | 4 | 0.035 | | | | | |

Sum | 18.52 | 18 | | | | | | |

**Table 7.**
The ANOVA results of independent variables in VA model.

**Table 7.**
The ANOVA results of independent variables in VA model.

Factors | Sum of Squares | DF | Mean Square | F Value | p Value | Significant |
---|

A | 13.90 | 1 | 13.9 | 125.78 | <0.0001 | **** |

B | 1.12 | 1 | 1.12 | 10.09 | 0.0112 | * |

C | 0.16 | 1 | 0.16 | 1.41 | 0.2648 | − |

AB | 1.08 | 1 | 1.08 | 9.78 | 0.0122 | * |

AC | 0.27 | 1 | 0.27 | 2.41 | 0.1549 | − |

BC | 0.00045 | 1 | 0.00045 | 0.004 | 0.9505 | − |

A^{2} | 0.00096 | 1 | 0.00096 | 0.008 | 0.9275 | − |

B^{2} | 0.84 | 1 | 0.84 | 7.58 | 0.0223 | * |

C^{2} | 0.42 | 1 | 0.42 | 3.78 | 0.0836 | − |

**Table 8.**
The ANOVA results of the MS model.

**Table 8.**
The ANOVA results of the MS model.

| Quadratic Sum | DF | Mean Square | R^{2} | Adj. R^{2} | F Value | p Value | Significant |
---|

Model | 3.01 | 9 | 0.33 | 0.9754 | 0.9509 | 39.69 | <0.0001 | √ |

Residual error | 0.076 | 9 | 0.0084 | | | | | |

Lack of fit | 0.061 | 5 | 0.012 | | | 3.40 | 0.1298 | × |

Pure error | 0.014 | 4 | 0.0036 | | | | | |

Sum | 3.09 | 18 | | | | | | |

**Table 9.**
The ANOVA results of independent variables in MS model.

**Table 9.**
The ANOVA results of independent variables in MS model.

Factors | Sum of Squares | DF | Mean Square | F Value | p Value | Significant |
---|

A | 0.052 | 1 | 0.052 | 6.14 | 0.0351 | * |

B | 0.032 | 1 | 0.032 | 3.85 | 0.0814 | − |

C | 0.079 | 1 | 0.079 | 9.39 | 0.0135 | * |

AB | 0.00005 | 1 | 0.00005 | 0.0059 | 0.9403 | − |

AC | 0.0024 | 1 | 0.0024 | 0.29 | 0.6031 | − |

BC | 0.0018 | 1 | 0.0018 | 0.21 | 0.6552 | − |

A^{2} | 0.16 | 1 | 0.16 | 19.34 | 0.0017 | ** |

B^{2} | 0.061 | 1 | 0.061 | 7.23 | 0.0248 | * |

C^{2} | 0.68 | 1 | 0.68 | 80.76 | <0.0001 | **** |

**Table 10.**
The ANOVA results of FV model.

**Table 10.**
The ANOVA results of FV model.

| Quadratic Sum | DF | Mean Square | R^{2} | Adj. R^{2} | F Value | p Value | Significant |
---|

Model | 3.80 | 9 | 0.42 | 0.9604 | 0.9209 | 24.28 | <0.0001 | √ |

Residual error | 0.16 | 9 | 0.017 | | | | | |

Lack of fit | 0.14 | 5 | 0.028 | | | 6.01 | 0.0535 | × |

Pure error | 0.018 | 4 | 0.0046 | | | | | |

Sum | 3.96 | 18 | | | | | | |

**Table 11.**
The ANOVA results of independent variables in the FV model.

**Table 11.**
The ANOVA results of independent variables in the FV model.

Factors | Sum of Squares | DF | Mean Square | F Value | p Value | Significant |
---|

A | 2.42 | 1 | 2.42 | 139.12 | <0.0001 | **** |

B | 0.098 | 1 | 0.098 | 5.63 | 0.0417 | * |

C | 0.62 | 1 | 0.62 | 35.35 | 0.0002 | *** |

AB | 0.0072 | 1 | 0.0072 | 0.41 | 0.5361 | − |

AC | 0.097 | 1 | 0.097 | 5.56 | 0.0427 | * |

BC | 0.084 | 1 | 0.084 | 4.83 | 0.0555 | − |

A^{2} | 0.26 | 1 | 0.26 | 14.87 | 0.0039 | ** |

B^{2} | 0.021 | 1 | 0.021 | 1.20 | 0.3025 | − |

C^{2} | 0.021 | 1 | 0.021 | 1.21 | 0.3001 | − |

**Table 12.**
The ANOVA results of MQ model.

**Table 12.**
The ANOVA results of MQ model.

| Quadratic Sum | DF | Mean Square | R^{2} | Adj. R^{2} | F Value | p Value | Significant |
---|

Model | 1.76 | 9 | 0.20 | 0.9594 | 0.9189 | 23.66 | <0.0001 | √ |

Residual error | 0.074 | 9 | 0.0082 | | | | | |

Lack of fit | 0.062 | 5 | 0.012 | | | 4.02 | 0.1013 | × |

Pure error | 0.012 | 4 | 0.003 | | | | | |

Sum | 1.83 | 18 | | | | | | |

**Table 13.**
The ANOVA results of the independent variables in the MQ model.

**Table 13.**
The ANOVA results of the independent variables in the MQ model.

Factors | Sum of Squares | DF | Mean Square | F Value | p Value | Significant |
---|

A | 0.83 | 1 | 0.83 | 100.86 | <0.0001 | **** |

B | 0.023 | 1 | 0.023 | 2.78 | 0.1298 | − |

C | 0.26 | 1 | 0.26 | 31.14 | 0.0003 | *** |

AB | 0.0011 | 1 | 0.0011 | 0.14 | 0.7201 | − |

AC | 0.0042 | 1 | 0.0042 | 0.52 | 0.4898 | − |

BC | 0.025 | 1 | 0.025 | 3.00 | 0.1173 | − |

A^{2} | 0.14 | 1 | 0.14 | 17.34 | 0.0024 | ** |

B^{2} | 0.0004 | 1 | 0.0004 | 0.049 | 0.8300 | − |

C^{2} | 0.093 | 1 | 0.093 | 11.31 | 0.0083 | ** |

**Table 14.**
The ANOVA results of the CPL model.

**Table 14.**
The ANOVA results of the CPL model.

| Quadratic Sum | DF | Mean Square | R^{2} | Adj. R^{2} | F Value | p Value | Significant |
---|

Model | 653.35 | 9 | 72.59 | 0.9556 | 0.9112 | 21.52 | <0.0001 | √ |

Residual error | 30.37 | 9 | 3.37 | | | | | |

Lack of fit | 26.92 | 5 | 5.38 | | | 6.25 | 0.0501 | × |

Pure error | 3.45 | 4 | 0.86 | | | | | |

Sum | 683.71 | 18 | | | | | | |

**Table 15.**
The ANOVA results of the independent variables in the CPL model.

**Table 15.**
The ANOVA results of the independent variables in the CPL model.

Factors | Sum of Squares | DF | Mean Square | F Value | p Value | Significant |
---|

A | 516.82 | 1 | 516.82 | 153.18 | <0.0001 | **** |

B | 12.75 | 1 | 12.75 | 3.78 | 0.0838 | − |

C | 39.16 | 1 | 39.16 | 11.61 | 0.0078 | ** |

AB | 0.068 | 1 | 0.068 | 0.020 | 0.8899 | − |

AC | 35.53 | 1 | 35.53 | 10.53 | 0.0101 | * |

BC | 17.05 | 1 | 17.05 | 5.05 | 0.0512 | − |

A^{2} | 0.12 | 1 | 0.12 | 0.036 | 0.8543 | − |

B^{2} | 4.00 | 1 | 4.00 | 1.19 | 0.3045 | − |

C^{2} | 24.59 | 1 | 24.59 | 7.29 | 0.0244 | * |

**Table 16.**
Target values of response variables.

**Table 16.**
Target values of response variables.

Response | VA (Y_{1}) | MS (Y_{2}) | FV (Y_{3}) | MQ (Y_{4}) | CPL (Y_{5}) |
---|

Units | % | kN | mm | kN/mm | % |

Target value | 18–22 | Maximize | 2–4 | Maximize | Minimize |

**Table 17.**
Optimal preparation parameters and prediction vs. experiment.

**Table 17.**
Optimal preparation parameters and prediction vs. experiment.

Response | A (%) | B (%) | C (%) | VA (%) | MS (kN) | FV (mm) | MQ (kN/mm) | CPL (%) |
---|

Prediction | 4.51 | 11.21 | 0.42 | 19.82 | 8.12 | 3.26 | 2.48 | 10.03 |

Experiment | 4.51 | 11.21 | 0.42 | 20.16 | 7.92 | 3.34 | 2.37 | 10.38 |

Chinese Standard | − | − | − | 18–25 | ≥5 | 2–4 | − | <15 |

Relative error (%) | − | − | − | 1.70 | −2.46 | −2.45 | −4.38 | 3.49 |