Table 1
Basic parameters of crushed stone.
| Parameter type | Test value (%) | Limit (%) |
|---|---|---|
| Los Angeles attrition rate (>1.7 mm) | 21.4 | ≤30 |
| Plasticity index (<0.5 mm) | 4.8 | <6 |
| Loss rate of sodium sulfate solution | 5.6 | ≤6 |
Table 2
CSCS sample particle size gradation (C5P0.1).
| Square hole screen aperture (mm) | 45 | 31.5 | 22.4 | 7.1 | 1.7 | 0.5 | 0.1 |
| Percentage of screen mass | 100 | 91 | 79 | 58 | 30 | 19 | 0 |
Figure 1
Flow chart of unconfined compressive strength test: (a) sample preparation, (b) sample curing, (c) sample soaking, and (d) unconfined compressive strength test.
Figure 2
Sample preparation for CT analysis: (a) core drilling from the larger cured specimen and (b) final cylindrical sample (Φ50 mm × 50 mm).
Table 3
X-ray CT equipment parameters.
| Equipment parameters | Specific range and values |
|---|---|
| Maximum sample size | Φ50 mm |
| Scanning voltage | 150 kV |
| Current | 60 μA |
| Exposure time | 0.55 s |
| Voxel resolution | 30 μm/pixel |
Figure 3
Representative grayscale histogram used for phase segmentation.
Figure 4
Industrial CT gray image underlying database processing: (a) extracting pore from original image, (b) extracting rubber powder from original image, and (c) the original figure distinguishes the pores and rubber powder.
Table 4
Unconfined compressive strength test results for extended F–T cycles.
| Sample description | C5R0 (MPa) | C5R10 (Mpa) | C5R20 (Mpa) | C5R30 (Mpa) | C5R45 (Mpa) |
|---|---|---|---|---|---|
| 7 days UCS | 10.48 | 4.56 | 2.72 | 1.68 | 1.35 |
| 28 days UCS | 11.62 | 7.41 | 5.24 | 2.38 | 1.74 |
| 5 F–T cycles UCS | 10.91 | 4.47 | 3.63 | 2.27 | 1.84 |
| 10 F–T cycles UCS | 10.41 | 4.31 | 3.22 | 2.21 | 1.70 |
| 15 F–T cycles UCS | 9.40 | 4.10 | 3.11 | 2.15 | 1.69 |
| 20 F–T cycles UCS | 8.80 | 4.02 | 2.93 | 2.11 | 1.67 |
| 30 F–T cycles UCS | 8.40 | 3.96 | 2.81 | 2.07 | 1.65 |
Table 5
Evaluation index of BDR.
| Sample | C5R0 | C5R10 | C5R20 | C5R30 | C5R45 |
|---|---|---|---|---|---|
| 5 F–T cycles BDR (%) | 93.9 | 60.3 | 69.3 | 95.3 | 105.7 |
| 10 F–T cycles BDR (%) | 89.5 | 58.2 | 61.5 | 92.4 | 97.7 |
| 30 F–T cycles BDR (%) | 72.3 | 53.4 | 53.6 | 87.0 | 94.8 |
Figure 5
Change in porosity of specimens during F–T cycling. The black bars represent the porosity increase after 5 cycles (compared to 0 cycles), and the red bars represent the additional increase after 10 cycles (compared to 5 cycles).
Figure 6
Volume proportion of rubber powder in each slice.
Figure 7
Correlation analysis of progressive versus initial pore expansion under F–T cycling for specimens with varying rubber content. Each point represents a single CT slice. The POEI, defined as the coefficient of determination (R 2), is shown for each specimen, along with the corresponding p-value indicating statistical significance. (a) C5R0 (0% rubber), (b) C5R10 (10% rubber), (c) C5R20 (20% rubber), (d) C5R30 (30% rubber), and (e) C5R45 (45% rubber).
Figure 8
Comparative trend chart illustrating the trade-off between 28-day unconfined compressive strength and BDR after 30 F–T cycles.
Figure 9
Correlation between the POEI (R 2) and the BDR (ten cycles) for materials with varying rubber content.
Figure 10
Quadratic model of the POEI (R 2) as a function of rubber content.
Figure 11
Change of the proportion of each pore number under the action of the F–T cycle.
Figure 12
Change of the pore volume ratio: (a) under F–T cycles and (b) proportion of ultra-large pore volume.
Figure 13
Changes in microstructure of CSCS before and after F–T cycles: (a) Cement stabilized macadam material five times F–T and non-F–T 3D pore diagram comparison chart. (b) Comparison of 3D pore diagram of cement stabilized macadam material between ten F–T cycles and five F–T cycles. (c) The 3D pore diagram comparison diagram of cement stabilized macadam with 30% rubber powder content after five F–T cycles and no F–T cycles. (d) The 3D pore diagram comparison of ten F–T cycles and five F–T cycles of CSCS materials with rubber powder content of 30%.
Figure 14
Schematic illustration of the proposed micro-mechanical model for F–T degradation. (a) In the low-content regime, isolated rubber particles act as stress concentrators, leading to the nucleation of new, disordered microcracks (low POEI). (b) In the high-content regime, an interconnected rubber network absorbs frost-heave energy, resulting in a more benign, orderly expansion of existing pores (high POEI).