| Aging period | |||||||||
| Samples | S0 | S1 | S2 | S3 | S4 | S5 | S6 | S7 | S8 |
| Wwp CW | 1.4 × 105 1.5 × 105 | 1.5 × 105 1.2 × 105 | 1.4 × 105 1.4 × 105 | 1.3 × 105 1.4 × 105 | 1.2 × 105 1.5 × 105 | 1.4 × 105 1.3 × 105 | 1.5 × 105 1.4 × 105 | 1.2 × 105 1.2 × 105 | 1 × 105 1.2 × 105 |