4.1.1. Raw Material

The use of aggregates and asphalt brought back from the construction site for the indoor tests prevented errors from arising due to differences in the test materials. The performance specifications of the materials used in this work are presented below.

(1) *Asphalt*

The SBS modified asphalt was selected to meet the requirements of the Chinese Code [15], and the test results are shown in Table 2.


**Table 2.** Technical indices of the SBS modified asphalt.

#### (2) *Coarse aggregate*

The coarse aggregate consisted of lava rock, with 5–10 mm and 10–15 mm sizes. The physical properties of the coarse aggregate were determined in accordance with the Chinese specification JTG E42-2005 [24], and the technical indicators satisfied the specification, as shown in Table 3.

**Table 3.** Technical indices of the coarse aggregate.


## (3) *Fine aggregates*

The fine aggregates in the asphalt mix consisted of 0–3 mm limestone, as shown in Table 4.


**Table 4.** Technical indices of the fine aggregates.

4.1.2. Gradation Composition

According to the technical indicators of the production mix ratio of the asphalt mix for the top layer of the expansion project, it was known that the optimal asphalt content was 5.9% and the amount of fiber was 0.35%. The composition of the grade is shown in Table 5.

**Table 5.** SMA-13 gradation composition.

