*2.2. Methods*

The 10 mm SMA mix containing varying percentages of capsules were evaluated following the TII Series 900 Asphalt mix design. The aim was to optimize the 10 mm SMA mix containing HealRoad capsules, i.e., to determine the optimum capsule content for the 10 mm SMA mix.

### 2.2.1. Binder Drainage Test

The binder drainage test was conducted in accordance with EN12697-18 using the Schellenberg method. A sample of mixed 10 mm SMA material was placed in the glass jar and kept at 180 ◦C for 1 h. The contents of the jar were then emptied out and the jar reweighed to calculate the amount of binder remaining on the inside of the glass jar.

The principle behind the binder drainage test is to quantify the amount of material lost by drainage, i.e., the material that has adhered to the truck or mixer at the plant. Therefore, it is important to verify what effect the addition of capsules would have on the binder drainage of the 10 mm SMA mix. The equation employed for calculating the binder drainage is as follows:

$$BD = 100 \times \frac{[W5 - W3 - W6]}{[W4 - W3]} \tag{1}$$

where: *BD* = the drained material (%); *W3* = mass of the empty beaker (g); *W4* = mass of the beaker plus batch (g); *W5* = mass of the beaker plus retained material after upturning (g); *W6* = mass of the dried residue retained on the sieve (g).

### 2.2.2. Water Sensitivity Test—Indirect Tensile Strength Ratio (ITSR)

An indirect tensile strength ratio (ITSR) was used to evaluate the asphalt mix resistance to the moisture damage. The ITSR test was performed in accordance with European standard EN 12697-12. For each mix, six specimens were prepared. The specimens were then divided into two subsets of three. One set was stored in the laboratory at room temperature, 20 ± 3 ◦C, and the second set was placed under distilled water and subjected to a vacuum of 6.7 kPa for 30 min. After conditioning in vacuum, the second set was placed into a water bath at 40 ◦C for 72 h. Both sets of test specimens were then conditioned at a test temperature of 15 ◦C for two hours prior to testing. The dry set was conditioned in a temperature-controlled air chamber, and the wet set conditioned in a temperaturecontrolled water bath. A Controls 34T-107 compression testing machine with a Controls Digimax Plus (ver2.11-1) data acquisition instrument was employed to complete the indirect tensile strength test (ITST) in accordance with EN 12697-23.

### 2.2.3. Indirect Tensile Strength Test

The indirect tensile strength (ITS) test was conducted in accordance with EN 12697-23. The test specimens were conditioned in a temperature-controlled chamber at 15 ◦C for 2 h. The tests were conducted at 15 ◦C. The ITS test applies a vertical compressive strip load at a constant loading rate, in this case 50 mm/min, to the cylindrical specimen. The load is distributed over the thickness of the specimen through two loading strips at the top and bottom of the test specimen [24]. The specimens were loaded until the load value had fallen back to zero or the specimen had fully split into two. Use of the ITS test created two halves of a test specimen that could then be recombined and subjected to induction heating.

### 2.2.4. Wheel Tracking Test

The wheel tracking test is a test conducted on an asphalt material in order to establish the asphalt materials ability to resist the accumulation of permanent deformation under repeated loading, also known as rutting. The wheel tracking tests were conducted out in accordance with EN 12697-22. These tests were conducted on specimens oscillating under a wheel with a load of 700 N at a frequency of 26.5 cycles per minute for 10,000 cycles at the temperature of 45 ◦C. The specimen slabs had a depth of 40 mm and a length and width of 305 mm × 305 mm. The wheel tracking test was conducted on asphalt mixes containing 0%, 0.44% and 0.64% of HealRoad capsules.

### 2.2.5. Extrinsic Healing Regime

The aim of the healing test was to determine the optimum volume of HealRoad capsules in the mix in order to achieve full repair of the test specimen after the ITS test. The healing was performed using the induction heating system Abrell EKO 10/100C, PWR, CNTRL EKOHEAT® 10/100C, ES, with a solid-state induction power supply CE rated (input: WYE configured, 360–520 VAC, 50/60 Hz, 3-phase; output: 10 kW terminal, 50–150 kHz). A solenoid coil was used to apply the induction heating to the test specimen. Figure 2 shows the induction system set up. The heating (healing) was performed at 7.6 kW and 148 Hz induction machine energy output for a duration of 300 s (5 min). The temperature of the specimen during the healing period was measured using Eventek Infra Red Non-Contact Digital Laser Temperature gun with a temperature range between −50 ◦C and 420 ◦C.

The healing index (HI) was calculated employing the following rule [16,25]:

$$HI = \frac{ITS\_h}{ITS\_i} \times 100 \, (\%) \tag{2}$$

where: *ITSi*—initial ITS test result (MPa), *ITSh*—ITS test result after healing (MPa).

**Figure 2.** Ambrell Ekoheat 10 kW induction machine—laboratory induction apparatus.
