One-year results of the first road surface with the addition of sunflower oil porous capsules

This paper presents findings from the first surface course in the UK employing sunflower oil-filled porous capsules as a self-healing additive. The capsules, designed to mitigate ravelling, were tested on a road constructed at an asphalt plant and subjected to a year of traffic in temperatures ranging from below 0°C to 35°C. Spherical in shape with a diameter of about 1.5 mm, the capsules possess a porous structure filled with sunflower oil. Each tonne of asphalt contained 5 kgs of capsules. The material used was Stone Mastic Asphalt (SMA), one of the UK's most utilised surface course materials. Eight sections were built, with four varying binder contents (6.4 %, 5.9 %, 5.5 % and 5.2 %), each with and without capsules. The road performance was evaluated by measuring two indicators: rut depth and surface macrotexture. Results show that the capsules delay fretting progression in wearing courses. Fretting could have resulted from the complex interaction between early life wearing and asphalt compaction by traffic that caused the mastic to move to the road surface. In addition, no considerable difference in rutting was observed between the different materials. Moreover, core samples were extracted from the road before and after traffic and age exposure for further laboratory analysis to assess the long-term performance. Results showed that stone loss resistance in asphalt-containing capsules was 30.02 % lower before ageing and 25.92 % lower after ageing. Furthermore, the stiffness ageing factor was 15–20 % lower in materials with capsules, while the fatigue life remained consistent across all materials.