はじめに

米国南部に位置する全米アスファルト技術センター（NCAT）は、舗装研究の最先端センターです。世界唯一の高速フルスケール加速舗装試験施設を備えています。KratonがHiMA技術を初めて開発した際、その性能を実証するのにNCATは最適な場所でした。

挑戦

While it is simple to design a pavement to be either rut resistant or crack resistant, it is not easy to make it resistant to both at the same time. The tradeoff becomes even more challenging to manage when the pavement thickness diminishes. This issue is precisely what we wanted to accomplish with our N7 test section.

決議

We built a three-layer pavement over 14 cm (5.5 in) of aggregate base. The 3.2 cm (1.25 in) wearing course was assembled with a 9.5 mm NMAS dense-graded mixture. We paved the base course with two layers, each 5.7 cm (2.25 in) thick and made with a 19 mm NMAS dense-graded mixture. All binder courses featured Kraton’s HiMA™ bitumen technology. Overall, the three layers amounted to 14.6 cm (5.75 in) thick pavement. Compared to the control section made with conventional PMB, the HiMA section was 18 percent thinner. HiMA mixes were produced at 174°C (345°F) and compacted at 115-147°C (240-295°F).

After 20 million equivalent single axle load (ESAL) applied to each section over five years, the HiMA section resulted in 70 percent less rutting. It also had no bottom-up fatigue cracking while the control had 18 percent area cracks.

The NCAT experiment proved that it is possible to make a pavement thinner and still make it last longer than the conventional alternative. Since then, HiMA has been successfully implemented in numerous places around the world, bringing along social, economic and environmental benefits.