Research results

Making National Highways of Strong Pavement: The Development of a Durable Mixture for the Road Surface Layer in Cold, Snowy Regions

 Photo 1 Failure on pavement
of national highways

 Figure 1 Characteristics of SMA
with rough pavement surface
(click to enlarge)

 Photo 2
Splashingduring driving in the rain

Less splashing occurs in the
"SMA with rough pavement surface"
lane than in the " dense-graded
asphalt concrete" lane.
(click to enlarge)

1. Problems with the surface layer mixture of national highways in cold, snowy regions

  To afford safe, high-speed driving, non-skid, well-drained porous asphalt pavement is commonly used for the surface layer of pavement on national highways. In cold, snowy regions, however, a number of failures have occurred on long-used sections of porous asphalt pavement (Photo 1). Pot holes and cracks in the tire running area of pavement or in the joints of bridges, and dispersion of the pavement surface material have caused problems such as poor trafficability and increased repair costs.

2. The development of a surface layer mixture for national highways in cold, snowy regions

  We are developing a high-durability pavement material that affords driving safety at the high speeds required of national highways.

  Studies to date indicate that "SMA with rough pavement surface" should be regarded as a prime pavement material. Stone Mastic Asphalt (SMA) is a highly durable pavement material. SMA with rough pavement surface is skid-proof and excels in drainability. Its suitability for national highways has been under review through tests in the laboratory and on the test track, and in test constructions on actual roads (Figure 1).

  The results confirmed four points. 1. SMA with rough pavement surface was effective in controlling splashing, which influences visibility during driving in the rain (Photo 2). 2. The pavement was also effective in controlling the reflection of oncoming vehicles' headlights on the road surface at night. 3. Black ice, which tends to occur in winter, tended not to occur on this pavement. 4. The surface material had less dispersion than that of porous asphalt pavement. It was found that, although the drainability of SMA with rough pavement surface is lower than that of porous asphalt pavement, the pavement's other capabilities were roughly the same as those of porous asphalt pavement, and SMA's durability is great, which is expected to make this pavement material effective for national highways.

  In future, long-term durability will be reviewed with more test construction sites on actual roads.

(Contact: Road Maintenance Research Team, Civil Engineering Research Institute for Cold Region)(CERI)