Environment

A pavement must function within its environment. Environmental variations can have a significant impact on pavement materials and the underlying subgrade, which in turn can drastically affect pavement performance. Hawai'i's key environmental parameters of concern are typically temperature, and moisture.

Temperature

Temperature acts on pavements in two principal ways. First, temperature extremes can affect asphalt binder rheology. Second, temperature variations can cause pavement to expand and contract.

Temperature Extremes

Asphalt binder rheology (deformation and flow characteristics) varies with temperature. Therefore, estimated temperature extremes and their effects are a primary consideration when selecting an appropriate asphalt binder. Older asphalt binder grading systems did not directly account for temperature effects and thus various empirical systems and thumb-rules were developed. The Superpave PG binder grading system corrects this deficiency by grading asphalt binder based on its performance in relation to temperature.

Expansion and Contraction

Pavements, like all other materials, will expand as they rise in temperature and contract as the fall in temperature. Small amounts of expansion and contraction are typically accommodated without excessive damage, however extreme temperature variations can lead to catastrophic failures. Flexible pavements in colder areas on the mainland can suffer transverse cracks as a result of excessive contraction in cold weather.  In Hawai'i, this cold weather contraction is typically not enough to cause cracking.

Durability Loss

The loss of durability over time due to environmental effects is probably more significant on pavement in Hawai'i than most other places.  This is because of two effects:

• Other significant pavement deterioration factors are either less severe or non-existent in Hawai'i.   First, trucks compose a smaller percentage of traffic in Hawai'i than in any other state. Even though the traffic volume on certain roads (like H-1) may be similar to that of other states, the actual loading is less because of the smaller truck percentage. Certainly, in recognition of this Hawai'ian pavements can be designed thinner, however for a given structural design a Hawai'ian pavement will likely encounter less loading and thus, less stress.   Second, aside from isolated parts of Mauna Kea and Mauna Loa, the ground does not freeze in Hawai'i.  Therefore, Hawai'ian pavements are not subject to the destructive effects of ground freezing, called frost action.  In northern states, such as Minnesota, Illinois and Alaska, designing for frost action is a major concern.
• Sunlight.  It is quite sunny in Hawai'i and constant exposure to sunlight will cause a pavement's surface to age more quickly (an increase in viscosity with age makes a pavement surface more brittle and prone to raveling) than it would in a less sunny mainland climate.

Moisture

Moisture (in the form of accumulated water or rainfall) can affect pavement design and construction as well as basic driving conditions.  Specific issues with moisture are:

• Design. Certain types of soils can be highly expansive when wet. Structural design must account for this expansiveness.
• Construction.
  • The subgrade should be compacted at an optimal moisture content. Excessive rainfall can raise subgrade moisture content well beyond this value and make it virtually impossible to compact.
  • HMA should not be placed in wet conditions because excessive water may damage the hot, fresh HMA by cooling it too quickly or getting into the mix and causing later stripping problems.
• Driving Conditions. Rainfall reduces skid resistance and can cause hydroplaning in severely rutted areas.