Single Lift vs. Two-Lift Paving: What's the Difference?
When asphalt is laid down, maximum thickness per pass is constrained by heat dissipation and roller compaction efficiency. If an asphalt layer is too thick (over 3.5 inches loose), steel rollers can only compact the top and bottom while the middle stays spongy and uncompacted.
1. Binder Course (Base Course)
Uses larger 3/4" to 1" aggregate stones with less liquid asphalt. The large stones interlock tightly under rollers to deliver extreme structural load-bearing capacity.
2. Surface Course (Wearing Course)
Uses smaller 3/8" to 1/2" fine aggregate with higher liquid bitumen content. Creates a dense, velvety, impervious waterproof seal that sheds rain and resists oxidation.
Climate Factors: Northern vs. Southern Paving Specs
In northern states subject to winter frost heave (temperatures dropping below 32°F repeatedly), the gravel sub-base must be deeper (minimum 6 to 8 inches of clean crushed aggregate) to permit free drainage. If water becomes trapped beneath the asphalt and freezes, it expands by 9%, fracturing the asphalt pavement from below.