Penetration surface treatment, micro-surfacing, and slurry seal are common preventative maintenance techniques. Their application thickness varies depending on material properties and functional requirements, as detailed below:

1. Penetration Surface Treatment
Thickness: Approximately 2–4 mm
Characteristics: Uses highly permeable emulsified asphalt combined with fine aggregate (e.g., 1–3 mm crushed stone) to form a thin seal.
Primarily used to seal minor cracks, improve skid resistance, and extend pavement life.
Requires compaction after application; the thickness is relatively thin and usually does not change the pavement elevation.
2. Micro-Surfacing
Thickness: 4–10 mm (commonly 6–8 mm)
Characteristics: Composed of modified emulsified asphalt, fine aggregate (maximum particle size typically ≤8 mm), filler, and water.
Used to repair ruts and fill minor defects; offers good wear resistance and skid resistance.
Single or double layer application is possible (thicker areas may be needed for rut filling).
3. Slurry Seal
Thickness: 3–6 mm (fine-grained and medium-grained)
Classification:
ES-1 (fine-grained): 2–4 mm, used for sealing small cracks.
ES-2 (medium-grained): 4–6 mm, commonly used as a general seal.
ES-3 (coarse-grained): 6–9 mm, less commonly used.
Characteristics: Cold-mixed asphalt and fine aggregate, fast construction speed, low cost, but slightly lower durability than microsurfacing.
4. Precautions
The actual thickness needs to be adjusted according to the original pavement condition, aggregate size, and design specifications (e.g., China's "Technical Specification for Maintenance of Asphalt Pavement" JTG 5142). Microsurfacing is usually thicker and more durable than slurry seal, suitable for high-grade highways; slurry seal is mostly used for light traffic roads. It is recommended to determine the optimal thickness and mix ratio through a test section before construction.