What is Crack Sealing?
Definition
Crack sealing is a pavement maintenance treatment that places sealant into or over a working crack to keep water and incompressible material out of it. FHWA defines it as the placement of specialized treatment materials above or into working cracks. The aim is to prevent water and incompressibles from entering the crack (FHWA-RD-99-147, section 2.3).
A working crack moves more than 3 mm each year in the horizontal direction. Most are transverse cracks. A non-working crack moves less and is treated by crack filling with a cheaper material. See crack filling .
Which cracks to seal
FHWA bases the choice mainly on the annual movement of the crack. Table 3 of the manual also gives these criteria for sealing:
- Crack width of 5 to 19 mm.
- Edge deterioration (spalls and secondary cracks) on less than 25 percent of the crack length.
- Typical crack types: transverse thermal cracks, transverse reflective cracks, and some longitudinal reflective and cold-joint cracks.
Crack filling takes cracks up to 25 mm wide with edge deterioration on less than 50 percent of the length. FAA AC 150/5380-6C treats cracks wider than 1 inch (2.5 cm) in flexible pavement as a case for partial depth or full depth repair.
How it is done on an airfield
AC 150/5380-6C, Appendix A1, gives the procedure for cracks narrower than 1 inch in flexible pavement:
- Clean the cracks with compressed hot air from a compressor that has an oil and water trap.
- If necessary, saw or rout the cracks to the width and depth that the sealant maker specifies.
- Install backer rod if the sealant maker requires it. The rod must meet ASTM D5249 and be 25 percent larger in diameter than the reservoir width.
- Apply the sealant from the bottom of the crack to the top, and keep its surface 6 to 9 mm below the pavement surface.
- Keep traffic off until the sealant has cured.
Do not seal a wet crack. Start only when the pavement is at 10 degrees C (50 degrees F) and rising, or as the sealant maker recommends. Hot-applied sealant must meet ASTM D6690.
For routing, Item P-101 requires the router or saw to remove at least 2 mm from each side of the crack. A hot air lance follows. On concrete, AC 150/5380-6C prefers a concrete saw to a router because a router can cause micro-cracks in the adjacent concrete. Item P-605 lists ASTM D5893 (silicone), D6690 (hot applied) and D7116 (jet fuel resistant, for concrete aprons where fueling occurs).
Timing and service life
Crack sealing is a preventive treatment. FHWA recommends it soon after working cracks form, in spring or fall at 7 to 18 degrees C, because the cracks are then partly open. FAA lists the routine cleaning, filling and sealing of cracks as preventive maintenance. It also says that early detection and repair of defects is the most important preventive step. AC 150/5320-6G adds that routine crack sealing is needed to get the full life out of a flexible or rigid pavement.
SHRP H-106 test sites gave these service lives (FHWA-RD-99-147):
| Treatment | Service life |
|---|---|
| Rubberized asphalt sealant in routed working cracks | 5 to 9 years |
| Rubberized asphalt sealant, overbanded in unrouted working cracks | 2.5 to 5 years |
| Self-leveling silicone, recessed in routed or sawn working cracks | At least 4 to 6 years |
Inspecting sealed cracks
Failed sealant lets water in. AC 150/5380-6C names five types of joint seal damage on concrete. They are stripping, extrusion, hardening, loss of bond to the slab edge and absence of sealant. The same list of defects is a practical checklist for a sealed crack on asphalt. A condition survey records crack length and width, as in pavement condition index work. It shows which cracks are candidates for sealing and which sealed cracks need a second look.
Frequently Asked Questions
- What is the difference between crack sealing and crack filling?
- Crack sealing treats working cracks, and crack filling treats non-working cracks. A working crack moves more than 3 mm each year. A sealed crack needs a sealant that adheres to the crack walls and stretches as the crack opens and closes. A non-working crack moves little, so a cheaper filler is enough.
- Which cracks should be sealed?
- FHWA recommends sealing cracks that are 5 to 19 mm wide and have less than 25 percent edge deterioration. Typical examples are transverse thermal cracks and transverse reflective cracks. Cracks wider than 1 inch (2.5 cm) in flexible airport pavement need a partial depth or full depth repair, as FAA AC 150/5380-6C describes.
- How long does a sealed crack last?
- In the SHRP H-106 experiment, rubberized asphalt sealant lasted 5 to 9 years in routed working cracks and 2.5 to 5 years in unrouted ones. Silicone placed recessed in routed or sawn working cracks lasted at least 4 to 6 years. These are test-site results, so a given airfield can see other lives.
- How is a sealed crack inspected?
- An inspector looks for sealant that is lifting from the crack wall, split, hard, pushed out of the crack or gone. On concrete pavement, FAA calls these defects joint seal damage. FAA AC 150/5380-6C lists stripping, extrusion, hardening, loss of bond and absence of sealant as the typical types.
References
- fhwa-rd-99-147
- Materials and Procedures for Sealing and Filling Cracks in Asphalt-Surfaced Pavements: Manual of Practice (FHWA-RD-99-147) Federal Highway Administration
- faa-ac-150-5380-6c
- AC 150/5380-6C, Guidelines and Procedures for Maintenance of Airport Pavements FAA
- faa-ac-150-5370-10h
- AC 150/5370-10H, Standard Specifications for Construction of Airports FAA
- faa-ac-150-5320-6g
- AC 150/5320-6G, Airport Pavement Design and Evaluation FAA
This is a reference entry. TarmacView provides drone inspection services and doesn't sell the equipment or materials described in this glossary.
