What is Routing and Sealing?
Routing and sealing is a crack treatment that cuts a reservoir along a crack, cleans it and fills it with sealant. It is also called rout-and-seal or saw-and-seal. The reservoir gives the sealant a defined shape and clean sides to bond to.
Which cracks it is for
The FHWA manual (FHWA-RD-99-147) separates crack sealing from crack filling. Sealing puts specialized materials above or into working cracks. It keeps out water and incompressible material. Filling puts ordinary materials into non-working cracks and mainly reduces water infiltration.
The main test is the annual horizontal movement of the crack. Cracks that move more than 3 mm each year are working cracks. Transverse thermal and reflection cracks are the usual examples. The manual sets the sealing range at 5 to 19 mm crack width, with edge deterioration under 25 percent of the crack length.
Cutting is not always required. AC 150/5380-6C says to saw or rout “if necessary”. Routing is common in sealing and rare in filling.
Steps
- Cut. A router or a saw widens the crack to the reservoir size. For airfield work, AC 150/5370-10H specifies removing at least 2 mm from each side of the crack. The sealant maker’s specification sets the final width and depth.
- Clean and dry. The crew blows the crack out with oil-free, water-free compressed air. A hot-air lance is used immediately before sealing. The FHWA manual says backpack blowers do not have enough blast velocity.
- Fill. The crew pours hot-applied sealant that meets ASTM D6690. Cold-applied silicone to ASTM D5893 is also used on concrete.
- Finish. On an airfield flexible pavement, AC 150/5380-6C keeps the sealant surface 6 to 9 mm below the pavement surface. Backer rod sets the depth in a deep reservoir.
Work needs a dry crack and a pavement at 10 degrees C (50 degrees F) or warmer and rising. The FHWA manual prefers a moderately cool time of 7 to 18 degrees C, in spring or fall.
Shape factor
The shape factor is the width of the sealant divided by its depth. The FHWA manual recommends 1 for rubber-modified asphalt sealants and 2 for silicone. A small shape factor risks loss of adhesion. The sealant maker’s data sheet gives the exact value.
Concrete pavement
AC 150/5380-6C prefers a concrete saw to a router, because a router can cause micro-cracks in the adjacent concrete. Shrinkage cracks are cosmetic and usually need no repair.
Service life
In the SHRP H-106 study, rubberized asphalt sealant in routed working cracks lasted 5 to 9 years. Placed over unrouted working cracks, it lasted 2.5 to 5 years. Silicone in routed or sawn cracks lasted at least 4 to 6 years.
Inspection
The FAA lists yearly crack sealing as routine maintenance. A sealing plan starts with a list of cracks, their width and their movement. A drone survey can map the cracks and measure their width. The movement of a crack over a year needs repeat surveys or a field measurement.
Frequently Asked Questions
- What is the difference between routing and sealing and crack filling?
- Routing and sealing treats working cracks, and crack filling treats non-working cracks. The FHWA manual defines a working crack as one that moves more than 3 mm each year. Sealing uses specialized materials and often a cut reservoir. Filling uses ordinary materials in cracks that move less than 3 mm.
- How big must the reservoir be?
- The sealant maker's specification sets the width and depth. AC 150/5380-6C tells the crew to use it for the reservoir dimensions. The FHWA manual recommends a shape factor (width divided by depth) of 1 for rubber-modified asphalt sealants and 2 for silicone.
- How long does a routed and sealed crack last?
- In the SHRP H-106 study, rubberized asphalt sealant in routed working cracks gave 5 to 9 years of service. The same sealant placed over unrouted working cracks gave 2.5 to 5 years. The FHWA manual says these figures assume proper installation.
- Should concrete pavement cracks be routed?
- A concrete saw is preferred over a router. AC 150/5380-6C says a router can cause micro-cracks in the adjacent concrete. The circular also says shrinkage cracks are cosmetic and usually need no repair.
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
- faa-ac-150-5380-7b
- AC 150/5380-7B, Airport Pavement Management Program (PMP) FAA
This is a reference entry. TarmacView provides drone inspection services and doesn't sell the equipment or materials described in this glossary.
