Cracks in concrete structures can significantly affect durability and appearance. One widely used method for repairing dormant cracks—those that do not require restoring tensile strength—is routing and sealing. This technique involves enlarging the crack’s exposed face to create a groove that is then filled and sealed with appropriate materials, providing a durable barrier against moisture ingress and further deterioration.
Procedure for Routing and Sealing
Routing entails creating a V-shaped groove along the crack, with minimum dimensions typically around 6 mm in width and between 6 to 25 mm in depth. This groove, once formed, is thoroughly cleaned and dried before being filled with a suitable sealant. For quicker repairs where high performance is less critical, the routing step can be omitted, although this may reduce the durability of the repair and affect the surface appearance, often leaving the repair material slightly raised above the surrounding concrete.
Applications of Routing and Sealing
This method is ideal for both fine pattern cracks and larger, isolated dormant cracks. On roadway pavements, a common and economical practice is pouring hot tar into cracks. When using hot-poured joint sealants, it is essential that they adhere well to the concrete and withstand operating temperatures without melting or flowing. Sealants used on pavements must also endure the stresses caused by moving traffic.
Groove Preparation and Cleaning
The groove can be created using hand-held tools, concrete saws, or pneumatic devices, depending on the scale of the repair. Thorough cleaning of the groove is critical for the sealant’s adhesion and is accomplished through air blasting, sandblasting, or water-jetting to remove any grease, oil, or dirt. After cleaning, the surface must be completely dried before the sealant application.
Surface Conditions and Sealant Use
Routing and sealing work best on flat horizontal surfaces but can also be adapted for vertical or curved surfaces by using non-sag sealants that remain in place without dripping. This method is particularly effective for waterproofing concrete surfaces exposed to standing water.
Suitable Sealant Materials
The sealants employed must be capable of withstanding cyclic expansion and contraction without becoming brittle over time. Common materials include epoxies, urethanes, silicones, polysulfides, asphaltic compounds, and polymer mortars. Cement-based grouts are generally avoided because they are prone to cracking again.
Sealant Application Details
The sealant is applied into the dry groove and allowed to cure properly. When it is necessary for the sealant to move freely at the bottom of the groove, a bond breaker such as a polyethylene strip, waxed paper, or foil is placed at the groove’s base. For elastic sealants, the groove—called a “chase”—is typically rectangular, and great care is taken to ensure the sealant bonds well to the sides without debonding.
Additional Treatments: Strip Coating and Over-Banding
To minimize edge spalling and improve the uniformity of the repair, strip coatings or over-banding can be applied over the sealed crack. This involves applying a band of urethane, typically 25 to 75 mm wide on each side of the crack and 1 to 2 mm thick. When performed on a larger scale, this process is referred to as “blanketing.”
Elastic Sealants: Design Considerations
Elastic sealants are materials that return to their original shape after external stress is removed. The chase dimensions must be designed such that tensile stresses in the sealant, caused by crack movement, do not exceed the material’s cohesive strength, usually with a safety factor of five to account for aging and fatigue. Tensile stresses typically range between 135 and 345 kPa. The chase width is usually at least six times the expected movement of the joint, ensuring sufficient room for compression. The minimum depth of the chase is about 20 to 25 mm. Rectangular chases are preferred to optimize performance.
Handling Reinforcement Exposure
If reinforcement bars are exposed during the groove cutting, the chase depth is increased to allow the sealant to extend behind the bars. The reinforcement should be cleaned and coated with bitumen before applying the elastic sealant to ensure proper adhesion and prevent corrosion.
Quality Control of Sealants
The quality of the sealant bond can be verified on site by pulling a layer of the cured sealant. The failure should occur either by stripping a thin mortar skin or within the sealant material itself, but never at the interface between the mortar and the sealant. This indicates a proper bond has been achieved.