Asphalt Crackfilling
Cracksealing is used a a first defense against pavement deterioration because it offers several important benefits. Effective cracksealing keeps water from entering and weakening the base or sub-base. It helps preserve the pavement adjacent to the cracks; prevents sand, stone and dirt from making its way into open cracks causing compressive stresses; and extends pavement life by minimizing crack growth.
Proper attention to cracks will prevent problems from spreading, and extend the life of the pavement. Treating the problem while it is still small will pay big dividends later by delaying costly resurfacing.
What Causes Asphalt to Crack?
Asphalt cracking is caused by both the freeze/thaw cycle as well as the effects of the sun and moisture. The sun oxidizes asphalt cement, causing shrinkage and creating separations which leade to cracks. Moisture is then able to reach the pavement’s subsurface and soften it. Surface traffic soon begins to deteriorate the pavement around the crack, creating a larger problem, … the pothole.
Crack Types
Reflective - This type of crack appears primarily in resurfacing projects, although it can also occur in a new pavement. It happens when an existing crack or joint in the underlying pavement structure reflects upward through the surface.
Block - Visually, this type of cracking forms a square pattern, with cracks intersecting each other at nearly right angles. A common cause of this on parking lots is lack of traffic, (steady traffic constantly kneads the pavement and keeps it flexible).
Joint - Pavement “joints” are created during initial construction when the edges of two pavement mats are placed next to one another. These constructed joints usually have a lower density of asphalt than that of the surrounding pavement. If the mats don’t bond properly (for a variety of reasons), joint cracks appear.
Slippage - Slippage cracks are usually crescent-shaped and caused by heavy traffic that is stopping, turning, or climbing a hill. Resulting stresses cause a bond failure between the upper and lower pavement layers. The open end of the U-shaped crack always points in the direction of the applied force.
Fatigue or Alligator - Over time, a flexible asphalt pavement becomes more rigid and is less able to tolerate vertical deflections. This causes tension in the pavement and results in alligator-type cracking. Such cracking can also occur from structural inadequacy, aging and oxidation.
It is generally recommended that alligator areas be removed and replaced rather than filled or sealed.
Crack Routing - In some cases, crack widening or routing is necessary. Routing is strongly suggested in truck areas, but not in cracks that have already been sealed. Configuration choice depends on factors such as crack type, pavement downtime and budget. Crack routing creates a proper reservoir to which the crack sealant material adheres.
The Remedy - Existing cracks are cleaned by high power blowers and in most cases crack routed. This allows for greater expansion and contraction of the pavement without cracking. A hot liquid asphalt cracksealing material is then applied to the cracks. A squeegee is used to “band” the crack and blend the material with the existing pavement.