413.5 Crack Treatment in Bituminous Pavements
|Maintenance Planning Guideline for Sealing Cracks, Joints and Edge Cracks|
413.5.1 Causes and types of Cracks
Cracking is the most common, and often the first distress encountered in an asphaltic concrete (AC) pavement. It occurs when a stress is built up in a surface layer that exceeds the tensile or shear strength of the pavement causing a fissure or crack to develop. Crack sealing and crack filling are methods, which can be used to repair these cracks in the pavement surface. The cause of the crack and its activity plan an important role in determining the success of crack sealing or filling operation.
Cracks in asphalt pavement are inevitable, and crack filling and sealing should be considered the first line of defense in asphalt pavement maintenance, whether it’s considered routine or preventive maintenance. Crack sealing and filling are necessary activities that are required to mitigate the infiltration of water and incompressible materials into the pavement structure. Crack types in AC pavements include, fatigue, longitudinal, transverse, reflective, block, edge, and slippage cracks. Cracking not related to a structural failure should be considered for sealing or filling. Cracking due to structural failures may require more extensive repairs, such as spot sealing of patching to repair the area.
413.5.2 Sealing vs. Filling
Should the crack be sealed or filled? To answer this question it must be established whether the crack is a working or nonworking crack. In general, if the annual horizontal movement of the crack is equal to or exceeds 0.1 in. the crack is considered to be a working crack. Since few people actually monitor the movement of the crack the type of crack can provide an indication of whether it is a working crack or not. Working cracks can be transverse or longitudinal to the pavement centerline, but are most often transverse. Working cracks with limited edge deterioration should be sealed, rather than filled. Crack sealing is usually triggered when the crack width exceeds 1/4 in. The criteria for deciding whether to seal or fill a crack are listed in the "Guidelines on the Use of Crack Filling and Crack Sealing" Table below.
Crack sealing and filling are two different activities. The methods vary in the amount of crack preparation required and the types of sealant materials that are used. For sealing working cracks a reservoir is cut or routed in the pavement and filled with an elastomeric sealant. This means the sealant has a low modulus of elasticity and will stretch easily and to high elongations without fracture. The reservoir should be at least 1/2 in. wide and 1/2 in. deep providing a 1:1 width-to-depth ratio. Depending on the maximum width of the cracks to be sealed the size of the reservoir may be bigger. The reservoir should be slightly larger than the crack to be sealed.
|Crack Characterisitics||Crack Sealing||Crack Fililing|
|Crack width, in.||0.25 – 0.75||0.25 – 1.0|
|Edge Deterioration (i.e., spalls, secondary cracks)||Minimal to None(≤ 25% of crack length)||Moderate to None(≤ 50% of crack length)|
|Annual Horizontal Movement, in.||≥ 0.1 inches of movement||≤ 0.1 inches of movement|
|Type of Crack||Transverse Thermal Cracks||Longitudinal Reflective Cracks|
|Transverse Reflective Cracks||Longitudinal Cold Joint Cracks|
|Working Longitudinal Cracks||Longitudinal Edge Cracks|
|Distantly Spaced Blocked Cracks|
|Preparation||Routing/Sawing||Blowing Out Debris|
|Source: (Smith and Romine 1993)|
413.5.3 Preparation and Procedure
Crack filling typically involves less crack preparation than sealing and performance requirements may be lower for the filler materials. For crack filling the crack preparation usually consists of blowing debris from the crack with a hot air lance. In both operations the sealant should be applied slightly overfilling the crack or reservoir. A follow-up should be done with a soft rubber, U-shaped squeegee to form a wipe zone approximately 1 in. wide on either side of the crack/reservoir and flush with the pavement surface. Care should be taken to avoid leaving an excess amount of asphalt material on the surface. This excess material can cause a problem when placing subsequent overlays.
Ideally, crack-sealing treatments should be applied when the crack width is at its midpoint to widest opening. This is usually in the spring, fall or winter months (i.e., during moderately cold weather conditions). Since non-working cracks do not change in width significantly with temperature, applications of crack filling treatments can proceed at any time of the year.
Cracks less than 0.1 in. wide or greater than 1 in. in width are generally not considered to be sealed or filled. Cracks greater than 1 in. in width should be considered for repair.
A surface treatment should be considered when it is no longer feasible to treat the individual cracks and/or to correct minor surface defects primarily caused by the environment of by pavement materials or construction deficiencies. However, it is always desirable to seal and/or fill open cracks before the application of a surface treatment. See Surface Treatments and Preventive Maintenance - Selection of Preventive Maintenance Strategy for more information.
413.5.4 Maintenance Planning Guideline
Index of all Maintenance Planning Guidelines.