Asphalt Contractor Tampa, FL

Asphalt Crack Repair

CRACK SEALING PROCEDURES

From the DOD/ Army Corps od Engineers UNIFIED FACILITIES CRITERIA ASPHALT CRACK REPAIR

9.1. Crack Size Guidelines. Procedures for sealing will vary depending upon the size of the crack. The following should be used as a guide.

9.1.1. Hairline cracks (less than 1/4 inch (6 millimeters)). It is very difficult to successfully insert sealant material into a crack that is less than 1/4 inch (6 millimeters). Normally, these cracks are not sealed unless they cover 80 percent or more of the pavement area. If the cracks do require sealing, a surface treatment could be the most effective method. The surface treatment used will depend upon the area being treated and the predicted future traffic. A single or double bituminous surface treatment could be satisfactory for a roadway or parking lot, but not for an airfield. Surface treatments and slurry seals are not recommended for airfields that will encounter jet and high-tire-pressure aircraft because the surface treatment or slurry seal will normally deteriorate quickly. Options such as an asphalt overlay or pavement recycling should be considered for airfield pavements. For additional information on various types of surface treatments, see Department of the Navy, NFGS-02788B, NFGS-02789B, NFGS-02787B; Department of the Army, Corps of Engineers CEGS-02745; or Departments of the Army and Air Force TM 5-822-8/AFM 88-6, Chapter 9.

9.1.2. Small and medium cracks (1/4 to 2 inches (6 to 50 millimeters)). After the crack has been cleaned and inspected, it is ready for sealing. The depth of the cracks to be sealed is determined and, if the depth is greater than 3/4 inch (19 millimeters), a backer rod material is inserted. If the depth of the crack is not deep enough to accommodate the backer rod and maintain a sealant depth of 1/2 to 3/4 inch (13 to 19 millimeters), then the crack can be routed or the backer rod material omitted.

9.1.3. Large cracks (greater than 2 inches (50 millimeters)). Cracks that are 2 inches (50 millimeters) and larger should be filled with a sand asphalt or fine-graded asphalt mix. The procedures and equipment used are identical to those used to repair potholes. The cracks should be squared by sawing, filled with asphalt mix, and compacted. To obtain a high-quality patch, the edges should be vertical and the crack must be clean. The asphalt material could prematurely fail if the proper cleaning and patching procedures are not followed. Additional information on these procedures may be obtained from Departments of the Army, Navy, and Air Force TM 5-624/NAVFAC MO-102/AFJMAN 32-1040.

9.1.4. Cracks in pavements that are to be overlaid. Small and medium cracks in pavements that are to be overlaid can be filled with an emulsion, a sand emulsion mixture (Figure 9.1.), or one of the types of sealants previously mentioned. The material should be recessed in the crack a minimum of 1/4 inch (6 millimeters) to prevent the material from “bleeding” through the overlay. Bleeding occurs when the asphalt cement in the crack sealant material is drawn to the surface of the overlay. Bleeding causes the pavement above the crack to become soft, and a crack in the overlay is usually the end result.

9.2. Backer Rod Material. The backer rod (Figure 9.2.) is a compressible, nonshrinking, nonabsorptive material whose melting point should be higher than the pouring temperature of the sealant. The backer rod should be approximately 25 percent wider in diameter than the nominal width of the crack. The larger size will enable the sealant to be inserted without dislodging the backer rod. The backer rod should be placed to a depth that will provide a shape factor (depth to width ratio) of approximately 1. However, the maximum depth that the backer rod should be placed is approximately 3/4 inch (19 millimeters). This will provide a reservoir for the sealant that will maintain the internal stresses in the sealant at a minimum. High internal stresses can create cohesion failure, a splitting of the material, or dislodge loose aggregate from the pavement, damaging the effectiveness of the seal. However, if the shape factor is too small, adhesion failure can occur; therefore, it is important to maintain the proper shape factor.

9.3. Inspection Prior to Sealing. The cracks should be inspected immediately prior to sealing. This will ensure that the backer rod is at the specified depth and that debris has not been blown back into the crack. Clean cracks are essential in obtaining adhesion between the sealant and the crack face.

9.4. Sealant Temperature and Application. The temperature of the sealant should be checked to make sure it is at the manufacturer’s recommended application temperature. The nozzle of the application equipment is inserted into the crack, allowing the crack to be sealed from the bottom to the top (Figure 9-3). Sealing in this manner minimizes bubbling of the sealant due to entrapped air. The sealant should be recessed approximately 1/8 to 1/4 inch (3 to 6 millimeters) below the pavement surface to prevent tracking. A squeegee may be used to remove excess sealant from the pavement surface when a crack is overfilled (Figure 9-4).

9.5. Crack Sealing Delays. Any cracks that are not sealed the same day they are prepared should be blown out with compressed air before the sealing operation continues. If rain delays the sealing operation, the cracks should be allowed to dry and may require additional cleaning to remove any debris that may have been washed into the crack by rain. This debris can be effectively removed by the sandblaster, wire brushes, or HCA heat lance, but not by using only compressed-air cleaning.

9.6. Inspection After Sealing. After the cracks have been sealed (Figure 9.5.), they should be inspected to ensure the sealant is bonding to the pavement and that the cracks were not overfilled. Overfilled material can track onto the pavement surface and/or stick to pedestrians’ shoes. The sealant should also be inspected to ensure the proper sealant recess has been obtained. Sealants that have not been recessed may be pushed above the pavement surface as the pavement expands and become damaged by traffic. Cracks that have been underfilled can have additional crack sealant applied.

PROBLEM AREAS

10.1. Categories of Problems. Many problems that arise during a sealing project can be divided into three categories—crack sealant materials, crack preparation, and crack sealant application. The following information is presented for these three sealing problems.

10.1.1. Materials. One of the main problems associated with the sealant materials is nonconformance to the required specification. This problem can be minimized by having the sealant tested by an independent laboratory. Another problem is a combination between materials and application which involves the sealant not setting up or curing once it has been applied to the crack. This problem is often caused by overheating the sealant before it is applied to the crack. The overheating can be caused by heating the sealant at too high a temperature or heating it at the recommended pouring temperature for an extended period of time. Most sealants used to seal cracks in asphalt concrete pavements are asphalt cement based materials, and overheating causes the light volatiles to “cook off” or evaporate. This causes the sealant to become brittle, resulting in premature failure of the sealant. This problem can be solved by monitoring the temperature of the sealant in the application equipment and discarding any material that has been heated for longer than 4 hours. It is also recommended that the sealant remaining in the equipment be discarded and the equipment thoroughly cleaned after each day’s work has been completed.

10.1.2. Preparation. The main problem associated with crack preparation is the cleanliness of the crack. The crack sealant will not adequately bond to the pavement if there is dust, debris, or loose aggregate remaining in the crack. Damaging the pavement during the routing process can also be a problem. Care must be taken by the equipment operator so that each crack is followed and the speed of the router is controlled to prevent the router from jamming in the crack. Careful quality control and inspection can minimize these problems.

10.1.2.1. Checking for dust and debris in the crack is a relatively simple procedure; rub a finger along the crack, and, if the finger gets dusty, the crack is dirty. Checking for moisture is more of a judgment decision. There is no test for checking the moisture of a crack except by observation or feeling with one’s hand. It is important that the crack is dry at the time of sealant application so that the sealant will bond to the pavement.

10.1.2.2. The last problem dealing with crack preparation is deciding which method to use. This is a problem because most cracks are not uniform in size and the surrounding pavement will have varying degrees of deterioration. Decisions must be made as work progresses. The main consideration for crack preparation is that the crack be cleaned without damaging the surrounding pavement.

10.1.3. Application. There are two major problems associated with crack sealant application. The first problem, brittleness of the sealant material due to overheating or prolonged heating, was discussed in the “Materials” paragraph. Brittleness is a materials problem because some sealant materials are more susceptible to overheating than others, but it is also an application problem because it can be corrected by implementing a good quality control program. The second problem is overfilling the crack. The sealant can be tracked onto the pavement and abraded if the crack is overfilled. Quality-control measures and inspection can reduce the overfilling of cracks. A squeegee or similar object can be used to remove areas of excess sealant.