Chapter 3: Crack Sealing, Crack Filling & Joint Sealing of Flexible & Rigid Pavements

3.0 Construction

3.1 Safety and Control

Field staff can examine and approve the contractor’s traffic control plan prepared in accordance with the Agency’s specifications and traffic control requirements.  The signs and devices used must match the traffic control plan.  The work zone must conform to the Agency’s specifications.  All workers must have all required safety equipment and clothing. Signage must be removed when it no longer applies.

3.2 Equipment Requirements

Equipment requirements vary according to the treatment method chosen.  Equipment may be required for:

• Routing or Sawing
• Crack Cleaning and Drying
• Backer Rod Placement (PCC Pavements)
• Application of Sealer or Filler
• Finishing Method
• Trafficking and Subsequent Treatments

Equipment requirements are covered in more detail in Sections 3.4 through 3.7 of this chapter.

3.3 Climatic Conditions

Crack sealing treatments should be placed when cracks are at their midpoint to maximum point of expansion.  This is not always practical because cracks are at their maximum point of expansion during the coldest months.  Most crack fillers and sealants have limitations to their ability to wet and form films at low temperatures.  This is due either to a high viscosity or the fact that they are emulsified.  Additionally, severe winter climates make working conditions difficult and in some regions impossible.  With these considerations in mind, typically the best time for application may be fall and spring when air temperature is between7°C and 18°C (45 to 65°F). 

Under these conditions, cracks are usually at or near their mid-point of movement, helping to ensure that the crack sealant or filler will not be overly extended or compressed when temperatures rise or fall, respectively, following application of the sealant or filler.  In addition, application in moderate temperatures ensures that temperatures have not dropped to a point where sealants will have difficulty wetting the crack walls or forming continuous films.  In colder climate areas, spring and fall work conditions are required to allow workers to properly prepare the pavement surface and install products.

3.4 Preparation

Site preparation requirements vary according to the sealing or filling method and materials chosen for the project. The following describes site preparation in further detail.

3.4.1 Routing or Sawing

When routing or sawing is incorporated, cracks need to be cleaned and dried prior to applying the filler or sealant.  When pavements are cracked extensively, routing or sawing of cracks may not be appropriate.  Crack cutting becomes especially important in climates where crack movement is very high.  Crack cutting allows more filler to be used and provides better control of the crack channel shape.  Secondary cracks along the primary crack are not usually routed.  Crack cutting and routing equipment includes vertical spindle routers, rotary impact routers, and random crack saws.  Damage to the pavement should be kept to a minimum by clean cutting.  The use of carbide bits improves the quality of cutting and typically produces clean reservoir cuts.  Figure 17 illustrates a rotary impact router in use.

Figure 17: Crack Routing Operation

3.4.2 Cleaning and Drying

Debris left in a crack, resulting from sawing, routing, or pavement use will affect the adhesion of the sealant or filler.  Debris also contaminates the sealing or filling material and reduces cohesion.  Reduced adhesion or cohesion normally results in early failures.  To avoid these contamination-related failures, sawed or routed cracks must be cleaned prior to being treated.  Several cleaning methods can be used, including:

• Air blasting
• Hot air blasting
• Sand blasting

Air blasting involves directing a concentrated stream of air into the crack or joint to blow it clean. Air blasting equipment is effective and efficient for cleaning cracks.  Air blasting is not efficient for drying cracks.  Should a crack require drying, hot air blasting should be used.  Air pressure should be a minimum of 670 kPa (97 psi) with a flow of 0.07 m3/s (2.5 ft3/s).  Air blasting equipment must be equipped with moisture and oil traps.

Hot air blasting is done using a hot compressed air heat lance.  While cleaning and drying the crack, hot air blasting also promotes enhanced bonding associated with the crack edges being warmed.  Care must be taken to ensure that the pavement is not overheated or heated for excessive periods of time as this will result in unnecessary hardening of the asphalt binder in the pavement adjacent to the crack.

Sand blasting involves directing a stream of sand entrained in compressed air into the crack. The abrasive nature of the sand cleans the crack or joint.  Sandblasting, which is used for cleaning cracks in PCC pavements by many states, is an effective treatment.  However, sandblasting is messy and typically requires a two-phase operation.  The first operation is cleaning the joint surface; the second cleans the sand from the joint and its surroundings.  On new PCC pavements, sand blasting is required to clean the surface prior to applying the sealant.

Wire brushing or brooming involves the use of a wire broom stock or stiff standard broom to brush out the crack or joint. Wire brushing can be an effective cleaning method.  Wire brushing may be done manually or using power driven brushes.  Figure 18 illustrates the manual crack cleaning method using a broom

3.4.3 Backer Rod (PCC Pavements)

Installation of a backer rod should be performed once a joint or crack channel has been cleaned.  Installation of the backer rod into the channel is accomplished either by manual means or through the use of a specialized three-wheel tool.  Two wheels ride on either side of the crack while the third rolls the backer rod into the crack channel.  Figure 19 illustrates a backer rod installed in a crack channel.

3.4.4 Application of Sealer or Filler

The material selected will in part determine the application method.  Typically, asphalt emulsions are applied directly to the cracks.  Hot applied rubber modified sealants, especially asphalt rubber, have excellent adhesion and do not require a thin sand coating (blotter coat) prior to traffic use.  Emulsions must be blotter-coated prior to being trafficked.  Emulsions may be applied via gravity feed devices, such as pour pots, or via pressure hoses.  Some emulsions may require heating to achieve an appropriate application viscosity.  Hot-applied rubberized sealants need to be agitated and heated and maintained at the correct temperature throughout their application.  For polymer and rubber-modified materials, control of temperature is important in preventing degradation.  For hot-applied fiber-filled materials, the fiber may settle and require agitation.  For such materials, indirect oil heating is recommended.  The required capacity of sealant or filler application equipment is determined by the job size.  Preheating the material before use is advisable to ensure optimal productivity.  Figure 20 illustrates a hot pressure feed sealing operation and a gravity-fed pour pot.

The application rate of a sealant or filler is important to the quality of a crack sealing or filling project.  Over-applied sealant or filler material can cause problems such as fat spots, localized tenderness, and flushing when treated areas are overlaid with hot mix.

3.5 Finishing

Finishing techniques will vary depending on the application and type of material chosen.  Flush finishes and overbanding methods require the use of a squeegee.  In some cases, a preformed plate on a hand lance assists in making the required flush result.  Figure 21 shows three typical flat finishing techniques.  (All sealant left on the surface should be squeegeed to prevent a rough ride.)

Blotter coats of clean sand are usually used with emulsion crack filling to prevent pick-up of an overband.  A blotter coat is often used to prevent pick-up upon re-opening the roadway to traffic.  To ensure a high quality blotter coat, only clean and dry sand should be used.  Figure 22 illustrates the brooming of a blotter coat over a treated crack.  This practice is not recommended because it leaves broom marks and voids in the sealant.

3.6 Trafficking and Subsequent Treatments

Sealants and fillers undergo a curing cycle depending on the type of material used.  Emulsions cure by water loss and reduce in volume.  This process usually takes several days and creates a concave surface in the crack.  Generally, cracks filled with these materials should not be overlaid for at least a year.  Traffic should not be allowed until after the emulsion has set sufficiently so that the sealant/filler will not be removed by passing tires.

Hot-applied materials are thermoplastic which set as they cool, provided that no diluents such as solvents are used in their formulation.  These materials produce a non-tacky finish once the material reaches ambient temperature.  A blotter coat can assist in this process.  In addition, hot applied sealants require a three- to four-month cure time prior to being covered with a blanket or seal.  Hot-applied materials should not be placed over cold mix patches because the hot-applied material will adhere to the patch and pull it out.

Silicone, along with two-part systems (used in PCC pavements), cure by cross-linking caused either by ambient moisture or a two-part chemical reaction.  When using these materials, the manufacturers’ recommendations must be followed.  Overbanding and capping must not be performed when using these materials and they should be applied such that they do not receive direct traffic.  Sanding the fresh crack seal reduces safety concerns (slick pavements) and improves the surface appearance (aesthetics).  Excess sand must be swept away before opening the road to traffic.  Cold-applied sealants require a one-year cure time prior to being covered with a blanket or seal.

3.7 Job Review - Quality Issues

Quality issues are typically related to the poor choice of sealing and filling methods and poor workmanship.  Common examples of poor sealing and filling methods include excessive use of sealant and multiple uses of treatments over several years.  One common example of poor workmanship includes over-filling without proper finishing.  Figures 23 through 25 illustrate these commonly addressed quality issues.  These practices directly impact traffic safety, smoothness and appearance for users.