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Joint Resealing

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Performed alone, joint resealing is a maintenance or restoration activity. However, performed in conjunction with tech­niques such as patching or surface grinding, joint resealing becomes a necessary part of concrete pavement restoration (CPR).

Good restoration project performance depends on the choice and timing of treatments for the condition of the pavement [1][2][3][4]. Techniques may enhance the effectiveness of other repairs performed together. Techniques which may enhance joint resealing include: full-depth repair, partial-depth repair, slab stabilization, diamond grinding, load transfer restoration, retrofit PCC shoulders and edge drain installation. In restoration, resealing joints and cracks is the last technique in the sequence (Figure 12).

Figure 12. The sequence of operations in a CPR project [5]. Note that the double boxes indicate core activities which almost always are necessary in a typical CPR project.

Traffic control costs play an important role in resealing operations and sealant selection [6]. An optimal rehabilitation design employs sealant that will last at least as long as the restored pavement [7]. With many materials, joint preparation will cost more than the sealant material itself [8]. That is why it is im­perative that a rehabilitation design process consider traffic control and sealant life expectation in life-cycle costing.

Slab Stabilization

Slab stabilization restores support to a pavement which has developed voids beneath slab corners or edges. Pozzolanic, asphalt or urethane-based materials pumped beneath the slab fill the voids and restore support. Lifting the slabs with the slab stabilization process is not recommended in most cases. See references 4[9],5[10],8[11],9[12], and 18[13] for more information.

Patching

Restoring structural integrity and ride quality may re­quire patching the pavement either full or partial-depth. Partial-depth repairs address spalling and can reestablish the joint reservoir through spalled areas. Full-depth repairs restore load transfer and provide completely new joints. For more information see ACPA bulletins Guidelines for Full-Depth Repair and Guidelines for Partial-Depth Repair [14][15].

Diamond Grinding

Diamond Grinding restores a smooth pavement pro­file by removing a small depth of the concrete sur­face [nominally 0.25 in. (6 mm)]. The operation blends low and high areas and smooths faulted joints. Diamond Grinding is almost always required with a CPR project. For more information see ACPA bulletin Diamond Grinding & CPR 2000 [16].

Retrofit Drainage

Edge drains along the pavement shoulder provide an avenue to remove water from the pavement system. Installing drains up to one year before rehabilitation helps the pavement seat itself and establish support. Retrofit drains also protect against recurrence of water damage in the future. See references 4[17],5[18],8[19],9[20] and 18[21] for more information.

Resealing Applications

Preparation is essential in joint resealing. One demonstration study of airports found a 50 percent savings in the annual cost of joint resealing on projects using proper preparation techniques [22]. Successful resealing consists of five steps:

  1. Old sealant removal.
  2. Shaping the reservoir.
  3. Cleaning the reservoir.
  4. Installing the backer rod.
  5. Installing the sealant.


Anticipating the time of year a pavement will be re­sealed is an important step in designing a resealing project. The time of year or temperature influences the amount and direction of joint movement after job completion. For example, installing a sealant during a region's warmest weather ensures that the sealant will always be in tension. This is because the joints will be fully closed during installation. However, a sealant installed during moderate regional temperatures will also undergo compression. The designer must verify that the sealant will be capable of handling the full range and direction of movement based on the anticipated installation temperature. Table 8 shows the range of movement placed on a sealant depending on the installation temperature. Probably the most favorable times of year are spring and fall because daily temperatures are moderate [23][24][25].

Another very important component of resealing joints and cracks is construction inspection. Several reports for airports and roadways cite a lack of emphasis on the importance of good joint sealing as a major prob­lem. With the proper emphasis, inspection can lead to vastly improved sealing technique and perfor­mance [26][27][28]. The inspection process improves the knowledge of contractor and agency personnel. This will heighten the level of competence and overall project quality.

Table 8. Example Range and Direction of Movement on a Liquid Sealant Placed During Cold, Moderate and Hot Temperatures
Temperature at Seal Installation Expected Movement Range (in mm) Movement After Sealing Reservoir Cut Width (in mm) Maximum Expected Width (in mm) Minimum Expected Width (in mm) Percent Sealant Stretch Percent Sealant Compress
Cold 0.15 (3.8) Closure 0.375 (9.5) 0.4 (10.2) 0.25 (6.4) 7 33
Moderate 0.15 (3.8) Both 0.375(9.5) 0.43 (10.9) 0.28 (7.1) 15 25
Hot 0.15 (3.8) Opening 0.375 (9.5) 0.5 (12.7) 0.35 (8.9) 33 7

Old Sealant Removal

Figure 13. Sawing/reshaping a sealant reservoir with a wet diamond blade.

Adhesion will not develop by simply filling over an existing sealant. Removal of the old sealant and joint face cleaning are essential. These processes provide a surface to which a new sealant can bond. It is im­perative that methods for removing old sealant do not damage the joint reservoir. The following provide acceptable results [29][30]:

  • Manual Removal: Typically, manual removal is easy for compression seals. This simple method provides a quick result whenever feasible and does not leave much material on the reservoir sidewalls.
  • Sawing: The most common removal and effi­cient method is sawing with diamond blades (Figure 13). It is efficient because sawing also shapes the reservoir for the new material. However, it may not be effective on sticky seal­ing materials such as PVC coal tar. Sticky materials clog diamond blades.
  • Plowing: Plowing can be very effective for removing most of the old sealant [31]. A small plow pulled through the reservoir dislodges the material. Operators must be careful in selecting the plow design. Avoid vee-shaped plows. The vee-shape tends to scour the reservoir corners and can easily spall surrounding concrete. Very little damage occurs with a rectangular plow.
  • Cutting: Cutting requires a laborer to run a knife blade along the face(s) of the joint. Afterward, the sealant easily pulls free by hand.

Shaping the Reservoir

Sawing/widening shapes the reservoir after sealant removal. Saws with dry or wet diamond blades are acceptable [32][33]. The blades remove any remaining old sealant and provide the proper dimensions for the new sealant.

In certain instances eliminating this step may be ac­ceptable. Shaping is unnecessary if sealant removal was by hand and the existing reservoir provides adequate dimensions. Sawing out the old sealant typically provides an adequate reservoir and should not require this step either.

Some minor spalling along the joint face will not in­hibit performance of most sealants. However, some patching is likely for larger spalls. The specifications should detail areas requiring patching so that it can be completed before reservoir cleaning and sealant installation operations.

Resealing pavements with plastic or metal joint in­serts requires first removing the insert [34]. Afterward sawing provides smooth vertical faces for the new sealant.

Cleaning the Reservoir

Cleaning is the most important aspect of joint seal­ing. For every liquid sealant, manufacturers require essentially the same cleaning procedures. Likewise the performance claims of any liquid sealant product is predicated on those cleaning procedures.

Reservoir faces require a thorough cleaning to be sure of good sealant adhesion and long-term performance. No dust, dirt or visible traces of old sealant should remain on the joint faces after cleaning. The ability to attain this condition may depend on the reservoir width. Most contractors report that it is easier to consistently get joints clean if they are at least 3/8 in (9 mm) wide. Cleaning 1/8 in (3 mm) or even 1/4 in (6 mm) is very difficult.

Do not use chemical solvents to wash the joint reser­voir. Solvents can carry contaminants into pores and surface voids on the reservoir faces [35]. Con­taminants will inhibit bonding of the new sealant.

Figure 14. Sanblasting a joint to remove any remaining residue and ensure a clean joint face to adhere to.

Proper cleaning requires mechanical action and pure water flushing to remove contaminants. The following outlines the recommended procedures [36]:

a) Immediately after sawing, a water wash removes the slurry from the sawing operation. Contractors perform this operation in one direc­tion to minimize contamination of surrounding areas.
b) After the joint has sufficiently dried, a sand­blasting operation removes any remaining residue. Do not allow sandblasting straight into the joint. Holding the sandblast nozzle close to the surface at an angle to clean the top 1 in. (25 mm) of the joint face provides cleaning where needed (Figure 14). One pass along each reservoir face provides excellent results. This not only cleans the joint faces, it provides texture to enhance sealant adhesion.
c) An air blowing operation removes sand, dirt and dust from the joint and pavement surface. Conducting this operation just prior to sealant pumping ensures that the material will enter an extremely clean reservoir. The contractor must provide assurance that the air compressor filters moisture and oil from the air. The com­pressor should deliver air at a minimum 120 cu.ft./min. (3.4 cu.m./min.) and develop at least 90 psi (0.63 MPa) nozzle pressure [37][38].
d) Some contractors also use a vacuum sweeper and hand brooms to keep the surrounding pavement clean.

Compression sealants do not require steps b or c.

Figure 15. A double-wheeled, steel roller for backer rod insertion to the desired depth.

Backer Rod Installation

Backer rod installation is made after cleaning and before liquid sealant installation. It must be compati­ble with the liquid sealant with a diameter about 25 percent greater than the reservoir width. Backer rod inserts easily with a double-wheeled, steel roller or any smooth blunt tool that will force it uniformly to the desired depth (Figure 15). Rehabilitation work with slightly faulted joints may require a single-wheeled roller. The tool must not puncture or stretch the material. A steel roller allows exchange of the center insertion wheel for different depths and pro­vides the most consistent results. Ensuring that the backer rod is at the proper depth cannot be over emphasized. Good practice is to roll the insertion wheel over the backer rod twice.

Sealant Installation

An inspector should not allow a contractor to begin installing sealant until the reservoir meets cleanliness requirements. With a finger the inspector should wipe the reservoir sidewalls to check for dirt and dust (Figure 16). The inspector should require further cleaning with any traces of contamination.

Installation requirements are slightly different for each sealant type. Manufacturers recommend some curing time before opening to traffic for most liquid sealants. Some liquid seal manufacturers also specify limits on the ambient and pavement temperatures for installa­tion. Compression seal manufacturers specify desirable limits on sealant stretch and lubrication. Table 9 provides general recommendations for dif­ferent sealants. It is important to always consult the sealant manufacturer's particular product recommendations.

Typical manufacturer's limitations on pavement and ambient placement temperature, and recommended curing periods for common sealing materials.
Sealant Type Min. Placement Temperature Concrete Curing For Non-Fast Track Project Time to Open Sealed Joint to Traffic
Asphalt Based 50°F (10°C) 7-days(1,2,3) Upon Cooling
PVC Coal Tar 50°F (10°C) 7-days(1,2,3) Upon Cooling
Cold-Pour Silicone 40°F (4.4°C) 7-days(1,2,3) Upon Cooling
Preformed Compression 30°F (-1.1°C) None Immediate
(1) For new concrete only. The seven days must be free of precipitation.
(2) Assumes the joint reservoir is dry and preparation removes all curing compound, dust, dirt and laitance.
(3) Most manufacturers provide more detailed recommendations and shorter curing time requirements for special applications (ie. Fast-Track paving).
Curing time varies by temperature and humidity. At 75°F (24°C) and 50% relative humidity, the sealant will cure to a tack free surface in 30 minutes. At 40&deg'F (4°C) it takes 2-4 hours to become tack free.
Figure 16. Noticeable dust on inspector's fingers.

Liquid - Liquid sealants require uniform installation. Over-filling or completely filling the reservoir is not desirable. Filling the reservoir from the bottom up­ward avoids trapping air pockets. Remember to recess the sealant at least 1/4 - 3/8 in. (6-1 0 mm) below the surface of the pavement.

It is important that the contractor pumps the sealant through a nozzle sized for the width of the joint reser­voir [39][40]. The nozzle should fit into the reservoir to allow pumping to the bottom. The injection nozzle forms the sealant bead. Good practice is to draw the nozzle toward the operator (Figure 17). Pushing the nozzle may result in voids and nonuniform sealant cross-section [41].

Special attention to the heating temperature is vital at the start of a work day [42]. No sealant should be installed before reaching proper installation temperature. About the first 1 gal. (4 liter) of material is unusable because cooled sealant and flushing oil remains in the pumping unit hoses and nozzle. Discard this material and begin pumping only after fresh sealant is ejected from the nozzle at an acceptable temperature.

Low-modulus silicone sealants which are not self-leveling require tooling to provide desired results. After sealant pumping, a laborer draws a tool or backer rod strip over the fresh silicone. This forces the sealant into contact with the sidewalls at the top of the reservoir and produces the desired shape fac­tor (Figure 18) [43][44]. Tooling is necessary within about 10 minutes of installation before the sealant begins curing and forms a "skin".

Figure 17. Drawing the nozzle toward the operator during installation of liquid seal.

It is extremely important that the reservoir walls be dry before installing any liquid sealant [45][46][47]. Moisture will boil in contact with hot-pour materials, forming steam that will bubble the sealant. Moisture will inhibit silicone sealant adherence. Moisture is not as critical for compression sealants. Most silicone manufacturers require a drying time or surface-dry condition before installation. This includes drying after wetting due to water flushing and even rainfall. Follow the manufacturer's guidelines for optimum seal adherence.

Figure 18. Close-up of low-modulus silicone sealant tooling.

The sequence of installation is important where transverse joints are sealed with silicone and longitudinal with hot-pour material. It is good practice is to seal transverse joints first. This prevents hot-pour material from flowing into and contaminating the transverse reservoirs. Some contamination of the longitudinal reservoirs will occur while placing the transverse silicone. However silicone is somewhat more viscous than hot-pour and the extent of longitudinal joint contamination is tolerable.

It is important to examine all sealant after installation. An inspector should look at the material and seal characteristics. The simple knife test can indicate how well the sealant adhered to the sidewalls. This early inspection provides assurance that the installation meets requirements.

Testing of silicone sealant curing can only be completed after 14 - 21 days. The inspector can remove small 2-in (5-cm) sample of sealant. Stretching the segment about 50 percent [1 in (2.5 cm)] for about 10 seconds before releasing gives a quick check. A fairly fast and uniform relaxation of the sample in­dicates adequate curing. Slow rebound and curling of the sample indicates differential curing. The curl results from the upper (cured) seal retracting faster than the lower (less cured) portion. It is important to repair the 2-in (2.5 cm) gap in the sealant where the inspector extracted the sample. Use the same brand of material to take advantage of the good adherence the material has to itself.

Compression - A compression sealing operation requires application of a lubricant/adhesive to the sealant edges and/or reservoir sidewalls. The com­pression seal is then mechanically compressed and inserted into the reservoir. The lubricant/adhesive material eases sealant insertion, and forms a weak adhesive to help hold the seal in place.

Figure 19. Compress-eject machine used for compression seal installation.

Joint wall inspection before installation will find any suspect areas. Raveling, spalling or other irregularity of the joint walls pose potential problems. These areas could reduce the seal's lateral pressure and allow the seal to extrude or pop from the joint [48]. Agreement between the engineer and contractor on potential problem areas will allow repair before the contract is complete and seal damage occurs.

Sealant stretch of three percent or less is desirable. Some neoprene seals are capable of stretching by as much as 50 percent. Stretching reduces the cross-section and compression recovery [49]. More than five percent stretch is excessive and could be detrimental. Some sealants can later break into pieces if stretched excessively during installation. Special attention during installation is essential to avoid twisting, nicking or stretching the sealant.

Monitoring sealant stretch is an important check of installation methods. Good specifications require the contractor to lay a length of sealant parallel to a joint and cut the seal to exact length. Excess seal protruding from the joint after the contractor installs the seal is due to stretch. A measurement of this pro­truding seal provides an accurate number for calculating stretch percentage.

Most compression seal manufacturers make equip­ment for accurate seal installation (Figure 19). The most common are compress-eject machines. The machines compress and insert a seal to a desired depth in continuous motion. The most advanced equipment automatically applies lubricant/adhesive along the sealant edges. Compress-eject machines remove most stretching and twisting problems that accompany hand installation [50]. The machines are usually self-propelled or semi-self-propelled with a guide that keeps them on course over a joint.

Burrs along the sawed joints may make seal installa­tion difficult. Dragging a blunt pointed tool along sawed joints removes sharp edges. A mechanized wire brush will also remove burrs and provides con­sistent results [51]. While this simple step eases seal installation, it may contaminate clean joints and should be done ahead of reservoir cleaning only when needed.

Avoid splicing compression seals as much as possi­ble [52]. Splices are discontinuities prone to moisture infiltration and dislodging by traffic. Use only one length of compression seal for transverse joints less than 25 ft (7.6 m) long. For transverse joints on wider pavements one splice is acceptable. For longitudinal joints cut the compression seal at the transverse joint crossings.

Preparing New Pavement Joints

Figure 20. Tining machine running over a blank out strip.

The steps for successfully sealing new pavement joints are very similar to those required for resealing joints. Because no old sealant is removed, reservoir shaping is simple. A single or double saw cut forms the reservoir.

Some agencies require contractors to blank-out tining at the location of skewed contraction joints. This prevents minor spalling at the intersection of the tine slots and the skewed reservoir. The blank-out is usually done with a 4 - 5 in (10 - 13 mm) wide piece of astroturf or other rugged fabric. Workers position the blank-out fabric at the joint location. The tining machine or hand tine operator pulls the rake over the blank-out fabric (Figure 20).

New pavement joints must also be clean and dry before installing the sealant. Curing compound on joint faces will inhibit sealant bond and require sand­ blasting. Airblowing with oil-free compressed air is equally important in sealing joints for the first time. Removal of dirt and other laitance in the reservoirs from construction traffic and dusty conditions is necessary.

Manufacturers of silicone sealants recommend that the standard concrete cure for seven dry days before sealing. For Fast Track operations, most manufacturers make some exception to this require­ment. It is important to contact the sealant manufacturer for advice on use of their product in Fast Track projects.

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