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Joint Sealing

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The purpose of joint sealant is to minimize infiltration of surface water and incompressible material into the joint system. Sealants can also reduce dowel bar corrosion potential by reducing entrance of de-icing chemicals. Sealant use dates back to the early 1900's.

Long-standing practice has been to seal all concrete pavement joints to minimize water and incompressible infiltration. Some owners/agencies no longer require joints to be sealed under certain conditions. Joint sealing may be omitted in newly constructed, doweled concrete pavement and some specialty concrete pavement types where erosion of the subbase is not of concern (e.g., undoweled bonded concrete overlays of asphalt pavements), but any previously sealed joint should be resealed as necessary during concrete pavement preservation activities. Joint sealing practices vary from location-to-location, but preliminary evidence suggests that while it might be acceptable to leave joints in high-speed highway pavements unsealed, joints in urban environments that service low-speed traffic should be sealed. In addition, airfields require sealed joints to prevent foreign object debris (F.O.D.) issues.

Introduction

The purpose of joint sealant is to minimize infiltration of surface water and incompressible material into the joint system [1][2][3]. Sealants also reduce dowel bar corro­sion potential by reducing entrance of de-icing chemicals. Pavement engineers have recognized the need for concrete pavement joint sealants for many years. Sealant use dates back to the early 1900's [4][5]. Today, nearly every agency building and maintaining concrete roadways or airports requires joint sealing.

Basic Considerations - Water can contribute to subgrade or subbase softening, erosion and pumping of subgrade or subbase fines. This degradation results in loss of structural support, pavement settlement and/or faulting [6][7][8][9]. Unfortunately it is not practical to construct and continually maintain a completely watertight pavement. Therefore engineers use joint seals to minimize passage of surface water through joints.

Sealing prevents incompressibles from entering joint reservoirs. Incompressibles contribute to spalling and in extreme cases may induce "blow-ups" [10]. In either case excessive pressure along the joint faces results as incompressibles obstruct pavement expansion in hot weather. Years ago, the term "joint fillers" de­scribed materials placed in joints [11]. These materials aided more in keeping out incompressibles than minimizing water infiltration.

Many factors play a role in joint and sealant design. Sealant material selection considers: 1) environment, 2) life-cycle cost, 3) performance, 4) joint type, and 5) joint spacing [12][13][14][15][16].

Required sealant characteristics differ for different joint types [17]. A sealant for a longitudinal joint does not need to be as elastic as one for a transverse joint. This is because tied joints, like those separating longitudinal lanes and shoulders, undergo virtually no movement.

Transverse joints in long-panel reinforced pavements open wide when air and pavement temperatures are cool. Transverse contraction joints of short panels [<20 ft (6 m)] undergo similar but smaller movements. These movements induce larger states of stress and strain within a sealant than typically found in a longitudinal joint. The sealant must be capable of handling these states in order to perform over the range of expected joint movement.

Reservoir dimensioning is a significant aspect of sealant design and performance. Reservoir dimensions are set to help the sealant material withstand joint opening and closure movements. An improperly dimensioned reservoir will not allow the maximum per­formance from any sealant.

The most critical aspect in sealant performance is reservoir preparation. A considerable investment in joint preparation and cleaning activities is necessary for almost all sealant types. There is little doubt that poorly designed and/or constructed joint sealants will perform poorly.

Some pavement design factors also influence sealant performance despite installation quality. Under high traffic conditions and poor drainage design even tradi­tionally non-erodible base materials can cavitate. Mechanical load transfer and positive pavement struc­ture drainage reduce potential for pumping and joint faulting. Sealants can be damaged by these problems. Slab size design is also critical to negate the impacts of temperature curling and moisture warping.

Use of expansion or pressure-relief joints in concrete pavement may negate the effectiveness of any sealant. In the past, designers placed transverse expansion joints to relieve compressive forces in the pavement and limit blow-ups. However, in many cases the ex­pansion joints allowed too much opening of adjacent transverse contraction joints which led to loss of ag­gregate interlock and sealant damage [18]. By eliminating unnecessary expansion joints, contraction joints will remain tight and provide good load transfer and effective seals.

Necessity

Figure 1. Avenues for water infiltration into a pavement system [19].

Debate on the need for joint sealing has raged for many years. The basis for debate hinges on the ef­fectiveness of joint sealants. Widespread belief is that sealing prolongs pavement life by providing protec­tion. This has been substantiated in many field studies [20][21][22][23][24][25][26]. However, there have also been studies which show a negligible or even negative impact of joint sealing [27][28][29].

Water is definitely a contributor to pavement distress. For many years, concrete pavement designs included relatively impermeable materials surrounding the pave­ment layers. These "bathtub" pavement sections were particularly prone to moisture-related problems [30][31][32]. The need to minimize water infiltration in these pavements focused increased attention to joint sealing.

To maximize pavement performance the designer must provide a means to control water. Limiting the amount of water that can get to the base and subgrade layers is one key element. Providing a system to efficiently remove water from within the pavement layers is another key. The pavement surface is just one of five points of water entry into a pavement and subgrade (Figure 1) [33]. Water present in the soil can migrate to critical locations in a pavement through capillary action and water vapor from the water table. Water may also come from the edge of shoulders, from poorly de­signed or maintained ditches and from natural high-ground runoff. However, surface water is typically the largest source and has the greatest impact on the pavement system.

Figure 2. Transverse joint spalling developed on short panel pavements with and without sealants. Note that the joints were sealed only once at initial construction - maintenance of joint seals would have decreased the development of spalling in joints sealed with hot-pour [34].

Justifiably, much attention is paid to sealant effec­tiveness because joints are controllable access points for surface water. In the past, some engineers thought sealing was not cost-effective because of poor perfor­mance of the most common materials [35]. Improve­ments over the past 30 years have produced effective sealing materials and procedures. Correct sealant application and maintenance can minimize water damage and increase pavement longevity [36][37].

Recently permeable bases have grown more pop­ular as a means to control water in a pavement system [38]. Permeable bases use a uniform grada­tion which leaves many voids for water passage. Under a pavement, water flows quickly through a permeable base to an edge drain system. The drainage system carries water away from the subgrade to ditches or storm sewer pipes. Many agencies are also successful installing edge drain systems along existing concrete pavement. These outlet systems require frequent maintenance for satisfactory long-term performance.

Joint sealing is still recommended, even on pavements supported by permeable base layers. Some agencies have hypothesized that a permeable base may make sealing unnecessary by negating the need for surface water control. Although this seems logical and some successful field experiments support the idea, significant substantiation is not yet available. An engineer should also consider the impact of incompressibles on the decision to omit joint sealing. Incompressibles that get into open joint reservoirs can cause spalling upon joint closure. This is less likely on slabs less than 20 ft. (6.1 m), because the closure is quite small. However, studies show sealing reduces joint spalling even on short-panel pavements (Figure 2) [39].

Materials

There are many acceptable materials available for seal­ing joints in concrete pavements. Sealants are either liquid or preformed. Liquid sealants depend on long-term adhesion to the joint face for successful sealing. Preformed compression seals depend on lateral rebound for long-term success. Table 1 gives descrip­tions and specifications of the available materials [40].

While many agencies specify single-component cold-pour sealants, there are no standard national specifica­tions for these materials. Each agency must either use the manufacturer's recommendations or develop its own specification.

Sealant properties necessary for long-term performance depend on the specific application and the climatic environment of the installation. Properties to consider include:

  • Elasticity: The ability of a sealant to return to its original size when stretched or compressed.
  • Modulus: The change in internal stresses in a sealant while being stretched and compressed over a range of temperatures (stiffness of material). A low modulus is desirable and is particularly important in cold weather climates.
  • Adhesion: The ability of a sealant to adhere to concrete. Initial adhesion and long-term adhesion are equally important. (Not applicable to com­pression seals.)
  • Cohesion: Ability of a sealant to resist tearing from tensile stresses. (Not applicable to compres­sion seals.)
  • Compatibility: Relative reaction of the sealant to materials which it contacts (such as backer rods and other sealants).
  • Weatherability: Ability of a sealant to resist deterioration when exposed to the elements (primarily ultra violet sun rays and ozone).
  • Jet Fuel Resistance: Ability of a sealant to resist degradation in contact with jet fuel. Some material swelling may occur in contact with jet fuel. Upon evaporation the sealant material must return to original shape and maintain adherence to the reservoir walls.


Specifiers and contractors should always contact the sealant manufacturer and read product literature for warnings of safety and environmental hazards. Project leaders should thoroughly explain potential health hazards to all project personnel. This ensures that in­spectors and contractor personnel are aware of any possible hazards before handling a product. Agency designers should also consider the costs of handling and disposing of environmentally hazardous materials in life-cycle cost analysis.

Table 1. Descriptions and Specifications for Common Sealing Materials
Sealant Type Specification Properties
Hot-Pour Joint Sealant Materials
Polymeric Asphalt Based AASHTO MO173 Self Leveling
ASTM D3405 Self Leveling
SS-S-1401 C Self Leveling
ASTM D1190 Self Leveling
Polymeric Low Modulus ASTM D3405
Mod.
Self Leveling
Elastomeric PVC Coal Tar ASTM D3406 Self Leveling
SS-S-1614 Self Leveling
Elastic ASTM D1854 Jet Fuel Resistant
Elastomeric PVC Coal Tar ASTM D3569 Jet Fuel Resistant
ASTM D3581 Jet Fuel Resistant
Cold Pour Single-Component Sealant Materials / Single Components
Silicone N.A. Non sag, toolable, low modulus
Silicone N.A. Self Leveling (no tooling), low modulus
Silicone N.A. Self Leveling (no tooling), ultra-low modulus
Nitrile Rubber Sealant N.A. Self Leveling (toolable), non sag
Polysulfide N.A. Self Leveling(no tooling), low modulus
Polymeric Low Modulus N.A. Self Leveling(no tooling), low modulus
Cold Pour Two-Component Sealant Materials
Elastomeric Polymer SS-S-200 Jet Fuel Resistant
Preformed Polychloroprene Elostomoeric (Compression Seals)
Preformed Compression Seals ASTM D2628-81 Jet Fuel Resistant
Lubricant Adhesive ASTM D2835 Jet Fuel Resistant
Preformed Expansion Joint Filler Material
Preformed Filler Material ASTM D1751
AASHTO M213
Bituminous, Nonextruding, resilient
Preformed Filler Material ASTM D1752
AASHTO M153
Sponge Rubber, Cork
Preformed Filler Material ASTM D994
AASHTO M33
Bituminous

Hot Pour Liquid

Hot-pour liquid sealants were the first type used for concrete pavement. They have evolved over many years of research and development. Manufacturers have improved their adhesive qualities and now pro­vide low-modulus materials with better elasticity.

The materials require heating temperatures usually from 350 - 400°F (177 - 204°C) for proper applica­tion. Most manufactures require melting the material in a double boiler. The inside melting vat is sur­rounded by a vat of oil. An agitator in the melting vat helps distribute the heat evenly. Both contractor and agency personnel should ensure that the material is prepared at recommended temperatures. Accurate temperature control is important for desired sealant properties [41]. Insulated hoses and applicator wands help make sure that the sealant does not lose temperature between the boiler and ejection nozzle.

Some hot-pour sealants contain poly-vinyl chloride (PVC) plastic with coal tar. These sealants are ex­tremely tacky and most are resistant to jet fuel. The PVC coal tar sealants require heating to only about 250°F (120°C) for installation. Polymer (PVC) liquid sealants require a special application nozzle that mixes two-components during application.


Silicone

Silicone sealants are a field-poured liquid with a base ingredient of silicone polymer. Agencies began using these materials in the 1970's [42]. Installation pro­cedures are similar to those for hot-pour materials. Silicone sealants come prepackaged and ready for immediate application. Most manufacturers recom­mend storing the containers out of the weather until use.

The silicone material is a single component which re­quires no mixing or heating. The material cures when exposed to the atmosphere during application. Moisture in the air helps the sealant cure to attain its final properties. However, manufacturers caution not to apply the sealant during rain, frost, or tempera­tures below the dew point.

Silicone sealants are suitable in climates with wide temperature ranges. Most develop a low elastic modulus which allows good extension and compres­sion recovery. Typical low modulus silicones can undergo at least 100 percent extension and 50 per­cent compression without detriment. Table 2 pro­vides distinction between the modulus levels of dif­ferent liquid silicone sealants [43].

Silicones require about 30 minutes curing time before opening to traffic and developing sufficient adhesion. However, the amount of time may differ depending on the manufacturer and environmental conditions. Contact a manufacturer's representative for consulta­tion on curing time needed for particular installation procedures and applications.

Table 2. Typical modulus levels of silicone sealant classifications (24).
Modulus Classification Force Required For 150% Elongation Ultimate Elongation
High >100 psi
(0.69 MPa)
<500%
Medium 40-100 psi
(0.28-0.69 MPa)
500-1200%
Low <40 psi
(0.28 MPa)
>1200%

Preformed Compression Seals

Manufacturers introduced compression seals in the early 1960's. They differ from liquid sealants because they are manufactured ready for installation. Com­pression seals do not require field heating, mixing or curing.

Unlike liquid sealants, which experience both com­pression and tension, preformed compression seals are in compression throughout their life. Therefore their success depends solely on the lateral pressure exerted by the seal.

The principle compound in compression seals is neoprene. Neoprene is a synthetic rubber which pro­vides excellent rebound pressure under compres­sion. The seals consist of a series of webs. The webs provide the outward force which holds the sealant against the reservoir walls.

If a compression seal is undersized, joint opening may become too wide at low temperatures. The seal will lose contact with the reservoir walls and loosen. Also expansion/isolation joints in the pavement may allow any contraction joints within about 100 ft (30 m) to open too wide. Careful consideration of these fac­tors is essential when sizing compression seals.

Manufacturers provide seals of various nominal widths and depths. The appropriate sealant width is greater than the maximum (coldest weather) joint reservoir width. This is about twice the width of the reservoir. The reservoir depth must exceed the depth of the compressed seal, but does not relate directly to the width of the reservoir. Good performance results when the seal remains compressed at a level between 20 and 50%. Table 3 provides typical com­pression seal dimensions for standard joint widths and slab lengths [44]. Final seal size selection must also consider placement temperature.

Table 3. Sizing recommendations for preformed compression seals (26).
Joint Spacing [ft(m)] Minimum Reservoir Width [in(mm)] Minimum Reservoir Depth [in(mm)] Relaxed Seal Width [in(mm)]
15 (4.6) 1/4 (6) 1-1/2 (38) 7/16 (11)
20 (6.1) 5/16(8) 1-1/2 (38) 5/8 (16)
25 (7.6) 3/8 (10) 2 (50) 11/16 (17)
30 (9.1) 1/2 (13) 2 (50) 1 (25)

Backer Rods

Table 4. Sizing recommendations for backer rods (26).
Reservoir Width Backer Rod Diameter
1/8 in. (3 mm) 1/4 in. (6 mm)
3/16 in. (5 mm) 1/4 in. (6 mm)
1/4 in. (6 mm) 3/8 in. (8 mm)
5/16 in. (16 mm) 3/8 in. (10 mm)
3/8 in. (10 mm) 1/2 in. (13 mm)
1/2 in. (13 mm) 5/8 in. (16 mm)
5/8 in. (16 mm) 3/4 in. (19 mm)
3/4 in. (19 mm) 7/8 in. (22 mm)
7/8 in. (22 mm) 1 in. (25 mm)
1 in. (25 mm) 1-1/4 in. (32 mm)
1-1/4 in. (32 mm) 1-1/2 in. (38 mm)
1-1/2 in. (38 mm) 2 in. (50 mm)

Backer rods are an important component for liquid sealant installation. Backer rods prevent sealant from flowing out of the bottom of a joint and adhering to the reservoir bottom. The backer rod also helps define the shape factor and optimize the quantity of sealant used.


There are no national specifications for backer rods; however, important considerations for various materials include:

  • Polyethylene Foam: Polyethylene foam is a closed-cell foam that does not absorb water and is moderately compressible. It is better suited for cold-pour sealants since it may melt in con­tact with hot-pour materials.
  • Crosslinked Polyethylene Foam: Crosslinked polyethylene foam is a closed-cell foam that is compatible with hot-pour sealants. It will not absorb water and is moderately compressible.
  • Polyurethane Foam: This open-cell foam absorbs water, but does not melt when used with hot-pour materials. It is very compressible, and commonly used with hot-pour sealants.

Backer rod size depends on the joint or crack reservoir width. Backer rods are compressed about 25 percent to assure they stay at the desired depth in reservoir. Table 4 provides the proper size for different joint widths.

Backer rods also act as a bond breaker to prevent adhesion to the reservoir bottom. The stresses within the sealant material increase if bond develops along the base of the sealant [45][46] Adhesion loss results because the sealant is constrained from neck down at the reservoir bottom during joint opening.

Reservoir Design

Reservoir sizing is done to permit the sealant to func­tion properly. The first step is selecting a sealant which meets performance and cost criteria for the pavement. This includes consideration of the potential need to reseal the pavement in the future. It is critical that the reservoir is not too wide to inhibit future resealing. Ideally the initial reservoir width should not exceed 3/8 in. (10 mm) for liquid sealants. Initial width for pre­formed compression seals depends on other design factors.

Expectations of sealant performance and potential resealing need are often neglected. A table or manual which details the year(s) for the expected resealing provides a needed programming tool. It also provides an operation plan for optimizing pavement perfor­mance. Such a table is an excellent tool to provide in the original pavement design documents and the pavement management system. It becomes the "Operation and Maintenance Plan" for the pavement. Designers are encouraged to develop and submit this type of plan to the maintenance and programming departments.

Joint Type & Movement

Figure 3. Pavement temperature differential map for the continental United States[47]. Indicates the difference between the maximum concrete temperature at placement minus the minimum ambient temperature in January.

The sealant must be capable of accommodating the anticipated joint opening and closing due to temperature changes. Figure 3 provides a pavement temperature differential map for the continental United States [48]. The map provides statewide averages for the worst case difference between maximum concrete temperature at placement and minimum yearly ambient temperature. It is useful in estimating maximum joint movement where more ex­act figures are not available.

Most sealant manufacturers recommend calculation of joint movement at transverse joints for proper dimensioning. Joint movement estimates are made with the following equation [49][50][51]:


ΔL = C L (α ΔT + ε)
where:
ΔL = the expected change in slab length, in. (mm)
C = the subbase/slab frictional restraint factor (0.65 for stabilized material, 0.80 for granular material).
L = the slab length, in. (mm).
α = the PCC Coefficient of Thermal Expansion (see Table 5).
ΔT = the maximum temperature range (generally the maximum concrete temperature at placement minus the minimum ambient temperature in January, °F (°C).
ε = the shrinkage coefficient of the concrete (see Table 6). Note: this factor should be eliminated on resealing projects, where shrinkage is no longer a factor).


It is important to remember that there is almost no movement of tied longitudinal and shoulder joints. Tiebars which hold these joints tight will not allow the movement calculated from the formula. Therefore these joints may not require the same material as might be determined based on the calculated move­ment range. Opening ranges determined from the formula for doweled or undoweled transverse con­traction joints will reflect actual field movements.

Tied centerline, highway shoulder or airfield longitudinal joints require sealing even though only small joint opening is likely. These longitudinal joints are often perpendicular to the drainage slope. Therefore they can allow significant access for water. On highways the lane/shoulder joint is the most critical and can let in as much as 80 percent of the total moisture [52][53][54][55]. Neglecting to sea! and maintain the longitudinal joints will negate the benefit of even excellent transverse joint seals. Figure 4 shows the dramatic reduction in water outflow from a pavement drainage system with good longitudinal seals.


Figure 4. Difference in water outflow from a pavement drainage system with unsealed longitudinal joints and well-sealed longitudinal joints [56].

Liquid Sealant Reservoir (Shape Factor) - ­The shape factor is the ratio of depth to width of a field poured liquid sealant. The saw cut width and insertion depth of the backer rod define the sealant shape. The shape factor is critical to long-term suc­cess of liquid sealants. The cross section of a joint sealant changes during the expansion and contrac­tion of the concrete pavement. The movement induces strains within the sealant and stress along the sealant/reservoir bond line. These material responses become excessive if the shape factor is not appropriate for the sealant material.

Different liquid sealant materials can withstand dif­ferent levels of strain. Strain on the extreme sealant fiber depends on the amount of sealant elongation (joint opening) and the shape factor (Figure 5). Most hot-pour liquids can withstand about 20 percent strain of their original width [57]. Silicones and some other low-modulus materials can undergo up to 100 percent strain. However, manufacturers recommend designing for total strains of no more than 50 percent and ideally only 25 percent.

Figure 6 shows ideal shape factors for liquid sealants. A shape factor equal or below one induces lower stresses on the joint sealant than a shape fac­tor greater than one. The lower or reduced internal stresses resulting from proper shape factors minimize adhesive or cohesive loss.

Figure 5. Strain on the extreme sealant fiber for different shape factors [58].

Shape factor design should include recessing the sealant from 1/4 - 3/8 in. (6-1 0 mm). This is impor­tant to avoid extrusion problems. Extrusion occurs where joint closure squeezes the seal material up through the reservoir exposing it to traffic.

Table 5. Typical Values for PCC Coefficient of Thermal Expansion (α) (1,2)
Type of Coarse Aggregate PCC Coefficient of Thermal Expansion (x10-6/degree)
° F ° C
Quartz 6.6 11.9
Sandstone 6.5 11.7
Gravel 6.0 10.8
Granite 5.3 9.5
Basalt 4.8 8.6
Limestone 3.8 6.8
Table 6. Typical Values for PCC Coefficient of Shrinkage (ε) (1,2)
Indirect Tensile Strenth PCC Coefficient of Shrinkage (strain)
<300 psi (2.07 MPa) 0.0008
400 psi (2.76 MPa) 0.0006
500 psi (3.45 MPa) 0.00045
600 psi (4.14 MPa) 0.0003
>700 psi (4.83 MPa) 0.0002

Preformed Sealant Reservoir

To size a preformed compression seal requires con­sideration of pavement temperature at installation and joint movement range [59]. The compression seal must work within the compression range (typically 20 - 50 percent).

The first step is to calculate the total range of joint movement using the formula previously discussed. The second step is to select a compression seal with an allowable movement less than or equal to the calculated movement range. If the range exceeds that allowable for the seal than a larger seal must be chosen. Consideration can also be given to decrease the joint spacing on the project.

Figure 6. Typical shape factors for liquid sealants [60].

The final step is to select a reservoir (saw cut) width to meet seal size, movement range and installation temperature criteria [61]. (Only a rough estimate of the pavement temperature is necessary.) Temperature is important so the seal will operate in the 20 - 50 percent compression range. Warmer installation temperatures require more seal compression at installation. Cooler installation temperatures require less seal compression because the joints are at least partially open.

The following equation calculates saw cut width [62]:

Sc = (1 -Pc) * w
where:
Sc = Joint saw cut width.
w = Width of the uncompressed seal.
Pc = Percent compression of sea! at in­stallation (expressed as a decimal).
Install. Temp. - Min. Temp.
____________________________ * (Cmax-Cmin)
Pc=
Max. Temp. - Min. Temp.
Cmin = Minimum recommended compression of seal expressed as a decimal (usually 0.2).
Cmax = Maximum recommended compression of seal expressed as a decimal (usually 0.5).


Of course the actual installation temperature cannot be accurately known during the design process. Therefore designers should calculate sizing for various potential installation scenarios (hot, moderate, cool). The designers should also examine the in­fluence of other design factors on seal sizing re­quirements. in particular, joint spacing significantly ef­fects total joint movement. Selecting a seal one or two sizes over that required from the calculations can also provide a factor of safety for installation condi­tions [63].

Evaluation of Existing Sealants

It is important to evaluate joint seals to ensure proper performance. For more information on evaluating existing joint sealants, see the joint sealant evaluation page.

Special Considerations

Nonuniform Joint Cracking

In plain jointed pavements initial cracking from shrinkage occurs at intervals from about 40 - 150 ft (12 - 46 m) [64]. The exact spacing varies depending on concrete properties, thickness, subbase friction and climatic conditions during and after placement. The cracks meet sawed joints at those intervals. The joints between those locations sometimes do not crack for several weeks to months after construction even though saw cut spacing is relatively uniform. As a result, all of the initial shrinkage and thermal move­ment occurs at the initially cracked joints. Those joints often become much wider than those in in­termediate locations. To account for this variability, agencies are encouraged to require the contractor to have several sizes of backer rod or compression seal available.

Expansion/Isolation Joints

Most steps for resealing expansion/isolation joints are similar to those for contraction joints. However, resealing expansion/isolation joints requires removing the sealant only down to the compressible filler. Compressible fillers are typically directly below the sealing material. The fillers are usually nonextruding and act as a backer rod in the wide reservoir. It may be necessary to place a bond-breaking tape above the filler before installing new sealant [65][66][67]. The tape will separate the new sealant from any old sealant that may have been absorbed by the filler. A tape width no more than 1/8-in. (3 mm) narrower than the joint width is acceptable. This ensures ade­quate separation and also eases installation. Contrac­tors report difficulty in properly placing a tape wider than the actual joint width.

Resealing the contraction joints within 100 ft (30 m) of an existing mainline expansion joint may require special consideration [68]. Expansion joint closure allows adjacent contraction joints to open. It is com­mon that the width of contraction joints increase near an expansion joint. To successfully seal these con­traction joints it may be necessary to use sealant materials with greater elongation capacity. Other options are to increase the width of preformed com­pression seals, backer rods and/or shape factor. The project documents should account for these adjustments.

Existing Lane/Shoulder Joints

Figure 21. Worker sawing the lane/shoulder joint reservoir. Note that the blade must remove a small amount of the concrete slab to ensure cleanliness and enable sealant adherence.

Studies show that effectively sealing shoulder joints improves highway shoulder and pavement perfor­mance [69]. It is simpler to seal the reservoir along concrete shoulders than along asphalt shoulders. Sealing and maintaining concrete shoulder joints re­quires no further effort than is required for centerline, lane-separation or other tied longitudinal joints. This assures the designer of a good shoulder seal.

Joints between concrete lanes and bituminous shoulders pose a more difficult sealing challenge. Bituminous shoulders tend to settle with time due to water accumulation, traffic encroachment, insufficient support materials and poor soil or bituminous com­paction. Often vertical settlement is greater than horizontal thermal movements [70]. Some spalling and loss of asphalt material is also common along the shoulder edge of older concrete pavements.

Sealing along bituminous shoulders may require a wide reservoir. One-inch (25 mm) or greater width and depth accommodates the lateral and vertical shoulder movements. This provides a reservoir shape factor of one and is good for most liquid sealants capable of 25 percent strain. Liquid seals for shoulder joint sealing should be capable of adhering well to both materials; rubberized asphalt and specially formulated silicone sealants provide good adherence [71].

As with all sealing, shoulder reservoir preparation is important. Sawing the joint reservoir delivers the most consistent width and depth dimensions (Figure 21). The saw should cut vertically and remove any bituminous material from the edge of the concrete slab. Immediately after sawing a water flush will remove sawing slurry. Both sides of the reservoir re­quire sandblasting. A lighter sandblast along the asphalt face is acceptable. Airblowing just before sealant installation dries the reservoir and removes dust and dirt.

Do not use a propane torch for joint drying and cleaning. Torching has led to concrete spalling and raveling.

Do not seal newly placed bituminous material until it cools to at least ambient temperatures. At higher temperatures bituminous material can ravel, erode and deteriorate under saw action [72]. A cleaner reservoir face results if sawing is delayed until after cooling. Certain mixes may require an extended cooling/aging period.

Special Considerations for Cracks

Like joints, some cracks also require sealing to prevent moisture and incompressible infiltration. The orientation and type of crack dictates sealing necessity. Cracking in concrete pavement initiates by one or a combination of seven factors:

  1. Plastic Shrinkage.
  2. Drying Shrinkage.
  3. Restrained Thermal Contraction.
  4. Thermal & Moisture Gradients.
  5. Non-uniform Support.
  6. Reflection of Underlying Distress.
  7. Load.

Cracks which remain tight usually do not require seal­ing. These cracks are typically very narrow (hairline) cracks. Table 10 provides guidance to determine where crack sealing, cross-stitching and load transfer restoration are necessary.

Table 10. Crack sealing and repair guidelines (33,52).
Crack Orientation Crack Type Description Spalling Condition Faulting Crack Width Recommended Repair Procedures
Transverse Plastic Shrinkage Partial-depth None 0 Hairline Do Nothing.
Transverse Random Low Severity None 0 Hairline Saw and Seal
Transverse Random Medium Severity Low [<0.3 in (76 mm)] <0.25 in (6.3 mm) ≤0.5 in (12.7 mm) Partial-Depth Repair, Saw and Seal, Load Transfer Restoration.
Trasverse Random Medium Severity Med-High [+3 in (76 mm)] 0 ≤0.5 in (12.7 mm) Partial-Depth Repair, Saw and Seal
Transverse Random High Severity Med-High [+3 in (76 mm)] ≥0.25 in (6.3 mm) >0.5in (12.7 mm) Full Depth Repair.
Longitudinal Plastic Shrinkage Partial Depth None 0 Hairline Do Nothing.
Longitudinal Random Low Severity None 0 Hairline Cross-Stitching.
Longitudinal Random Low Severity Low [<3 in (76 mm)] 0 Hairline Cross Stitching.
Longitudinal Random Medium Severity Low-Med [<3 in (76 mm)] <0.5 in (12.7 mm) ≤0.5 in (12.7 mm) Partial-Depth Repair, Saw and Seal.
Longitudinal Random Medium Severity High [+ 6 in (152 mm)] 0 ≤0.5 in (12.7 mm) Partial-Depth Repair, Saw and Seal.
Longitudinal Random High Severity High [+6 in (152 mm)] ≥0.5 in (12.7 mm) >0.5 in (12.7 mm) Full Slab Replacement or Full-Depth Repair.

Working Cracks

Figrure 25. Cross-section through a longitudinal crack showing the orientation of tiebars for cross-stitching.

Once started, a crack may develop full-depth through a slab or traverse only partial-depth (Eg. plastic shrinkage cracks). The crack may also begin moving and functioning as a joint. Cracks which function as a joint are "working" cracks. Working cracks are subject to nearly the same range of movement as transverse joints and therefore require sealing.

It may also be necessary to establish pavement integrity at working cracks. Those cracks with signifi­cant spalling, pumping or faulting require full-depth repair. Load-transfer restoration can repair cracks with low efficiency levels.

Figure 26. Cross-stitching tiebars ready for final insertion on an airport pavement.

For longitudinal cracks which are in reasonably good condition, cross-stitching is an alternate repair tech­nique. Cross-stitching has been successful on both roadway and airport pavements [73][74]. The purpose of cross-stitching is to maintain aggregate interlock and provide added reinforcement and strength. The tie bars used in cross-stitching prevent the crack from vertical and horizontal movement or widening.

Cross-stitching uses deformed tie bars drilled across a crack at angles of 35° (Figure 25). A number 6 bar is sufficient to hold the joint tightly closed and enhance aggregate interlock [75]. The bars, spaced 20 - 30 in. (50 -75 cm.) from center to center, alter­nate from each side of the crack (Figure 26). Heavy truck traffic and airplane traffic require the 20 in (50 cm) bar spacing. A 30 in (75 cm) spacing is ade­quate for light traffic and interior highway lanes.

Do not stitch a transverse crack which has assumed the role of an adjacent joint. Stitching will not allow transverse joint movement (open and closure). A new crack will likely develop near a stitched working crack or the concrete will spall over the reinforcing bars.

Always use smooth dowel bars in repairs of transverse cracks or joints in jointed plain pavement. This includes application in full-depth repair or load transfer restoration. Dowel bars allow necessary movement for proper repair function. In repairing mid-panel cracks in jointed reinforced concrete pave­ment (JRCP) it may be acceptable to use deformed tiebars. However, the joints on each side of the crack must be handling cyclic temperature movements. If they are not, also use smooth bars in repairing the intermediate crack.


Hairline Cracks

Most hairline cracks require no special treatment or sealing, mainly because they do not allow significant water to penetrate the pavement substructure. Some hairline cracks, particularly plastic shrinkage cracks, are very tight and do not extend through the full slab depth. Plastic shrinkage cracks rarely deteriorate or influence the ride or life of concrete pavement. Tight cracks held by reinforcing bars, such as those found on continuously reinforced concrete, also do not require sealing.

Figure 27. Crack sawing equipment. Note the small diameter blade and pivoting front wheel.

If a hairline crack begins to deteriorate, remedial treatment may become necessary. Load transfer restoration and sawing and sealing provides the best long-term repair. Using low viscosity epoxy to glue working cracks in pavement is often unnecessary and usually not effective. A slab will eventually crack again near the vicinity of an epoxied crack due to thermal restraint [76].

Crack Sealing/Resealing

Cracks are not straight and are therefore more dif­ficult to shape and seal [77]. Avoid trying to follow crack wander with a standard blade. Manufacturers provide special crack-sawing blades to help the operators follow crack "wander". The special blades with diameter from 7 - 8 in (18 - 21 cm) are also more flexible to aid in crack tracing.

Special crack saws are usually supported by three wheels and are smaller than most joint sawing equip­ment (Figure 27). A pivot wheel on the saw allows the saw to easily follow crack wander. Even with special blades, a sawed crack reservoir will not be as uniform or clean as a straight joint reservoir. However, it is desirable to attempt to obtain the same shape factor at working cracks that is developed at joints on a project.

Avoid using routers for concrete pavement. Routers were used extensively in the past to create the seal reservoir above cracks [78]. Routers use a vertical spinning bit with a diameter and length that produce the desired reservoir dimensions. Most contractors no longer use routers because the they achieve bet­ter reservoir results and increased productivity with diamond saws.

After repair and sawing, crack sealing requires all of the cleaning steps used in joint sealing. That includes the use of a backer rod and uniform sealant installation.

Additional Information

Additional information on sealing and resealing joints in concrete pavement is available by contacting the American Concrete Pavement Association.

Conclusions

  1. Proper joint sealing contributes to good perfor­mance on roadways and airports. With proper design and construction joint sealants minimize in­filtration of surface water and incompressible material into the joint system.
  2. The hypothesis that sealing is unnecessary for pavements with free-draining base materials is logical but currently unsubstantiated. Sealants are needed to reduce incompressible infiltration even in pavements with open-graded base materials.
  3. It is not realistic to construct and maintain a com­pletely watertight joint. Periodic surveys and a ra­tional sealant rating system provide the necessary criteria to judge seal effectiveness.
  4. Sealant selection considers pavement life expec­tancy, classification, joint type, climate and cost of traffic control over the economic analysis period. Comparison of different sealant materials based on their individual life expectations is a necessary part of project design and life-cycle analysis.
  5. Liquid and compression seals can provide accep­table performance. Proper reservoir sizing and preparation are essential to maximizing perfor­mance of any sealant.
  6. Joint type and spacing influences the choice of sealant materials and reservoir design. Tied longitudinal joints (centerline or lane/shoulder) do not stress sealant materials as do transverse joints, since their movements are considerably smaller. An agency should optimize project cost by considering this in sealant selection.
  7. Longitudinal joints are often perpendicular to the drainage slope providing significant access for water. Neglecting to seal and maintain longitudinal joints may negate the benefits of even excellent transverse joint seals.
  8. Resealing joints and cracks requires good preparation to maximize sealant life. The necessary steps include: old sealant removal, reservoir shaping, reservoir cleaning, backer rod installation, and sealant installation.
  9. Resealing joints is a necessary maintenance ac­tivity for jointed concrete pavement. An Operation and Maintenance Plan developed by the design engineers will provide a tool to engineers charged with maintaining a pavement after construction.
  10. Concurrent rehabilitation techniques may be necessary with a joint resealing operation.
  11. An agency can establish and maintain pavement integrity at working cracks through full-depth repair or load transfer restoration. Retrofit dowel bars are the most consistent load transfer restora­tion design.
  12. An alternative for longitudinal crack reinforcement is cross-stitching. Stitching has been successful on both highways and airports in otherwise good condition. Cross-stitching is not for transverse working cracks or transverse joints.

Resources and Applications

Seal/No Seal Group

Joint and Sealant Movement Estimator App

Compression Seal Joint Width Calculator App

Joint Noise Estimator


References

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