2. Literature Review
Sealing cracks in the asphalt binder of bituminous concrete pavements is a common roadway maintenance activity. To prevent the intrusion of water and incompressible material, it is imperative that cracks be sealed by placing specialized material into or above the cracks. Asphalt cracking is unavoidable, and neglecting preventive maintenance of the pavement structure leads to accelerated cracking, which further reduces its ability to sustain traffic.
The phenomenon of cracking in asphalt pavements has been a problem for pavement design and maintenance engineers for many years. This observable fact is one of two major considerations in the pavement design process, fatigue cracking and rutting, and is often the principal manner of deterioration in asphaltic pavements (SHRP, 1999).
Remedial efforts to maintain a serviceable pavement structure range from preventive surface treatments coupled with regular maintenance activities to full-depth rehabilitation. To address the problem of cracking itself, it is common for maintenance departments to employ crack sealing and filling techniques. These techniques have been utilized for many years, with the primary purpose of extending the service life of the pavement structure. Crack sealing and filling operations can extend the pavement life past the point where the benefit of added pavement life exceeds the cost of conducting the operation (SHRP, 1999).
If a particular asphalt pavement structure exhibits cracking, the appropriate rehabilitation decision is based on the condition of the pavement structure, and on the condition of the cracks. The potential for moisture-related pavement damage must be evaluated to determine both the need and urgency for treatment. When crack treatment, either sealing or filling, is selected, the proper crack preparation methods, sealant materials, and sealing techniques can also be selected. A number of factors should be considered in this selection. Factors affecting the decision to treat the cracks include (NCHRP, 1982):
- Functional classification of roadway (arterial, collector, local).
- Traffic characteristics (volume and type).
- Climate conditions (precipitation, temperature, etc.).
- Pavement type.
- Pavement condition (Pavement Condition Index).
- Subgrade characteristics (type, permeable or impermeable).
- Crack type (transverse, longitudinal, etc.).
- Crack condition (width, depth, secondary cracking, etc.).
- Crack density (frequency).
The functional classification is primarily used for determining cost-effective procedures and materials. High-traffic-volume arterials are much more difficult to repair than low-volume collectors or locals, and it is cost-effective to use more durable materials to reduce the frequency of repairs and the need for expensive traffic control. For low-volume collectors and locals, the functional classification does not justify the use of more durable materials because the frequency of repair and traffic control is usually not an issue.
Climatic conditions present a critical problem. Contraction and expansion of the pavement structure is a direct result of ambient temperature fluctuations and solar heating by radiation on the pavement surface, which initiates the opening and closing of asphalt cracks. Once asphalt cracks have formed, the crack must be sealed to prevent the intrusion of water and incompressible material. Water entering the pavement structure can have a detrimental affect on the performance of the pavement by causing changes in the subgrade support and causing the binder to strip away from the aggregate (NCHRP, 1982).
Knowledge of the pavement condition is necessary to determine the type and extent of treatment required. The Pavement Condition Index (PCI) is the most widely used measure of the existing condition of the pavement structure. PCI is a measurement of surface condition from an operational standpoint and structural integrity, on a scale of 0 to 100 (ACE, 1982). The main types of distresses in asphaltic pavements are alligator cracking, reflection cracking, maintenance patching, potholes, rutting, weathering, and raveling. The results of the PCI survey are used to identify sections requiring preventive maintenance or rehabilitation. The type of maintenance required depends on the present crack condition, crack width, and type as indicated in the PCI. If a pavement exhibits cracks with widths ranging from 0.2 in. (5 mm) to 1.0 in. (25 mm), then crack sealing and filling strategies are appropriate (SHRP, 1999).
Knowledge of subgrade characteristics and the potential effects of intrusive water are also beneficial in the determination of appropriate maintenance strategies. If the subgrade material is susceptible to water damage when subjected to traffic loading, then timely treatment is essential to maintain the integrity of the pavement structure.
Once the surveys and the collected data have been reviewed, a decision can be made concerning the appropriate type of maintenance to perform and its priority.
The appropriate type of maintenance for cracked pavements often depends on the density and present condition of the cracks. In general, a high percentage of cracks or severely deteriorated cracks indicate a pavement in an advanced state of decay. For such a pavement, crack treatment would not be cost-effective because the structure is in need of more extensive rehabilitation.
If cracks are of a low to moderate density and exhibit moderate to low edge deterioration, then crack sealing or filling strategies may be appropriate. Most state highway agencies (SHA) have established policies, taking into account their climates and environmental conditions that specify the type of maintenance strategy to be performed and its frequency. These policies are often based on their assessment of the overall pavement condition, crack density, crack characteristics, and crack type and width. Table 2.1 presents guidelines for determining the type of maintenance strategy to perform (SHRP, 1999).
|Crack Density||Average Level of Edge Deterioration|
(Percentage of Crack Length)
(0 to 25)
(26 to 50)
(51 to 100)
|Low||Nothing||Nothing or Crack Treatment||Crack Repair|
|Moderate||Crack Treatment||Crack Treatment||Crack Repair|
|High||Surface Treatment||Surface Treatment||Rehabilitation|
Cracked asphaltic pavements can exhibit other types of deficiencies, such as vertical displacements, which require alternative repair strategies that are beyond the scope of this research.
As previously mentioned, the maintenance strategies focused on in this research pertain to crack sealing and filling. A distinction between crack sealing and filling is necessary to allow the SHA to select the most cost-effective and durable treatment.
Crack sealing involves the placement of specialized treatment materials above or into working cracks. Working cracks experience a considerable amount of vertical and horizontal movement as a result of temperature change or traffic loading. Sealant must be applied to cracks in a configuration that prevents the intrusion of water and incompressible material, such as sand, stones or dirt, into the pavement structure.
Crack filling involves the placement of ordinary treatment materials into non-working cracks to substantially reduce the infiltration of water and to reinforce the adjacent pavement structure. Non-working cracks experience relatively small amounts of vertical or horizontal movement as a result of temperature change or traffic loading.
As these definitions indicate, crack sealing is a significantly more involved procedure, is more costly, and requires the use of specialized equipment.
The amount of annual horizontal movement should be the principle basis for the decision to seal or fill. Working and non-working cracks can be determined by their type. Working cracks are most often transverse cracks. However, some longitudinal and block cracks may meet the minimum movement criteria. Non-working cracks typically include longitudinal and block cracking. These cracks usually exhibit relatively close crack spacing with little movement. Minimal crack movement is very advantageous to the SHA, because it permits the use of less expensive, specialized materials and equipment.
The proper maintenance strategy for treating a particular cracked pavement requires knowledge of the pavement and crack characteristics, and the materials to be utilized. Once the decision has been made to treat the cracks, there are several factors to be considered in the selection of the type of maintenance strategy to employ.
Crack sealing is a preventive maintenance activity, and is ideally conducted shortly after working cracks have widened to the minimum width necessary to perform crack sealing. Typically, crack sealing is performed when temperatures are moderately cool, approximately 45° to 65°F (7° to 18°C). Such temperatures occur in the spring and fall seasons of the year. Sealing asphaltic cracks during this time period minimizes the adverse effects of secondary cracking which is inevitable if cracks are filled during extreme temperatures that occur in summer and winter.
Sealing or filling during the spring and fall is desirable because the moderately cool conditions allow the asphalt cracks to open up sufficiently to permit the material to be placed in the crack without cutting. The width of the crack channel is at the average of its working range and the sealing material will not have to undergo excessive expansion or contraction due to temperature fluctuations.
Crack filling can be either a preventive or routine maintenance strategy, depending on the SHA's maintenance approach. Like crack sealing, preventive crack filling is performed shortly after non-working cracks have widened to the minimum width necessary to perform the procedure, typically during the moderately cool seasons of the year. Table 2.2 contains the Federal Highway Administration's recommended criteria for determining whether to seal or fill (SHRP, 1999).
|Crack Characteristics||Crack Treatment Activity|
|Crack Sealing||Crack Filling|
|Width||0.2 to 0.75 in.|
(5 to 19 mm)
|0.2 to 1.0 in.|
(5 to 25 mm)
|Edge Deteroration||Minimal to None|
(25% or Less of Crack Length)
|Moderate to None|
(50% or less of Crack Length)
|Annual Horizontal Movement||0.12 in. or Greater|
|Less than 0.12 in.|
|Type of Crack||Transverse Thermal|
Distantly Spaced Block
The range of sealant materials available for sealing and filling use is broad, with each individual product having distinct characteristics pertaining to the type of use. Traditionally, these products are grouped into one of three families: cold-applied thermoplastic bituminous materials, hot-applied thermoplastic bituminous materials, and chemically cured thermosetting materials (SHRP, 1999). Thermoplastic materials have properties that enable the product to become soft when heated and hard when cold. Thermosetting materials harden permanently as a result of heat generated by chemical reactions.
Cold-applied thermoplastic bituminous materials are emulsions of polymer-modified liquid asphalt in water. Liquid asphalt pertains to any asphalt that has been liquefied by blending with petroleum solvents. Polymer-modified liquid asphalts are modified with latex polymer or rubber polymer with resins, oils and additives. The polymers give the asphalt increased temperature range performance, rendering it more flexible in cold climates and not as soft in hot climates.
Hot-applied thermoplastic bituminous materials are comprised of asphalt cement, fiberized asphalt, asphalt rubber, rubberized asphalt and low-modulus rubberized asphalt. Hot-applied materials generally behave the same as their cold-applied counterparts, but vary only in the manner of application. To enable the hot-applied material to enter the crack, it must be heated to temperatures in excess of 380°F (193°C), while cold-applied materials are applied at ambient temperatures (Solaimanian, 2002).
Chemically cured thermosetting materials are generally multi-component materials that cure by chemical reaction from a liquid state to a solid state.
Material selection is based on the properties the material must possess to be effective at sealing the asphalt crack. These properties include the following (SHRP, 1999).
- Short preparation time
- Short cure time
- Resistance to softening and flow
- Resistance to aging and weathering
- Abrasion resistance
Actual field performance should be considered when determining the appropriate material. Selection of the sealant material is an involved process, which varies by SHA and their particular experience with the individual products.
There are several seal configurations in use by many SHAs. The four most common material configurations are: flush filled, reservoir, overband, and combination.
The flush filled configuration is achieved when the material is dispensed into an existing, uncut crack, and the excess is eliminated, so that the material is flush with the pavement surface. This material configuration is the most common placement employed by SHAs.
The reservoir configuration is accomplished by placing the material in the confines of a routed crack. The material can be flush with the pavement surface or recessed.
The overband configuration is executed by placing the material into an uncut crack and above the pavement surface. A band-aid configuration exists if the overband material is shaped into a band using a squeegee, and a capped configuration exists if the material is left unshaped. The band-aid dimensions are typically 3 to 5 inches (75 to 125 mm) wide, and 0.12 to 0.25 inches (3 to 6 mm) deep (SHRP, 1999).
In combination configurations, the material is placed into and over a routed crack. Typically, a squeegee is used to shape the overband into a band configuration centered over the crack reservoir.
Selection of the material configuration is an involved process, and varies by SHA according to their particular experience with the different types of configurations. Figure 2.1 illustrates the four categories and combinations of material configurations (SHRP, 1999).
Crack surfacing is a relatively new concept and the terminology applies only to this research. The term crack surfacing was developed by WYDOT to describe the process of sealing extra wide pavement cracks in excess of one inch in width, with a selected manufacturer's pavement preservation product.
In accordance with the main objective of this research, three manufacturer's products were studied: PolyPatch manufactured by Crafco Inc., and Level & Go, and Recessed Repair Mastic manufactured by Deery American Corporation. In general, these products are designated as pavement preservation products by their respective manufacturers.
Crafco Inc. manufactures PolyPatch pavement preservation products. The PolyPatch products utilized in this research are hot-applied, pourable, self-adhesive materials used for maintenance and repair of both asphalt and concrete pavements, and are produced in two grades: PolyPatch and PolyPatch Fine Mix (Crafco, 2003). PolyPatch Fine Mix contains small aggregate, as opposed to PolyPatch which contains well-graded aggregate, and results in a more uniform texture and improved feathered edges. These products are composed of a highly modified polymer asphalt binder and selected light weight aggregate. They are specifically formulated to repair pavement distresses which are larger than those typically repaired by crack sealing, but smaller than those requiring repair patching procedures. Crafco claims that PolyPatch's unique design features produce materials which are both flexible and resistant to vehicle loadings when properly applied. The PolyPatch products are supplied in four types for use in different climates and applications.
The PolyPatch product is available in four formulations: Types 1, 2, 3 and 4. Three types of PolyPatch Fine are available: Type 1, 2 and 3. The manufacturer has recommendations for usage, based on climatic conditions and the desired application, to ensure a well bonded, flexible, load resistant, lasting repair for the applicable pavement distress. Table 2.3 outlines the manufacturer's guidelines for usage (Crafco, 2003).
|Climate Characteristics||Thermal Crack Repair|
(Cracks 1-2" (26 mm - 5cm) Wide)
|Leveling and Skin|
Patch Repair (> 1/2" (13 mm) Deep)
|Leveling and Skin|
Patch Repair (< 1/2" (13mm) Deep)
|Surface Void Repair|
(Max. 4" (10 cm) Deep by 12" (30cm) Diameter)
|Wheel Rut Repair|
|Hot Climate: High Temp Range: PG* 70, 64 Low Temp Range: PG* - 10||1-2" Type 3 (Fine Mix) > 2" Type 3||Type 3||Type 3 (Fine Mix)||Type 3||N/A|
|Moderate Climate: High Temp Range: PG* 58, 64 Low Temp Range: PG* -16, -22||1-2" Type 2 (Fine Mix) > 2" Type 2||Type 2||Type 2 (Fine Mix)||Type 2||Type 4|
|Cold Climate: High Temp Range: PG* 52, 58 Low Temp Range: PG* -28, 34||1-2" Type 1 (Fine Mix) > 2" Type 1||Type 2||Type 2 (Fine Mix)||Type 2||Type 4|
The following application procedures are applicable to all types of PolyPatch and PolyPatch Fine Mix material.
The product is stripped from the manufacturer's supplied strippable container and placed into the Crafco PolyPatch Applicator to melt, heat and apply the product. The applicator is designed with electric heating element to expedite material heating. During melting and heating, the heat transfer oil should be heated to 450° to 525°F (232° to 274°C). Once the transfer oil is properly heated, the product is then added to the melter. After sufficient melting has occurred, the agitator is engaged for material agitation. The material is then heated to the application temperature range of 375° to 410°F (190° to 210°C) before application.
Prior to application to the pavement, the surface must be properly prepared to ensure an adequate bond. The surface must be clean, sound, dry and free from dust and debris. Caution should be taken to avoid highly distressed areas requiring reconstruction. The application area should be blown with dry, oil-free compressed air to ensure a clean, bondable surface.
In cold, wet climates with a potential for freezing, the manufacturer recommends preheating the pavement surface. This technique is also required on all applications in areas when ambient temperatures fall below 40°F (4°C), or where moisture is present. A heat lance is recommended for high-BTU, quick heating to allow the area to be blown with compressed air.
The material must be applied at least six inches (15 cm) beyond the distressed area to sound pavement surfaces. It is highly recommended that the material be applied at a temperature as close as possible to 400°F (204°C). The thickness should exceed 3/8 inches, to achieve longer heat retention times and proper drainage of the binder. Overworking and down pressure on the product should be avoided to avoid excessive heat loss and segregation which lessens the integrity of the adhesive bond and leads to unnecessary thinning of the product.
After the product has been applied to the pavement the edges should be melted down. A torch or lance is required for this procedure, and it should be accomplished while the product is still warm to reduce the amount of additional heating required. This technique assures that the repair is well-adhered and encapsulated along the edges to prevent the intrusion of moisture under the product.
PolyPatch and PolyPatch Fine Mix both have an application life 12 to 15 hours at the application temperature. The application life may be extended by adding additional kegs of product to the applicator with continual agitation. The material may be reheated to application temperature once following the initial heating. Further heating of the material may result in the degradation of material properties. Once the application life is exceeded, the material will begin to thicken and eventually gel. If this occurs, the material should be immediately removed from the applicator and discarded.
Both the PolyPatch and PolyPatch Fine Mix products may be applied to cracks with a broad range of configurations. For PolyPatch, the manufacturer's suggested uses include repair of pavement cracks or joints more than 2 inches (5 cm) wide, small potholes up to 4 in. (10 cm) deep and 12 in. (25 cm) in diameter, pavement depressions up to 2 in. (5 cm) deep and 24 in. (60 cm) wide, skin patching in alligator-cracked and other distressed areas (avoiding deteriorated areas in need of reconstruction), leveling recessed transverse thermal cracks, and capping settled utility cuts.
Following proper application, the modified asphalt binder self-adheres and develops a strong bond to the adjoining pavement. The material undergoes shrinkage of approximately 5% as the material cools from the application temperature to the surrounding ambient temperature. No compaction is required. Before opening the area to traffic loading, sufficient time must be allotted for the material to cool. Cooling times will vary, depending on the size of the application and the ambient temperature. Generally, approximately 30 to 60 minutes of cooling should be allowed for each 1 in. (2.5 cm) of material depth.
For areas requiring deep applications, the material should be applied in two separate lifts to reduce the amount of shrinkage as the material cools. The initial lift should fill the work area to within 1/2 in. (12 mm) to 1 in. (25 mm) of the desired height, and should be allowed to cool prior to placement of the final lift. After cooling, the final lift should be applied level with the surrounding surface.
PolyPatch Fine Mix may be applied in a wide range of configurations as well. However, the recommended configurations are different from those for the PolyPatch product. For PolyPatch Fine Mix, the manufacturer's suggested uses include repair of pavement cracks or joints more than 1 in. (2.5 cm) to 2 in. (5 cm) wide, small potholes up to 2 in. (5 cm) deep and 12 in. (25 cm) in diameter, pavement depressions up to 2 in. (2.5 cm) deep and 18 in. (45 cm) wide, skin patching of alligator-cracked and other distressed areas (avoiding deteriorated areas in need of reconstruction), leveling recessed transverse thermal cracks, and capping settled utility cuts. It is highly recommended by the manufacturer that PolyPatch Fine Mix not be used to fill long stretches of longitudinal ruts in pavement wheel paths, nor for surfacing skin patches near intersections. For cooling times and deep applications follow the procedures outlined for PolyPatch.
For quality control, Crafco Inc. requires five standard test methods for their PolyPatch products: PolyPatch Viscosity Test, PolyPatch Stability Test, PolyPatch Flexibility Test, PolyPatch Adhesion Test, and PolyPatch Melting Procedure Test (Crafco, 2003). The following paragraphs give a brief summary of the testing procedures. The complete procedures can be found in Appendix A.
The PolyPatch Viscosity Test should be performed on each lot of PolyPatch batch. The test is intended to assure that PolyPatch product flows from the melter easily during field applications without becoming too thin, or being too weak to withstand traffic loading. The procedure requires the PolyPatch sample to be heated to 400°F ± 2° (204°C ± 2°), and the initial weight recorded. The sample is then allowed to flow from its container into a receiver container for five seconds. The weight of the receiver container is recorded and compared with a specified range (Crafco, 2003).
The PolyPatch Stability Test is used to determine the stability of PolyPatch under vehicle loading at elevated ambient temperatures. The test is intended to assure that it has the rut resistance and stability required to perform properly as a repair material. Initially, the PolyPatch is heated to 400°F (204°C), and then poured into a containing ring. The PolyPatch is then allowed to cool for two hours before trimming off the excess material to make it level with the surface of the ring. The material is then allowed to cool to ambient temperature overnight. Once cool, the material is removed and the diameter of the specimen is recorded. The sample is then placed into a Parallel Plate Plastometer and heated in an oven at 158°F (70°C) for 10 minutes. After completion of this conditioning period, the top plate of the plastometer is placed on the specimen for 30 minutes ± 1 minute, and then removed. The diameter of the sample is recorded after a 60-minute conditioning period at ambient temperature. The stability is recorded as the difference between the initial diameter and the final diameter.
The PolyPatch Flexibility Test is used to determine the flexibility of the material at low ambient temperatures. If flexibility is not maintained at low temperatures, the material will become brittle and will break easily when subjected to traffic loading or snowplow abrasion. Initially, the PolyPatch is heated to 400°F (204°C) and placed into a keystock reservoir. Excess material is trimmed to achieve a surface level with the top of the keystock. The specimen is then allowed to cool to ambient temperature for one hour. The specimen is then placed into a freezer maintained at a specified temperature for at least one hour. The specified temperatures for PolyPatch and Fine Mix Type I is -20°F (-29°C); PolyPatch and Fine Mix Type II is 0°F (-18°C); PolyPatch and Fine Mix Type III is 20°F (-7°C). PolyPatch Type IV is not tested. After conditioning, the specimen is removed from the freezer and bent over a mandrel for a period of ten seconds. Any specimen that does not fail or break passes this test.
The PolyPatch Adhesion Test determines the material's ability to adhere to concrete, a vital property to assure the long-term durability of a crack seal. Initially, the PolyPatch is heated to 400°F (204°C) and allowed to cool for one hour. A 1 in. by 1 in. by 2 in. (25 mm by 25 mm by 51 mm) bond specimen is then produced, and allowed to cool for two hours at ambient temperatures. The specimen's dimensions are recorded, and it is placed into a device which applies tensile force. The tension test is run at a rate of 0.5 in. (13 mm) per minute until the specimen fails. The adhesion is reported as the tensile force divided by the cross-sectional area (pounds per square inch).
The final standard test is the PolyPatch Melting Procedure, and is intended to confirm production quality control measures. Initially, the Crafco PolyPatch Applicator is preheated from 420° to 500°F (216° to 260°C). Once the appropriate temperature is reached, a gallon can of PolyPatch is placed in the melter. After sufficient melting, the material is then stirred by a spiral stirrer. The material is then poured from the melter at 400°F (204°C), as measured by a thermocouple.
Deery American Corporation (DAC) manufactures Repair Mastic pavement preservation products. The Repair Mastics utilized in this research are hot-applied, ready-to-melt repair mastics for concrete and asphalt pavements. Two grades are produced: Level & Go Repair Mastic and Recessed Repair Mastic (Deery, 2003). Both the Level & Go and Recessed Repair Mastics are composed of quality-selected asphalt and/or resins, and include wear-resistant aggregates that are clean, hard, and durable, synthetic rubber polymers, anti-oxidants, and naturally occurring and man made reinforcing materials. The Level & Go Repair Mastic is intended for use in the repair of unconfined, feathered edge, extra wide pavement cracks. Recessed Repair Mastic is intended for high performance, confined repair of extra wide pavement cracks. Deery claims that both products provide a waterproof, flexible and durable repair system that is usually ready for traffic loads in less than 30 minutes.
The manufacturer supplies the repair mastic in cardboard boxes containing 40 pounds of the material. Each individual box contains a quick melt liner, which is dissolved and incorporated into the melted material (Deery, 2003). Both the Level & Go and Recessed Repair Mastics are formulated for applications in all climates. The difference between the products lies in the applications for which they are used.
These following application procedures are applicable to both the Level & Go and Recessed Repair Mastics for repair of extra wide pavement cracks and distresses, and for non-recessed and recessed installations.
Prior to application, the mastic should be heated to the application temperature of 380° to 400°F (193° to 204°C) in a thermostatically controlled mastic mixer that utilizes oil as a heat transfer medium, and is equipped with a full sweep horizontal shaft agitator capable of gently lifting the material from the bottom of the reservoir and repeatedly turning the material.
Before application to the pavement, the surface requiring repair must be dry and free from dust, dirt, grease, loose particles and any other material that will inhibit bonding of the mastic to the surface (Deery, 2003). Because of unpredictable site and asphalt conditions, it is recommended that the owner determine the required preparation for a particular situation.
For confined repairs in asphalt surfaces, the repair should be centered over the crack within the distress area, and additional material be placed so that the repair area will extend onto adjacent, sound pavement surfaces. The repair cavity should be at least 1 in. (25 mm) deep and have a perimeter bonding face that is approximately perpendicular to the original surface with a minimum depth of 3/4 in. (19 mm) (Deery, 2003). The repair cavity may be created by methods such as milling, grinding, saw cutting, and chipping with hammers, or pavement breakers. The loosened material is then removed from the cavity, without causing further damage to the remaining pavement. Once the cavity is cleared, the cavity edges should not be feathered. The removal depth is based on the condition of the underlying pavement. Preparation for unconfined spaces is accomplished in a similar manner.
Prior to placement of repair mastic, the surface must be clean and dry. All loose particles and moisture must be removed from the bonding surface to allow the conditioner and repair mastic to properly bond with the asphalt. To accomplish the cleaning and drying, methods such as high-pressure air blasting, hot air blasting or grit blasting can be employed singly or in combination. When utilizing high-pressure air blasting, the equipment should be capable of providing a continuous, high-velocity air stream of 125 cubic feet per minute that is free of oil and moisture. Hot air blasting equipment should be capable of producing a minimum temperature of 2500°F (1371°C) with a blast velocity of 1900 feet per second. Grit blasting should be accomplished during dry weather followed by air blasting to ensure complete removal of grit from the repair area.
Once the repair area is clean and dry, an even coating of Deery Surface Conditioner should be applied to the prepared surface by brushing or spraying, avoiding puddles or other irregularities. The conditioner should be allowed to dry completely prior to application of the repair mastic. If the conditioner is not completely dried and cured, proper bonding of the repair mastic will be inhibited.
The repair mastic should be heated to the application temperature, placed into the repair area in layers, and allowed to cool. Layering of the material is necessary to minimize the effects of shrinkage. The final layer should be tooled smooth with the surrounding pavement surface. To provide a skid-resistant surface, aggregate chips are broadcast onto the hot mastic surface and lightly tamped to ensure adequate embedment of the chips.
Both the Level & Go and the Recessed Repair Mastic can be installed in the following situations: random crack and joint repair with average crack widths of 2 in. (5 cm); longitudinal and traverse crack repair; paver seam repair, with an average crack width of 2 in. (5 cm); leveling of cupped transverse cracks with depressions less than 2 in. (5 cm) deep and 24 in. (61 cm) wide; leveling depressions at bridge approach slabs and around utility openings with widths of 12 in. to 36 in. (30 cm to 91 cm); repairing small pavement defects, with average depths of 1 in. (2.5 cm) or less, and 20 ft2 (1.9 m2) or less in area; repairing pot holes, with average depths of 1 in. (2.5 cm) and 20 ft2 (1.9 m2) or less in area (Deery, 2003).
The manufacturer does not recommend the use of repair mastics for leveling wheel path ruts, or filling pot holes in asphaltic bridge plug joints, alligator cracks, highly distressed areas or areas exposed to heavy static point loads.
For quality control, DAC requires their repair mastics to be tested in accordance with American Society for Testing and Materials (ASTM) test methods. The physical properties tested are the wear resistance of the coarse aggregate (ASTM C131), the mastic binder (ASTM D5329, ASTM D36, and ASTM D3111), and the finished mastic product (ASTM D3111 and ASTM D517); these testing procedures can be seen in Appendix A.
Wear resistance of the coarse aggregate to abrasion and impact is governed by ASTM C131. In this test, coarse aggregate smaller than 1 1/2 in. (37.5 mm) is tested for resistance to degradation using the Los Angeles testing machine. In general, this test method is a measure of the degradation of mineral aggregate of standard grading under a combination of actions, including abrasion, impact, and grinding. The Los Angeles testing machine employs a steel drum containing a specified number of steel spheres, the number depending upon the grading of the test sample. As the drum rotates, the steel spheres are picked up by a shelf plate that raises the spheres until they drop free onto the opposite side of the drum, creating an impact-crushing effect. The contents then roll within the drum, with an abrading and grinding action, until the shelf plate picks up the sample and steel spheres again. This process is repeated for a prescribed number of revolutions. Once complete, the contents are removed from the drum and the aggregate is sieved to remove small fragments (ASTM C131, 2003). DAC requires the aggregate to have 20% or less degradation. Aggregate not meeting this standard should be discarded and quality aggregate obtained.
The mastic binder is tested under several ASTM test methods. DAC follows the procedures outlined in ASTM D5329 when testing the mastic for penetration and flow properties; ASTM D36 when testing the softening point of the mastic; and ASTM D3111 when testing the flexibility of the mastic.
The ASTM D5329 penetration test applies to hot-applied types of joint and crack sealants and fillers for Portland cement concrete and asphaltic pavements. DAC prefers the cone penetration, non-immersed penetration test. The total weight of the cone and attachments shall be 150.0 ± 0.1 gram. A sample of the material is poured into a six ounce tin, filled flush with the rim, and allowed to cure at ambient temperatures. Once cured, the specimen is placed in a water bath maintained at 77 ± 0.2°F (25 ± 0.1°C) for two hours immediately before testing, DAC modifies the ASTM test method by placing additional specimens in a water bath at 122 ± 0.2°F (50 ± 0.1°C). After the required time has lapsed, the specimen is removed from the water bath and dried. Three cone penetration determinations are made at locations 120° apart and halfway between the center and outside of the specimen. Results are reported by averaging the three penetrations in 1/10 mm units (D5329, 2003). DAC requires the mastic to have a maximum penetration at 77°F of 1 mm, and 1.5 mm at 122°F.
ASTM D5329 also contains a test to measure the flow of the mastic. A mold measuring 1.57 in. by 2.36 in. by 0.125 in. deep (40 by 60 by 3.2 mm) is placed on a bright tin panel. The mold is filled with an excess amount of mastic and allowed to cool for at least 30 minutes. Then the excess mastic is removed with a heated metal knife. Reference lines are marked on the panel containing the sample before it is placed in a forced-draft oven, where it is maintained at 140°F (60°C) for five hours. The mold is mounted so that the longitudinal axis is at 75 ± 1° with the horizontal, and the traverse axis is horizontal. After the specified test period, the panel is removed from the oven and the movement of the mastic is measured in millimeters (ASTM D5329, 2003). DAC requires the mastic to have a maximum flow of 3 mm.
ASTM D36 covers the determination of the softening point of bitumen in the range from 86°F to 315°F (30°C to 157°C). A ring-and-ball apparatus is immersed in ethylene glycol bath ranging from 86°F to 230°F (30°C to 110°C). Two horizontal disks of bitumen binder are cast in shouldered brass rings and heated at a controlled rate in the liquid bath, while each supports a steel ball. The softening point is reported as the mean of the temperature at which the two disks soften enough to allow each ball, enveloped in bitumen binder, to fall a distance of 1 in. (25 mm). (ASTM D5329, 2003) DAC requires the binder to soften at a minimum temperature of 190°F (88°C).
ASTM D3111 determines the flexibility of hot-melted adhesive in sheet form under specific test conditions. Test strips measuring 0.4 by 3 by 0.05 in. (10 by 75 by 1.25 mm) are conditioned at 73 ± 2°F (23 ± 2°C) and 50 ± 5 % humidity for 24 hours. After conditioning, the test strips are bent 180° over mandrels of decreasing diameters until the test strip fails. The flexibility is reported as the smallest diameter mandrel over which four out of five test strips do not break (ASTM D3111, 2003). DAC has modified this test by changing the temperature to 32°F (0°C) and utilizing a single mandrel of 0.25 in. (6.35 mm) diameter. The test strip is bent only 90° and is held for 10 seconds. The test strip passes if it bends without cracking (Deery, 2003).
DAC utilizes the ASTM D517 procedure for their finished mastic product. The test determines the amount of water absorbed by asphalt planks and their ability to withstand significant water absorption. Resistance to water absorption is a measure of the porosity of the mastic, and therefore of its ability to withstand freezing and thawing conditions. Initially, a 2 by 6 in. (50.8 by 152.4 mm) specimen is cut from an asphalt plank in such a manner so that all edges are freshly cut. The mass of the specimen is determined to the nearest 0.1 gram, and it is then immersed in water for 24 hours. After the required time has elapsed, the specimen is removed and the surface wiped off with a slightly damp cloth. The mass after immersion is determined to the nearest 0.1 gram, and the percent absorption determined (ASTM D517, 2003). DAC modifies the standard ASTM test method by immersing the specimen into a water bath at 122° (50°C) for 24 hours. DAC requires the finished mastic to have a maximum absorption of 1% (Deery, 2003).
This literature review chapter describes in detail, various factors associated with crack sealing and filling techniques that are currently employed by SHA. The initial steps of assessing the need for treatment are described. Different strategies are detailed which can be employed for crack sealing and filling, to include the types of materials available and the different configurations that are typically utilized for the sealing material. In addition, this chapter introduces the new concept of crack surfacing that is the subject of this research project. Crack surfacing materials are identified, which are available through Crafco Inc. and Deery American Corporation. Material configurations are described and the respective manufacturer's quality control measures are summarized.