The go-to solution extends pavement life and prevents problems
By Jeff Winke
The superstition has many people avoiding stepping on cracks. Early folk beliefs held that cracks were not something to trifle with because danger lurked in these empty spaces. The cracks signal gaps in the boundaries between the earthly realm and the metaphysical realm.
As an old schoolyard rhyme cautioned: “Step on a crack, break your mother’s back.” Fortunately, mothers’ backs have remained intact, when the absent minded to the malicious have stepped on pavement cracks.
However, for asphalt pavement pros, cracks represent a very real danger. They indicate a pavement failure caused by the penetration of weather-related moisture or too much weight atop the pavement. Whether water or load related causes, cracks are unsightly, dangerous, and costly. As asphalt pavement problems develop, they become increasingly dangerous to drive on and become even more costly to repair if not immediately fixed.
Several different types of cracks can develop in asphalt pavements.
• Fatigue cracking or alligator cracking due to the interconnected cracks which resemble an alligator’s skin is caused by load-related deterioration resulting from a weakened base course or subgrade, too little pavement thickness, overloading, or a combination of these factors.
• Block cracking is a series of large (typically one foot or more), rectangular cracks on an asphalt pavement surface. Typically, block cracking covers large areas and can happen in areas where there is no traffic. The cause is shrinkage of the asphalt pavement due to temperature cycles.
• Edge cracks are longitudinal cracks which occur within a couple feet of the outer edge of a pavement. These cracks form because of a lack of support at the pavement edge.
• Longitudinal cracks happen near the centerline of the pavement. Typical causes: a poorly constructed joint, shrinkage of the asphalt layer, cracks reflecting up from an underlying layer, and longitudinal segregation due to improper paver operation. These cracks are not load-related.
• Transverse cracks occur perpendicular to the pavement centerline. Usually caused by shrinkage of the asphalt layer or reflection from an existing crack. They are not load-related.
• Reflection cracks form over joints or cracks in an overlay of a deteriorated asphalt pavement. The cracks form because of movement of the old pavement.
• Slippage cracks are crescent-shaped cracks which form because of low-strength asphalt mix or a poor bond between pavement layers. The cracks form due to the forces applied by turning or braking motion of vehicles.
“Once a pavement has been installed it begins to degrade,” stated Rick Stone, sales/business development manager, Maxwell Products, Inc., Salt Lake City, Utah. “Generally, the first signs of cracking will begin in the first 18-24 months. Hairline cracking should be observed and monitored to know when to begin crack sealing. Keep in mind that in order for a sealant to prevent water infiltration it first has to be able to be placed in the crack.
“For sealant to penetrate into the crack the width must be in the 1⁄8” – 1⁄4” range, if you are not going to rout the crack wider. This generally will be in the 24-month period after the pavement has been laid. One can wait longer but I find that most asphalt pavements will require some attention to crack sealing by the 36th month. Waiting longer and letting cracks open wider invites moisture into the pavement and accelerates the overall pavement deterioration.”
Crack sealing is considered by many to be the lowest-cost-with-highest-benefit pavement preservation treatment.
“As the result of extensive research programs funded by Strategic Highway Research Program (SHRP) and Federal Highway Administration (FHWA), it has been amply demonstrated and documented that sealing cracks in flexible pavements is a sound preventive maintenance procedure, which adds many years to the life of the pavement, especially when used in conjunction with other preventive techniques such as slurry seal, chip seals and sealcoating,” stated Girish C. Dubey, president of STAR, Inc., Columbus, Ohio. “According to National Asphalt Pavement Association (NAPA), 94% highways in the US are paved with asphalt and the practice of crack sealing has been used for decades quite effectively for their preservation and maintenance.”
How can you tell if a crack is beyond repair for cracksealer?
“Generally, we look at the cracks edges to tell us how best to proceed with a repair,” stated Ben Thielbar, director of sales, Cimline, Inc., Plymouth, Minn. “Are they crumbling or spalling with additional wide spread cracking like an alligator area. If they are crumbling or spalling it generally needs to be removed. The sealant will stick to the asphalt that is not the issue–but if the asphalt can adhere to itself, you will have the crack sealant pull out of the repair area along with chunks of asphalt. In this case, it is also nearly impossible to prevent water intrusion and that is a good indicator. Alligator areas should be repaired with a spray patch, or rubberized mastic material in these instances.
“Cracksealer is best used on early stage cracks. Early stage is identified as years 1-3 of the pavement life in most cases. Crack sealing should be done each year. The early years are most effective to prevent additional cracking or deterioration to the base below the asphalt which will result in more cracks and potholes.”
Not all cracks can be filled. Crack sealer has its limitations. As effective as crack sealing is, it isn’t suitable for every type of pavement distress.
“Typically, anything over two inches, in my opinion, would require an asphalt paving material repair,” stated Robb Archie, owner of U.S. Seal International Inc., Reno, Nev. “If it is too wide, then the contractor would need to saw cut approximately one foot on both sides of the crack, re-compact the base material, or add more and re-compact, and then add three inches of new asphalt and compact. The asphalt should be crowned upwards before compacting, so as to force the material tightly against the sidewalls of each side of the crack walls. That will keep the crack from sinking.”
Archie continued, “If the crack runs through the middle of alligatored asphalt then repairing it is not an option. Instead, you will need to saw cut on all four sides of the alligatored asphalt, just beyond the alligatoring, re-compact the base, then add new asphalt as a patch repair.”
“Cracks that are wider than two inches will need asphalt. Some crack-fill-material companies suggest three inches but that is a very big span for a flexible material to hold to both sidewalls and stay connected under contact vehicular traffic as well as the constant tension of two independent pieces of asphalt constantly pulling away from each other.”
Mark McLeod, president/CEO at Maintenance, Inc., Wooster, Ohio offered perspective. “How you judge if a crack can be sealed is dependent on how wide, two-inch maximum, and how deep. An area that is deep and wide will require a backer rod installed to reduce settling and material waste. Bituminous concrete (asphalt) is a floating mat that lays on top of base of crushed stone material and as it ages cracks will develop since asphalt has no expansion joints like concrete has. It has to crack! Early treatment of the cracks will prevent moisture intrusion causing the under stone base to soften and rim cracking will occur. Early crack maintenance is imperative for extending the service life of the pavement.
“Large cracks that are alligatored or spiderwebbed will require a gator patch application, which is a short term fix for these areas. Removing those areas and placing new asphalt becomes the remedy. Sealcoating those areas will also ensure no further moisture intrusion in that area.”
Early folk beliefs on cracks exist today in the transformed practice of current day asphalt pavement maintenance professionals that fill the cracks not so much to prevent the nether world escaping to wreak havoc, but to prevent elements penetrating the pavement and creating cracks and deterioration — a different kind of havoc!
Jeff Winke is a business and construction writer based in Milwaukee, Wisconsin. He can be reached through email@example.com