This article was ghostwritten for an online construction magazine.
The Difference Between Crack Sealing and Crack Filling
Cracked asphalt is a safety hazard – but it’s also just ugly. This may not matter on a back road somewhere in the boonies but cracked asphalt in front of a commercial business is an eyesore. It could turn some customers away. It also poses a safety hazard; wide cracks can cause a person to trip. In this article, we talk about the different types of asphalt cracks and the best way to fix them.
Asphalt Crack Repair
There are two ways to fix cracked asphalt: you seal it or you fill it. Some people use these terms interchangeably, but they are not the same thing. One is not better than the other. It depends on the type and severity of the asphalt cracks.
Crack sealing uses rubberized products to temporarily repair asphalt cracks. The rubberized material is flexible and can better handle movement – such as expansion and contraction in harsher weather. Crack sealing should be done in good, dry weather. Not too hot or too cold. Prepare the crack by using a router or saw to cut in a reservoir. This results in greater adhesion of the sealer to the walls around the crack, increasing the life of the crack repair.
Crack filling is used as a quick-fix for certain types of cracks that are thinner and not too deep. A homeowner fixing their driveway can use a caulking gun and a trowel. The pros use equipment such as a crack cleaning machine and crackfill melter applicator. Crack filler material can vary. For example, cold-application filler products may include a polymer-modified, asphalt emulsion liquid. Crack filling should also be done at ambient temperatures.
Causes of Cracks
Asphalt pavement is going to crack. The loads and elements the asphalt is exposed to can impact how quickly cracks are formed. These are common causes of asphalt cracks.
Any kind of moisture – rain, snow, etc., starts to break down the asphalt pretty quickly. The situation gets worse as moisture seeps into these newly-formed cracks (even tiny ones) and begins to wash away the sand and gravel base.
Asphalt pavement that is not designed for the intended load and / or is poorly constructed will quickly cause cracks.
A lot of vehicles stopping and starting constantly – such as they do in daily rush hour traffic – results in cracks.
Regular traffic will cause cracks over time. But even just leaving a very heavy vehicle parked for a long time in the same place will result in cracks. Vehicles that exceed the designed maximum pavement capacity traveling over the asphalt is another type of load damage.
Asphalt pavement exposed to a wide range of temperatures throughout the year (for example, hot humid summers and harsh, cold winters) results in cracking. Asphalt pavement that is exposed to annual cycles of freezing and thawing are also more likely to crack.
Types of Cracks
Cracks generally fall into two categories: working and non-working. Basically, thinner cracks (not thicker than 0.1 inches) that are not moving are non-working. Working cracks are thicker and are moving – expanding and contracting. You want to identify crack repair that is still in the non-working phase. These can be filled instead of sealed, which is easier and cheaper. However, a non-working crack that is deep, will require sealing.
There are several different types of non-working and working asphalt cracks, including:
Diagonal. Cracking at approximately a 30-to-60-degree angle from the pavement’s centerline.
Longitudinal. These cracks are parallel to the asphalt’s laydown direction. They are caused by inadequately constructed lane joins. Other causes include temperature shifts and shrinkage of the pavement.
Alligator. Also called fatigue cracking. This type of crack consists of several interconnected cracks that are close to each other – giving it an appearance of alligator skin. It is caused by extensive traffic loading.
Transverse. This type of crack runs perpendicular to the asphalt pavement’s centerline. Also called thermal cracking. It is typically caused by exposure to cooler temperatures while the asphalt mixture is still warm; before it has had a chance to harden.
Edge. Cracks that develop between the edge of the asphalt pavement and concrete curbs. As snow and ice thaws each season, these cracks grow wider and deeper.
Seam. These cracks appear along the asphalt pavement’s joints. They are due to poor paving.
Block. These cracks indicate pavement that is at the end of its lifecycle. They appear as square pieces typically spaced four to twelve feet apart. They are caused by poorly constructed base courses or inadequate drainage.
Reflective. Also called reflection cracking. These are cracks that “reflect” the cracking that exists underneath an asphalt or tar overlay on a PCC slab. Movement related to thermal changes and moisture are usually the cause. Proper sub-base courses are key to eliminating (or at least reducing) this type of surface material crack.
Slippage. Crescent shape cracks that form due to inadequately bonded pavement layers. An asphalt mix of insufficient strength can result in slippage cracks. It is also caused by asphalt pavement stressed by the constant braking and turning of vehicles over time.
Fill or Seal?
Let’s first point out that proper paving is the first step in avoiding cracks. (LINK to asphalt series.) You can fill cracks if they are non-working and not too deep. Sealing will be required for working cracks of any depth. Either filling or sealing is a temporary fix. That said, annual inspection can help identify problem areas early on. Crack sealing or crack filling usually costs less than replacing a section of asphalt. (Link to article about Pavement, Compacting, and Milling Guide).
There are several reasons why asphalt pavement cracks. The first preventative measure is using an appropriate asphalt mixture and proper construction processes. In other words, build it right the first time. Cracking will happen over time – even when the asphalt paving is well designed and built. Changing weather and heavy traffic loads will result in cracks. Annual inspections can help reduce the cost of maintenance. Ultimately, cracks can only be sealed or filled so many times. Asphalt replacement is inevitable.