Asphalt Pavement Crack Sealing and Filling : A Preventive Maintenance Treatment.
Pavement distresses contribute to pavement failure in different ways. The most common flexible pavement distresses are cracking, roughness, weathering, raveling, rutting, and bleeding. Cracking is the most common, and often the first distress encountered in an asphalt pavement. It occurs when a stress is built up in surface layers that exceeds the tensile or shear strength of the pavement causing a fissure or crack to develop. Pavement cracking shows up in many forms: transverse, longitudinal, block and fatigue (alligator) cracks.
Why Does Asphalt Pavement Crack?
There is no one explanation as to why asphalt pavement cracks, there are a number of factors that contribute to the cracking of asphalt pavement. Some of the few common reasons include :
• A weak base. Weak subgrade can cause alligator cracking, particularly if excessive weight is put on the surface often. Alligator cracking appears in a pattern of small cracks that look, appropriately, like alligator skin.
• The asphalt has aged. If the asphalt surface is older and dried, it can cause block cracking down the road due to a lack of flexibility in the asphalt. When first laid, asphalt has it's proper oil content and appears very black in color. As time goes on, the asphalt oxidizes and ages. The oil essentially leaves the asphalt and causes it to become more rigid and prone to cracking.
• Poor drainage. Lack of drainage access can cause a buildup of water, mud & dirt, etc., which eventually wears on the asphalt surface and may cause cracking. Worse yet, when cracking begins, water then penetrates the surface and can compromise the subgrade, causing further damage.
• Settlement of underlying material. An issue that is often unavoidable, as is nature, sometimes earth underneath a heavy surface begins to settle after some time, which can cause unevenness and crack on an asphalt surface.
• Daily temperature changes. Another force of nature, sometimes the weather can cause unwanted, and difficult to predict, changes in asphalt. Cold weather can cause the pavement to shrink, while UV rays from the sun can result in brittle asphalt — both of which weaken the asphalt and make it prone to cracking.
Addressing Cracks in Asphalt Pavement
It's no secret that cracks in asphalt surfaces allow water to penetrate the surface, softening the stone base and leading to alligator cracking/spider webbing, potholes, and other forms of degradation. Left unfilled, cracks will allow rain and moisture to flow through the pavement and erode base materials; resulting in potholes, and ultimately in premature failure. Cracks leftover in the winter can grow quickly due to the freeze/thaw cycle. In warm and sunny climates, oxidation and humidity have a similar effect. Patching often doesn't last and can cost several times what timely crack-sealing costs. In the end, the useful life of the surface is shortened, forcing the premature and costly replacement of the surface.
The appropriate type of maintenance for cracked asphalt pavements depends on the type, density, and general condition of the cracks. If cracks are low to moderate in density, with a high degree of edge deterioration, then maintenance such as partial–depth patching or spot patching may be warranted. Chip seals, slurry seals, etc. may be more appropriate for pavements where cracks are abundant and exhibiting a low degree of edge deterioration. Pavements having low to moderate crack density with little to no edge deterioration can potentially be treated effectively through sealing or filling operations.
Crack Filling and Sealing
Crack sealing and filling are imperative preventative maintenance tools. As part of a preventative pavement maintenance program, crack sealing can reduce pavement deterioration by restricting water penetration into the underlying base and sub-base layers. Crack sealing/filling prior to surface treatments enhances the treatment and further extends the pavement life, and stands out as an economical maintenance technique.
Should the crack be sealed or filled? To answer this question it must be established whether the crack is a working or nonworking crack. Normally, working cracks with limited edge deterioration should be sealed, while non-working cracks with moderate-to-no edge deterioration should be filled.
Crack sealing is the placement of materials into working cracks. Crack sealing requires thorough crack preparation and often requires the use of specialized high-quality materials placed either into or above working cracks to prevent the intrusion of water and incompressible materials. Crack sealing is generally considered to be a longer-term treatment than crack filling.
Due to the moving nature of working cracks, a suitable crack sealant must be capable of :
• Remaining adhered to the walls of the crack,
• Elongating to the maximum opening of the crack and recovering to the original dimensions without rupture,
• Expanding and contracting over a range of service temperatures without rupture or delamination from the crack walls, and
• Resisting abrasion and damage caused by traffic.
Crack filling is the placement of materials into nonworking or low movement cracks to reduce infiltration of water and incompressible materials into the crack. Filling typically involves less crack preparation than sealing and performance requirements may be lower for the filler materials. The filling is often considered a short-term treatment to help hold the pavement together between major maintenance operations or until a scheduled rehabilitation activity.
Crack filling is for active or non-active cracks created by the aging of the binder. Such cracks are not completely inactive and require some flexible characteristics. A suitable filler material must be capable of :
• Remaining attached to the walls of the crack,
• Possessing some elasticity, and
• Resisting abrasion and damage caused by traffic.
• Materials for Sealing/Filling Asphalt Pavement Cracks
Materials for sealing/filling asphalt pavement cracks may be divided into three categories :
1. Cold applied thermoplastic materials such as a) liquid asphalt (emulsion or cutback), and b) polymer-modified liquid asphalt.
2. Hot applied thermoplastic materials such as a) asphalt cement, b) mineral-filled asphalt cement, c) fiberized asphalt, d) asphalt rubber, e) rubberized asphalt, and e) low-modulus rubberized asphalt.
3. Chemically cured thermosetting materials.
Asphalt cement, liquid asphalt, mineral-filled asphalt cement, and fiberized asphalt possess little flexibility and are very temperature susceptible. Therefore, their use as fillers for nonworking cracks is limited.
The addition of rubber polymer improves the flexibility of the asphalt. The degree of flexibility depends on the type and nature of the asphalt, the percentage of vulcanized rubber used, and how the rubber is incorporated into the asphalt (i.e., mixed or melted in). Other additives are often incorporated into the asphalt, either exclusively or along with rubber, to increase resilience. In general, the performance increases in the order of polymer-modified liquid asphalt, asphalt rubber, rubberized asphalt, and low-modulus rubberized asphalt.
Chemically cured thermosetting materials are cured by a chemical reaction from a liquid state to a solid-state. Self-leveling silicone is one of these sealant materials that is cold-applied and does not require tooling since it is self-leveling
Current Issue
12-2025
