5 Types of Asphalt Cracking and Their Causes

Of all the road damages that are most likely to occur, cracking is perhaps the most frequent on asphalt surfaces. It occurs when pavement material fails or cracks into two or more parts for various reasons. It leads to a high cost of maintenance and may be a safety risk to vehicles if it goes unaddressed. There are five major types of asphalt cracking:

1. Fatigue/Alligator Cracking

Fatigue cracking, or alligator cracking as it is commonly referred to, occurs after the asphalt pavement has reached its structural failure point. It is among the most frequent and severe forms of damage that can affect asphalt surfaces.

Causes:

– This type of cracking results from the cumulative effect of placing constant pressure on the sub-layered pavements with frequent traffic loads and offloads

– The most common problem associated with poor drainage and causes high moisture content in base and sub-base courses

– Lack of coating for pavements and insufficient pavement thickness to accommodate traffic loads

– Lack of proper preparation and compaction of the sub-grade

In its initial stage, fatigue cracking manifests itself in the form of several small adjacent cracks connected, and later on, the surface will be made up of many-sided sharp-angled fragments that resemble the skin of an alligator. It means that the pavement has failed and requires either rehabilitation or reconstruction.

2. Block Cracking

Block cracking develops extensive cracks that split the top layer into rectangular shapes or blocks. The cracks propagate through the entire pavement thickness from the surface down to the subgrade.

Causes: 

– Basic poor mixture quality that does not offer the necessary durability

– This is due to oxidation and hardening of the asphalt binder, which occurs over time 

– Reduction in the size of the pavement is caused by low temperatures

– These cracks form due to a shift in the stratum below a structure

There are several factors that may contribute to block cracking; however, good asphalt mix design and installation best practices can substantially reduce the chances of block cracking. Sealing of cracks helps avoid introducing water and subsequent damage to the structure.

3. Edge Cracking

Edge cracking develops along the lane or carriageway edge and within one to two feet from the outer edge of the pavement. They form crescent-shaped cracks that extend across the pavement edge.

Causes: 

– Insufficient shoulder support

– Establishment on the edges of roadways or even on slopes or banks of a road.

– Poor compaction along the pavement edges

– Water retained at the sides

Edge cracking indicates a need to resurface or reinforce pavements at the edge and provide adequate drainage.

4. Longitudinal Cracking

These cracks extend from the top of the pavement. They are aligned along the direction of traffic in the middle of the pavement and may appear as a single solid line or multiple lines across the carriageway or road lane.

Causes:

– Lack of proper joint construction practices resulting in desired shapes, patterns, or formations

– Occurs because pavements shrink when temperatures are low

– This aggression leads to the enhancement of the hardening and brittleness of the asphalt mix

– May exhibit gaps that are visible from the bottom layers

Some solutions must be applied to control the cracks, and drainage fixes can also be effective. These are severe cases requiring patchwork or overlays, or a similar type of project.

5. Transverse Cracking

These transverse cracks run across the pavement and are generally at right angles to traffic flow. They are somewhat similar to a grid system on the actual roadway.

Causes: 

– Exposure to heat and complex processes of hardening in heat and cold

– The deterioration of the pavement surface due to age and fatigue

– The visible reflection of the cracks on the surface from the underneath layers

– Improper mixture composition

Sealing of transverse cracks and correctly filling them helps to prevent an increase of moisture damage. However, the existence of multiple transverse cracks suggests that an overlay solution or complete road rehabilitation is required.

Conclusion

Some of the most common asphalt cracking include alligator, block, edge, longitudinal, and transverse cracks. They occur due to weathering, poorly done construction, traffic loads, changes in temperature, excess moisture, and deterioration over time. To increase the life expectancy of the pavements, it is necessary to inspect them periodically and repair them promptly. In some cases, pavements that have severely deteriorated may require rehabilitation that involves the placement of overlays or reconstruction. Analysis of cracking patterns and these causes assist agencies in choosing the best method of repairing.