Pavement Cracking Analysis for Asphalt Pavement

Asphalt concrete pavements are vulnerable to cracking due to different factors, including traffic loading, environmental conditions, aging, and construction works. Cracking is the result in water penetrating the pavement layers and subsequently hastening the process of deterioration and shortening the pavement service life. Hence, the cracking analysis greatly helps pavement maintenance and rehabilitation efforts. This paper discusses major cracking types in asphalt pavements and how they can be analyzed.

Asphalt Pavement Cracks: Inclinations and Applications

Fatigue Cracking

Alligator cracks are multiple interconnecting cracks resulting from traffic loading. They develop at the bottom of the asphalt layer near the location with the most stiffness, which is typically over the wheel paths; they spread to the surface in a fashion similar to that of chicken wire or alligator skin. So, a severe fatigue crack implies structural failure and needs to be rehabilitated.

Transverse Cracking 

Transverse cracks run across the pavement surface, and they are usually straight. They are brought about by low temperatures or hardening of asphalt. While widely spaced transverse cracks are not necessarily a structural concern, closely spaced cracks may cause roughness or additional decay. 

Longitudinal Cracking

Longitudinal cracks run parallel with the pavement centerline, with poor construction joints being the cause. They allow more water infiltration, resulting in potholes, raveling, and fatigue cracks. Vertical cracks parallel to the edge are more extensive because water gets into the pavement edge and washes the base.

Block Cracking

Block cracking separates the surface into rectangular areas between 1 and 100 square feet. This is because thermal contraction at low temperatures plus aging hardening leads to shrinkage. While low-severity block cracking is just a cosmetic problem, high-severity block cracking is a sign that the structure is weakening. 

Edge Cracking

These include crescent shapes or fairly continuous cracks which are nearer to the edge of the pavement. They are brought about by inadequate support at the edges of the pavement due to erosion of the shoulders or the influence of tree roots. The secondary cracks at pavement edges also enable water to penetrate the pavement base, contributing to further deterioration.

Reflection Cracking

These are present over existing joints and cracks in the pavement layer beneath due to movement and cracking. It mimics the joints or cracks from the layer underneath it. The same principle applies in prevention; joints/cracks must be treated before being overloaded in existing layers.

Methods for Analyzing Cracks 

Visual Inspection 

The current approach to cracking evaluation entails the use of trained engineers for visual examination. Defects such as cracks are rated according to the type and the extent of damage through procedures such as the PAVER system. However, the findings may be inconclusive based on the discretion of the inspector.

Photographic Analysis

It is possible to use high-resolution digital cameras where photographic logs can be taken and cracks measured more accurately than using the eyes. Geo-location image analysis gives the crack amounts, and their severity is interpreted by the software. However, it is time-consuming since it involves specific repetitive steps that must be completed before a definite outcome is achieved.

Automatic Imaging Processing 

Newer ways of imaging that entail the use of cameras and computers installed in vehicles can image at traffic speeds. Advanced pattern recognition determines various crack types and measures densities and severities similarly. However, they call for substantial pre-investments and training data.

Deflection Testing 

Non-destructive techniques that can be used to evaluate structures include surface deflections using a Falling Weight Deflectometer (FWD) and mechanical properties. When used in conjunction with visual cracks, FWD offers a full assessment, but performing these tests is a lengthy process and requires traffic management.

3D Laser Scanning

Laser road imaging systems are based on special 3D laser scanners that produce detailed images of the pavement surface with very high accuracy. Specialized software detects the tiniest of fractures from the generated 3D surface model. The equipment, however, is very costly.

Sealing and Monitoring

If you want detailed information on the growth of a particular crack, you can then place seals over the said cracks and wait for some time before checking on the extent of growth. A sealant technology that promotes automatic imaging allows monitoring thousands of sealed cracks. However, sealing a large number of points is time-consuming.

Selecting Appropriate Method

There are various types of transport mode integration depending on budget, size of the transport network, data needed, and mode of use. Small networks require comprehensive visual checks and documentation by photographs. Extended highway networks require automated imaging for asset management. Three dimensional (3D) laser scanning provides precise cracking data but can only be justified at the project level.

Conclusion

Asphalt pavements deteriorate in various ways during their use, and this may be as a result of loading, extreme climatic conditions, or problems concerning construction of the pavement. Categorizing and selecting the proper cracking analysis methods are crucial in recognizing distress modes and undertaking prompt repairs, making pavements durable while controlling the cost of maintenance. It is common to observe that agencies use an appropriate mix of VIs, photography, automation, and HI&T depending on the agency’s requirements and constraints.