Over the past 10 years, Simpson Strong-Tie has developed their Composite Strengthening Systems™ (CSS), becoming industry leaders in the strengthening of concrete and masonry structures with composites. As America’s roadway infrastructure continues to age, Simpson Strong-Tie has again risen to the challenge, now providing a solution to asphalt cracking in the form of prebituminized composite grids for pavement reinforcement.
Asphalt pavements are used extensively for road construction due to their durability, flexibility, and cost-effectiveness. These pavements are designed to withstand the weight and traffic of vehicles, pedestrians, and other forms of transportation. However, over time, they can develop cracks due to a multitude of factors such as heavy traffic, temperature fluctuations, and moisture penetration. One type of cracking in particular is commonly observed in asphalt pavements: reflection cracking. (See Figure1, below.)
What Is Reflection Cracking?
Reflection cracking is the type of cracking that occurs in asphalt pavements due to the movement or shifting of the underlying layers of the pavement. This type of cracking is usually seen in areas where there are joints, cracks, or other defects in the underlying layers. As traffic passes over these areas, the stress from the weight of the vehicles can cause the pavement to crack along the same line as the underlying defect.
There are several methods for repairing reflection cracks in asphalt pavements. One of the most common methods is to mill off the affected layer of the pavement and replace it with new asphalt. This method is effective in cases where the reflection cracking is not too severe and has not spread to other areas of the pavement. However, if the cracking is extensive, a full-depth reconstruction of the pavement may be necessary.
In order to avoid reflection cracking in asphalt pavements, the use of reinforcement grids has become increasingly common over the past two decades. In this blog post, we will explore how Simpson Strong-Tie prebituminized asphalt reinforcement grids can be utilized to prevent reflection cracking.
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How Our Asphalt Reinforcement Grids Work
Our grids are placed between pavement layers to act as a reinforcement, distributing the load across a wider area and reducing the movement of the underlying layers. This mechanism improves the overall strength of the pavement and reduces the likelihood of reflection cracking.
Our prebituminized asphalt reinforcement grids can be installed in either of two ways:
- Interlayer Reinforcement: In this method, a layer of grid is placed between the existing distressed asphalt layer and a new asphalt layer. (See Figure 2a.) The grid helps to bond the two layers together and provides reinforcement to prevent reflection cracking. Read more about it in one of our case studies, here.
- Full-Depth Reinforcement: In this method, the grid is installed in beneath every layer of asphalt through the entire pavement structure, from the top of the subbase to just beneath the surface layer. (See Figure 2b.) This method is more effective in preventing reflection cracking, because it provides reinforcement throughout the entire asphalt pavement structure.
Testing the Solution
To put our solution to the test, we’ve partnered with the Advanced Pavement Research Center at the University of Texas in Arlington (UT Arlington) and successfully completed a one-of-a-kind reflection cracking test at their Accelerated Pavement Testing Facility (APTF).
The APTF at UT Arlington is an internationally recognized, state-of-the-art outdoor laboratory used for testing and evaluating various pavement materials, designs, and construction techniques. The facility is designed to accelerate pavement performance testing, allowing researchers, transportation officials, and product manufacturers to evaluate performance and durability under simulated heavy traffic loads in a much shorter time than traditional pavement testing methods, such as monitoring in-service pavement sections, allow. (See Figure 3.)
The APTF boasts several unique characteristics, including the Pavement Testing Machine (PTM), which has the ability to apply bidirectional loads of up to 40,000 lb. on either a single or a dual tire axle arrangement, and can reach speeds of up to 7.5 mph, all while maintaining precise control over pavement surface temperature. (See Figure 4.) The ability to age asphalt surfaces for testing using innovative oxidation chambers is another distinctive feature of the APTF. These chambers subject the test sections to the equivalent of years of oxidation in just a few weeks.
For our test, two 70‘ x 12‘. asphalt pavement test sections were constructed using full-scale highway paving techniques and equipment. The sections were built on a layer of improved subgrade and consisted of 8“ of granular foundation and 4“ of distressed asphalt. To replicate typical asphalt pavements ready for rehabilitation, saw cuts measuring 1/8“ wide and 2“ deep were created 5‘ apart on both sections. One of the sections was reinforced using our Carbophalt G200/200 prebituminized asphalt reinforcement grid, while the other was left unreinforced to function as a control section. Finally, a 3“ asphalt overlay was placed on both sections. (See Figure 5.)
The sections were subjected to 1.2 million equivalent single axle loads (ESAL) at a constant temperature of 77±2°F at 3 mph, while cracks and rutting profiles were closely monitored. ESAL is a hypothetical value that represents the number of times an axle with a standard load of 18,000 lb. would have to pass over a pavement section to cause the same amount of damage as the actual number and type of axles that have passed over it.
The Mechanistic Empirical Pavement Design Guide (MEPDG) rutting and cracking threshold for secondary streets governed the failure criteria for the test. The criteria are defined as a rut depth of 2/3“ and 35% of the surface cracked in the wheel path.
After reaching 1.2 million ESAL, the control section was severely damaged, making it difficult for the PTM to keep running, thus the testing was stopped. (See Figure 6.)
At the end our test, we reported that:
- It took four times as long for an initial crack to appear in the reinforced section than in the control section.
- The reinforced section suffered 61% less alligator cracking and 57% less rutting than the control section.
- It took more than twice as long in the reinforced section for the reflection cracks to fully expand on the width of the wheel path. (See Figure 7.)
From these results we can infer that the presence of the grid reinforcement kept the surface of the pavement intact, which in turn also mitigated the appearance of alligator cracking.
Due to the condition of the control section, the test had to be stopped, necessitating the use of linear interpolation to evaluate the performance of the reinforced section in terms of cracked surface area. (See Figure 8.)
From a pavement management standpoint, the beneficiary would have to mill and fill the same pavement two more times before the reinforced section would reach its end of fatigue life. (See Figure 9.)
Simpson Strong-Tie is committed to providing innovative solutions for the infrastructure industry, and our prebituminized asphalt reinforcement grids are just one example of our dedication to improving the safety and longevity of pavement structures. Contact us today to learn more about our product line and how we can help you prevent reflection cracking in your asphalt pavements.
For complete information regarding specific products suitable to your unique situation or condition, please visit strongtie.com/asphalt or call your local Simpson Strong-Tie Pavement Specialist at (800) 999-5099.