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Technical review of Indirect Tensile Strength testing advises caution in relying on results

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ACE XP Polymer Fiber
Alternative tests, plus a balanced mix design, can improve predictions of asphalt performance

The indirect tensile strength (ITS) test has been utilized for more than 40 years as a definitive method for predicting the performance of asphalt mixtures. But the test, at 25°C, can render misleading results, according to a recently released technical brief by Phil Blankenship, P.E.

indirect tensile strength (ITS) test“While the indirect tensile strength test at 25°C is sensitive to changes in mixture properties such as air voids, asphalt binder content, binder grade, aggregate properties (angularity, texture, etc.), the resulting indirect tensile strength does not always equate to positive field results,” he writes. “In other words, high tensile strength alone does not always relate to improved cracking resistance.”

The author discusses various developments taken over the past 10 to 15 years in ITS testing to achieve more predictive results for top down cracking. However, differences in testing temperatures and loading rates may not, in reality, conform to ASTM D 6931 standards.

Blankenship presents data from various experiments that show a weak correlation between strength (at 25° C) and ALF cycles to failure. Various results of other tests also show that indirect tensile strength testing alone (at 25°C) can be misleading.

Instead, Blankenship advises that other cracking tests produce good correlations to field performance, and the types of tests and standards are provided within the paper. The author further explores taking a “balanced mix design” approach, or performance-based testing.

To explore the various testing methods for yourself, click here.

IDEAL-CT & Hamburg Wheel Tracker meet the need for crack/rut balanced performance testing in asphalt mixes

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ACE XP shows 30% to 50% improvements in both tests

 Indirect Tensile Cracking Test at Intermediate Temperature (IDEAL-CT)

Figure 1. Indirect Tensile Cracking Test at Intermediate Temperature (IDEAL-CT)

Asphalt pavements need to be stiff enough to minimize rutting, but resilient enough to bend without breaking to prevent cracking. The trend over the last 20 years has been one-sided — fixing the ruts at the expense of the cracks. Many in the industry have begun to recognize the need for a “balanced approach” to developing pavement designs that will perform well in resisting both rutting and cracking.

There are seven key existing performance or index tests for asphalt cracking (see Table 1). These tests vary in complexity and cost, and as a result, the asphalt industry has not traditionally performed cracking performance tests on every project.

Hamburg Wheel Tracker (HWT) Test

Figure 2. Hamburg Wheel Tracker (HWT) Test

For rut testing, the Hamburg Wheel Tracker (HWT) test tends to be the most widely used method. However, many agencies and specifiers, including DOTs, are moving toward adopting performance-based specifications where both mix designs and daily production will need to meet certain minimums in both cracking and rutting parameters in order to be considered.

A new and promising cracking test has recently been developed by Dr. Fujie Zhou and his colleagues at the Texas A&M Transportation Institute. The Indirect Tensile Cracking Test at Intermediate Temperature (IDEAL-CT) is a reduced cost method that provides consistent results to predict field performance in cracking. This test, along with HWT, can be used daily to ensure that asphalt mixes meet both rutting and cracking performance criteria in a balanced manner.

For example, tests utilizing the HWT and IDEAL-CT methods on ACE XP asphalt mixes can be seen in Figures 1 & 2. The results compare mixes with and without ACE XP and show clear performance advantages with ACE XP in both rutting and cracking sample results.

Bottom line: In balanced performance testing, ACE XP Polymer Fiber yields an improvement of 30% to 50% in both rutting and cracking performance. To learn more about ACE XP or how to achieve a balanced approach to testing using the IDEAL-CT method, contact us.

Asphalt crack testing

Fig. 1 - Hamburg Wheel Tracker (HWT) Test Example:

Fig. 1 – Hamburg Wheel Tracker (HWT) Test Example

 

IDEAL-CT Crack Test

Fig. 2 – IDEAL-CT Crack Test Example:

94th Annual AAPT Annual Meeting — we’ll see you there!

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AAPT Annual MeetingThe AAPT annual meeting is just a few weeks away, and our Chef Technical Officer Joe Dennis will be on hand to share the latest updates on ACE XP Polymer Fiber —a product that can make asphalt stronger than steel. The schedule includes several technical presentations on asphalt binders, strength testing techniques and mix designs, plus some social opportunities.

We especially encourage everyone to attend the Leading Edge Workshop on Monday, March 4, at 9:45 a.m. Phil Blankenship, P.E., a leader in the asphalt industry, will preside over the session of Automation in the Paving Industry. This session features two cutting-edge topics of: 3-D Paving: Advances and Limitations and Automation in Testing from the Lab to the Field.  This session will be livestreamed on Youtube.

The line-up of presentations looks both comprehensive and potentially groundbreaking. Check it out here, and plan to join us as we convene in Fort Worth March 3 through 6. To plan a meet-up, contact us.

What do bowstrings, hockey sticks and skis have in common with asphalt?

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ACE XP aramid polymer fiber additiveAll require strength, flexibility and abrasion tolerance to achieve high performance. The common ingredient that delivers those winning traits is aramid fibers. These polymer synthetic fibers provide advantages that make them ideal for a wide range of products. So it’s not surprising that more than 60,000 tons of aramid fibers are produced annually, and demand continues to grow as new applications emerge.

Years ago, Surface Tech recognized the superior advantages that aramid fibers, particularly para-aramid fibers, could provide to asphalt applications. The company began offering the ACE XP aramid polymer fiber additive after years of painstaking research and multi-geographical testing. Back then, the challenge was to find a way to harness millions of tiny fibers into a final product that could be easily managed. By combining para-aramid with a wax treatment, Surface Tech achieved its goal of creating an additive that successfully reinforces and properly doses the entire matrix of asphalt.

The wax binds the polymer fibers to allow for an easy, reliable method for feeding into the asphalt mix. Once added, the wax melts and is fully soluble within the mix to release the polymer fibers in a uniform distribution. This unique delivery process produces the highest performing blend of Fiber Reinforced Asphalt Concrete (FRAC) on the market, and any asphalt project can benefit from ACE XP.

If you want an asphalt surface that resists cracking and rutting and dramatically extends the life of your pavement, call us. With para-aramid fibers, you’ll get asphalt that’s stronger than steel, and only from ACE XP — the Number One choice for strength, flexibility and abrasion tolerance.

Turn to ACE XP for Extreme Performance Asphalt

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ACE XP Polymer Fiber for asphalt

Contractors have come to depend on ACE XP Polymer Fiber from Surface Tech to make asphalt more durable and long-lasting. How does this high-tech additive deliver on its promise to produce extreme performance asphalt? The key lies in its chemical makeup — it’s composed of aramid polymers.

Aramid polymers contain a set of chemical properties that give them outstanding strength, flexibility and abrasion tolerance. They’re particularly useful in applications where flexing tolerance is important, like armor, airplane wings, ropes, cables, undersea pipelines, and of course asphalt applications.

To create ACE XP, high-strength aramid fibers are bundled and coated with wax to produce an asphalt additive that is simple and dependable to mix with any WMA or HMA in both drum and batch operations.  In fact, this binder use insures proper aramid delivery into the WMA/HMA; and coupled with our precise dosing equipment, delivers consistently intended amounts into every ton of asphalt.

One of the most outstanding performance benefits of ACE XP lies in its micro roots. These tendrils tenaciously anchor themselves into the bitumen of the asphalt, providing 400,000 psi tensile strength. The result is a three-dimensional reinforcement throughout the asphalt and a flexibility that resists rutting during hot summers and cracking through cold winters.

Contractors will also appreciate the fact that ACE XP is a “dry” polymer fiber. Comparatively, it’s less expensive, more reliable, and easier to adopt. The MD3+ dosing system from Surface Tech delivers an easy, foolproof way to add ACE XP to any asphalt mixture.

Yet the ultimate beauty to ACE XP is its scalability and batch-to-batch reliability. Combined with the life-span improvements it provides, it’s a winning way to armor your asphalt for the long haul. That kind of reliability allows contractors to sell and place with confidence, knowing the asphalt they provide will deliver extreme performance based on an excellent polymer.