Scientists introduce new basis for measuring Asphalt binder characteristics

New York, Feb 27, IRNA - In a new research at National Center for Asphalt Technology (NCAT) at Auburn University, Iranian scientists proposed a new method for measuring asphalt binder properties that can save millions of dollars worldwide.

Scientific research has always been a basis for the transformation of human life, whether it comes from foreign or Iranian influential researchers. The more extensive they become, the more positive impact they will leave on the society and global population. If the research is on the roads and highways, which provides enormous benefits to countless people, they will leave even more economical and social impacts.

Mostafa Nakhaei and Farhang Jalali are Iranian PhD students and research assistants at the National Center for Asphalt Technology (NCAT) who have spent the past two years studying asphalt materials and recently have been able to improve the theory behind asphalt binder characterization which first was proposed by Dr. Anderson, a prominent asphalt research scholar, almost thirty years ago. The theory has been around, unchallenged, for almost thirty years and are implemented currently in most countries to categorize different types of asphalt binders based on the specific climatic conditions.

We sat to talk with the Iranian scientists at the 2019 Transport Research Board (TRB) conference in Washington DC who have conducted innovative, impactful research related to measuring and rating of bitumen that is used in asphalt pavements. This study was the result of an idea that initially evolved at the Technical and soil mechanic laboratory (TSML) in Iran with a team of researchers, including Koorosh Naderi and Aliasghar Akbari Nasrekani. The study continued later in the US and expanded shortly after with participation of scientists at the heart of asphalt research in the USA, the National Center for Asphalt Technology (NCAT), a subsidiary of Auburn University in the state of Alabama.

Mostafa Nakhaei, who was awarded a David R. Jones IV Scholarship from the Association of Modified Asphalt Producers (AMAP) in 2018, said in an interview with IRNA reporter: 'about 30 years ago, the United States began an intensive research study on highways called Strategic Highway Research Program (SHRP), in which it introduced a scientific approach to grade the asphalt binders which eventually improved the quality of roads and highways. This grading system is called “Performance Grade” or PG system for short, which is recently implemented in Iran as well.

The Iranian student living in the United States added: 'The research has categorized asphalt binders scientifically. That is, if a highway is to be made in northern part of the united states, it is necessary to use a specific bitumen for that climate in the construction of pavement, or also in the rest of the climate zones, binders with different grades should be used.”

Nakhaei further explained that the asphalt binders are graded and categorized based on temperature, such that it has the highest and lowest values representing temperatures as in the motor oil, and each asphalt binder can only function in this temperature range. This concept was done in the SHRP research and under Dr. Anderson's supervision, and everyone in the world works with this grading system.

In response to the question of whether road damage results from this difference in bituminous temperature, Jalali said not all asphalt pavement failures are related to this criterion. For example, potholes seen on many rods are caused as a result of chemical reactions happening between bitumen and aggregates, because some aggregates love water more than they love binder which causes disintegration and subsequent performance problems.

Jalali added: 'But other failures are structural.' Imagine if you have a glass table and a heavy load on it, it will crush. The signs of the structural failures in asphalt pavement usually show on the surface in the form of “alligator” crack patterns because of its similarity to an alligator skin. These cracks start from the bottom of asphalt layer and is a sign of pavement systematic failure.

To shed light on the importance of the present study, Nakhaei went on to explain that “there is another breakdown that occurs at certain intervals, for example, every 10 feet of a transverse cracks in roads. This is related to our research, that is, asphalt is contracted due to the very cold temperatures. If the selected binder has enough elasticity, these cracks can be prevented.” The asphalt expert added: Imagine if in the harsh winter we encounter temperatures below what specification has specified, even just for one time, it's enough for crack formation.

He stated that all transactions and international sales of asphalt binder are conducted using this grading system. “To test an asphalt binder for classification, the possibility of bringing the temperature to, say, -22 degrees Celsius or lower in the laboratory due to the long process of testing and reduction of asphalt binder deformation is impractical.” Therefore, scientists test the asphalt binder at 10 degrees warmer so that the asphalt binder is softer to get faster and yet precise results. However, the final results then added with 10 to account for the increase in testing temperature.

The Iranian researcher continued: 'In our research, we were looking for the answer to the question of whether adding 10 degrees holds true for all binders around the globe'.

Hence, we tested 64 asphalt binder from different sources in the United States and 16 binders from Iran. Nakhaei said the result was that adding a fixed universal value of 10 degree was not always correct and 97 percent of the examined asphalt binders had a transition temperature of more than 10 degrees with an average of 12. In response to the question of what the 2-degree impact would be, he stated: similarly, one referee also posed the question that there is only a slight difference between 2-3 degrees of temperature difference.

But this very small difference caused the 33 percent of the American asphalt binders to be misclassified and ultimately to be mischaracterized. Although it looks unimportant at the first glance, when you buy asphalt binder incorrectly, it is like buying a wrong motor oil for your car engine!

On this subject, Jalali further explained that: “the number of mischaracterized binders in Iran was nearly 40 percent; this means that almost half of the binders in Iran are misclassified and purchased incorrectly.” He continued: “Pavement construction is extremely costly and should be viewed as a long-term investment. To put this into perspective, each mile of highway pavement construction costs from 1 to 3 million dollars in the US. If a binder that is not suitable for an environmental condition be used in the mixture, then a loss of investment due to under- or over-performance is expected.” The current classification of the asphalt binder is based on 6 °C intervals; and each 6-degree intervals is in one category, adding that the effect of these 2-3 degree different between the current and standard approach becomes clear in the change of these categories, and these categories have completely different temperatures.

The Iranian researchers responded to the question of whether this theory was accepted in scientific communities by saying that the result of our research has been accepted by the American scientific community. The idea presented at the 2019 Transportation Research Board in Washington DC and the complete research work will be published in another ISI journal. Nakhaei continued: “At the same conference, we met Dr. Anderson, and got endorsed for our achievements.” It is noteworthy to say that during the meeting it was emphasized that the implementation should proceed with caution, and also it must be realized on a large international scale, as bitumen producers work globally in line with previous standards.

Nakhaei reminded that in many countries, recycled binder is mixed with the virgin binder for environmental and economic reasons. To compensate the lower performance of recycled binders, a material called rejuvenator is usually added since recycled binder is oxidized. With this new finding it may not be at all necessary to add these costly additives to binders anymore.

Asking regarding the difference in American or Iranian based produced binders, he reminded,” The binders are physically and elastically different, and all manufacturers work with the same standard, but they are chemically distinct.' Buying and selling bitumen is based on with physical tests and not based on chemical properties.

Nakhaei added that binders are tested based on physical properties and less likely based on chemical characteristics, adding that our research is more applicable to Iran. In this study, we showed that in Iran 40% of the binders are used at inappropriate temperatures and regions leading to higher life-cycle costs. The significant point is that this 10-degree criterion in the specification is decided based on researches in the United States and is used elsewhere, including Iran, which may not be the case.

He said that in the past, an outdated system of penetration has been used for binder grading in Iran. He continued: 'For several years now, according to the Ministry of Roads directive, previous standards have been changed, and now such binders are classified internationally.”

Jalali stated that adding the 10 degrees in laboratories across the country is not correct and the criterion will be different for different binders. Therefore, in the next phase it was necessary for us to turn our attention to design and implement a software capable to address this shortcoming. At NCAT we created the software that will show how much temperature addition is needed for different binders to get the correct binder low performance grading. “The noble thing about our method is that no further tests are needed to get new values, since the established scientific theories are consulted, and results are validated.” he added.

As mentioned before, the initial idea of this research was born in the TSML laboratory in Iran, and we think the result would be more useful to them,' Nakhaei said, hoping that the results of this research would be taken into consideration in Iran. They added that although new researches are welcomed in Iran, the conditions in Iran are such that unlike the US, with many of the new ideas, the studies remain only in the study phase and cannot be implemented after completion, and the final intellectual output is hard to sell.

Nakhaei, in response to the question of whether according to new research refineries are capable of producing such bitumen, he said: You know that bitumen was a refinery waste in the past, but now it is not a waste solid, and it is a valuable substance that can even be refined to gasoline and other compounds. Thus, refineries can produce any bitumen.

The refineries produce bitumen based on market demand, and if the customer needs a specific binder, let’s say with a maximum performance grade temperature of 64 and minus 22, refinery is easily able to produce it. What is important is that the customers should know what kind of binder they need to order based on their regions’ environmental conditions that asphalt is to be paved.

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