Irvin Pinto is a postdoctoral researcher at the Department of Civil, Construction and Environmental Engineering at Iowa State University. He completed his Ph.D. studies focused on asphalt emulsion-based pavement preservation treatments in the Spring of 2020. His research focuses on pavement preservation treatments, asphalt emulsions and the material properties of bituminous materials. He has extensive experience in formulating asphalt emulsions for different pavement preservation treatments like fog seals, microsurfacing and chip seals. Current projects include recommendations for cold in-place recycling project selection in Iowa, developing formulations and testing a soybean oil-based rejuvenating fog seal for the Minnesota Department of transportation and incorporating Recycled Asphalt Pavement (RAP) into microsurfacing and chip seal mix designs for the Ohio University and Ohio Department of Transportation. His future goal is to incorporate sustainability into pavement preservation treatments to ensure roadway infrastructure can be optimally maintained.
Pavement preservation refers to the actions that tend towards the qualitative functionality of pavement infrastructure during the overall life cycle. Beyond the purpose of sustaining and improving the pavement condition and structural responsiveness, sustainability strategies in terms of pavement preservation deal with the use phase:
Pavement sustainability deals with materials, design and preservation strategies and is necessarily one of the highest-level considerations for a transportation infrastructure system and not just an added feature. Preservation is an asset to pavement sustainability.
Preservation treatments are categorized according to pavement type and mainly for the purpose of each implementation. Specifically, preservation treatments are commonly based on the type of potential surface deterioration.
In this article, Global Road Technology discusses all things pavement preservation with a young professional in pavement preservation. Irvin Pinto is a Postdoctoral researcher at Iowa State University in Ames, Iowa in the United States of America.
I’m in my second year as a Postdoctoral researcher at Iowa State University in Ames, Iowa. I started graduate school at Iowa State University in the Fall of 2014 as a Master’s degree seeking student, researching smart cementitious materials. I got to do some amazing research on using smart concrete for nondestructive evaluation of large-scale concrete structures by adding conductive carbon black to concrete and using an eddy current probe to locate damage.
My PhD degree switched my focus to asphalt materials, and it was here that I really found my calling in sustainable pavement preservation techniques. My research on asphalt emulsions and emulsion-based pavement preservation showed me the tremendous scope pavement preservation techniques have in extending the life of pavements and reducing both long term repair costs and dependence on virgin construction materials.
During my time as a postdoctoral researcher, I had the opportunity to contribute directly to pavement preservation projects that used recycled and sustainable materials, namely a soybean based rejuvenating emulsion spray and the use of recycled asphalt pavement in pavement preservation treatments.
Simply put, smart materials are materials that change their intrinsic properties in response to changes in their environment. In the case of smart cementitious materials, the intrinsic property in question is its conductivity. If you add conductive material like carbon black, carbon nanotubes or other conductive fibers to concrete, you create conductive paths through the material, essentially turning it into a conductor. Electrically conductive material changes its conductivity when its shape changes, since the resistance of a conductor is inversely proportional to its surface area. When conductive concrete blocks are placed under stress, their cross-sectional area changes, however minutely, and hence so does its resistance, which can be measured and quantified. In terms of nondestructive evaluation, cracks and defects decrease the effective surface area available for electrical conductivity or conversely break conductive paths, in the case of cracking. This can also be picked up by equipment that can measure voltage changes across a conductor. While these signals initially might not make sense, after a little signal processing and mapping over changes in strain or the original signal from the material in its undamaged state, it’s possible to make a prognosis about damage or strain changes in smart concrete.
Bitumen is a chemically complex material. Its comprised mainly of Saturates, Aromatics, Resins and Asphaltenes, commonly referred to as SARA fractions. These SARA fractions play a major role in the properties of the asphalt. There are several possible ways that these SARA fractions can impact pavement preservation techniques, and research continues to uncover their impacts on asphalt material performance. One example is the ratio of asphaltenes to the other components that can play a major role in the ability of an asphalt to be emulsified. Asphalt for emulsions typically contains a higher fraction of asphaltenes, which aid in the emulsifying ability of asphalt.
Foamed bitumen is a product of forcing hot asphalt through small amounts of cold water. When the water and asphalt come in contact with each other, the water evaporates and forms steam, which becomes entrapped in the asphalt bubbles, giving it a high coating ability.
Bitumen emulsions on the other hand are a product of mixing asphalt and water with the help of an emulsifying agent or ‘soap’, which helps give the asphalt-water mixture stability. The emulsifier plays a critical role in emulsion formulation, given that water and asphalt, being an oil, don’t mix. The emulsifier provides the surface energy needed for asphalt particles to overcome their surface tension, break down and remain suspended in water. Foamed asphalt is used primarily in stabilizing roadway bases and is mainly used with recycled asphalt. Asphalt emulsions can also be used for base stabilization and cold in-place recycling but have wider applications that include other pavement preservation treatments like slurry seals, chip seals, tack coats and fog seals.
Bitumen is a product of fossil fuels, a finite resource. Therefore, it’s all the more important to come up with sustainable ways of using bitumen, either through novel pavement preservation techniques or sustainable asphalt alternatives. The current state of research seems to be moving in this direction, with asphalt emulsions becoming more and more popular in pavement preservation. Asphalt emulsions contain both asphalt and water, with residual asphalt amounts ranging from 50% to 65% depending on the treatment being used. They are also applied at ambient temperature and are more easily transported, saving heating and transportation costs. More importantly, they are incredibly versatile, and can be used with several sustainable alternative materials like soybean oil and recycled asphalt. Plastic and rubber-based additives are finding increased use in asphalt mixes and biomass, waste cooking oil and biobased polymers show promise as sustainable additives and alternatives to asphalt. The research on these materials is only scratching the surface of numerous alternatives that exist for asphalt-based treatments.
There are a number of factors that affect field performance of asphalt emulsions, which often make emulsions very complex materials to work with. These factors range from ambient conditions like temperature and type of aggregate being used to the formulation parameters for each emulsion. My research showed a link between emulsion formulation parameters like emulsion pH and emulsion performance. Emulsion formulation parameters and temperature control emulsion stability, and this can often be the difference between a successful treatment and a poor final product. Asphalt emulsions can vary mainly based on the type of emulsifier being used and its dosage. Slow setting emulsions need to be highly stable and therefore need a higher dosage of emulsifier than say a rapid set emulsion. Then again, quick set emulsions need to be extremely stable when stored, have enough stability to allow them to be mixed with the aggregate but set quickly once laid out on the road to ensure good cohesion development.
Along with the emulsion properties, the nature of aggregate being used is equally important in ensuring a good final product. Since emulsions are essentially made up of charged asphalt droplets suspended in water, they need a compatible aggregate with an oppositely charged surface area to set properly.
Since all of this may sound extremely complicated to a contractor using an emulsion, it’s important that research moves in a direction that can better understand and simplify these chemical and physical processes at play and bridge the gap between the vast science on emulsions and field application.
The possibilities for sustainable pavement preservation are endless. With rapidly depleting natural resources, there is an increased understanding that sustainable pavement preservation is the need of the hour, and both academia and the industry are rising to this challenge. The increase in demand for asphalt emulsions and sustainable alternatives like bio-based additives and the recycled pavement has fueled a greater need for research that can help understand these materials better and improve treatments, and this, in turn, has led to them being used more and more in field applications. I envision a future where sustainability is a cornerstone of pavement preservation treatments around the globe, with bio-based asphalt alternatives being better understood and more readily used in pavement preservation and rehabilitation and the future of asphalt technology having sustainability as its core tenet.
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