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ASU-designed fiber-reinforced concrete speeds up Phoenix rapid transit construction

May 22, 2023

Removing rebar from Valley Metro light rail cuts construction time, costs; increases worker safety

Using fiber-reinforced concrete instead of rebar-supported slabs for constructing Metro Phoenix light rail extensions is giving new meaning to rapid transit. Months of construction time are being reduced to weeks, adding cost savings, sustainability and worker safety to the mix.

A collaboration between Arizona State University, the Phoenix Valley Metro Regional Transportation Authority and Kiewit-McCarthy, the project’s construction firm, began with a materials upgrade proposal from Barzin Mobasher, an ASU professor of structural engineering in the School of Sustainable Engineering and the Built Environment.

The project, which extended the light rail by 1.5 miles, incorporated the fiber-reinforced concrete design and was completed in early May.

Video by Stephen Filmer/ASU

Reinforcing bar, or rebar, is made of steel and embedded in concrete to strengthen structures. According to Mobasher, more than 60% of the volume of concrete used throughout the world has zero tensile efficiency and is unable to carry load. This makes concrete used in load-bearing structures like the light rail susceptible to cracks, which begin very small and grow unhindered until there is a fault in the structure.

Incorporating rebar provides the loadbearing strength required for most concrete-based construction. However, laying rebar is costly, leaves a dramatic carbon footprint, presents worker safety risks and above all, takes a great deal of time. As the inevitable concrete cracking escalates and the rebar corrodes, additional maintenance, repair and rehabilitation are required, further adding to costs and neighborhood disruption.

Mobasher’s proposal simplified challenges for the light rail extension project and delivered a successful new system “just by making one change in the design criteria – using fibers in the concrete mix instead of reinforcing with rebar,” he said.

Instead of using two layers of rebar in cross directions to support the light rail's electrified track in the extensions, Mobasher’s design and validation approach considered both steel and polymeric fibers added directly into the concrete, completely eliminating the need for rebar reinforcement. Finally, steel fibers were chosen by Valley Metro for the northwest extension project.

To validate the proposal, a series of serviceability tests were conducted in ASU’s Structural and Materials Lab. Testing involved creating full-size mock-ups for both rebar-reinforced concrete and fiber-reinforced concrete, in the same ratios as full-size sections. Side-by-side testing allowed comparisons of strength and flexibility as well as documentation of concrete cracking and fatigue susceptibility.

The testing process also projected cost and construction time savings. For example, the per mile construction of the extension using rebar was projected at 231 days, while using fiber-reinforced concrete reduced it to 121 days, with a cost savings of more than $12 million.

“The idea of taking several long rebars that are half an inch in diameter, separated by 12 to 18 inches and built into a cage that is 12 inches above ground and replacing them with a fiber material, which is 2 inches long and only 1/32nd of an inch in diameter and mixed in with the concrete, might seem on scale non-competitive,” Mobasher said.

“But if you have thousands of those small fibers distributed in there, they become much more effective in arresting the cracks — working as small Band-Aids to keep the cracks closed and transfer the load. (Fiber-reinforced concrete) can be designed to bear up to an unprecedented 40% of the tensile load capacity of concrete.”

“We did the fatigue tests to simulate conditions for up to 45 years of service at much higher expected loads as proof of concept, and they accepted the proposed approach,” said Mobasher of the approvals from Valley Metro and the city of Phoenix. “It’s been a tremendous experience for them to save the amount of materials used and, at the same time, to be able to meet the project at costs much lower than the original budget and in a much faster time frame.”

The Valley Metro project is expected serve as a prototype for similar light rail upgrades nationally and will be presented at an international Fiber-Reinforced Concrete Workshop hosted by ASU in September.

Construction time

A major obstacle for community approval of light rail transit is months of neighborhood disruption during construction. Using fiber-reinforced concrete instead of rebar-supported designs significantly reduces disruption to weeks or, in some cases, days.

Andrew Haines, project manager for Jacobs Engineering in Tempe, attributed the success of the materials change to “challenging the accepted.”

“There’s an accepted way of doing reinforced concrete in the United States, especially with regard to light rail,” Haines said. “I think engineers get into this track of just, ‘We’ve got to do it a certain way, that’s how it’s always been done,’ and it’s been very difficult to change that — to accept something new.

“The placement of the concrete with the fibers has been very simple,” Haines said. “There’s no reinforcement — there’s no bars in the track slab for workers to try to walk on and perhaps slip on. So, it’s just the prepared earth and the rails are in place and the concrete gets placed around it — the reinforcement is integral with the concrete.”

The ability to develop material samples and test them in the ASU labs was a major component of implementing the change, according to Haines.

“We did all the right things to get this implemented in the field,” he said. “And the result seems to be phenomenal.”

According to Mobasher, the fibers are added into the concrete mix at the plant before being transported by the ready-mix trucks to the construction site. The entire mix is then discharged and self-consolidates, leaving a smooth, finished concrete surface.

“The work that used to take weeks to be done is finished in a matter of hours because we don’t need a crew laying up the steel rebars, connecting them, making sure they are all adequately welded together and that the components are all grounded,” Mobasher said.

Construction and materials costs

In addition to cutting worker and equipment costs, there are savings associated with shorter security requirements at construction sites and lower shipping and concrete production costs. Also, the traffic delays and lost productivity due to lane closures are significantly reduced.

And while there are significant cost savings due to switching from rebar to steel fibers, additional savings are realized by the different types of fibers as well.

“With steel versus polymetric fiber there’s a tremendous difference in weight,” Haines said.

With rebar, “we’re using 65 pounds of steel,” Haines said. “The production of steel produces a lot of greenhouse gasses — and a lot of energy to produce steel. There’s a lot less energy in using polymeric and synthetic fibers. We’re only using 12 pounds of polypropylene fibers vs. 65 pounds of steel, so there’s a savings there.” 

The project also uses thinner sections of concrete than required to support and protect rebar.

“We’re using about 20% less concrete, which means we’re using 20% less cement,” Haines said.

A not-insignificant side benefit of eliminating rebar is a reduction of associated potential corrosion from the stray currents in an electrified transit system.

Worker safety

Walking on unstable rebars buried in fresh concrete is a challenging task. 

“Imagine walking on shredded glass in a dark room while shoveling wet mud that weighs about 80 pounds. That is how the previous 25 miles or so was built,” Mobasher said.

“All we did was take out the rebar cage out so workers are finishing the slab without tripping as they navigate rebar in a 12-inch layer that can’t support their weight. Now, they are standing on solid ground as they pour the concrete around the rails.”

“The type of concrete we are using here is fiber-reinforced concrete,” said Farhad Rahimi, quality assurance manager for the city of Phoenix. “There is no rebar in this. It’s fiber inside the concrete, which makes the constructability much easier than rebar, and much faster. As for the quality, we get the same quality as we get from (standard) concrete. And, we got the tensile strength we need.”

Laying the concrete is “still very hard, labor-intensive work," Mobasher said, “but definitely more humane. I have so much respect for these construction workers.

“The mission of sustainable engineering is to focus on long-lasting improvements of the human conditions, which includes both worker and environmental safety,” he said.

Sustainability benefits

“What we have learned in the last 50 years in materials science is that the closer we look at a microstructure, the better we can understand materials at a macro level,” Mobasher said. 

The whole purpose of sustainable engineering is to design the material at a different level that may not sound intuitive, but that has load-bearing qualities that enhance longevity while reducing the carbon footprint.

“When we look at the carbon footprint of the construction materials, when we consider concrete and steel, we realize that we use about 30 billion tons of concrete every year throughout the world. We also use about 500 million tons of rebar for reinforcing that concrete to carry the load.

“That is a significant amount of carbon footprint because of just these two ingredients, because you cannot use concrete without providing reinforcement for it.”

Additionally, the testing validates stability for more than 45 years, with a likely service life under Phoenix climate conditions of more than 100 years, according to Mobasher.

One of Mobasher’s missions is to make these sustainable concrete technologies available to other cities and communities. Similar concrete formulas have been employed around the world, but they often come with proprietary constraints.

“In our laboratory, we provide a scientific basis for the design validation of structural components by combining the design codes, analytical and computer simulation design tools,” Mobasher said.

“Then we go a step further to verify the results with full-scale tests under the same loads the designers are concerned about. This approach gives us the ability to dial in the level of over-strength and conservativeness the engineers are comfortable with for the service life.”

ASU structural research labs have been involved with many such challenges – dealing with mining applications, environmental structures, canals, bridge design and steel structures – and have been an ongoing resource for testing new technologies in for both industry and communities.

“We want to show that the (fiber-reinforced concrete) construction process can be a do-it-yourself project for local communities working with local construction companies,” Mobasher said. “We can show that collaboration between municipalities, industry, government agencies and universities can come together to share resources, cut costs and increase sustainability.”

Top photo: Workers from Kiewit-McCarthy Joint Venture, Arizona Materials, Fleming and Sons Concrete Pumping and Valley Metro prepare to pour the last section of the northern spur extension of the Phoenix Valley Metro light rail line north of Dunlap Avenue on 25th Avenue on May 5. Photo by Charlie Leight/ASU News

Pilot study shows first molecular links behind successful PTSD treatment

May 22, 2023

According to the National Institute of Mental Health, post-traumatic stress disorder, or PTSD, affected an estimated 3.6% of Americans in 2022, with women (8%) and veterans (10% of males and 19% of females) experiencing even higher numbers. In fact, according to the National Center for PTSD, about 60% of men and 50% of women experience at least one severe trauma in their lives. 

“Rates of childhood and adult trauma are high all around the world, even in the U.S.,” said Candace Lewis, an ASU School of Life Sciences assistant professor who is exploring the biological roots of people’s response to trauma and stress. Candace Lewis and her lab assistants, standing behind her, posing for a photo in lab gear and in a lab setting. ASU School of Life Sciences researcher Candace Lewis (foreground) and her lab team explore the possible biological reasons for the role the psychedelic drug MDMA may be playing in the successful treatment of PTSD. Her lab includes the work of (back row, from left) neuroscience graduate student Allison Hays, BASIS Chandler High School senior Alyssa Ford and graduate psychology student Taena Hanson. Download Full Image

While most people have a resiliency to bounce back and resume daily activities in a few weeks or months, for some, PTSD can result in a severe and debilitating mental health condition that can require months or years of intervention and psychotherapy to return people to a sense of normalcy.

At the root of PTSD is trauma.

“Trauma comes in many forms, whether it’s childhood abuse/neglect, poverty, racial, combat or domestic partner violence — many of us are living with trauma,” said Lewis, who is also an assistant professor in the Department of Psychology. “For some, these experiences increase vulnerability to develop maladaptive behavioral and cognitive patterns. Stress-related disorders, such as PTSD, depression and anxiety — we can define them as maladaptive behaviors.”

PTSD is usually triggered by a terrifying event that is either experienced or witnessed. It can result in severe anxiety, flashbacks or nightmares that go on for months or years. For those requiring medical intervention, a groundbreaking treatment has been the drug 3,4-methylenedioxymethamphetamine, or MDMA.

MDMA is not without controversy. It’s currently an illegal drug, popularly known as ecstasy or Molly. It became associated with the up-all-night rave culture starting in the early 1990s. More recently, the topic entered the public zeitgeist in 2018, with the runaway No. 1 best-seller “How to Change Your Mind: What the New Science of Psychedelics Teaches Us About Consciousness, Dying, Addiction, Depression, and Transcendence” by Michael Pollan.

The book delved into the science of psychedelics and psychotherapy. And, after decades of anecdotal data of success from mental health professionals, MDMA has been fast-tracked for approval by the FDA — specifically for the treatment of PTSD.

For scientists like Lewis, this has also opened a new avenue of research to explore the possible biological reasons for the role that MDMA may be playing in the successful treatment of PTSD.

Lewis is trying to get at the data between behavior, mental health and our biological response to stress. To do so, she is examining in greater detail how experiences can alter the molecular regulation of systems involved in stress and mental health.

Now, she has completed a pilot study that shows the first molecular links behind successful PTSD treatment and new evidence that may explain the reasons behind its success.

Behavior and biology

Lewis wants to help revolutionize mental health treatment, grounded by the motivation of her own family experiences and the struggles of others.

“I grew up witnessing severe mental health problems,” Lewis said. “Data shows that this is becoming more and more common.”

She studies the impact of our social environments on molecules, all the way up to the brain and behavior, with the goal of making healthier lives for everyone.

“We don't know what we don't know yet,” Lewis said, “but your experiences have the ability to alter you at the molecular level that changes downstream gene transcription in a way that changes brain structure, function and behavior.”

An exciting new area linking experiences with behavior and biology is the field of epigenetics, which involves chemical modifiers that act as traffic signals to help modify the turning on or off of genes.

“The epigenome is referring to this infinitely complex regulatory system on top of our genome,” Lewis said. Research has shown that one’s experiences and exposures alter how genes are expressed through epigenetics.

Before returning to ASU to join the faculty, Lewis did her PhD work on behavioral neuroscience in the ASU Department of Psychology, at Professor Foster Olive’s lab. Her doctoral research examined how early experiences increase vulnerability to addiction. Lewis identified epigenetic markers of stress experienced early in life that increased drug intake in an animal model. She was also able to reverse the epigenetic markers in the model, which reduced drug intake behavior.

So, it was natural for Lewis to extend her research and wonder whether severe forms of PTSD could also be under epigenetic control.

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The research team explores the molecular links behind biology and behavior. Photo courtesy Candace Lewis

Piloting downriver

Lewis relies on data from a large MDMA clinical trial run by researchers sponsored by the Multidisciplinary Association for Psychedelic Studies (MAPS). Lewis performed an epigenomic pilot study that examined a subset of 23 people for molecular clues to successful MDMA therapy for PTSD. 

Recently, another colleague, Rachel Yehuda from Mount Sinai’s Icahn School of Medicine, reported positive results on the phase-three clinical trial, showing high efficacy of MDMA-assisted therapy for treating patients with severe PTSD compared with a placebo group. 

Lewis and her research team found epigenetic changes in three key genes before and after MDMA and the placebo with therapy. All three genes are known to be implicated in the way humans respond to environmental perturbations with a stress response. They are major components of the homeostatic response in the hypothalamic-pituitary-adrenal (HPA) axis, an intricate, yet robust, neuroendocrine mechanism that mediates the effects of stressors.  

“The epigenome is referring to an infinitely complex genomic regulatory system,” Lewis said. “However, DNA methylation is the most commonly studied epigenetic mechanism, which is the covalent addition of a methyl (CH3) group to a CpG site.”

The CpG sites refer to two of the four chemicals/letter abbreviations that make up the rungs in the iconic model of the twisted-helical DNA ladder structure: the A, G, C or T nucleotides that make up the genetic code.

“A CpG site is a cytosine upstream of a guanine,” Lewis said. “CpG sites tend to cluster in gene promoter regions that need to be available for transcription and later translation into a protein product. These methyl groups are just a physical blockade of transcribing a gene.”

A CpG site acts like a red traffic light, telling the genome to stop making its protein products or, in this case, turning off the key genes involved in the stress response.

This study assessed DNA methylation levels at all 259 CpG sites annotated to the three HPA axis genes (CRHR1, FKBP5 and NR3C1). Importantly, the methylation changes only occurred across groups that significantly predicted symptom reduction on 37 of 259 CpG sites tested. In addition, the MDMA-treatment group showed more methylation change compared to placebo on one site of the NR3C1 gene.

“This gets back to the point of our CpG site lesson,” Lewis said. “We assessed CpG sites across the gene body, instead of only looking at the promoter region. While functional consequences of CpG methylation outside of the promoter is less understood, it may still be an important player in trauma — and treatment — response. It is not surprising that we found effects on NR3C1. If there ever was a famous gene, this glucocorticoid receptor would be it."

“Changes in glucocorticoid receptor gene expression from early life trauma was the first epigenetic finding that really initiated this field. Now, studies show epigenetic regulations of many genes are associated with mental health problems,” said Lewis. “Those who have experienced trauma are more likely to have a different expression of glucocorticoid receptors and a different cortisol profile than those who have not.”

Next steps

The findings of this study suggest that therapy-related PTSD symptom improvements may be related to DNA methylation changes in the HPA axis genes — and such changes may be greater in those receiving MDMA-assisted therapy.

“The results of the study are exciting and parallel findings from another psychotherapy study in PTSD,” said clinical trial director Yehuda. “More research is needed to fully examine how this new approach may be associated with epigenetic change to promote enduring transformation.”

Lewis is now turning to expanding and refining her pilot study results.

“Our ASU BEAR (Brain, Epigenetics and Altered States Research) Lab is interested in measuring epigenetic biomarkers for treatment response with various treatment options, including psilocybin, ketamine and, of course, a larger sample size with MDMA,” Lewis said. “We're also hoping it stimulates others to really start diving into biomarkers.”   

With collaborators at ASU and other local institutes, Lewis is leading the charge on starting a research and clinical group focused on psychedelic-assisted therapies called Translational Research in Psychedelics (TRiP).

Talking about it

Lewis emphasizes that a better understanding of the biology behind MDMA treatment will further improve psychotherapy, and the time and experiences necessary for healing from a severe trauma experience. 

“What I hope to convey as a take-home message is that healing has to be salient. ... Some patients need assistance to shatter the walls and cognitive barriers built around their traumatic experiences. For many people suffering from trauma, typical talk therapy may not penetrate them enough for real change. If one cannot talk about their trauma with a therapist and (is) struggling with mental health symptoms, then MDMA-assisted therapy may be a more efficacious treatment option for them.

"The psychopharmacology effects of MDMA are actually quite extraordinary: reduced anxiety, acute positive affect, increased insight, accelerated thinking and euphoria, and increased sense of trust and bonding. It’s in this state that patients are finding the ability to work through what it needed. It’s an intense experience; it’s intense healing.”

Lewis’ ultimate end goal is to turn psychotherapy on its head by asking: “If trauma is shaping the epigenetics that lead to an increase in symptoms, what can be such a healing experience that it shapes epigenetics in a way to decrease the symptoms?”

“People are hurting, right? There's a reason they have maladaptive behaviors and cognitive distortions. How do we help them? Surely we can do better than the current paradigm of chronic medication. I want to know, what do we need to heal? I am a neuroscientist, so I stick to data. I think that all output is biology, and experiences shape biology. We know we have trauma experiences, and I'm in search of the healing experiences. We sure are in need of them.”

Joe Caspermeyer

Manager (natural sciences), Media Relations & Strategic Communications