According to the Federal Highway Association, “Fly ash is the finely divided residue that results from the combustion of pulverized coal and is transported from the combustion chamber by exhaust gasses.” Fortunately, fly ash can be collected from these exhaust gasses and used in products such as Portland cement concrete, soil and road base stabilization, flowable fills, grouts, structural fill, asphalt filler and — water piping?
According to an award-winning poster created by Stephen Gordon, a Ph.D. student at Louisiana Tech University, the answer is yes. In his poster titled “Vitrified fly ash pipe (VAP) as an alternative to VCP” — which won the third place prize at the 2024 No-Dig Show — he examines the possibility of using VAP in place of vitrified clay pipes and concludes that it can be done.
Gordon belongs to Louisiana Tech’s NASTT Student Chapter and is studying civil engineering in pursuit of a Ph.D. in material science and infrastructure systems. This was his third No-Dig win in three years.
Project start
“Fly ash got its name from flying upwards into the air with coal flue gasses, but it’s actually made of nanoparticles, which is mostly aluminum and silica,” Gordon says. “As it turns out, fly ash has a composition very close to certain clays. So the idea came to me that, hey, we have this material that has a lot of aluminum and silica, which is one of the primary strength sources for clay. What if we melted it as a waste product at high temperatures? What would the result be? And it turns out you get a glass-like material or at lower temperatures, you get a ceramic-type material.”
Having discovered that vitrified fly ash can be processed into a ceramic-type material, Gordon wondered if it could be used as a replacement for vitrified clay products.
“That was where that process began,” he says. “We took fly ash material and molded it to make a pipe because if you’re going to use clay for pipelines, you’re going to do it by using a vitrified clay pipe material. So we put the VAP pipe into an oven and found that we could fire it successfully at around 900 degrees Celsius, which is a good bit lower than your traditional clays.”
Being a first attempt at making VAP, the initial pipe prototype didn’t turn out as well as hoped.
“We adjusted the water-to-fly ash ratio until we got it right,” Gordon says. “Being a nanoparticle, fly ash has a very large surface area, so you end up having to add quite a bit more moisture to it. Eventually we created a material that we could work with and did compression tests and porosity tests. It was a little bit higher porosity than what you typically see compared to a clay pipe. So that was one avenue of improvement.”
Detailing these small scales of results, and where comparative testing of VAP and VCP could go using larger samples, was the central theme of Gordon’s poster.
“We need to get some clay and do some side-by-side tests,” he says. “Ideally, we want to be able to present the industry with, ‘Hey, here’s a waste material that they have to throw away or put into landfills, but we can directly turn it into a construction material for you with just a little bit of heat.’”
A bright future
Reflecting back on his 2024 No-Dig win, Gordon says that attendee response to his poster was positive.
“I think the judges quite liked it, which is why I got third place,” he notes. “They gave me some good feedback on what I can improve in the poster. I think some of my figures might need to be increased in size to make them a bit more clear. As well, vitrified clay is not a very common material for trenchless applications because it’s got some fracturing issues, but with the material we’re working with, you can introduce a woven fiber that might make it better for trenchless technology.”
Meanwhile, winning awards for three years running at the No-Dig Show has helped raise Gordon’s profile in the trenchless industry.
“Every time I go to No-Dig, it’s a good opportunity to meet with these folks that could be future employers,” he says. “So hopefully it opens up doors when I graduate to have a job in this industry.”
Gordon started out his academic career in electrical engineering, until his Ph.D. faculty adviser got him interested in civil engineering. His adviser, Dr. Shaurav Alam, is an associate professor in Louisiana Tech’s departments of civil engineering and construction engineering technology; an associate director of research at the University’s Trenchless Technology Center; and a SWEPCO-endowed professor.
“You can have a successful career as an electrical engineer and as a civil engineer, but I think you can have a very successful career if you merge the two and find the middle ground,” Gordon says. “There are needs for electrical and there are needs for civil, but there’s really a need for people who know both. My goal here at Louisiana Tech is to pursue that path.”
For his part, Alam sees great opportunities for Gordon when he completes his Ph.D.
“Stephen has the electrical background that the trenchless industry needs,” Alam says. “Meanwhile, with his civil engineering background, he can actually become one of its leaders in the future if he chooses a career path in this industry.”
