Stopping Corrosion in Concrete to Save our Infrastructure
When Richard Weyers was growing up in Pittsburgh, Pennsylvania, he attended church regularly. “We had a priest that presented the most boring homilies in the world,” he recalls. While most little boys would squirm in their pew, fall asleep, or wrestle with a sibling behind their parents’ backs, Weyers took a different tack. “At any church, if you look at the inside, you can see the structural members. Typically, they’re exposed. Because he was so boring, I used to look up at the ceiling at the structural members and wonder, ‘How did they do that? How do you analyze that? How do they know how to do that?’”
Such fascination with engineering structures at an early age led Weyers to a career in civil engineering with an academic bent. The professor of civil and environmental engineering at Virginia Tech has become a specialist in materials and bridge construction. In particular, he focuses on the corrosion of steel reinforcement bar in concrete, a major cause of the deterioration of bridges. Like many transportation experts around the country, he labels the crumbling of our roadways an infrastructure crisis waiting to happen. Motivated by this, he has conducted research that is helping transportation departments cope with the problem.
Coming from a family of eight children, Weyers considered it financially impossible for him to go to college. During high school, he attended trade school and took up cabinetmaking so he would have a skill to market. Then the military drafted him during the Vietnam era. When he got out, he used the GI Bill to attend a private high school in Pittsburgh and gain enough credits to get into college. He later went to Penn State and received his B.S. in civil engineering 1972 and stayed on to get his master’s, also in civil engineering.
About that time, Weyers started on a path toward his current area of interest. “The corrosion of steel in concrete reinforcing material and different protection methods on it started during my MS work,” as he tells it. “I took a class on the durability of concrete offered at Penn State by Phil Cady, and I really got interested in the material and its behavior in that class. He offered me an assistantship to stay on for my MS work, and its primary function was to stop the corrosion process of steel in concrete. That’s where I really started to get interested in that subject.”
A look back in history shows why he made such a vital choice. As the U.S. came out of the depths of the Great Depression in the 1930s, public work programs were created to reduce unemployment, and this included expanding the highway system. Later, in the late 1950s, construction began on our interstate highway system. These highway systems were typically designed for a 50-year service life. Highway bridges typically need rehabilitation in 35 years and replacement in 70 years. Some quick math shows that the time has come to replace the 1930s infrastructure and rehabilitate the interstate system.
The single most detrimental factor leading to the deterioration of concrete structures is corrosion of its reinforcing steel, known in construction vernacular as rebar. The steel in concrete is normally in a non-corrosive condition because the pH is so high (12-13) that a protective, passive layer forms on it. Infiltration of aggressive chloride ions from road salt applied in winter to melt snow and ice destroys this barrier and promotes corrosion. These ions diffuse through the concrete, a porous material with up to 20 percent voids.
Officials estimate the total cost of corrosion for highway bridges in the U.S. at $8.3 billion annually. Of the 500,000-plus highway bridges over 20 feet in length, 40 percent classify as structurally deficient or functionally obsolete. The current backlog of bridge work stands at about $70 billion, with $28 billion attributed to the corrosion of rebar in concrete bridge members. Dismal consequences of this situation loom say Weyers and other transportation experts.
Consulting Leads to Teaching
Weyers started his teaching career at Lafayette College in Easton, Pennsylvania. He and his cohorts began research on a grant given by Bethlehem Steel on epoxy-coated reinforcing steel, and he did research on a grant from the Pennsylvania Department of Transportation for bridge maintenance, repair, and rehabilitation. In 1984, Cady and Weyers presented the first theoretical model for the deterioration of concrete bridge decks in corrosion environments. Also in 1984 Weyers, Cady and another researcher presented cost-effective decision models for the maintenance, rehabilitation, and replacement of bridges.
Then in 1985, Weyers went to Virginia Tech and brought his research with him. When he joined the Civil Engineering Department, materials research hadn’t been conducted there since 1965. He was the only materials faculty, and there was no required materials course, materials teaching laboratory, or materials research lab. Seeing this, he developed the Structures and Materials Research Laboratory and several new courses, including Civil Engineering Materials; Rehabilitation of Bridges; Infrastructure Condition Assessment; Maintenance, Repair and Rehabilitation Materials; and Rehabilitation of Infrastructure Systems.
In tests, researchers in Weyers’ lab submerge rebar in chemicals that may be present in concrete such as chloride and measure the corrosion potential (volts) and then corrosion activity or rate and current. They also put rebar in concrete to test it; it may take a year and a half to see corrosion. They take concrete samples apart and do an autopsy, looking at the bar and measuring the amount of chloride it took it to initiate the corrosion. They then use data obtained from tests to develop models.
In a project called the Strategic Highway Research Program, Weyers and his group advanced their model to where they could apply it to field conditions. The model had four parameters, including how much chloride it takes to initiate corrosion, how fast the chloride diffuses, amount of chloride on the surface, and depth of the reinforcing bar. As Weyers states, “You can put these into a diffusion relationship model and determine how long it takes to initiate corrosion and how long from there it takes to cracking of the concrete.” With Florida leading the way, a number of state DOTs began to use the procedures he developed, as did practicing engineers.
Refutes Prevalent Material
By 1986, trouble started. Engineers noticed early failures of ECR in Florida’s bridge substructures where salt water was involved. A subsequent study concluded that the epoxy debonds from the steel in as little as four years when the chloride arrives at the steel depth.
But ECR notwithstanding, Weyers maintains that technology exists for improving bridges. “It’s there today. There’s varying degrees of what you can apply to increase your timeframe,” he states. “You can use a corrosion inhibitor,” such as calcium nitrate mixed into the concrete. “You can use a higher quality steel.” You can apply a sealer or polymer coating to the bridge surface to slow chloride ingress.
For an ultimate scenario, Weyers says, “If you asked me to build a bridge deck or component exposed to chloride to give 100 years of life, I would build that with 316 LM stainless steel and low-permeable concrete.” This contains fly ash, blast furnace slag, or microsilica. ”The initial cost is high, but all I have to do is save one bridge deck overlay in 100 years, and it will more than pay for the extra cost of the stainless steel.”
Although Weyers has spent most of his career teaching and researching, he looks back on his consulting work at Warzyn Engineering as a “highlight in my life because I grew more professionally there than I could have ever accomplished in an academic environment,” he says. “There are some rewards you get in a consulting environment you don’t get in an academic environment.” In Madison, he could go around and point to projects he worked on. ”You can see it, it was tangible.”
Weyers says he continues to do occasional outside work. “I still do consulting just to keep my feet on the ground. Being in education, that’s my primary business. Whatever I do in consulting, I bring right into the classroom as real-world experience.”
When it comes down to it, Weyers sees himself doing the most good in the academic world. He notes the two types of research, basic and applied. “I like the challenge of looking at and identifying causes. I like finding solutions to unique problems. I like doing a little bit of basic and a lot of applied research. I’m interested in having it used for the betterment of society.” In studying corrosion in reinforcing steel in concrete, he has found an endeavor that involves plenty of applied research for improving our infrastructure. And it all started from the pew of his childhood church.