For thousands of years, people have built civilizations with concrete made from readily available local materials. Just mix and heat, add sand, stone and water and put it where you want it … and give it time to harden. Concrete is the world’s most widely used construction material. Twice as much concrete has been used to build Pittsburgh—and everything else in the world—than wood and steel combined, says concrete expert Julie Marie Vandenbossche, Ph.D., Civil Engineer-University of Pittsburgh.
There is far more to concrete, and how these materials bond themselves together, harden, and maintain their shape over long periods of time involves common materials and complex chemistry. Various factors influence strength and durability, down to the concrete’s concentration of air bubbles. The continuing academic interest in concrete, with the University of Pittsburgh (Pitt) Swanson School of Engineering serving as a research mecca, given its team of four notable research scientists devoted to concrete: Mrs. Julie Vandenbossche, Ph.D., Civil Engineering; her husband Mark B. Snyder, Ph.D., Civil Engineering and Concrete Consultant with Pitt.; Lev Khazanovich, Ph.D., Civil Engineering, Endowed Chair in Engineering, with a reputation for developing design methods for high-quality and low-cost concrete pavement, and a recent arrival from the University of Minnesota; and Steve Sachs, Assistant Professor-Civil Engineering, another recent addition.
Mrs. Vandenbossche said no other university in the nation has as many researchers focused on concrete pavements. Pitt also has an accelerated loading facility—or ALF—working steadily in Pitt’s Pavement Mechanics and Materials Lab in Benedum Hall, Oakland campus. It applies repeated, high-pressure loads on concrete slabs, simulating the physics of heavy traffic. The specialized equipment tests the strength and durability of dowel bars, which are embedded in highway concrete to transfer the load across joints. The ALF is the only such equipment currently being used nationwide to evaluate new, innovative designs and materials for long-life dowel bars, she said.
The team also continues studying concrete-pavement dynamics on Route 22 in Murrysville, Pennsylvania, with computerized equipment recording temperature, expansion and contraction, and traffic pressures and strains, all of which affect its stability and longevity. “We’ve used it extensively over the last 10 years,” Mrs. Vandenbossche said, “to study how climate changes affect the structure.”
LONG-LIFE CONCRETE: Pitt is active on numerous fronts — and surfaces
Concrete Overlays:
The university’s importance in concrete science was most apparent in June 2017, when it hosted the “U.S. Research Board meeting of its Standing Technical Committee on Design and Rehabilitation of Concrete Pavements”. “The key to the team here is that we do impactful research in terms of concrete pavement,” said Ms. Vandenbossche, whose research includes developing concrete overlays. They would allow cheaper repair of highways, much the way new layers routinely are added to asphalt pavement.
Georgene Geary, Owner-GGfGA Engineering Consulting Firm, who headed the standing committee said, “The work she’s doing on concrete overlays is phenomenal. She’s doing research on concrete overlays and better design tools to make sure highways are built right and build to last.
Lifetime Concrete:
Mr. Snyder was key in convincing the Pennsylvania Department of Transportation (PennDOT) to develop specifications for long-life concrete, designed to last 40 to 50 years and as long as 60. The ultimate goal is formulating concrete to last a lifetime rather than a generation.
Neal Fannin, Pavement Materials Engineer-PennDOT, recently wrote the state specifications for long-life concrete is already being used in construction of interstate highways, and time will tell if the long-life concrete mixture will meet expectations. Gradations of stone (aggregate) is key in allowing the concrete to compact better than stone of one size. Better compaction helps prevent slumping of pavement especially at the edges. Also the new concrete involves less cement, which contributes to concrete shrinkage after it hardens. Less shrinkage means more stability, Mr. Fannin said. As the specs were being completed, the long-life concrete was already being used in the Southern Beltway project Route 22 to Interstate 79, in Washington and Allegheny counties, he said.
Hard as Rock:
The U.S. Department of Transportation reports that there’s an estimated 465,800 miles of concrete highways, most of them interstate, that account for about one-quarter of the total miles driven each year. There are limited financial resources for highway construction, the reason that the 2.74M miles of U.S. roads are 83% asphalt. Also, southwestern Pennsylvania’s hills and rivers require many more bridges than other states, with Pittsburgh alone having about 460 bridges—second nationally to New York City’s 778 bridges.
A good recipe for concrete is a necessity. Portland cement, the most common in concrete, is made from “a closely controlled chemical combination of calcium, silicon, aluminum, iron and other ingredients”, according to the Portland Cement Association (PCA). Materials used can include “limestone, shells, and chalk or marl” combined with another large assortment of materials—shale, clay, slate, blast furnace slag, silica sand, and iron ore. PCA stated that combinations of ingredients are heated at high temperatures—about 2,700 degrees Fahrenheit—to form a “rock-like substance that is ground into the fine powder/cement”, then mixed with sand, aggregate and water, resulting in strong concrete.
From Volcanic Ash to Flyash:
Concrete research has progressed with an “eye on the rear-view mirror”. Ancient Romans were expert concrete makers, having used volcanic ash in its concrete mix. The result is concrete that’s lasted 2,000 years, in many cases, with a mix that hardens through time to produce nearly rock-like strength. Flyash, a byproduct of coal combustion in power plants, is Pennsylvania’s version of volcanic ash that makes stronger concrete but not nearly as long-lasting as Roman concrete, at least not to date, Mr. Khazanovich said. America’s oldest concrete, created experimentally in 1891 to build Court Avenue in Bellefontaine, Ohio, was controversial at the time. George Bartholemew had to post a bond to build his street made of “artificial stone”. As it turned out, he accidentally happened upon the perfect recipe that Mr. Khazanovich attributes to perfect-sized air bubbles—about 6% of air by volume—that accommodates expansion and contraction of water and ice during Ohio’s freeze-thaw cycle. Air is now added to most outdoor concrete in northern states. Many people/pavement engineers and enthusiasts visit Bellefontaine to see the concrete.
Mr. Khazanovich, said, now more than ever, governments must develop and use longer-lasting concrete pavements, which can cost 5% to 13% more, but in the long run, cost less, improve ride quality, reduce traffic closures, and reduce the number of accidents associated with construction: “We don’t have enough money to build cheap roads,” he said.
Pitt researchers and Mr. Fannin also stress the point that Pennsylvania faces more construction challenges than most states, given a freeze-thaw cycle that’s one of the most dramatic in the nation. But, Mr. Fannin said the long-life concrete is key to better highways: “We want to build roads as [inexpensively] as we can, but the highest quality that we can, so you are always seeking a balance.”
For the entire The Pittsburgh Post Gazette article titled, “Concrete—a hard material Pitt hopes to make harder”, please go to: http://www.post-gazette.com/local/city/2017/10/24/Concrete-University-of-Pittsburgh-world-experts-Pitt-chemistry-long-life-concrete-pavement/stories/201708040137
For this month’s ISCP article on the history of Concrete titled, “Rock Solid History of Concrete—How Limestone, Rocks, and Volcanic Ash Built the Modern World”, that explains volcanic ash in ancient concrete, please go to: https://www.concretepavements.org/2017/10/18/rock-solid-history-of-concrete-how-limestone-rocks-and-volcanic-ash-built-the-modern-world/
For the ISCP articles on the Bellefontaine, Ohio concrete road:
May 23, 2016: “125th Anniversary Commemoration & Tour of First U.S. Concrete Street Held in Bellefontaine, Ohio (Audio & Video)”: https://www.concretepavements.org/2016/04/28/125th-anniversary-celebration-tour-of-first-u-s-concrete-street-held-in-bellefontaine-ohio-audio-video/
May 3 2016: “Commemorative Program Now Available: 125th Anniversary Tour of the Oldest Concrete Street in America”: https://www.concretepavements.org/2016/05/03/commemorative-program-now-available-125th-anniversary-tour-of-the-oldest-concrete-street-in-america/
Home page photo: Accelerated Loading Facility (ALF)
University of Pittsburgh Swanson School of Engineering Pittsburgh
(Peter Diana/Post-Gazette)