High-tech concrete technology has a famous past

National Institute of Standards and Technology (NIST) ^ | March 16, 2011 | Unknown

[decimon]

In the business of concrete making, what's old—even ancient—is new again.

Almost 1,900 years ago, the Romans built what continues to be the world's largest unreinforced solid concrete dome in the world—the Pantheon. The secret, probably unknown to the Emperor Hadrian's engineers at the time, was that the lightweight concrete used to build the dome had set and hardened from the inside out. This internal curing process enhanced the material's strength, durability, resistance to cracking, and other properties so that the Pantheon continues to be used for special events to this day.

But it is only within the last decade or so that internally cured concrete has begun to have an impact on modern world infrastructure. Increasingly, internally cured concrete is being used in the construction of bridge decks, pavements, parking structures, water tanks, and railway yards, according to a review* of the current status of the new (or old) concrete technology just published by the National Institute of Standards and Technology (NIST).

The virtues of internally cured concrete stem from substituting light-weight, pre-wetted absorbent materials for some of the sand and/or coarse aggregates (stones) that are mixed with cement to make conventional concrete. Dispersed throughout the mixture, the water-filled lightweight aggregates serve as reservoirs that release water on an as-needed basis to nearby hydrating cement particles.

According to one study cited in the review, bridge decks made with internally cured, high-performance concrete were estimated to have a service life of 63 years, as compared with 22 years for conventional concrete and 40 years for high-performance concrete without internal curing.

"As with many new technologies, the path from research to practice has been a slow one, but as of 2010, hundreds of thousands of cubic meters" of the lighter and more durable material have been successfully used in U.S. construction, write the report's co-authors, NIST chemical engineer Dale Bentz and Jason Weiss, Purdue University civil engineering professor.

Compared with conventional varieties, internally cured concrete increases the cost of a project by 10 to 12 percent, Bentz and Weiss estimate on the basis of bridge-building projects in New York and Indiana. The increased front-end cost, they write, must be evaluated against the reduced risk of cracking, better protection against salt damage, and other improved properties that "should contribute to a more durable structure that has a longer life and lower life-cycle costs," they write. "Further, this could have substantial benefits in a reduced disruption to the traveling public, generally producing a more sustainable solution."

The 82-page report summarizes the current practice and theory of internal curing, reviews project experiences and material performance in the field, and describes opportunities for research that could lead to enhancements in the material.

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* D.P. Bentz and W.J. Weiss. Internal Curing: A 2010 State-of-the-Art Review (NISTIR 7765). Feb. 2011. Available at: www.nist.gov/manuscript-publication-search.cfm?pub_id=907729.

[AFreeBird]

So in other words; if you build it right the first time, even if it costs a little more, it holds up better.

Hmmm.... Who would have thunk it.

[wildbill]

I think it is a mistake to take the knowledge of the Roman engineers lightly and assume they used this special lightweight concrete by accident.

They built many specialized projects out of concrete using various techniques that could be used today. I remember one article on FR about the way they built a harbor in the eastern Med by setting down forms under the sea to build concrete piers. I think they were ‘internal cured’ concrete as well.

Then there are their acqueducts with concreted tunnels and pipes that had to have very precise ‘drops’ to harness gravity to move the water while still keeping the flow under control.

Once the Roman engineers were gone, the world lost the formula for concrete for a millenia.

[colorado tanker]

Wow. Wouldn't have happened in ancient Rome. No slave would want to face crucifixion for not epoxying the rebar. :-))

[SunkenCiv]

Somewhere in the FRchives there’s a topic or two about a recently discovered room that apparently was the only survival of the Aurea.

[SunkenCiv]

I wholeheartedly agree.

They were also better than pretty much anyone at building enormous wooden ships.

[wildbill]

I gonna take this opportunity to re-recommend the novel, “Pompeii”, by Robet Harris to our God, Graves, & Glyphs faithful readers as the subject matter of concret brought it to my attention again.

NOt your average story of the Vesuvius eruption, the novel is seen through the eyes of the chief engineer of the enormus aqueduct, the Aqua Augusta, that brought water from the mountains to the city.

The failure of the aqueduct because of seismic activity becomes the focal point of the story and serves as a backstory to give the reader so much wonderful information on Roman engineering in general and hydrolic engineering in particular.

[Travis T. OJustice]

Wish I still had pics of the concrete canoe I was project manager for my junior year of college, won the regional “best final product” trophy.

12,000 PSI floating concrete, less than 1/2” thick max.