Advanced software codes being developed with the aid of the world’s fourth-fastest supercomputer are expected to significantly speed the process of choosing the right concrete for a construction job, saving millions of dollars.
Researchers also expect the codes to significantly aid efforts to develop much more durable concrete, which may last more than half a century.
The new codes may be available on CD ROMs to ready-mix producers, cement companies, contractors and other users as early as 2009. Instead of evaluating perhaps several hundred batches over one week or longer, users employing the programs on their computers could find, and test, several “optimum” mixtures for their jobs in just a few hours.
A layman may see a concrete mixer on the street and figure there’s no big science involved. Actually, though the basic process is relatively simple — mixing perhaps 15 percent cement with 60 to 75 percent aggregates (small rocks), 15 to 20 percent water, and often other substances such as silicates, fly ash and slag — the science of finding the best mixtures for different concrete applications is mind-boggling.
“It’s a huge computational problem because concrete is getting much more complicated all the time,” said Edward Garboczi, leader of the Inorganic Materials Group at the National Institute of Standards and Technology (NIST) Building and Fire Research Laboratory in Gaithersburg, MD.
As one of four winners of a national “grand challenge problem” competition, NIST has just received one million hours of computer time to work on such mixtures for optimum concrete using the Columbia supercomputer at the National Aeronautics and Space Administration’s Ames Research Center, Moffett Field, CA.
NIST has been working on a software package for optimizing concrete for 13 years. It formed an NIST/industry consortium to develop this software, called the Virtual Cement and Concrete Testing Laboratory (VCCTL). The supercomputer will allow further development, including the flow, dispersion and merging of materials for concrete under a variety of flow conditions.
The supercomputer, valued at approximately $120 million, includes 10,240 processors. Its speed is 51.87-trillion floating point operations per second.
Occupying approximately 15,000 sq. ft. at the Ames Center, Columbia (named for the space shuttle that exploded) offers approximately 1 PB (petabyte or 1,000,000,000,000,000 characters) in disk storage and a 10 PB-capacity tape archive.
That’s a lot of power, but the research program on concrete needs it. Columbia will be able to compare an astounding number of standard and specialty combinations of concrete mixtures, including many variables like different local materials and environment conditions.
The computer can calculate optimum tradeoffs while users will only have to make a handful of tests on the most likely combinations, instead of today’s time-consuming trial batches, to confirm the results.
A new version of VCCTL is released each year. An initial version of the software (Version 1.0) was released five years ago. Version 6.0 is about to be released.
The CD ROM holding the code can be used on normal desktop computers. It is expected to offer many benefits to ready-mix suppliers, cement manufacturers and larger contractors.
The consortium includes such industrial members as the Portland Cement Association (PCA), the Ready Mixed Concrete Research Foundation (RMCRF) and the National Stone, Sand and Gravel Association (NSSGA).
Besides providing faster, more accurate preconstruction testing and evaluation, the code is regarded as a big step toward much longer-lasting concrete, potentially saving millions of dollars in maintenance and other costs.
“Durability is our main concern; once the models are in place, the industry can do a much better job of predicting concrete durability, and therefore make the concrete last longer,” said Tennis. “Users will be able to chemically predict what will happen in five, 10, 20 or more years, projecting long-term properties rather than waiting five years to actually physically test real specimens.
“The code will, for instance, allow people to factor in environmental effects, like sulfate-bearing soil of a certain concentration, or the local freeze-thaw environment. They will have a lot more confidence in specifying certain mixtures to be durable in certain environments.
Tennis said the computer codes could help prevent early cracking of bridge surfaces.
Tennis said that “it is not unreasonable to expect the industry to save millions of dollars by using the computer models.
“Industry spends tens of millions of dollars on developing and testing thousands of batches every few years, typically testing for a strength profile over one, three, seven and 28 days,” he said.
The United States used 127 million tons (115.2 million t) of cement in 2005, an increase of 5.9 percent from 2004. An increase of 3.5 percent is expected this year. U. S. cement production is expected to increase by 16.2 million tons (14.7 million t) by 2010.
An estimated 35.2 million tons (31.9 million t) of concrete are used on U.S. highways and streets each year.
In its simplest form, concrete is a mix of paste and aggregates. The paste, composed of portland cement and water, coats the surface of the fine and coarse aggregates. Through a chemical reaction called hydration, the paste hardens and gains strength to form a rock-like mass.