Masonry Magazine February 1987 Page. 54
NBS Using Sound Waves
to Spot Flaws in Concrete
Researchers at the National Bureau of Standards report they have developed a nondestructive method to detect flaws in concrete. Known as the "impact-echo," the technique works on the same principle as the sonar pings used to locate and determine the depth of a submarine.
An impact on the concrete generates sound waves which are reflected by flaws inside the concrete. A receiver mounted on the concrete's surface picks up the reflections, or echoes. The location of a flaw is determined by measuring how long it takes to receive the reflected echo.
So far, the NBS researchers have successfully used the technique to find artificial flaws embedded in a number of different concrete slabs. In addition, they have been able to detect pockets of unconsolidated concrete and the depth of cracks which are perpendicular to the surface. They also have been able to distinguish a hollow metal duct from one that is filled with grout.
The NBS team plans to test the technique on other structural elements such as rectangular beams and round columns. Also they want to investigate its potential for detecting other types of flaws, such as voids beneath pavements.
A report on the technique, Impact-Echo: A Method for Flaw Detection in Concrete Using Transient Stress Waves (NBSIR 86-3452), can be ordered from the National Technical Information Service, Springfield. VA 22161. for $24.95 prepaid. Order by PB #87-104444/AS.
Number of U.S. Buildings
to Double by Year 2040,
McGraw-Hill Study Says
If current growth trends continue, the number of buildings in the United States will double by the year 2040, according to the first comprehensive Building Stock Database and Forecast Study, introduced by McGraw-Hill's Dodge/DRI Construction and Real Estate Information Service.
The study is the first of its kind to estimate existing stock for 15 different types of buildings at the national, state and county levels. For each structure type and geographic area, historical data on the number of existing buildings and total square footage is provided annually starting with 1970; forecasts are presented through 1990.
According to the report, 75% of all commercial floorspace standing in 1985 was built prior to 1970. Regionally this percentage varies from a high of 91% in the Mid-Atlantic states to a low of 61% in the West South Central.
As new construction represents an increasingly smaller share of the overall stock, building products manufacturers are turning their attention to the renovation potential that existing floorspace provides. This landmark study represents the most comprehensive stock estimation effort to date, incorporating F. W. Dodge construction statistics with a nearly exhaustive list of government and other private data sources.
To obtain additional information about the Building Stock Database and Forecast, contact Eileen Anderson at Dodge/DRI, telephone 617/863-5100.
Book Published on
Fire Damaged Concrete
Evaluation and Repair of Fire Damaged Concrete is the title of a new book published by the American Concrete Institute. It comprises a compilation of 11 papers dealing exclusively with the analysis and repair ability of concrete damaged in building fires.
The 220-page work is available for $26.50 to ACI members and $34.95 to nonmembers from: ACI, PO Box 19150, Detroit, MI 48219.
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54 MASONRY-JANUARY/FEBRUARY, 1987