Assessment of Concrete Floor Slab Crack Frequency and Radon Flux

Radon, a naturally occurring radioactive gas, is blamed for approximately 13,000 lung-cancer deaths each year in the United States. One of the major entry routes for radon has been previously assumed to be joints and random cracks in floor slabs. Preliminary data from another FAMU-IBS project indicated that the quantity of radon entering the indoor environment through floor slab cracks may be impossible to estimated from visual inspection alone. This has significance to the code development process, since entirely preventing floor slab cracks may be impossible in practice.

This project refined a radon flux measurement device designed originally by Arthur Scott, a Canadian physicist active in radon research. All specialized equipment was fabricated in the School of Architecture research labs by an architecture graduate student. The principle investigators established a standardized crack measurement protocol, developed a theoretical basis for the measurement calculations from principles of fluid dynamics, and conducted a three-county survey of approximately 200 floor slabs.

In addition, a pilot project was begun to assess the effect of aging and changing construction practices on slab cracking. This consisted of a mail survey to carpet installers and remodelers, who often see older slabs when completing their work.

The conclusion drawn from analysis of the data is that random cracking of concrete floor slabs cast on sand and directly on a polyethylene vapor retarder does not typically constitute an important entry path for radon. The implications for the construction industry are significant, estimated at roughly $10-million per year.

Sponsor:
Florida Department of Community Affairs

Principal Investigators:
Thomas D. Pugh
Walter T. Grondzik

Consultants:
Arthur G. Scott and Associates:
Arthur G. Scott

Southern Research Institute:
Ashley Williamson
Susan McDonough

University of Florida:
Tony White
James West

Duration:
May '91 - April '92

External Funding Level:
$100,000

Resulting Presentations:

Effects of Random Cracks in Concrete Floor Slabs on Radon Entry, Proceedings of the 7th International Conference on Indoor Air Quality and Climate - Indoor Air ‘96, Nagoya, Japan, July 1996

Assessing the Significance of Random Cracking on the Radon-Resistance of Concrete Floor Slabs, Conference of the Consortium of Environmental Science, Battelle Pacific Northwest Laboratory, Hanford Washington, October 1994