99
LABORATORY ASSESSMENT OF FLEXIBLE THIN-FILM MEMBRANES AS A PASSIVE BARRIER TO RADON GAS DIFFUSION

W. Z. Daoud and K. J. Renken
University of Wisconsin-Milwaukee, Mechanical Engineering Department, Radon Reduction
Technology Laboratory, 3200 N. Cramer Street, Milwaukee, WI 53211 USA

This paper presents the experimental results of utilizing a flexible thin-film membrane as a passive
barrier to radon gas diffusion. Nine commercially available membranes of various compositions and
thicknesses were evaluated as retardant to radon gas diffusion. The radon gas concentration ratios
across the thin-film membranes alone and in combination with an adjacent concrete sample (effective
diffusion coefficient) were measured in a laboratory system with state-of-the-art instrumentation. An
8.89 cm diameter, 10.2 cm thick concrete sample of standard composition (w/c = 0.5 and cement:
sand: gravel = 1:2:4) was used to simulate a basement and slab-on-grade foundation typical of
Wisconsin. The radon gas transport characteristics of this concrete sample (porosity, permeability and
diffusion) are documented.
The experimentation has identified two superior flexible thin-film membranes that may be employed
as effective barriers to radon gas diffusion. These include: Polyethylene Naphthalate (7.62x10 -5 m)
and Polyethylene Terephthalate Glycol, PETG (7.62x10 -5 and 1.27x10 -4 m) which had average
diffusion coefficients, D of 4.10 x 10 -14 m 2 s -1 and 1.66 x 10 -14 m 2 s -1 , respectively. Measurements of
the effective membrane/concrete diffusion coefficient yielded a further average reduction in D of 98%
for the Polyethylene Naphthalate and 96% for the PETG. Details of the experimental set-ups and
procedures are described. The results of this investigation have shown that the application of an
effective thin-film membrane adjacent to an intact concrete slab can significantly reduce the diffusion
of radon gas entry. Therefore, the employment of a flexible thin-film membrane should be considered
as a viable radon reduction technology method for residential new construction.
Key words: Radon; Diffusion; Films; Membrane; Concrete