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Radon Penetration of Concrete Slab Cracks, Joints, Pipe Penetrations, and Sealants.

Nielson, Kirk K.; Rogers, Vern C.; Holt, Rodger B.; Pugh, Thomas D.; Grondzik, Walter A.; de Meijer, Robert J.
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Radon movement through 12 test slabs with different cracks, pipe penetrations, cold joints, masonry blocks, sealants, and tensile stresses characterized the importance of these anomalous structural domains. Diffusive and advective radon transport were measured with steady-state air pressure differences controlled throughout the dP = 0 to 60 Pa range. Diffusion coefficients (dP = 0) initially averaged 6.5 x 10-8 m2 s-1 among nine slabs with only 8% standard deviation, but increased due to drying by 0.16% per day over a 2-y period to an average of 2.0 x 10-7 m2 s-1. An asphalt coating reduced diffusion sixfold but an acrylic surface sealant had no effect. Diffusion was 42 times higher in solid masonry blocks than in concrete and was not affected by small cracks. Advective transport (DP < 60 Pa) was negligible for the slabs (10-16 m2 permeability), pipe penetrations, and caulked gaps, but was significant for cracks, disturbed pipe penetrations, cold joints, masonry blocks, and concrete under tensile stress. Crack areas calculated to be as small as 10-7 m2 significantly increased radon advection. Algebraic expressions predict air velocity and effective crack width from enhanced radon transport and air pressures. Masonry blocks, open cracks, and slab cold joints enhance radon penetration but stressed slabs, undisturbed pipe penetrations, and sealed cracks may not.

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