Assessment of pressure-field extension below slab-on-grade concrete floors

Abstract

This paper discusses studies of the sub-slab depressurization performance of radon mitigation systems in four schools after floor replacement, and in one newly built school, in Cornwall, England. Sub-slab pressure-field extension was assessed by means of small bore plastic tubing laid below slab-on-grade concrete floors with ‘standard’ U.K. type radon sump (sub-slab depressurization) systems. A variety of hardcore types and floor constructions were used. Improvements over the pressure-field obtained in normal U.K. floor construction were readily achieved by careful selection of hardcore free from fine material and by avoidance of sand blinding directly on the hardcore. However, the performance achieved in a similar American study was not consistently reproduced. Even with close supervision of labour and correct construction, optimum pressure-field extension was not consistently achieved. The thickness of the permeable layer and the method of laying blinding materials may be critical to success. A polyethylene membrane can keep blinding materials out of the permeable layer and may allow the usual sand blinding to be used. Careful floor construction and selection of hardcore materials could result in new-build properties requiring fewer radon sumps and/or a reduction in fan power consumption. However, this must be balanced against the increased construction costs and current inconsistency in results.