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The ability to be able to predict the state of dryness of a concrete floor slab is a practical need in the construction industry. Current popular methods, including the surface hygrometer and vapour emission tests, only indicate surface dryness, with consequent uncertainties in the quantity of residual moisture deep within the slab. This paper describes the variation in moisture condition with depth for a number of slabs under different drying conditions, as established using a new probe which can reliably determine the relative humidity at any depth. From this it is concluded that results from the conventional tests need to be treated with caution due to wide variations in the residual moisture, which could give rise to defects in impermeable floor coverings due to trapped moisture leading to excessive vapour pressures.
West, R., Holmes, N.: Experimental Investigation of Moisture Migration in Concrete. Colloquium on Concrete Research in Ireland, pp. 39-44. NUI, Galway, September, 2001.