THE VARIATION OF RADON EXHALATION RATES FROM CONCRETE SURFACES OF DIFFERENT AGES

The radon exhalation rates from four concrete blocks cast with ordinar y Portland cement (OPC) and four with substitution of pulverized fuel ash (PFA) were monitored for 34 months starting fi om November 1992. A t the end of the 28th month, two OPC blocks and two PFA blocks were im mersed in water, one from each group for 5 days the other one from eac h group for 10 days. These were then taken out of water and the radon exhalation rates monitored as usual. It was observed that the radon ex halation rate in general decreased with the age of the concrete blocks and the rate increased after the blocks were immersed in water. An ex planation for the first result is that the gradual dehydration of conc rete as it ages will reduce the water content in the pores of the conc rete, thus reducing the probability of retaining radon within the pore s and the probability of radon emanation from these pores. The second result gives strong support to this assertion. Copyright (C) 1996 Else vier Science Ltd.