| Popis: |
Radon emanation rates from 48 concrete blocks have been monitored throughout a period in excess of 1 yr. These blocks have been produced for three distinct mixes of materials, i.e. mix A with 25% by weight substitution of type A pulverized fuel ash (PFA), mix B with 25% by weight substitution of type B PFA and mix C without PFA. Each mix is represented by four sets of concrete blocks with curing periods of 1, 3, 7 and 28 days. Every set comprises of four blocks each with the same composition and curing period. From the results, rates of change of radon emanation have been identified for two distinct periods, i.e. for the first month following curing and for the period following the first month. The different emanation rates are linked to the role of the superficial and inner pores of the concrete. It is also seen that the radon emanation rate tends to decrease with the age of the blocks for curing periods of 1, 3 and 7 days, but tends to increase for a curing period of 28 days, all of which can be rationalized in terms of the gradual dehydration of concrete as it ages. The patterns are similar for the different mixes, although the exact effect of PFA upon radon emanation rates remains unresolved. |
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