A new technique to reduce the radioactivity of fly ash utilized in the construction industry

Abstract

High volume utilization of industrial wastes and by products is the solution for high disposal costs. Acceptable radioactivity levels in addition to other environmental factors is a key factor for safe utilization of wastes and byproducts of coal burning power plants. In general the radioactivity levels of most fly ashes are similar to natural materials. For higher radioactivity fly ash the radioactivity values must be reduced to acceptable limits. This can be done by mixing the fly ash with less radioactive natural materials. In this study a new technique involving the use of snow as an additive to the compaction water of fly ash is presented. Fly ash at optimum water content, and fly ash with additional 10% by weight snow are compacted, hermetically sealed to allow for equilibrium of Ra-226 and Th-232 with their decay products and cured for 28 days at the curing room. Radioisotope activity analysis are conducted with a gamma analyst integrated gamma spectrometer. The activities of U-235, Ra-226, U-238, and Th-232 of the fly ash and snow-added fly ash samples compacted at optimum moisture content are determined. The control samples revealed radioactivity values above UNIPEDE maximum allowable limits. Addition of snow caused a decrease of 31-42% in the radioisotope activity levels to that of control samples in Bq kg (1). The decrease in radioactivity is linked to increased void ratio after melting of ice, increased densification of matrix around the pores due to higher level of cementitious mineral formation. The decrease in the radioisotope activity levels will allow utilization of fly ash in highway embankment construction where large surface area exposure and large volume usage makes it more critical for human health. Another advantage of the developed technology is the reduction of transportation costs by more than ten per cent by using less material for construction. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.