A new technique to improve freeze-thaw durability of fly ash
Özet
High volume utilization of industrial wastes and by products is the solution for high disposal costs. Acceptable durability levels in addition to environmental factors are a key factor for safe utilization of wastes and by products of coal burning power plants in road construction activities. The durability levels of most fly ashes are similar to concrete if the strength and air content are kept constant. To obtain a better freeze-thaw performance from the fly ash samples, an air entraining agent must be added into the matrix. Snow can be added to the fly ash samples as an air entraining agent as presented. In this study a new technique involving the use of snow as an additive to the fly ash is presented. Compaction of fly ash is very sensitive to water content which complicates the use of fly ash in highway embankment construction. One or two percent additional water over optimum moisture content makes compaction of the fly ash impossible. On the other hand, an excess amount of water is needed to enhance the reactions leading to formation of cementitious products, which increases strength. The extra water is added in solid phase as snow, which allows compaction of the samples without liquefying. The 10% extra water added in the solid phase caused a 30% increase in the void ratio. The main objective of this investigation is to evaluate whether the increased void ratio causes a similar behavior expected from air entraining agents on the freeze thaw durability of fly ash. Type C fly ash at optimum moisture content and fly ash with additional 10% by weight snow are compacted, sealed and cured for 90 and 180 days at the curing room. After the curing period, freeze-thaw durability tests are conducted with a freeze-thaw cabinet. The development of deterioration, resonant frequency variation and weight losses of fly ash and snow added fly ash samples compacted at optimum moisture content are determined throughout the test period. The relative dynamic modulus of elasticity of the control samples decreased to 55% of their original value after 90 freeze thaw cycles, for snow added fly ash samples the same amount of reduction occurred after 120 freeze thaw cycles for 90 and 180 days cured samples. Higher freeze-thaw performance of the snow added samples is related to the increased void ratio after melting of snow and densification of the matrix around the pores due to higher level of cementitious mineral formation. The increase in the freeze-thaw performance of snow added fly ash samples will allow utilization of fly ash in highway embankment construction activities where large surface area exposure and large volume usage makes it more critical for the service life and longevity of the constructed road in cold regions. Another advantage of the developed technique is the reduction of transportation costs by more than 10% by using less material for construction. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.
