Study on mechanical properties and leaching of heavy metals in the artificially produced fly ash aggregates

Abstract

The present study focusses on fly ash as an industrial by-product which can be utilised in the production of artificial lightweight aggregates using activator solution as a binder. Artificial aggregates in the form of pellets would be an alternative for the natural coarse aggregates which is currently being used in the construction industry. The production of pellets was done such that the water content in the pellets were fixed at 20% of the weight of fly ash, and the Na2O content in the pellets was varied between 4 and 7% of the weight of the pellets. The mechanical properties were studied such as specific gravity, particle-size distribution (sieve analysis), water absorption, crushing strength of individual pellets and aggregate impact value. Further, the leaching tests were carried out to estimate the leaching of metals such as iron, chromium and sodium from the pellets. The effect of different curing conditions such as ambient, heat and solution was also studied in this study. From the test results, the pellets size distribution was found to be well graded and specific gravity of pellets was found to be in the range from 1.88 to 1.96. There was an improvement in the mechanical properties of the artificially produced fly ash aggregates as the Na2O content increased in the alkaline solution. It was found that heat-cured pellets showed a significant advantage over solution and ambient-cured pellets in crushing strength. It was found that leaching of the heavy metals are decreased as the percentage of Na2O content increased, indicating that the addition of Na2O enhances the encapsulation of heavy metals.