Dynamic behavior of sand-fly ash mixture by element testing

Abstract

High energy demand forced many countries to reopen or expand production of electricity from coal power plants. Apart from being one of the most polluting technological processes emitting millions of metric tons of carbon dioxide in the atmosphere. This process also produces an enormous quantity of coal fly ash which has been successfully used as a mineral admixture in concrete industry and also as a feed material for producing Portland cement for many decades. A lot of efforts have been made to find a way to use fly ash in geotechnical engineering. Numerous studies show the benefits of using fly ash as a mixture for soil replacement and for limited use as soil improvement. Using fly ash for geotechnical purposes in seismic prone regions requires behavior of soil - fly ash mixture in static and dynamic conditions. This paper presents the results from laboratory testing performed on mixtures of natural sand material (Skopje Sand) and 5, 10 and 20% fly ash. Before using fly ash in element tests, extensive investigation was done on chemical and mineralogical composition as well as on classification of used fly ash. Cyclic and monotonic triaxial tests and direct simple shear tests were performed on sandy-fly ash mixtures specimen. The results of the mixtures are compared with existing results for clean Skopje Sand. The results from this study show that as the fly ash amount increases in the mixture, the relative density has more influence on the peak and residual strength of the material. The strength properties of natural Skopje Sand can be improved with low quantities of fly ash, around 5%, and there is no regular trend of the liquefaction resistance in function of the amount of fly ash, for high percentage of fly ash.