An Investigation of the Geotechnical Properties of Coal Combustion By-products from Matimba Power Station in Lephalale, South Africa

Abstract

The production of electricity by burning coal produces huge amount of fly ash and bottom ash; hence, with the increase in the quantum of the thermal power generation, the production of the fly ash also rises to the top. The hanging of the by-product of the coal is considered to be the problematic issue at Matimba power station. The objectives of this investigation were to investigate the geotechnical properties of fly and bottom ash to establish their possible utilisation as a construction material, to determine the grain size distribution, therefore, to analyse the consistency of coal fly ash and bottom ash and perform comparative analysis of the geotechnical properties for suitability of the material as a building material, as well as to identify geotechnical constraints that may have an adverse effect on the project. The methodology used included preliminary studies, reconnaissance survey, soil sampling and laboratory tests. This involved determination of Atterberg limits, sieve analysis, moisture content and soil classification. Results of the laboratory tests indicate that the material of coal fly ash is mainly clay, while bottom ash is mainly silty. The coal fly ash was found to have low plasticity, low liquid limit as well as low plasticity index with low moisture content. The bottom ash on the other hand had considerable plastic limit and liquid limit with high moisture content. The plastering sand was determined to have low plastic limit, considerable liquid limit with low plasticity index. In comparison with the mixture of ashes with plastering sand, the material can be used as plastering material for building purposes.