Abstract
Natural aggregates are a low commodity, high-value material. It plays a major role in creating, maintaining, and enhancing the infrastructure in society. With this comes the responsibility to select the best possible aggregate based on the physical and chemical compositions. Even though Fiji has an extensive distribution of natural aggregates over a range of geologic settings, not all of them are readily accessible or available for use. A systematic investigation of different chemical and minor physical properties of natural aggregates was undertaken in this study. For the purpose of this study, the term aggregates have been applied to deposits of bedrock or naturally occurring rocks.
This thesis aims to characterise the mineralogical and chemical properties of rocks (natural aggregates) from various lithologies. A total of 5 sites were investigated on Viti Levu, Fiji Islands. Seventeen different samples were collected from these sites which represented nine different lithologies (trachyte basalt, basalt, basanite, andesite, monzonite, granite, syenite, limestone, and sandstone). Their physical and structural features were determined in the field and the predictive aggregate grade was determined based on weathering and strength of the rock units. The mineralogy and the chemical composition were determined using bulk geochemistry analysis using XRF and XRD techniques.
The whole-rock geochemistry distinguished the different rocks studied. A total of 17 rock samples from functional and prospective hard rock quarry sites were studied. These different rock types are from volcanic, plutonic, and sedimentary origins. Out of the seventeen samples, eleven rock samples were characterised as a satisfactory aggregate grade based on the physical characteristics with four of these classified as a strong natural aggregate by means of rock strength parameters. The different feldspar and the pyroxene members were identified using the an-ab-or and wo-en-fs plots. The clay minerals were identified based on the XRD analysis. A total of eleven samples showed a substantial amount of illite, kaolinite, chlorite, and montmorillonite mineral content.
The physical and structural data collected during this study categorises eleven rock samples as satisfactory aggregate grades based on their physical characteristics. In terms of strength, only four are classified as strong. The laboratory results provide in-depth knowledge of the mineralogical and chemical components. These data help in categorising these rocks in terms of their possible use in the different stages of construction.