A structural and physico-chemical investigation of mineral/organic composites as novel components of engineered fill

Abstract

Sustainable engineering fill represents an increasingly important approach to the management of bulk non-marketable materials and the restoration of brownfield land, particularly land arising from mining and metallurgical activities. Embankments and restoration of brownfield sites are examples that already make use of engineering fill from bulk wastes in order to provide stable ground. Biostore, the subject of this research, is a novel type of stable engineering rockfill proposed for composite utilisation of bulk organic and mineral material, which would otherwise be waste.The thesis presents a literature review regarding environmental problems of bulky wastes such as coarse mineral wastes, construction and demolition material, green waste, fine pozzolanic pulverised fuel ash and digested sewage sludge. It also discusses current remediation practices for brownfield land. The main body of the thesis reports methods and results of an environmental and geotechnical study of the composites, based on laboratory investigation.Formulation of the composites using statistical factorial design has ensured proper understanding of component interaction and subsequent optimisation of the composite parameters. Solidification and stabilisation of the materials took place by compacting and cementing the wastes together. The coarse minerals formed a skeletal support whereas fine pozzolanic material (sewage sludge and pulverised fuel ash) cemented the components together with the aid of calcium oxide.The composites were tested for their porosity and micro-structure using novel methods (for these kinds of materials), e.g., nuclear magnetic resonance and super-critical drying. Furthermore, the Biostore was tested for uniaxial and triaxial strength, hydraulic conductivity, chemical leaching and cementatious mineralogy.The investigation demonstrated an inverse linear relation between decreasing porosity and increasing uniaxial strength with time. Micro-structural investigation revealed that this was due to crystallisation of ettringite and portlandite. The results indicate the potential for application of Biostore at a field scale.