Most of the previous research on plain and fibre reinforced geopolymer concrete (FRGC) has concerned on the properties of geopolymer mixtures hardened under heat curing conditions, which is a severe limitation for on-site, cast-in-place applications. This study focuses on the material and structural properties of novel fibre reinforced geopolymer concretes cured under ambient temperature. The overall aim of the study was to develop and test a more environmentally sustainable concrete material with improved structural characteristics, which utilises waste rather than primary mineral products, suitable for cast-in-place applications and for the structural strengthening of existing buildings.
In the first part of this thesis, the material behaviour of FRGC cured under ambient temperature was examined. Initially, the work identified the role of various parameters which may affect material compressive strength, in order to enhance overall performance. In addition, the mechanical and microstructural properties of geopolymer mortar with different slag contents and variant silica fume types (densified, undensified and slurry) were assessed. Following this, the effect of slag content and silica fume particle size on the properties of steel fibre reinforced geopolymer composites (SFRGC) was examined. The optimum FRGC mixtures were further investigated in term of its durability characteristics and mechanical properties, in order to provide strain hardening characteristics. In the examined mixes, different fibre types, aspect ratios, and volume fractions, and its comparison with Portland cement based conventional concrete, have been assessed and appropriate mixtures have been identified with multiple fine cracks and strain hardening in tension.
In the final part of the thesis, the structural behaviour of FRGC is examined at larger scale application. PVA and steel fibre reinforced geopolymer concrete mixtures were used as strengthening and repair materials for the protection of steel bars in a new material layer, and for subsequent improvement of the flexural strength of existing beams. Large scale beams strengthened with additional FRGC layers reinforced with steel bars have been examined. Also, an additional investigation was conducted in beams where part of the concrete cover at various depths was replaced by FRGC. In all the examined cases respective beams with conventional concrete were examined in order to evaluate the efficiency of the proposed technique. Accelerated corrosion tests were performed using the induced current technique by applying a nominal 300 mA constant anodic current. The results of this investigation showed significant improvements in the structural performance of the examined beams following strengthening or repair with FRGC. The outcomes of the experimental work indicate that FRGC considerably enhanced both the flexural strength capacity and the durability of strengthened and repaired reinforced concrete elements.
|Date of Award||Sep 2017|