Mechanical, Durability and Structural Evaluation of Geopolymer Concretes

Abstract

Alkali–activated aluminosilicates, known as geopolymers, have the potential to be used for sustainable concrete. Geopolymers encompass any binder systems derived from the reaction of an alkalis reagent with aluminosilicate rich materials that can harden at room (ambient) or elevated temperatures. The use of industrial waste materials in the manufacture of concrete not only introduces economic and structural performance benefits, but it also provides environmental benefits associated with reducing large volumes of disposed waste materials, such as ashes from coal–fired power stations and slags from metal production operations. Despite the commercial promise of geopolymer concrete technology, its widespread use is hindered by the lack of fundamental understanding of its potential long–term behaviour. Moreover, an understanding of the behaviour of reinforced geopolymer concrete, including the interaction between the reinforcement and surrounding concrete and its resistance to corrosion is sparse. This lack of information is significant, as it delays compliance with regulatory design standards and hence limits practical structural applications. This thesis explores the mechanical and structural characteristics of geopolymer concretes that are derived from class–F fly ash and granulated lead smelter slag. Significant aspects of these geopolymer concretes are investigated and the results are presented by compiling a series of journal papers. Firstly, mix designs utilising fly ash and lead smelter slags are developed and appropriate mix design guidelines are prescribed. For these mix designs, the material and mechanical properties of the concretes at both fresh and hardened states are then investigated. Having developed mix designs and quantified basic material behaviour, the long–term durability characteristics of both fly ash and lead smelter slag–based geopolymer concretes are extensively investigated. Particular attention is paid to the long–term durability of geopolymer concrete through consideration of the bond strengths of corroded and non–corroded steel reinforcement. The structural mechanisms related to the bond strength are investigated to quantify the formation of cracks, tension–stiffening and crack widening. Finally, the structural behaviour of granulated lead smelter slag–based geopolymer concrete short and slender columns was investigated through axial compression subjected to different eccentricities. From the investigation conducted in this thesis, it is shown that fly ash geopolymer concrete has comparable mechanical and structural behaviour to that of Ordinary Portland Cement (OPC) concrete. For a given compressive strength of concrete, the mechanical properties, durability, bond strength, tension–stiffening, and structural performance exhibited in geopolymer concrete are slightly higher than the corresponding measures of these properties in OPC concrete. Similarly, granulated lead smelter slag–based geopolymer concrete is shown to have potential as a cementitious material if the slag particles are crushed to a size similar to that of fly ash and OPC. Alternatively, granulated lead smelter slag is shown to be of use as a partial replacement for fly ash, which results in a blended binder. Significantly, based on the results obtained from this research, it can be stated that the current design provisions contained in the standards for Ordinary Portland Cement concrete can easily be modified and adopted for the applications of geopolymer concrete.