Durability and diffusive behaviour evaluation of geopolymeric material
Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2006.
The study presented in this thesis symbolises one of the first ever efforts to better understand and describe the durability of geopolymers used in large scale commercial applications. In terms of the construction industry, geopolymers can be seen as a value-added approach to substitute the Ordinary Portland Cement (OPC) monopoly. It is particularly the fly ash-based geopolymers that are the main attraction, due to their economic and environmental advantages, over and above the large quantities of this material that are commonly available. Despite the fact that geopolymers have been around for thousands of years, it is only now that the accumulation of research across the globe has pooled their knowledge to broadly define this material in terms of its physical and chemical composition. The development of geopolymers for construction applications remains quite new, therefore requiring insight into the durability that can be expected from these materials, consequently leading to this work. Concrete technology and -science is one of many techniques which can offer considerable insight into effective durability studies, in addition to acting as a reference for firm material comparisons. Thus, this work is based on a collection of concrete durability studies and recommendations which resulted from a broad range of investigations. Principally, this work aims to confirm the superiority of geopolymers in terms of corrosion resistance. Chloride induced corrosion has been identified as being the main cause for deterioration of OPC structures and subsequently the origin of very costly, and frequent, reconstructive requirements. Geopolymers now have the opportunity to be introduced into this monopoly due to its advanced, yet credible, chloride penetration resistance. This thesis reports the development of the experimental design, as well as the associated analyses to describe the diffusive properties exhibited by fly ash-based geopolymers. Ultimately, two independent methods showed that Chloride Diffusion Coefficients (CDC) for all of the geopolymeric formulations are significantly lower (typically 1.43 x 10-15 cm2/s) than for cement (typically 0.5 x 10-8 cm2/s) or any other concrete mixture. Furthermore, the work presented here will consider the diffusive behaviour of the geopolymer formulations in an acidic sulphate environment, presenting this material’s superior resistance not only to the sulphate ion, but more so to the acid attack. Probable geopolymer applications are now further expanded to industrial applications, due to its acid resistance along with reduced Sulphate Diffusion Coefficients (SDC). In addition, the development of a time-to-corrosion software-tool is discussed. This tool may prove to be a valuable instrument for future geopolymer durability research, as well as iv commercial users in which extended material comparisons can be made. It may even assist the formulation-tailoring process where the relevant CDC/SDC can be chosen for a specific life-expectancy, reaching far beyond the limited scope of recipes covered in this work. Finally, this thesis provides the stepping-stone in proving geopolymer durability superiority. The formulations which proved to show the best results in terms of durability and acid resistance are highlighted and valuable recommendations are made towards the selection of suitable starting materials for optimum material robustness. The findings of this work, however, can be fortified by future research and exposure.