Improving the Nanostructure, Sustainability, and Durability of Metakaolin-Based Alkali-Activated Materials through Additives

Abstract

Portland cement (PC) is a major source of greenhouse gases and produces 8% of the world’s anthropogenic carbon dioxide. Alkali-activated materials (AAMs) are cementitious alternatives that are capable of the same structural performance as PC (i.e., hydrated PC powder) while reducing carbon dioxide emissions. However, AAMs are currently not commonly used in industry, partly due to issues with lack of performance-manipulating additives like those available on the market for PC, as additives made for PC often are not effective in AAMs. In literature, cations and nano sodium aluminosilicate NPs have shown promising results for use as additives in AAMs. Additionally, there is currently no consensus on the extent of carbon dioxide reductions provided by different types of AAMs or cost compared to PC, especially when considering transportation-related emissions and current supply chain in the United States. Hence, this dissertation focuses on studying the impact of two types of potential additives, sodium aluminosilicate nanoparticles (NPs) and cations, on the structure, durability, and sustainability of alkali-activated metakaolin (AAMK). The first part of this dissertation focuses on the synthesis of sodium aluminosilicate NPs (nano zeolites, nano nepheline, and nano sodium-alumino-silicate-hydrate (N-A-S(-H) gel)) using low-rpm ball-milling with in-situ recrystallization and their subsequent use as additives in AAMK. Multiple characterization techniques such as isothermal conduction calorimetry (ICC), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) are used to analyze the impact of NPs on the AAMK N-A-S(-H) gel nanostructure, reaction kinetics, and sulfuric acid durability. The second segment of this dissertation shifts to the use of cations (Ca, Ti, Mg, and Fe in the forms of portlandite, rutile, brucite, and hematite, respectively) as additives in AAMK, specifically investigating their impact on physical and mechanical properties, N-A-S(-H) gel nanostructure, and sulfuric acid durability. Additionally, using data gathered from a variety of techniques including inductively coupled plasma optical emission spectroscopy (ICP-OES) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), a mechanism of sulfuric acid attack in AAMK is hypothesized. The final segment of this dissertation estimates the carbon emissions and cost of AAMK dosed with the most successful additive tested, Mg, using specific locations and current market costs.