Thesis

Corrosion mechanisms and structural performance evolution of alkali-activated fly ash and slag concretes

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Awarding institution
  • University of Strathclyde
Date of award
  • 2025
Thesis identifier
  • T17360
Person Identifier (Local)
  • 202076739
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Department, School or Faculty
Abstract
  • Alkali-activated materials (AAMs) have garnered significant interest as sustainable alternatives to Portland cement, playing an important role in the transition towards a low-carbon society. This research is focused on understanding the chloride-ingress-induced corrosion in reinforced alkali-activated fly ash and slag (AAFS) mortars and their structural implications. The influence of aggregate types (gravel and limestone) and precursor composition on the mechanical and fracture properties of AAFS concrete and mortar were investigated. While concrete generally shows lower compressive strength than mortar, the 50SA-50FA gravel and 30SA-70FA limestone concretes exhibit higher strength due to improved particle distribution and precursor effects. Furthermore, limestone aggregates further enhance fracture energy and toughness compared to gravel. Additionally, increasing slag content boosts early strength and toughness but also increases brittleness of AAFS concrete. By systematically investigating electrochemical parameters, including corrosion potential, linear polarisation resistance, and Tafel constant values under both passive and active conditions, this study provides critical insights into the corrosion behaviour of reinforced AAFS mortars. It has been found that Tafel constant values range from 20 to 22 mV for the passive condition and from 50 to 58 mV for the active condition. These values serve as key indicators for assessing the corrosion rate of embedded steel reinforcements. In addition, the chloride thresholds for reinforced AAFS mortars at the steel-mortar interface were determined upon corrosion initiation. The chloride thresholds were found to be inversely proportional to the slag content in AAFS mortars. This phenomenon was thoroughly analysed in conjunction with the morphological characteristics of the steel-mortar interface. Both microcell and macrocell corrosion were identified at the steel-mortar interface. Microcell corrosion, characterised by localised corrosion cells, was found to dominate in regions with thicker interfacial zones (>10 μm), while macrocell corrosion was prevalent in areas with thinner interfacial zones (<2 μm). Furthermore, the role of each corrosion cell was classified and validated through numerical simulations. Finally, a practical corrosion determination method for reinforced AAFS mortars is proposed to help engineers and asset managers make informed decisions regarding the long-term performance of AAFS structures.
Advisor / supervisor
  • Yang, Shangtong
Resource Type
DOI

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