Durability of alkali-activated calcined clay - GGBFS concrete against carbonation and chloride diffusion

Several studies have emerged in recent years on the production of alternative cementitious materials with less environmental impact (zero clinker), focusing on fewer emissions of CO₂ in its production compared to Ordinary Portland Cement. One of these binders, called geopolymer, is obtained from the alkaline activation of raw materials rich in SiO₂ and Al₂O₃, which can be derived from by-products or industrial residues. Calcined clay has emerged as a potential candidate as a precursor for this type of material. Large amounts of suitable clays are available in Australia and around the world. However, there is not enough data allowing to assess their durability, which is much needed to evaluate the service life and potentialities of this material. The present research proposed to evaluate the durability of alkali-activated low-grade calcined clay blended with Ground Granulated Blast Furnace Slag (GGBFS) through tests assessing the performance in chloride and carbonation-rich environments. The results show that the inclusion of GGBFS as a rich calcium source, notably improves the mortar microstructure and increases the pH of the pore solution, enhancing the carbonation resistance. Concretes activated with NaOH showed better compressive strength than those activated with KOH. Adding MgO enhanced the concrete's water absorption capacity and resistance to carbonation. The results indicated that increasing Na₂O% from 8 to 10 led to enhanced the compressive strength, led to a more refined microstructure, and reduced carbonation (both accelerated and natural). The electrochemical measurements strongly indicate that the alkali activated concrete used in this study do not pose a risk of steel corrosion aside from the high carbonation’s depth shown by the phenolphthalein test because the pH of carbonated alkali-activated concretes remains high compared to carbonated OPC systems. While a higher alkaline activator concentration resulted in an increase in shrinkage for mixes with high percentage of GGBFS, overall the total shrinkage of all alkali-activated concrete tested was similar or lower than typical values obtained for OPC concrete. Regarding their chloride penetration resistance, while alkali-activated concretes exhibited average compressive strengths, ranging from 31.5 to 63.5 MPa, their performed was not suitable for exposure to chloride-rich environments except for one concrete mix using high reactivity calcined clay. Indeed, a higher Na₂O concentrations and the use of high-grade calcined clay significantly reduced the chloride diffusion coefficient (Da) value, indicating improved chloride diffusion resistance equivalent to that of OPC concretes currently used in chloride environments in accordance with AS3600 specifications.

Author dc:creator

• De Carvalho Gomes, Samuel

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• info:eu-repo/semantics/openAccess
• The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
• © 2024 Samuel De Carvalho Gomes
• au.edu.uts.lib/cph

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en_US

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http://hdl.handle.net/10453/182358

OAI identifier oai:identifier

oai:opus.lib.uts.edu.au:10453/182358