Investigation of Strategies for Risk Minimisation of Adverse Alkali-Silica Reaction in Concrete

Nsiah-Baafi, Elsie

Investigation of Strategies for Risk Minimisation of Adverse Alkali-Silica Reaction in Concrete

Nsiah-Baafi, Elsie

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Publication Type:: Thesis
Issue Date:: 2021

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Field	Value	Language
dc.contributor.author	Nsiah-Baafi, Elsie
dc.date.accessioned	2021-11-02T00:11:35Z
dc.date.available	2021-11-02T00:11:35Z
dc.date.issued	2021
dc.identifier.uri	http://hdl.handle.net/10453/151301
dc.description	University of Technology Sydney. Faculty of Engineering and Information Technology.	en_US.UTF-8
dc.description.abstract	In recent decades, many structures worldwide have suffered damage due to alkali-silica reaction (ASR). This reaction is one of the most recognised chemical reactions leading to the deterioration of concrete. ASR is an alkali-activated process that causes concrete to expand with time. To minimise the risk of expansion, major focus has been placed on reducing the alkali content in concrete. This is achieved by: (i) limiting the total alkali content in concrete to 2.5-2.8 kg/m3 Na2Oe; and, (ii) adding supplementary cementitious materials (SCMs) as partial replacement of cement. While these practices have shown desired outcomes, recent challenges surround the implementation of such practices due to a shortage of SCMs and the economic cost associated with using such solutions. Furthermore, the validity of classifying the reactivity of aggregates against the current short-term test methods employed for assessing ASR is also under conjecture by researchers. This has left the concrete industry with the inconvenient option of performing long-term tests extending up to 24 months to obtain a reliable prediction of an aggregate’s reactivity potential. Consequently, a delay in decision-making leading to a decrease in productivity from the concrete industry is likely. This study has been undertaken to explore sustainable and novel techniques for mitigating ASR that also encourage the conservation of natural resources. Different aggregates have been studied using a suite of test methods comprised of petrography, chemical tests, expansion tests and analytical techniques. This comprehensive testing framework has been employed to determine the reactivity potential and establish the specific alkali limit relative to the mineralogical composition and reactivity classification of the aggregates. Subsequently, the potential of ground reactive aggregate fines (GRAFs) as alternative additives for mitigating ASR has been evaluated. The effect of GRAFs on the modification of the pore solution, reduction in Portlandite amount, mitigation of ASR expansion and changes in mechanical properties have been investigated. Further, the relationship between aggregate reactivity predictions based on the different test methods has been studied via a statistical approach to establish a correlation between short-term and long-term test methods. Ultimately, the outcomes of this study provide a novel strategy for mitigating ASR in concretes by introducing aggregate dependent alkali limits to allow the full utilisation of locally available aggregate sources and employing the addition of GRAFs in the absence of SCMs. Furthermore, the results obtained support the use of specific short term tests as a reliable predictor for the reactivity potential of aggregate.	en_US.UTF-8
dc.format	Thesis (PhD)
dc.language.iso	en_US	en_US.UTF-8
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/151301/2/02whole.pdf
dc.rights	info:eu-repo/semantics/openAccess
dc.rights	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.
dc.rights	au.edu.uts.lib/ppc
dc.title	Investigation of Strategies for Risk Minimisation of Adverse Alkali-Silica Reaction in Concrete	en_US.UTF-8
dc.type	Thesis
utslib.copyright.status	open_access	*

Abstract:

In recent decades, many structures worldwide have suffered damage due to alkali-silica reaction (ASR). This reaction is one of the most recognised chemical reactions leading to the deterioration of concrete. ASR is an alkali-activated process that causes concrete to expand with time. To minimise the risk of expansion, major focus has been placed on reducing the alkali content in concrete. This is achieved by: (i) limiting the total alkali content in concrete to 2.5-2.8 kg/m3 Na2Oe; and, (ii) adding supplementary cementitious materials (SCMs) as partial replacement of cement. While these practices have shown desired outcomes, recent challenges surround the implementation of such practices due to a shortage of SCMs and the economic cost associated with using such solutions. Furthermore, the validity of classifying the reactivity of aggregates against the current short-term test methods employed for assessing ASR is also under conjecture by researchers. This has left the concrete industry with the inconvenient option of performing long-term tests extending up to 24 months to obtain a reliable prediction of an aggregate’s reactivity potential. Consequently, a delay in decision-making leading to a decrease in productivity from the concrete industry is likely. This study has been undertaken to explore sustainable and novel techniques for mitigating ASR that also encourage the conservation of natural resources. Different aggregates have been studied using a suite of test methods comprised of petrography, chemical tests, expansion tests and analytical techniques. This comprehensive testing framework has been employed to determine the reactivity potential and establish the specific alkali limit relative to the mineralogical composition and reactivity classification of the aggregates. Subsequently, the potential of ground reactive aggregate fines (GRAFs) as alternative additives for mitigating ASR has been evaluated. The effect of GRAFs on the modification of the pore solution, reduction in Portlandite amount, mitigation of ASR expansion and changes in mechanical properties have been investigated. Further, the relationship between aggregate reactivity predictions based on the different test methods has been studied via a statistical approach to establish a correlation between short-term and long-term test methods. Ultimately, the outcomes of this study provide a novel strategy for mitigating ASR in concretes by introducing aggregate dependent alkali limits to allow the full utilisation of locally available aggregate sources and employing the addition of GRAFs in the absence of SCMs. Furthermore, the results obtained support the use of specific short term tests as a reliable predictor for the reactivity potential of aggregate.

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