Balanced alkali limit in cement for alkali-silica reaction risk-free concrete production

Sanchez Roboredo, Cibele

Balanced alkali limit in cement for alkali-silica reaction risk-free concrete production

Sanchez Roboredo, Cibele

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Publication Type:: Thesis
Issue Date:: 2020

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Field	Value	Language
dc.contributor.author	Sanchez Roboredo, Cibele
dc.date.accessioned	2020-08-25T05:01:54Z
dc.date.available	2020-08-25T05:01:54Z
dc.date.issued	2020
dc.identifier.uri	http://hdl.handle.net/10453/142351
dc.description	University of Technology Sydney. Faculty of Engineering and Information Technology.	en_AU
dc.description.abstract	The effect of alkali concentration on the alkali-silica reaction (ASR) is presented in the context of balance alkali content in ASR risk assessed concretes. In order to investigate the effect of alkali concentration on ASR, the reactivity of the non-reactive micro-diorite aggregate and reactive greywacke aggregate, classified by the Australian Standard AS 1141.60.2 were investigated. Slurry tests in the presence and absence of calcium hydroxide (CH), dissolution tests to monitor the rate of release of alkali, calcium, silica and aluminium ions into solution and mortar bar and paste tests were carried out as a function of alkali concentration of the immersion solution with and without the addition of the supplementary cementitious material (SCM) fly ash. Aggregate reactivity in ground aggregate slurry tests as a function of pH and temperature demonstrated that reactivity of ASR increased with temperature, pH and reactivity of the aggregate. The relative reactivity of these aggregates was further confirmed by dissolution tests showing that the rate of dissolution of silica, in particular, increased with aggregate reactivity. The dissolution test for fly ash also showed significant reactivity with respect to the rate of silica dissolution. Slurry tests in the presence and absence of CH showed that, in the presence of CH, the rate of reaction increased markedly, demonstrating the importance of calcium ions on ASR gel formation. Under the experiment conditions, fly ash happened to consume more calcium which indicates high reactivity. The degree of consumption of CH did not increase with pH. This lack of dependence on the pH was ascribed to diminishing solubility of calcium ions with increased pH and suggests that the composition of the ASR gel formed is dependent on the pH of the solution. Accelerated mortar bar tests (AMBT, AS 1141.60.1) were carried out as a function of alkali concentration with and without fly ash addition. Expansion rates were observed to increase with aggregate reactivity and with pH. The addition of the Australian fly ash class F significantly reduced expansion suggesting that fly ash acts in mitigation of ASR through competitive reaction inhibiting the progression of the aggregate reaction. Ground aggregate slurry and mortar bar and paste tests showed increased reaction with pH and reactivity of the silica components present in aggregates. Reduced alkali concentration simply reduced the reaction rate. The continuing reaction even at low alkali concentrations suggests that ASR occurs irrespective of the pH. The potential for deleterious ASR is, however, dependent on the action of the silica gel formed on the concrete and therefore further work is required into the complete mechanism of ASR to complement the current study.	en_AU
dc.format	Thesis (ME)
dc.language.iso	en_US	en_US
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/142351/2/02whole.pdf
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.rights	info:eu-repo/semantics/openAccess
dc.title	Balanced alkali limit in cement for alkali-silica reaction risk-free concrete production	en_AU
dc.type	Thesis
utslib.copyright.status	open_access	*

Abstract:

The effect of alkali concentration on the alkali-silica reaction (ASR) is presented in the context of balance alkali content in ASR risk assessed concretes. In order to investigate the effect of alkali concentration on ASR, the reactivity of the non-reactive micro-diorite aggregate and reactive greywacke aggregate, classified by the Australian Standard AS 1141.60.2 were investigated. Slurry tests in the presence and absence of calcium hydroxide (CH), dissolution tests to monitor the rate of release of alkali, calcium, silica and aluminium ions into solution and mortar bar and paste tests were carried out as a function of alkali concentration of the immersion solution with and without the addition of the supplementary cementitious material (SCM) fly ash. Aggregate reactivity in ground aggregate slurry tests as a function of pH and temperature demonstrated that reactivity of ASR increased with temperature, pH and reactivity of the aggregate. The relative reactivity of these aggregates was further confirmed by dissolution tests showing that the rate of dissolution of silica, in particular, increased with aggregate reactivity. The dissolution test for fly ash also showed significant reactivity with respect to the rate of silica dissolution. Slurry tests in the presence and absence of CH showed that, in the presence of CH, the rate of reaction increased markedly, demonstrating the importance of calcium ions on ASR gel formation. Under the experiment conditions, fly ash happened to consume more calcium which indicates high reactivity. The degree of consumption of CH did not increase with pH. This lack of dependence on the pH was ascribed to diminishing solubility of calcium ions with increased pH and suggests that the composition of the ASR gel formed is dependent on the pH of the solution. Accelerated mortar bar tests (AMBT, AS 1141.60.1) were carried out as a function of alkali concentration with and without fly ash addition. Expansion rates were observed to increase with aggregate reactivity and with pH. The addition of the Australian fly ash class F significantly reduced expansion suggesting that fly ash acts in mitigation of ASR through competitive reaction inhibiting the progression of the aggregate reaction. Ground aggregate slurry and mortar bar and paste tests showed increased reaction with pH and reactivity of the silica components present in aggregates. Reduced alkali concentration simply reduced the reaction rate. The continuing reaction even at low alkali concentrations suggests that ASR occurs irrespective of the pH. The potential for deleterious ASR is, however, dependent on the action of the silica gel formed on the concrete and therefore further work is required into the complete mechanism of ASR to complement the current study.

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