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Controlling alkali silica reaction by understanding the contribution of aluminium provided by supplementary cementitious materials



Author(s): T. Chappex, K. Scrivener
Paper category: Conference
Book title: 2nd International conference on Microstructural-related Durability of Cementitious Composites
Editor(s): Guang Ye, K. Van Breugel, Wei Sun, Changwen Miao
Print ISBN: 978-2-35158-129-2
e-ISBN: 978-2-35158-123-0
Publisher: RILEM Publications SARL
Pages: 605-612
Total Pages: 7
Language: English


Abstract: 
The real mechanism by which supplementary cementitious materials (SCM) control alkali silica reaction (ASR) is not well understood. Some previous studies, principally done on synthesized specific cement phases show the immobilization of sodium and potassium ions in
the C-S-H phase. The assimilation of Si by C-S-H is involved in the alkali fixation. The better ASR resistance of aluminium rich SCMs was often attributed to the alkali fixation potential of Al incorporated in C-S-H. However, this behaviour has never been confirmed in real cement pastes.

In a first part of the study, the alkalinity of the pore solutions and the C-S-H composition of different SCM blended paste were analysed. It appeared that the aluminium incorporation in the C-S-H has no contribution on the alkali immobilization of pore solution.

It is proposed that the role of aluminium takes place in the aggregates themselves. Aluminium species present in the pore solution, provided by SCMs, are incorporated on the silica surface and limit the dissolution of amorphous silica of the aggregates. The reacted fraction of aggregates put in simulated pore solutions was studied and could confirm the inhibiting effect of aluminium species on the ASR gel formation.

This approach indicates a new mechanism that controls ASR in presence of aluminium in the pore solution. Improving the understanding of aluminium on silica dissolution could enable to specify the precise amount of known SCM for a given type of reactive aggregate to avoid or significantly reduce ASR expansion.


Online publication: 2013
Publication Type: full_text
Public price (Euros): 0.00