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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Title: Release of Alkalies from Feldspar in Concrete and Mortar
Author(s): E. Poulsen, T. S. Hansen, and H. E. Sørensen
Publication: Special Publication
Appears on pages(s): 807-824
Keywords: alkali-aggregate reactions; chert; expansion; mortars; quartz; silica fume; thickness
Abstract:A necessary condition for crack development in concrete due to alkali-aggregate reaction is that the concrete contains: *Reactive rock types or minerals, e.g. porous, opaline chert. *Alkali metal ions, e.g. sodium ions Na+ and potassium ions K+ *Water, e.g. concrete humidity more than 80% RH. Aggregates with alkali minerals may release alkalies in concrete, since the pH values are often 12-13 in most concrete. If alkalies are released from the aggregates it might increase the risk of getting 'deleterious' alkali relations, when alkali reactive aggregates are resent in the concrete in a sufficient intensity. So far, this question has not been given much attention, when specifications for the maximum alkali content in fresh concert has been made. A test series was carried out in order to subject this question to a critical examination. It was decided to perform two main series o mortar bar test with: *Water/cement-ratio=.40 by mass. *Binder/aggregate-ratio=.42 by mass *Flow of mortar+130 mm and variable parameters: *Chert/aggregate-ratio, which varied from 0 to 10 percentage by volume *As inert aggregate either quartz or feldspar were chosen *Concentration of alkali metal ions in the mortar, which was given the values 3.0 and 6.0 kg of equivalent Na 2O per m3 mortar *In order to study the influence of added silica fume systematically, the ratio of silica fume to binder was chosen as 0,4 and 8 percentage by mass. The following conclusions were drawn from the test series performed: * The maximum expansion increases (at pessimum proportion) when feldspar is used as inert aggregate instead of quartz, other parameters being equal *A delay of expansion is observed when silica fume is added to the mortar *The delay increases with the amount of silica fume added.
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