Mechanism of preventing the alkali–aggregate reaction in alkali activated cement concretes Pavel Krivenko a,⇑ , Rostislav Drochytka b , Aleksandr Gelevera a , Elena Kavalerova a a Kiev National University of Civil Engineering and Architecture, Scientific Research Institute for Binders and Materials, Kiev, Ukraine b Brno University of Technology, Institute of Technology of Building Materials and Components, Brno, Czech Republic article info Article history: Received 25 October 2012 Received in revised form 24 September 2013 Accepted 4 October 2013 Available online 11 October 2013 Keywords: Alkali activated cement Alkali Alkali–aggregate reaction Alkali–silica reaction Concrete Expansion Hydration products Interfacial transition zone Petrography Portland cement X-ray diffraction abstract Processes of structure formation taking place in the interfacial transition zone ‘‘cement paste – aggre- gate’’ have been studied on a variety of cement model systems. The results of this study suggest that, depending upon the contents of components capable of actively interacting with alkalis in the presence of reactive SiO 2 in the cement and aggregate, the processes taking place during an alkali-aggregate reac- tion could be constructive or destructive in character. So-called ‘‘constructive processes’’ are attributed to binding the corrosion reaction products with the formation of the alkaline aluminosilicate hydrates. The results of this study have been taken as a base in developing a mechanism of preventing the alkali–aggre- gate reaction in the alkali activated cement concretes through the introduction of additional quantities of Al 2 O 3 -containing substances. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction First observations of reactivity of the alkalis contained in some mineral constituents go back to 1916 when a geologist E.A. Ste- phenson has reported about a reaction between feldspar and so- dium carbonate which resulted in the formation of a gel. Degradation of concrete as a result of this reaction between the alkalis contained in cement and some ground rocks was first ob- served in the USA. In 1922 similar deteriorations took place in the New River Hydropower Station (Virginia, USA) 10 years after it had been erected. In 1940 Stanton [1] has reported about an ‘‘alkaline reaction’’ (alkali–aggregate reaction, AAR) due to opal- containing fractions of the rocks used for the diverting dam in Cal- ifornia. These deteriorations have initiated a number of extensive studies to be held in the USA to reveal causes for taking appropri- ate measures. In 1947 a reaction between the alkali and silicic acid (alkali–sil- ica reaction, ASR) was described by Bogue [2]. A few years later, in 1952 this reaction was described by Kuehl in his book, in which he made references to the data obtained in the USA [3]. Starting from 1950s this reaction is also known in Australia and since the mid of 1950s more and more countries (Canada, Iceland, South Africa and other countries) report about deteriorations of bridges, sleepers, dams, roads due to the ASR. Very often these deteriorations are attributed to other causes such as low frost resistance or other aggressive exposure. The losses were huge, which is why the problem became urgent and required prompt actions to be taken. As a result of extensive studies and experimental works [3–6], basic fundamentals of the ASR mechanism have been formulated. These are:  sources of alkalis are cement, concrete admixtures, outdoor aggressive environment;  limit values of the alkalis (Na 2 O + 0.658 K 2 O) contained in portland cement (expressed in terms of Na 2 O-equivalent content) should be less than 0.6% by mass;  expansion due to the ASR is associated with osmotic pres- sure from the aluminosilicate gel- a product of reaction between the active silica and alkali. This gel acts as a 0958-9465/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cemconcomp.2013.10.003 ⇑ Corresponding author. E-mail address: pavlo.kryvenko@gmail.com (P. Krivenko). Cement & Concrete Composites 45 (2014) 157–165 Contents lists available at ScienceDirect Cement & Concrete Composites journal homepage: www.elsevier.com/locate/cemconcomp