Abstract
Alkali silica reaction (ASR) is a harmful phenomenon occurring as a result of chemical interactions between sodium and potassium hydroxides in the pore solution and reactive minerals contained in the aggregate. Reactive minerals like microcrystalline, cryptocrystalline or strained quartz dissolve in the alkaline solution and form an expansive gel product. Proper selection of concrete constituents is necessary to ensure the durability of concrete structures. The proper recognition of the aggregate mineralogical composition is a very important element in the process of selection of concrete components due to the risk of ASR occurrence. This paper presents the results of detailed microscopic analysis of alkali-silica reactivity of domestic fine aggregates of various origins. Six siliceous sands from different locations in Poland and one limestone sand were tested. Detailed petrographic analysis was performed on thin sections. In all siliceous sands micro- and cryptocrystalline quartz was recognized as a reactive mineral. Digital image analysis was performed for quantitative assessment of the potential of reactivity of sands. It revealed, that siliceous river sands were the most susceptible to an alkali-silica reaction, which was confirmed by mortar bar expansion test performed according to the standard test method.
Highlights
The issue of alkali-silica reaction (ASR) is known and discussed by scientists around the world
Proper selection of concrete constituents is a key issue in preventing the occurrence of an alkali-silica reaction, especially in structures such as road pavements and bridges, which must be durable for several dozen years [3]
Petrographic analysis was focused in identification of the reactive minerals in fine aggregate, Fig 2
Summary
The issue of alkali-silica reaction (ASR) is known and discussed by scientists around the world. Problems related to the reactivity of fine aggregate were described by Lukschowa et al [7] They suggested the simultaneous use of several methods of testing for potential of alkaline reactivity, since one may be ineffective. Results of petrographic analysis on thin sections made from different Polish aggregates were presented in [8], including these from glacial deposits Such evaluation of the mineral composition of aggregates enabled preliminary classification of aggregate into one of the three classes of reactivity according to RILEM. Naziemiec [9] presented diversity of Polish fine aggregates in relation to their alkali-silica potential. He did not get clear results, both non-reactive and highly reactive sands were recognized. The digital image analysis of minerals and microstructural features enabled a comparison of results with mortar bar expansion according to accelerated mortar-bars test at 80oC in 1M NaOH solution
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