Published: 2024-12-17

Scandinavian pebbles as material for the production of crushed aggregates – petrographic identification of potentially alkali-reactive minerals

Andrzej K. Dubiniewicz

Abstract

The paper presents the results of detailed petrographic studies of 15 rock fragments, selected from 102 Scandinavian pebbles collected from the last glacial sediments in a gravel pit in north-western Poland and post-glacial crushed aggregate from north-eastern Germany. The aim of the study was to identify the presence of potentially reactive forms of silica and rock fragments prone to ASR (Alkali-Silica Reaction). During field work, it was observed that crystalline rocks dominated over sedimentary rocks in the rocky material. Post-glacial crushed aggregate consisted mainly of grains of various varieties of granites, limestones, gneisses, and sandstones, with a share of 30.8%, 20.6%, 15.6%, and 15.0% by mass, respectively; the share of grains of sedimentary and igneous rocks was similar, while the share of grains of metamorphic rocks was lower. This aggregate also contained reactive chert and flint fragments, which constituted slightly over 1% of its mass. Two forms of alkali-reactive silica were found in the analyzed pebbles – strained quartz and microcrystalline quartz. The former was present in all plutonic, metamorphic, and sedimentary rocks in varying proportions, from 7.7% to 96.4% by volume, while the latter was the cement in sandstones. Apart from those forms, myrmekite was found in uneven crystalline granites with white-cream and light pink feldspars, whereas fine crystalline quartz-feldspar mass was found in porphyries. Only black fine crystalline diabase did not contain these types of constituents.

Keywords:

petrographic studies, post-glacial crushed aggregate, silica, Scandinavian pebbles, alkali-reactivity

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Dubiniewicz, A. K. (2024). Scandinavian pebbles as material for the production of crushed aggregates – petrographic identification of potentially alkali-reactive minerals. Roads and Bridges - Drogi I Mosty, 23(4), 419–436. https://doi.org/10.7409/rabdim.024.020

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