Polished Stone Value of Volcanic Rocks Used as Aggregates: A Case Study from the Bohemian Massif, Czech Republic

Abstract

Volcanic rocks represent about 34 % of the crushed stone marketed in the Czech Republic. These rocks are used for all kinds of construction purposes including roads. In a recent study, we focused on their performance in asphalt concrete designed for road surfacing. The samples were from 39 active quarries, representing all major volcanic rock types, and belonging to three different geological epochs—Neoproterozoic, Upper Palaeozoic, and Tertiary. The rocks under study encompassed numerous rock fabric subtypes including fine- to coarse-grained, porphyritic, hemicrystalline, etc. These rocks have been studied for their mineralogical composition and rock fabric quantitatively (including image analysis). The polished Stone Value (PSV) of each rock type has been determined following the respective standard. According to Czech standards for road surfacing, PSV above 53 is required, PSV over 56 is required for high traffic and dangerous road sections. From the 39 rock types studied, only 17 (3 basaltic rocks, 5 spilites, 5 melaphyres, 2 rhyolites, 1 porphyry, 1 diabase) fulfil the criteria for general road surfacing. When considering the stricter requirement (PSV above 56), only 5 rock types (3 melaphyres, 1 porphyry, 1 diabase) under study were suitable. Correlations between the selected petrographic features (mineralogical composition, grain size, type of phenocrysts) and the PSV failed. Only for basalts, did an increasing content of olivine phenocrysts lead to a drop of the PSVs, which is in contradiction to the heretofore accepted views on the PSV-petrographic feature relationships.