Characterization and quality assessment of granitic building stone deposits: A case study of two different Portuguese granites

Abstract

Several factors determine building stone exploration in order to maximize the extraction, processing and application of these natural materials. Some factors are intrinsic to stones, such as their physical-mechanical properties, while others are related to their exploitability, such as quarry reserves or fracturing density. During an exploration campaign, these factors are not always considered or properly weighed in terms of the negative consequences on quarry activities or rock behaviour under particular conditions. In this study, two well-known Portuguese granites are assessed to highlight the main factors. These granites have different characteristics, weathered and sound, and are exploited in quarries with different joint densities. The most relevant physical-mechanical properties were evaluated and related to the specific petrophysical features of each granite. The fracture patterns were identified in the quarries and then modelled in order to compute the quarry yield. The weathered granite shows an important microcrack network and a general alteration of the rock-forming minerals, which has an important impact on its physical-mechanical properties and on the resistance to environmental factors. Moreover, the extreme differences in the degree of weathering require careful choices for the possible applications. In both quarries, the joint sets are similar to the regional faulting, but some random joints can be found and, consequently, diminish the quarry yield. The development of horizontal sheet joints during the exploitation process could have a great influence on the quarry productivity if they are not used do delimitate the extracted blocks. The modelling of the natural fracture pattern allows us to determine the potential volume of blocks that could be exploited. However, the quality of the information gathered could lead to an over-estimation of the quarry production.This example shows the importance of the exhaustive researches during a building stone assessment campaign.