The bedrock in Finland consists of crystalline rock types, which are generally good source for durable aggregates after crushing. As the quality requirements have increased at various construction sites, increasing attention has been paid to the heterogeneity of the bedrock and the resulting quality variations. At the Geological Survey of Finland (GTK), inventories of hard rock aggregate outcrops in Finland have been in progress since 1989. The aim has been to explore the quality and amount of rock aggregates containing in the bedrock outcrops suitable for high-quality rock aggregate production without excluding the environmental aspects. The inventories have been focused on those regions where the needs for rock aggregates have been significant, i.e. densely-populated regions where good quality natural sand and gravel above the groundwater level have practically been used up. Rock aggregates produced from crushed bedrock are used to replace sand, gravel and crushed gravel products.
Regional inventories have been carried out jointly with environmental authorities, regional land-use planners and producers of aggregates in the separate project (POSKI) seeking to reach a balance between groundwater protection and aggregate supply. The POSKI project has aimed at protecting the environmental value of geological formations as well as securing the supply of high quality groundwater to communities, and high quality aggregate for construction purposes. The role of GTK in this project has been to map and estimate the volumes and quality of both hard rock aggregate and sand and gravel resources.
The inventories of rock aggregates currently include observations from a total of 12 000 bedrock outcrops. Mechanical-physical tests, mainly the Los Angeles and Nordic ball-mill tests, have been performed on over 880 rock samples in order to evaluate the quality of the rock aggregates. According to this inventory, less than 1.0% of the studied bedrock outcrops meet the highest quality requirements. The best rock types are fine-grained felsic and intermediate metavolcanic rocks in which mineral grains are tightly interlocked, as well as some strongly-deformed tonalitic and granodioritic plutonic rocks. The regional inventories have played a significant role in identifying the local occurrences of high-quality rock aggregates found within low-quality regions. For example in Uusimaa region the best quality rock types are situated nearly 100 km away from the Helsinki city.
However, high-quality aggregates should only be used for applications where they are essential. The demand of these aggregates will increase and the reserves will decrease. Therefore, it is necessary to determine the distribution and quality variations of rock aggregates, and the rock aggregate resources should be utilized reasonably and sustainably.