Status of Soil Mapping in Finland

Natural aggregates can be naturally occurring graded material or mechanically crushed from mineral soils or rock mass. Mineral soils consists of mainly inorganic stone types which over the years under the influence of water, weather and pressure have been reduced in size and formed in shape.

In Finland repeated glacial periods have significantly affected the development of soils, and different types of soils have separated and formed layers. Because of this aggregate fractions suitable for use in concrete production are readily available. The most common soil type in Finland is moraine. The consumption of aggregates in concrete production is very high, which means that sources need to be readily available. When aggregates need to be transported from further costs will raise and options may be limited. Especially in southern Finland it is difficult to find suitable naturally graded fine aggregates. (Suomen Betoniyhdistys, 2005a, p.32) Good sources of suitable naturally graded aggregates are diminishing since removal of aggregates has begun to endanger the ground water sources; for this reason the possibility of underwater aggregate sources has been studied since 1980s. (Uudenmaan ympäristökeskus, 2006)

In Finland mainly granite based aggregates are used and more and more often they are mechanically crushed. Rock masses in Finland are mainly hard enough for concrete production, but weathering of rock mass can be a problem in particular areas. Naturally graded and crushed aggregates have slightly different properties, mainly caused by different grain shape and surface textures. Using crushed aggregates the voids content and the combined aggregate friction are greater than when naturally graded aggregates with same grain size distribution are used. To achieve the same consistency with crushed aggregates higher percentage of finer part of combined aggregates and increase of water is usually needed. Increase of water leads to increase of cement to achieve the same water-cement ratio. On the other hand, the bonding between cement stone and crushed aggregates is stronger than the one between cement stone and naturally graded aggregates; also the impact resistance of crushed rock is greater. At least in theory this allows higher water cement ratios to reach certain strength with crushed aggregates.

However it has to be noted that shrinkage and creep of hardened concrete depend on the volume percentage of cement stone and water-cement ratio; these deformations increase with higher water-cement ratios. (Suomen Betoniyhdistys, 2005a, 46.)