Natural aggregates can be classified materials occurring naturally or mechanically broken down from mineral soils or rock masses. Mineral soils consist mainly of inorganic stone types which over the years, under the influence of water, weathering and pressure, have shrunk in size and molded in shape. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essayIn Finland repeated glacial periods significantly influenced the development of soils, and different types of soil separated and formed layers. For this reason, aggregate fractions suitable for use in concrete production are readily available. The most common terrain type in Finland is moraine. The consumption of aggregates in concrete production is very high, which means that sources must be readily available. When aggregates need to be transported from other countries, costs will increase and options may be limited. Especially in southern Finland it is difficult to find suitable fine aggregates with natural grain size. (Suomen Betoniyhdistys, 2005a, p.32) Good sources of naturally graded suitable aggregates are declining as aggregate removal has begun to endanger underground water sources; for this reason the possibility of underwater aggregated sources has been studied since the 1980s. (Uudenmaan ympäristökeskus, 2006)In Finland mainly granite-based aggregates are used and are increasingly crushed mechanically. Rock masses in Finland are mostly hard enough for concrete production, but erosion of rock masses can be a problem in particular areas. Naturally sorted and crushed aggregates have slightly different properties, mainly due to the different grain shape and surface structure. By using crushed aggregates, the void content and combined friction of the aggregate are higher than when natural grade aggregates with the same grain size distribution are used. To achieve the same consistency with crushed aggregates usually requires a higher percentage of the finer part of the combined aggregates and an increase in water. The increase in water leads to an increase in cement to achieve the same water-cement ratio. On the other hand, the bond between cement stone and crushed aggregate is stronger than that between cement stone and natural aggregate; the impact resistance of the crushed rock is also greater. At least in theory this allows for higher water-cement ratios to achieve some strength with crushed aggregates. Please note: this is just an example. Get a custom paper from our expert writers now. Get a Custom Essay However, it should be noted that the shrinkage and creep of hardened concrete depends on the volume percentage of the cement stone and the water-cement ratio; these deformations increase as the water-cement ratio increases. (Suomen Betoniyhdistys, 2005a, 46.)