The term aggregate or granulate is understood to be a crushed stone of a certain size. The aggregate can be natural or artificial. The natural aggregate originates when the running water, glaciers and the wind carry and deposit pieces of a decomposed rock far away from the place of origin. A material of sharp or rounded edges is thus produced and is called gravel or sand.
Gravel and sand can be from a river or from a quarry. Grains of river gravel and sand have rounded edges due to mutual hitting and hitting of waves onto the river bottom and due to a long transport in the river bed. They consist mainly of quartz, which, as the most resistant, does not decompose and remains undissolved.
Mountain or quarry gravel and sand are formed by decomposing of rocks and their transport down the slope to the foot of the mountain, due to the wind and the effects of the atmosphere. The grains of this aggregate have sharp edges. They are not always clean. They contain a lot of clay, which either covers certain grains or is free in the form of dust.
Artificial aggregate is obtained by crushing and grinding of granite, porphyry, quartz, limestone and other rocks. This aggregate has sharp edges as well as mountain aggregate, but it is of a better quality. It is cleaner and its grains are not affected by the decomposition process.
The difference between gravel and sand, whether natural or artificial, is in the grain size. Grains of 0 to 4 mm are referred to as sand, and from 4 to 31.5 mm gravel. By means of sifting through a series of sieves, certain groups of grains of approximately the same size are obtained. These groups are called fractions. The following fractions are applied: 0 to 4mm, from 4 to 8mm, from 8 to 12mm, from 12 to 16mm, from 16 to 31.5mm. A single fraction is a grain material that passes through a sieve with large openings, which is located on the upper part and remains on the sieve with smaller openings on the lower end. Thus, for example, a fraction of 8 to 12 mm represents a material that passed through a sieve with openings of 12 mm, and remains on the 8 mm - opening sieve.
River sand and gravel are taken out from the riverbed by machines. The places where the river aggregate is stored is called separation. There is also the sifting and separation of gravel by fractions. From there, they are transported by means of transport to place where they will be used.
Gravel and sand are used for making concrete, in the construction of roads and streets, for the production of various types of plaster, for filling, as a preparation for a foundation, etc.
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