Stone powder

Subbase is in fact the second stage of road construction operations after compaction. At this stage, a layer of building materials and stones and adhesives, each with its own rules and regulations, are poured on the road surface and beaten by special machines.
It should be noted that the stones used in this layer have criteria such as the appropriate size and also the residue on the sieve number 4. Also, materials and adhesives should be made of high quality materials and according to their rules. The reason for the high importance of this layer is that all the loads of the cars that are transported are on this layer and must be made very durable and well.
After making this layer and also pounding it to achieve high density, a sample of this layer will be randomly selected and taken to the laboratory. It should be noted that for most road construction projects, a field laboratory will be built on site.
After the subbase layer sample has been tested and the required density percentage has been obtained, we can perform the next steps of road construction, but if the density percentage obtained from the test sample is not acceptable, the project engineer must give the order to repeat the density. Until the layer reaches the desired density.
However, it should be noted that the same layer of road construction sub-base has many types and in accordance with the conditions of the land and its nature, as well as the amount of traffic passing through this road, each type of sub-base is suitable for some of these conditions. Here are some common types of subbases.
1. Subbase consisting of sand in the riverbed
2. Subbase composed of rock or broken rocks
3. Subbase consists of lime, cement and bitumen, which is known as a substrate.
I must say that even the type of granulation of the materials used must be exactly according to their specific criteria. Here are some of the criteria. The first is that the largest size of stones or material in the base layer should be about 2 inches in size. The second case is that after the density test, the dough limit test should be performed and the number obtained should be about 6. Also, a psychological limit test should be performed for that sample and the obtained number should be about 25.
At least 30 must be obtained to test the sand value. But these experiments, if it is the type of important and main way, have become much more and have many criteria that we do not have time to express in full in this article. The reason for the large number of these experiments is that this layer, as mentioned in the above lines, is very valuable and it can be said that it is the most important part of the road. Here I need to say that this layer is known as the base layer.