Why in the concrete add gravel?
The strength of any stone is many times the strength of high quality concrete. Therefore, to improve resistance to weight and other loads in a cement-sand mortar added gravel. Such a concrete is called heavy. It lay rebar or other metal rods and manufactured concrete products: rings, building blocks, floor slabs, etc.
Crushed stone is a large aggregate, small is sand. From the strength of stone and type of cement used depends on grade of concrete. As the filler use the average fraction of gravel – 20/40 mm. It can be different strengths, depending on the type of rock, which are made. In some cases, the hardness of the stone can reach 1000 MPa or higher. This filler is used to manufacture concrete of the highest marks.
For laying in cement sand mortar suitable crushed Ferroalloy and blast furnace slag, copper and Nickel. It can be used to build the foundations and forming the building blocks. Before using gravel of this type shall be tested for the absence of radiation.
Another reason why the composition of concrete is crushed – a significant shrinkage of the cement during its solidification. The filler interferes with this process and not allow the cement to crack. In the construction work guided by the following rule: the greater the thickness of the concrete layer, the larger should be the fraction of filler. The amount of crushed stone or gravel the average shall be not less than 30% of the total volume of cement-sand mortar.
Has the meaning and form of crushed stone, laid in concrete. The closer to square, the more stones are placed in the solution. Therefore, he will be stronger. The cost of this material is slightly higher than conventional aggregates. When buying stones, pay attention to the percentage content of harmful impurities. There are rules that define allowable mineralogical composition of filler. According to them, the aggregates for concrete shall contain not more than 1.5% sulfites, 4% of pyrites, 1% coal, etc.
What is the rubble stronger?
The high strength concrete provides granite rubble. It has the best performance. But this stone one of the most expensive, so for laying in cement-sand mortar is used infrequently. Its more familiar use as a decorative element in landscape design.