The difference in the methods of laboratory assessment of the quality of crushed stone according to GOST 32703-2014 and GOST 8267-93 is one of the urgent problems for Russian road builders. It was solved by a series of studies conducted in the laboratory of the BCC ROSDORNII in 2020. The specialists of the Institute have developed a methodology that allows classifying according to GOST 32703-2014 crushed stone produced according to GOST 8267-93. Mikhail Slavutsky, the head of the construction laboratory, told about this at the VII annual conference "The Rubble Market of Russia", which was held on June 9 and 10, 2021 at the Intercontinental Tverskaya Hotel in Moscow.
GOST 8267-93 "Crushed stone and gravel from dense rocks for construction work. Technical conditions" for a long time remained the main standard by which crushed stone producers worked in Russia and the countries bordering it. However, in June 2015, GOST 32703-2014 "Public automobile roads" was introduced in the field of road construction. Crushed stone and gravel from rocks. Technical requirements". At the moment, crushed stone manufacturers use both standards, which creates a problem when using products in road construction.
It consists in the fact that when defining granulometric composition of crushed stone of narrow fractions, its laboratory studies according to GOST 8267-93 are carried out on sieves with round holes, and according to GOST 32703-2014 – on sieves with square cells. Due to geometric differences, even with the same cell area, they have different throughput, which is reflected in the test results. At the same time, studies of grain compositions of crushed stone of different fractions indicate that there is no definite correlation between sieves with round and square cells.
To solve this problem in 2020, a series of studies based on a theoretical assessment of the size dispersion of crushed stone grains using the requirements imposed on crushed stone by regulatory documents was carried out in the laboratory of the BCC ROSDORNIA.
"Since crushed stone is a set of crushed particles of random size and shape, the possibility of sifting them through sieves with cells of various sizes implies certain restrictions on the size of the sifted crushed stone particles. However, within these constraints, the size and shape of the particles continue to remain random and correspond to the original size distribution of crushed stone particles. Exactly that this consideration justifies the possibility of carrying out a classification assessment according to a specific standard of crushed stone produced according to another specific standard," explains Mikhail Slavutsky.
As a result of a series of tests, a methodology for classification assessment according to GOST 32703-2014 of crushed stone produced according to GOST 8267-93 was developed. In its development, theoretically obtained dispersions of crushed stone grain sizes of different quality and different width of fractions were used. In particular, it was established the correspondence between certain fractions of crushed stone, classified according to GOST 8267-93, and mixtures of fractions according to GOST 32703-2014:
|
Fraction according to GOST 8267-93 |
Mixture of fractions according to GOST 32703-2014 |
|
5-10 mm |
4-8 mm |
|
10-15 mm |
8-16 mm |
|
15-20 mm |
11.2-22.4 mm |
Also studies have shown that the wider the crushed stone fraction and the lower its quality, the greater the value of particle size dispersion.
The conference "Crushed Stone Market of Russia" annually gathers industry participants from the Russian Federation and neighboring countries: manufacturers and suppliers of non-metallic building materials, consumers of crushed stone, equipment manufacturers and logistics companies. During the two days of the forum, its participants discussed the prospects for the development of the non-metallic materials market, the problems of providing crushed stone for road construction facilities, the requirements for stone materials for roads with high traffic intensity, considered the possibilities of using cement concrete in road structures and many other issues.