Specialists from Perm Polytechnic University (PNIPU) and St. Petersburg Mining University have developed a method for calculating the maximum density and optimal moisture content for mixtures of sandstones and argillites. This was reported in the press service of the Ministry of Education and Science of the Russian Federation. The method allows forming a stable compacted mixture with specified properties on site, suitable for road construction. Builders strive to maximize the use of local soils, but in their pure form they are usually not suitable for foundations, so they are mixed with imported cement or lime. The new method provides an accurate recipe for such a mixture.
How PSU found the optimal proportion
Argillites are solid, rock-like rocks formed from clay. Scientists tested a series of samples in which sandstone and argillite were mixed in different proportions. Each mixture was compacted according to GOST 22733, simulating the process of soil compaction in real conditions — during the construction of an embankment or road surface. Key indicators were measured: optimal moisture content and maximum density.
The results showed that there is an optimal proportion at which the mixture will have maximum density. This effect is achieved with an argillite content of 40% to 50%. This is explained by the fact that small clay particles fill the voids between larger sandstone particles. The result is a dense, homogeneous mass
The accuracy of the density forecast using the developed method exceeds 99%.
Economic effect and practical application
According to preliminary estimates, for a large infrastructure project of a 50 km long road, builders will be able to save about 300–400 million rubles on transportation costs due to less imported crushed stone and other materials. Savings are achieved through the use of local soils (argillite and sandstone) in optimal proportions, which reduces the need for imported components.
Traditionally, during road construction, the soils on site often do not meet the density requirements, and they have to be either replaced with imported ones or strengthened with cement or lime. The new method gives engineers an accurate tool for calculating a mixture of local materials, which, after compaction, will have the specified characteristics. This is especially true for remote regions, where the delivery of crushed stone and cement accounts for a significant part of the estimate.
For the road industry, the introduction of the method means a reduction in construction costs by 10–15% by replacing imported materials with local raw materials. In addition, the load on transport logistics is reduced and the volume of quarrying is reduced. Accuracy of more than 99% allows designing road bases with guaranteed parameters, which increases the durability of the pavement. The method can already be used in the design of highways in regions where sandy-clay rocks are common — in the Urals, in Siberia and in the Far East.