Adjusting the grain size distribution of the road sub-base ensures the optimal mix of particle sizes, eliminates errors associated with standard mixes, incorporates precise methods and quality control, and doubles the road’s load-bearing capacity and service life, thereby reducing maintenance costs.
The road sub-base is not merely a layer of crushed stone and sand, but the living foundation of the entire road; adjusting the aggregate mix allows it to adapt to loads, settlement and temperature fluctuations, preventing subsidence and cracks, and extending the road’s service life several-fold.
The gradation of a road sub-base refers to the ratio of particles of different sizes, ranging from coarse crushed stone to fine sand; adjusting this involves selecting the optimum ratio, whereby the larger particles form a rigid framework, whilst the finer particles fill the voids between them, leaving no free space for settlement.
In standard construction, ready-mixed aggregates are often used without taking specific operating conditions into account, which results either in an excess of fine particles, turning the sub-base into a soft layer under load, or a shortage of fine particles, leaving voids into which moisture seeps over time, causing structural damage when it freezes.
Modern technology involves the preliminary screening of raw materials into 8–10 fractions, laboratory load modelling for a specific route and the metered addition of missing particles directly at the laying site, which makes it possible to achieve a customised particle size distribution with a margin of error of no more than 2% for each fraction.
After mixing, rapid analyses are carried out on samples taken from different sections of the layer being laid, along with a ring test to check the density, to ensure that the resulting structure meets the design specifications; and any deviations are immediately corrected by adding the necessary fractions.
When carried out correctly, grading adjustment increases the subgrade’s bearing capacity by 30–40%, reduces the cost of routine maintenance during the first five years of operation by almost 60%, and extends the road’s overall service life from 7–10 to 15–20 years without the need for major works.
