Strength-Testing of Crushed Stone: Lab Verification of Road-Building Material

Incorrect selection of crushed stone grade can lead to deformation of road bases and pavement failure. This is especially critical for high-traffic roads. Our article examines how crushed stone strength is tested in laboratories, what grades exist, and which applications they are best suited for.

How to measure strength

Crushed stone strength is its ability to resist compression, mechanical loads, and abrasion. This parameter directly affects the reliability of road bases and concrete structures. It is therefore crucial to understand which specific grade is required for your project during the design phase.

To determine the grade of crushed stone, it is tested for resistance to crushing — the ability of the material to withstand destruction and compression under external mechanical loads. The testing techniques are strictly regulated by state standards.

Key stages of laboratory tests for crushing resistance:

• A sample of crushed stone is placed in a steel cylinder with a plunger and compressed using a hydraulic press until the specified load is reached,
• Mass loss is measured, or the amount of fines generated relative to the original sample weight,
• The percentage of crushed particles is calculated using a formula,
• The result is checked against GOST (State Standard) reference tables, which specify crushing strength values for each grade and type of crushed stone.

Testing is conducted in two conditions:

• Dry state — the sample is dried to a constant mass,
• Water-saturated state — the sample is soaked in water for 2 hours.

This allows for an accurate assessment of the material's behaviour under real-world conditions.

What strength grades mean

The test result yields a strength grade, denoted by the letter “M” followed by a numerical index. The grading scale ranges from M200 to M1400. The higher the index, the stronger the material.

High strength enables the use of crushed stone for:

• Construction of reinforced concrete structures and foundations,
• Road construction (as base material and for asphalt concrete mixes),
• Bridge piers, hydraulic facilities, and heavily loaded concrete elements in high-rise buildings (these applications require the strongest crushed stone).

High wear resistance is particularly important for the upper layers of road surfaces, as crushed stone is subjected to daily abrasion under heavy traffic.

Strength of blast-furnace slag aggregate

BF aggregate is crushed stone obtained by crushing and screening of steelmaking by-products. Key advantages include high strength, frost resistance, good compaction in various structural layers of road pavements, exceptional bonding properties, and a competitive cost compared with natural aggregates.

Crushed stone grades:

• M800–M1000 — the most common high-strength grades,
• M400–M600 — widely used in structural layers of road bases (the material’s activity allows for reduced layer thickness, and the optimal grain size distribution facilitates compaction).

BF aggregate is available in a range of size fractions, as well as in crushed stone and sand mixes. Active mixtures based on blast furnace slag exhibit an increased modulus of elasticity and are more cost-effective compared to aggregates derived from sedimentary and igneous rocks, as confirmed by regulatory standards.*

Need help selecting the right grade for your project? Andrey Ryabov, Head of Development for Bulk Materials, will advise you on choosing the right BF slag aggregate grade for your specific objectives.

Contacts for your inquiries:

Phone: +7 (980) 192-88-89

Email: ryabov_am2@nlmk.com

For more information about the properties and applications of NLMK bulk materials, please visit the dedicated section on our portal.

* According to GOST 71404-2024 “Roads of General Public Use. Semi-Rigid Pavements. Design Rules” (Order No. 1022-st of 05.08.2024, effective from 01.09.2024, with provisions for early application).