Granite crushed stone: fractions, flakiness, strength grades and classes

Granite crushed stone is a bulk construction aggregate produced by crushing hard rock and then screening it into fractions. It is used in concrete mixes, road construction, foundations, drainage layers, reinforced concrete products and landscaping.

The quality of granite crushed stone is not determined only by grain size. When choosing the material, it is important to consider the fraction, grain shape, strength grade, frost resistance, water absorption, content of dust and clay particles, and radiation class. These indicators are usually listed in the quality passport or certificate for the batch.

Categories of crushed stone

Granite crushed stone is valued for its high strength, wear resistance and good frost resistance. These properties make it suitable for loaded structures and road bases. However, the exact area of use depends on the characteristics of the specific batch.

For concrete and road works, stable particle size distribution, low flakiness and sufficient strength grade are usually important. For drainage, the fraction size and the ability of the layer to pass water matter more. For decorative works, color, cleanliness and the appearance of the grains are also considered.

Fractions of crushed stone

A crushed stone fraction is a grain size range, for example 5-10 mm, 5-20 mm, 20-40 mm or 40-70 mm. Smaller fractions can fill voids more densely, while larger fractions are often used in bases, bedding layers and massive construction works.

The 5-20 mm fraction is often used in concrete mixes and reinforced concrete products. Fractions of 20-40 mm and 40-70 mm are used for road bases, drainage, bedding and large construction works. Fine screenings from crushing may be used in mixes, bedding and landscaping if their properties suit the task.

In practice, other sizes are also common, including 5-10 mm, 10-20 mm, 20-65 mm, 25-60 mm and fine screenings such as 0-5 mm. Naming can vary between suppliers, so an order should specify not only the fraction name but also the required grading according to the batch documents.

Flakiness and grain shape

Flakiness shows the share of flat and elongated grains in crushed stone. The lower this share is, the closer the material is to a cubical shape, the better it compacts and the more reliably it works in concrete mixes or road bases.

By flakiness, crushed stone is usually divided into groups. Cubical crushed stone has the lowest content of flat and elongated grains. Improved and ordinary crushed stone contain more such grains, so they may compact worse and require more careful selection for demanding work.

In standard practice, flakiness groups are often defined by the share of flat and elongated grains: up to 10 %, 10-15 %, 15-25 %, 25-35 % and 35-50 %. For concrete and road surfacing, lower flakiness is usually preferred, while less demanding bedding layers may allow softer requirements.

Grades of crushed stone

The strength grade of crushed stone shows how resistant the material is to crushing under load. In construction, grades range from low-strength options to high-strength materials such as M1000, M1200 and higher. The higher the grade, the more loaded the structures and road layers where such crushed stone can be used.

For landscaping and lightly loaded works, the requirements are usually lower. For concrete, road pavements, bridges and large reinforced concrete structures, materials with higher strength and confirmed batch test results are selected.

Classes of crushed stone

Frost resistance shows how many freeze-thaw cycles the material can withstand without significant loss of properties. This indicator is especially important for outdoor structures, roads and paved areas.

Water absorption affects how crushed stone behaves in wet conditions and during freezing. The less water the material absorbs, the more stable it is in base layers and concrete mixes.

Radiation class is important when choosing crushed stone for residential and public construction. For such works, material is used only if laboratory tests confirm that it is allowed for the relevant area of application.

How to choose granite crushed stone

Before buying, determine the purpose of the material: concrete, foundation, road, drainage, bedding or decorative work. Then select the fraction and check the strength grade, flakiness, frost resistance and quality documents.

If crushed stone is needed for critical work, do not rely only on the price and the fraction name. It is better to clarify the batch characteristics, certificates and compliance with project requirements in advance. This makes it easier to choose granite crushed stone that is suitable for the task and will not cause problems during use.