Construction crushed stone: types, characteristics, use

Recommendation points

• The main parameter of crushed stone
• Crushed stone characteristics
• Frost resistance
• Strength
• Varieties of rubble
• Crushed gravel
• Limestone (dolomite) crushed stone
• Granite crushed stone
• Crushed slag
• Secondary crushed stone GOST 25137–82

The article presents the main characteristics of crushed stone as a building material. We will tell you about the difference between different types of crushed stone, what each of them is intended for. You will learn how to determine the main performance indicators (fraction, strength) depending on the purpose of the work.

Crushed stone is a building material obtained by crushing and sieving rocks, heavy industrial waste or processing. Represents separate stones of different sizes (fractions). It is widely used in construction as a structural and bulk material. A single crushed stone is called grain. The quality and scope of natural crushed stone is standardized by GOST 8267-93 “Crushed stone and gravel from rocks for construction work”.

The main parameter of crushed stone

Flakiness is the main indicator for crushed stone of any origin. It reflects the presence of relatively flat flat edges on individual stones. The larger these edges are, the higher the flakiness is considered. Grains with edges of a relatively large area are acicular (acicular) or lamellar. Other grains (with conventionally the same edges) are called cuboid. The operational properties of the mass depend on the percentage of the content of such grains, especially in the “dry” bulk form.

Crushed stone groups by grain shape

Group (characteristic)	Group (designation)	Lamellar and acicular grains content,%
Cuboid	1	Up to 15%
Improved	2	Up to 25%
Regular	3	Up to 35%

The ability to determine flakiness by eye will help when choosing crushed stone for your own needs. To do this, it is enough to know how this indicator affects the properties of the material:

1. Cuboid grains are better for compaction, resulting in a denser base. This is important when constructing a foundation cushion and filling under the road. They are also the most durable (compared to other forms).
2. The spiky grains create voids in the mass of the stone. When creating a concrete structure, more mortar will be needed to prepare the mixture, and the compressive strength will be slightly less.
3. At the same time, voids are useful for drainage. Providing sufficient packing density, crushed stone of the usual group removes atmospheric water.

Crushed stone characteristics

This material has two main performance indicators that you should be guided by when choosing for your own construction – frost resistance and strength.

Frost resistance

According to their resistance to freezing cycles, grains are divided into 3 categories. Marked with the letter F and a number indicating the number of freezing cycles:

1. Highly resistant. Brand F200, F300, F400. It is used for all types of critical structures, bridge supports, reinforced concrete products, high-rise construction, external dumping, offshore facilities and for the Far North.
2. Resistant. F150, F100, F50 brands. Used in construction in the southern regions and the Middle Lane.
3. Unstable. F50, F25, F15 brands. They are introduced as a bedding and drainage at a level below the GWL. Used for interior work and heated structures.

It should also be noted that laboratory studies of the frost resistance of crushed stone are carried out on a separate grain. In the structure (in concrete), the grain receives plus 30-40% to frost resistance due to the pressure inside the structure.

Strength

This most important indicator is determined by simulating the actual exploitation of the embankment – crushing, wear and crushing. Thus, the ability of the material to resist these influences is revealed..

Table of dependence of the field of application on the strength grade

Brand	Group characteristics	Application area
M1600 – M1400	Super strong	Foundations of bridge supports, towers, towers
M1400 – M1200	High strength	Bridge supports, foundations of high-rise buildings, embankments, hydraulic structures, towers
M1200 – M800	Lasting	Bearing walls of buildings, industrial structures, piles, columns, foundations, fences, supports, dumps for railway tracks
M800 – M600	Medium strength	Unloaded structures, walls, backfill, limited from 4 sides
M600 – M300	Weak strength	Unloaded dump, unloaded (open) drainage, filters, treatment facilities
M200	Very weak strength

The strength grade depends on the amount of impurity of weak rock in the mass of crushed stone. In this case, the prototype is subjected to a load of 20 MPa. Allowable content of weak rocks:

1. М1600 – less than 1%.
2. М1400 – М1000 – no more than 5%.
3. М800 – М400 – no more than 10%.
4. М300 – М200 – no more than 15%.

Rock with a weak rock content of more than 20% is called gravel and is mainly used for filling local roads, “change houses”, creating temporary structures and other irresponsible work. It is quite acceptable to use washed gravel as crushed stone in private construction (except for foundations).

Varieties of rubble

Each of the items has its own classification by strength, size, frost resistance and other indicators. We will focus only on practically useful aspects of the description..

Crushed gravel

This type of crushed stone is obtained by screening open pit rock and explosive mining of a stone rock. It is somewhat less durable than granite (limit grade M1200) and has an unsightly gray appearance. Moreover, its advantages are undeniable:

1. More quarries, competition.
2. Lower cost price (due to the spread of raw materials).
3. Easier to mine (granite is harder than rock).
4. Extremely low radioactive background.

At the same time, the limiting grade and other properties of crushed gravel make it possible to use it for critical structures in all sectors of the national economy. There are four fractions of this material:

1. 3-10 mm – elimination.
2. 5–20 mm – “seed”. Used for small-piece products (paving slabs, etc.).
3. 5-40 mm – used for medium-sized factory products – concrete and well rings, curbs, lintels, etc..
4. 20–40 mm – the main material for the production of concrete and road filling.

Limestone (dolomite) crushed stone

Calcite carbonate (CaCO₃), compressed by time to a state close to a rock mass. According to the main indicators, it is identical to gravel. It is used for concrete products and road construction. Distinctive feature – white.

Granite crushed stone

Obtained by explosion of a granite massif, crushing and sifting the mass. In most cases it has a red tint. The torn edges of the grains provide the best adhesion to the mortar. The shiny texture gives a good appearance to polished monolithic floors and other concrete products on crushed granite.

This type of crushed stone is recognized as the most popular because it has the highest strength. Accordingly, enterprises offer the largest assortment of sieving fractions – from 0–5 mm to 70–120 mm. There is a whole range of applications for each faction..

Crushed slag

This material is the result of crushing and screening of metallurgical dump slags and melts. Concrete products based on this crushed stone are 20-30% cheaper than conventional ones.

Secondary crushed stone GOST 25137–82

Material that is obtained during the targeted processing of construction waste. It is produced in the same way as natural, only it is not a piece of rock that acts as a raw material, but a monolithic element. After the primary split, steel elements (reinforcement) are removed from it, then it is sent to the screen.

Such material could save a lot of money: energy costs are up to 8 times lower, and the cost of concrete with such crushed stone is 25-30% less. Artificial crushed stone is on sale 2 times cheaper than granite. Although its strength and frost resistance are inferior to natural ones (maximum M800 and F150), there are many areas of application for such indicators..

Having the necessary knowledge about the choice and merits of different types of crushed stone, you can accurately determine its quality and acquire exactly what you need..