Information

granite crushed-stone (MACADAM)

Macadam refers to non-metallic construction materials.

Non-metallic materials – are materials of mineral origin, used in construction natively, without extracting certain minerals from them.

Crushed-stone of rocks is – in conformity with the GOST 8267-93 –non-organic discrete bulk material with particles larger than 5 mm, obtained by crushing rocks, gravel and boulder stones, produced overburden and enclosing rocks or off-standard wastes of mining plants on processing ores and non-metallic fossils of other industries and subsequent classification of crushing products.

Application

Crushed-stone consumers are enterprises, performing their activity in various segments of construction market. Depending on an enterprise’s specialization, crushed-stone may be used in various ways:

Plants of reinforced concrete products and constructions, house building factories, ready mix producers use it as a filler for concrete and ZhBI
Road-building organizations; organizations engaged in roads maintenance – use it for making motor road covers and bases
Organizations repairing railroads use it as ballast bed for rail tracks. Companies and businessmen, providing services in the sphere of landscape industry and landscape design use it for covering and bases of pathways and grounds.
Companies, providing works connected with housing and utilities infrastructure and land improvement use it for making coverings and bases of pathways and grounds.

Crushed-stone main features

The main features of crushed-stone on natural stone materials are:

Activity of natural radionuclide (radioactivity);
Grading and grain shape
Strength
Cold resistance
Content of dust and clay particles
True, medium and bulk densities

Additional features of crushed-stone on natural stone materials are:

Adhesion or adhesiveness (tractive resistance with bitumen)
Contents of impurities and chemically harmful additives, etc.

Macadam radioactivity

One of the most important features, which usually opens discussion of construction crushed-stone quality, is its radioactivity.

Natural radionuclides (NRN) – the main radioactive nuclides of natural origin, contained in construction materials: Radium (226Ra), Thorium (232Th), Kalium (40K);
Radionuclide volume activity (A) – ration of a radionuclide activity in the sample to its weight, Bq/kg
NRN volume effective activity (Aeff) – NRN total volume activity in the material, determined with taking into account their biologic influence on a person’s organism.

Aeff is a criteria for making a decision as for using crushed-stone in conformity with sanitary norms:

up to 370 Bq/kg – crushed-stone is applicable for all types of construction works (I grade)
Higher than 370 Bq/kg – it is applicable for road construction (II, III, IV grade)

Macadam grading:

By grain size crushed-stone is graded into fractions, for example: 5-10 mm; 5-20 mm; 10-20 mm; 20-40 mm; 25-60 mm; 40-70 mm; if agreed between consumer and manufacturer, other parameters and grain size can be set.

Grain size in each crushed-stone fraction, depending on its application, should correspond to technical requirements (GOSTs).

For example, for construction crushed-stone with fraction 20-40 mm (GOST 8267-93), requirements are the following:

Contents of 20 mm grains (d), % by weight – from 90 to 100%;
Contents of 30 mm grains (0,5(d+D)), % by weight – from 30 to 80%;
Contents of 40 mm grains (D), % by weight - up to 10%;
Contents of 50 mm grains (1,25D), % by weight – up to 0,5%.

Adhering to these requirements is reflected in grading.

MAcadam grains form

Crushed-stone has norms for containing grains of flaky and needle-like forms.

By grain form crushed-stone is divided into four groups (contents of flaky and needle-like grains, % by weight):

I group – up to 15%;
II group - from 15% to 25%;
III group - from 25% to 35%;
IV group - from 35% to 50%;

It’s necessary to note that “flakiness” is one of the most important features of crushed-stone quality. The lesser is flakiness, the higher is crushed-stone quality. The presence of flaky and needle forms leads to increasing intergranular openings in mixture. In its turn, it leads to increasing consumption of binding agent which causes additional financial expenditures.

Lately so-called “cubical” crushed-stone has been becoming more and more popular, in which contents of flaky and needle-like grains doesn’t exceed 15% (i.e. it refers to the I group).

The use of cubical crushed-stone assures the most dense ramming.

Macadam strength

Crushed-stone strength is characterized by initial rocks ultimate compressive (crushing) strength in a cylinder. This factor is imitated, for example, by stone material resistance at exposure to transport means going by the road or mechanical attacks during construction of road constructions (laying and compaction by rolling).

Depending on weight loss during tests, crushed-stone is assigned a certain mark: 200; 300; 400; 600; 800; 1000; 1200; 1400. The higher the mark – the stronger crushed-stone is.

Depending on rocks type and crushability mark crushed-stone has norms for contents of poor rock grains and is assigned a mark from 300 to 1400.

Macadam cold resistance

Crushed stone cold resistance is characterized by the number of freezing and melting cycles. It is allowed to evaluate crushed-stone resistance by the number of saturation cycles in sodium sulfate solution and drying. By cold resistance crushed-stone is divided into marks: F15; F25; F50; F100; F150; F200; F300; F400. The higher the mark is – the more frost-resistant crushed-stone is.

Factors of crushed-stone and gravel cold resistance is determined at testing by freezing and melting or saturating in sodium sulfate solution and drying. In construction mainly crushed-stone with strength mark not less than F300 is used.

Contents of flour and clay particles, contents of clay in globs:

Crushed-stone has norms for contents flour and clay particles (with a size less than 0,05 mm).

For all types and marks of crushed-stone by strength contents of clay in globs in the total amount of flour and clay particles shouldn’t exceed 0,25% by weight.

Bulk density

The amount of crushed-stone supplies is defined by volume or weight. Crushed stone measured in carriages and trucks.

Crushed-stone loaded in carriages and trucks is weighted with wage or truck scales. Shipped crushed-stone weight is determined by sea-gauge. Crushed-stone amount from weight units is recalculated into volume units by the value of crushed-stone bulk density, determined at its humidity during unloading.

Crushed-stone volume, delivered in a carriage or in a truck is defined by measuring, the obtained volume is multiplied by crushed-stone compacting factor at its transportation, which depends on loading method, transportation range, grading. The maximum admissible humidity value and compacting factor, which should be over 1.10, is stipulated in a delivery agreement.