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History, classification, processing, recycling, machinery, technology and applications

Aggregates

Caesar Luaces, technical director of the National Association of entrepreneurs manufacturers of aggregate (Anefa)22/01/2010

January 22, 2010

Arid-producing industry, i.e. sand or fragmented rock, is currently one of the basic sub-sectors of the Spanish mining and world. Without the construction of homes, offices, airports, hospitals, streets, roads, highways, railways and ports would not be possible, nor could have many industrial products of daily use.

Aggregates are material granular inert consisting of fragments of rock or sand used in the construction (building and infrastructure) and in numerous industrial applications. They are colloquially known as sand, gravel and gravel, among others.

Each Spanish consumed, without being aware of this, 11.650 kg per year, i.e. approximately 150 times its weight. Virtually all that a person can be seen to its around comes from a quarry or mine, with the exception of the coming of the worlds plant and animal (furniture, textiles...).

Normally, because of its characteristics and the large volumes used, aggregates are marketed in bulk in trucks with box (known as the 'baths' seen often on roads). Aggregates are mineral raw materials essential for the society. In general, it's cheap and abundant materials that exploit necessarily close to the centres of consumption, in order to reduce transport costs.

Depending on the application to which they are intended, aggregates must meet different characteristics associated to its petrográfica nature or the process used for their production, which include:

Geometric properties: size, shape of particles (for example, if they are elongated or not), faces of fracture, quality of the fine, etc.
Mechanical and physical properties: resistance to wear (for example, for cars no slipping on roads), resistance to fragmentation, polishing, density, porosity, content of water, etc.
Alteration and thermal properties: resistance to the ice and thawing cycles, etc.
Chemical properties: content in sulfur chlorides, organic matter, polluting light, potential reactivity, etc.

These properties are evaluated through a set of more than 50 test and standards specifications common to all countries of the European Union.

The adequacy of the control of production companies who develop is regularly verified by notified bodies with independent, by issuing a certificate certificate. Thanks to the control of the process, provides of contrasted quality products, after the continuing subjection of aggregates at laboratory tests, to determine if their properties comply with the requirements of the applications in those who are going to usewhich means that the manufacturing processes are perfectly controlled in its different stages. Since June 1, 2004, aggregates should be mandatory CE marking both for their marketing use. Therefore, every user has the right and duty to ask for the existence of this marking in the arid, as an indicator of compliance with the essential requirements laid down by the European Union.

Aggregates, for applications such as concrete or roads, are governed by official technical regulations known as EHE (instruction for structural concrete) and the PG-3 (roads).

Currently, many businesses in the sector have company of quality management systems registration, according to the standard UNE en ISO 9001-2000. Today, brands of quality for aggregates are being developed.

Classification

Aggregates can be classified by the type of rock from which they come, by the application to which they are intended and because of its size.

By type of rock

Depending on the type of rock, aggregates can be classified into the categories in the following table:

Natural aggregates can be obtained from:

Detrital deposits not consolidated, type sand and gravas, on farms known as like.
Through the grinding of massive rocks and consolidated type granite, diorite, limestone, quartzites, on farms, referred to as quarries.

Aggregates may have rounded forms, when it comes to flood that they are not subjected to crushing, or angular materials elsewhere in cases where there is crushing.

By type of application

Depending on your application, aggregates can be classified in the categories in the following table:

By size

In the size, aggregates are designated through the grading fraction comprised d/D between the lower size (d) and the upper size (D), for example, an arid 6/12 mm.

A journey through the history

Since antiquity, the aggregates have accompanied the development of human civilization. Indeed, since the beginning of time, man has used natural materials for the construction of its habitats and the management of their environment.

In the period ranging from ancient times until the Industrial Revolution of the 19th century, aggregates production was handmade by using manual means, breaking and chipping rocks with rudimentary as Maces and hammers tools.

To avoid its transport, aggregates were produced in the vicinity of the place where were to be used. At that time, a person could reach producing 125 tons per year. The end of the 19th century marked a revolution in the art of building, thanks to the emergence of industrial cement and concrete. At the same time, the creation of networks of railway, the infrastructure of roads and public works necessary to overcome obstacles, required the use of large amounts of economic and new materials.

Starts then the real boom aggregates as productive, dependent on sector greatly of the construction activity.

Throughout the 20th century, were developing new technologies that allowed increased production by incorporating the process of fixed and mobile machinery, each time with greater capacity. Thus, it has been growing the size of aggregate open farms, quarries and the like. Today, a modern exploitation can produce more than one million tonnes per year with approximately a dozen workers.

Evolution

At the beginning of the 21st century, extractive industry aggregates stands out as one of the most important, to provide society with primary natural resources for the economic development of mining. The growing professionalization is one of the goals of companies belonging to this sector, which are, increasingly, innovative technologies to optimize and control processes.

Currently, aggregates production is carried out within the framework of sustainable development, seeking to obtain quality products with consideration of the environment and the prevention of occupational hazards.

Processes of transformation and recycling

The treatment of aggregates process allows to obtain finished products suitable for consumption. It's a very automated process and technologically complex, because they involved a large number of disciplines. However, as its basic principle applies that is simple, as it is to grind the todo-uno coming from the exploitation to obtain smaller sizes and classify them in order to store separately each particle size. In some cases, it is necessary to wash the material to improve their characteristics. The basic steps are:

Scheme of exploitation of aggregates.

Crushing and grinding

Crushing and grinding can decrease, in successive stages, the size of the particles, using equipment of crushing of different features such as the of JAWS, the percussion, the rotating or the mills of balls or rods. In the sand and gravel of alluvial origin, only grind higher sizes and, therefore, the number of stages of crushing is usually less.

The classification

Between the stages of crushing, appear interspersed teams classification, the screens, which allow to select the size of the particles separating them between those who pass and which does not pass through the mesh. In this way, they are aggregates of all possible sizes, depending on the demand of the market.

Schematic of a sieve.

Washing

The operations of desenlodado and wash the material are made when the site is mud, clay or other substances that affect the quality of aggregates, and allow for dry clean in order to respond to the needs of certain applications in the industry, thus avoiding the alteration of the adhesion with the binders (cement, lime, obtained from bituminous or other) thereby proceed to its correct application.

The storage

At the stage of storage, thanks to the control of the manufacturing process, products of quality classified according to their particle size, that are stored in silos or in stacks in the open or covered, called stocks are already available.

The recycling of construction and demolition waste

In some cases, work of recycling of waste from construction and demolition (RCD) or casts of works from the building, the demolition of buildings and structures or civilian work (tunnels) may be possible.

Recycled aggregates suitable to be consumed, provided they meet the quality requirements for each of the different applications are available from the above-mentioned RCD. To this end, it is very important that the waste has been selected in origin, so to avoid the mixture of unwanted materials, which hurt the quality of the final product.

Machinery and technology

The process of aggregates production requires the use of a very robust, resistant machinery and large, to be able to handle large volumes of raw material demanded by society. Obtaining aggregates with the quality characteristics required by the market, is possible thanks to the control systems used are every day more complete and automated and may, at any time, regulate the production.

Startup and loading equipment

Boot and load operations are performed in quarries and like, primarily with mobile teams as you loaders on wheels, (front or vindicated) excavators and bulldozers, drills and crawler.

The drill performed, in quarries, boreholes filled with the necessary explosive for the blasting. The wheel loader is a team of versatile cargo by their great mobility and easy maneuverability, which is used, especially in the movement of land, either discovered or the restoration, in the load on the front and the load on the Park of aggregates of dumperstrucks and feeding hoppers. The hydraulic excavator is a widely used excavation and loading equipment which can be front boot, or retro. Used in the excavation of land, not consolidated materials startup and the burden of materials in dumpers, truck and feeding hoppers.

The dragline can extract the material when it is below the level of the water. Consists of a bucket which is suspended from a pen via cables, which allow launch it empty and pick it up with the sieve material. Finally, the bulldozer or tractor is used in the boot, pushing and stacking of the material for his subsequent loading and transport, in the clearing of the land and the thrust and widespread of filler material, not to mention work assistants as openingleveling and cleaning of tracks.

Transport equipment

Transport in quarries, and like operations are carried out with the dumper or the truck. The dumper, truck tipper (rigid or articulated), is the main means of transport on wheels in exploitation of aggregates and also in the public work. Use focuses on the transport of material uploaded on the front to its point of discharge hoppers, intermediate stocks or heaps.

The other vehicle, truck, is similar to the dumper, but of smaller dimensions and carrying capacity. Like this, it is used in the transportation of material uploaded on the front to its point of discharge, or hoppers, intermediate stocks heaps, and also in the external road transport to distribute products to end users.

The treatment plant equipment

Fixed process equipment used in a treatment plant for aggregates include hoppers, feeders, crushing and grinding equipment, conveyor belts, the screens, the silos, washing equipment, engines and pumpselectrical and control systems.

The growing application of the criteria linked to the sustainable development on farms can look to the future, with the confidence to face the new challenges demanded by society. Since the beginning of the operation until its closure, companies that produce aggregates should implement a number of techniques to prevent or minimize the effects of the activity on the environment.

Systems and equipment for the protection of the environment

The implementation of these measures will depend on the circumstances of each operation, because it is difficult to speak of universally applicable actions. The variety of equipment and techniques available is very wide, as examples, include:

Control systems of the dust (aspiration, sleeve filters and water spraying).
Systems for the protection against noise (screens and fairings).
Waste minimisation, collecting them selectively to the correct management.
Purification of water from washing, by sedimentation of solids in rafts or thickeners tanks, or by filtering.
Exploitation shielding to reduce the visual impact.

In addition, the restoration or recovery of exploited land, which is the last stage of the production process, aims refurbish the grounds in accordance with environmental quality guidelines, in order to restore the area to its environment. Restoration legislation obliges companies a:

Have a project of restoration of land approved by the competent authority.
To deposit a guarantee to ensure the realization of this project.

Applications and uses of aggregates

Aggregates used in considerable quantities in all areas of the building, either in housing, infrastructure, avenues of communication, equipment, or industry. However, this raw material is nothing known by the general public who, usually, uses or acquires the already finished goods where this raw material is already integrated and not in its natural state.

The use of aggregates in construction

Aggregates are the first raw material consumed by humans after water. Suffice it to say that each person consumes in his life about 850,000 kilos of aggregates, more than 10,000 times its weight, equivalent to carried in 32 trucks bath. Whether a highway, airport, or railway, the construction techniques require huge amounts of aggregates. The ballast for the railway, the foundations of the buildings, multiple layers, - linked or not linked-, which form the roads are essentially aggregates.

Applications of aggregates under construction.

The main applications in construction are:

Mortars; employees to join bricks or take walls. 1 cubic metre mortar contains 1.3 tons of aggregates.
Concrete; that can be structural (foundations, beams and pillars) or mass (pavements, etc.). For the manufacture of 1 cubic metre of concrete are needed between 1.8 and 1.9 tons of aggregates.
Prefabricated; as bricks, blocks, beams, curbs, sidewalks and pipes, among others.
Bases and subbases one ply plywood; What are the components of roads, freeways, streets, parking lots or tracks. About 30,000 tons are needed for 1 kilometer of highway.
Ballast; for construction of railways, and on which sit the sleepers and Rails. 1 km of railways requires some 10,000 tons of aggregates.
Stones and blocks of riprap for ports.
And other applications such as: dams, bridges, airports, streets, malls, amusement parks, housing, Fairgrounds, unique buildings, skyscrapers, tunnels and universities.

Industrial applications

In addition to being present in the construction, aggregates are also in countless items of everyday life. It is surprising to discover how many common objects have been produced with aggregates and in how many industrial processes are used. Aggregates are also applications to improve the environment: reduction of emissions of sulphur and the acidity of the soil and filters for purification of water, among others.

Intended for industrial uses aggregates require very specific properties, such as a greater purity in terms of their chemical composition, and a very small size (micronized), obtained through the fine grinding of materials.

Industrial applications of aggregates.

Manufacture of cement. 80% Of the cement is calcareous.
Ceramics and glass industry. 1 tonne of glass requires 700 pounds of very pure silica sand, 300 kilograms of limestone and dolomite, and 130 kilos of sosa.
Manufacture of steel. The limestone is used as a flux.
Abrasive materials.
Paper industry. 1 tonne of paper contains about 300 kilos of mineral load.
The plastics industry.
Detergents and paint industries. The limestone is used as a load in paintings and even as a pigment. In the manufacture of detergents, involved the silica sand.
Computer industry. The silica sand allows the manufacturing of components of computers.
Chemical and pharmaceutical industries. The finely ground limestone is involved in the composition of numerous chemical products such as the pulp of teeth, cosmetics or drugs.
Water treatment. Filtration of water for human consumption, wastewater treatment and neutralization of acid water.
Production of electric power. Loads for thermal power stations, desulphurisation of gases and dams for hydroelectric power.
Food. To manufacture 100 kg of sugar, they are required 20 kilograms of limestone. It is also used in the process of manufacture of bread, wine and beer.
Other industrial applications. Agricultural uses, correction of soils, fertilizers, additives for animal feed, filter beds, insulation and refractory coatings.