Aggregate types and sources

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Types of Aggregates:

Aggregate is the fundamental component in the construction of concrete structures. It is the concrete material other than cement. The large portion of the concrete mixture consists of aggregate. The actual mass of the concrete structure is composed of aggregate. The only purpose of cement is to bind the different types and sized aggregate to bind with one another. Aggregate consists of stone, boulder, sand, slag, gravels, and other admixtures. The difference between aggregate and cement functions is; an aggregate acts as the composition-material of concrete, while the cement is the binding material for aggregate and the reinforcing material. The body of the structure is composed of aggregate and reinforcing material. Cement acts as jointing these two things.

  1. Crushed Stone and Manufactured Sand: Crushed stone and sand are the naturally found aggregate. In mountainous, hilly, and streams, this type of aggregate is available in large quantities. By the erosion, weathering, and denudation of bed rocks, this type of aggregate is obtained. It is the cheapest (cost-wise) type of aggregate.
  2. Gravel: Small pebbles of stone of size ranging from 1 cm to 1 inch are called gravels. Gravel is obtained from natural sources as well as from the crushed stones. Gravels are the basis of the concrete structure. Gravel is added with other types of components to form a concrete mixture. 
  3. Boulder: The difference between the boulder and the gravel is their size difference. The boulder is used in the construction of larger structures like roads, bridge abutments, dams, canal beds, and other types of larger structures. Boulder is either used with or without gravel. The size of boulder ranges from 1 inch to several inches depending on type of structure to be made of it. 
  4. Sand: Sand is the name of fine crystal particles of glass sand. Sand is composed of 88 to 99 percent of Silica. Sand is used to fill the gaps among the gravels and boulders. Sand mixed with cement and admixtures, flows and sinks through the gaps among the stone pebbles, gravel and boulder. The liquid mixture of sand cement has an adhesive quality, which sticks with the surface of gravels and holds them tightly. 
  5. Light Weight Aggregate: Light weight aggregate, as the name mentions, are lighter than the stone/rock aggregates. These can be obtained from the natural resources as well as can be man-made. These types of aggregate are made up of gravels of sedimentary rocks. Lower compacted sedimentary rocks are lighter than fully compacted sedimentary rocks, igneous rocks and the metamorphic rocks. This type of aggregate has lesser specific gravity, thus the structure composed of this type of aggregate, has less dead weight. However, the strength of the concrete structure is not impacted by its low weight. Strength remains high as desired. The light weight aggregate is porous and pervious to the cement grout. The permeability allows the cement grout fully absorbed in the aggregate, resulting higher strength.
  6. Recycled Concrete Aggregate: Recycled concrete is obtained from the broken concrete pieces of an existing concrete structure by breaking, removing, and crushing it. It can be used as aggregate in new concrete structures. Generally, the based layer, like floor and laying foundation, is constructed by the recycled concrete aggregate. The recycled aggregate has, comparatively, higher absorption quality. If properly not soaked with water, it can cause higher drying shrinkage. Another drawback of this type of aggregate is the large quantity of chloride. The excessive quantity of chloride is concerning. The chloride concentration can result in corrosion of reinforced material. 

Where the Aggregate is extracted from?

  1. Rock Quarries: 

Quarry is place which aggregates, rocks, sand and mineral are extracted by means of collection and excavation. The biggest source of obtaining aggregate is the rock quarries. Rock quarries are natural sites, enriched with all of the above mentioned materials.

  1. Crushing Plant:

The crushing plants are the artificial method for obtaining the concrete gravels. The crushing plants crush and grind the large sized stones into boulder, gravel of large and fine sizes, coarse and sand. Today, the crushing plants are meeting 60 % aggregate demand for the construction all through the globe.

  1. Sand and Gravel Quarries:

Natural streams in the hilly and mountainous areas are enriched with sand and gravel. Sand and gravel, being the fundamental constituents of civil construction are obtained from natural quarries.

  1. Marine Aggregate:

Marine aggregate is obtained from coasts of seas and continental shelves. Marine aggregates are the gravels and sand dredged from the sea bed. However, the aggregate may also be obtained from the land/continental land.

Washing and Cleaning the Aggregate: 

Aggregate in clean and washed form is essential for durable and strong construction work. Generally, aggregates are not found in clean form. The surfaces aggregate gravel are found covered with dirt and lime and other types of impurities, which negatively influence the binding characteristic of the concrete. Water is used as primary tool for cleaning and washing the aggregate material. Water is poured on the gravels and sand, to wash out the clay, silt and organic matters from them.


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