what is asphalt aggregate and different types to be used
Sand, gravel, and crushed stone are examples of different types of aggregates, which are mineral materials that are combined with a binding agent (such as water, bitumen, Portland cement, lime, etc.)
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to create compound materials such as asphalt to be used in pavement.
The name "aggregate" refers to what is called to be used in these mineral components as a group (such as asphalt concrete and Portland cement concrete).
Aggregate is typically responsible for 92 to 96 percent of the volume of HMA and around 70 to 80 percent of the volume of Portland cement concrete.
Additionally, aggregate is utilized in the construction of flexible and rigid pavements' base and subbase courses.
Both natural and synthetic aggregates can be used in construction.
The majority of the time, natural aggregates are removed from bigger rock formations by the use of open excavation (quarry).
Crushing the extracted rock into smaller, more manageable pieces is often the method used.
Aggregate that has been manufactured is frequently a waste product of other types of manufacturing enterprises.
This section will begin with a brief discussion of aggregate sources and mining operations.
After that, it will describe the fundamental mineral, chemical, and physical properties of aggregates that are most important to pavements, as well as the typical tests that are used to determine these properties.
The source listed below is where you may find more specific information regarding aggregate:
Aggregate sources
Aggregates can originate from either naturally occurring or artificially produced sources.
Rock is the source of natural aggregates, which can be divided into the following three categories according to geological principles:
Igneous rock
The crystallization of molten rock material beneath the crust of the earth results in the formation of these rocks, which are predominately crystalline (magma).
Sedimentary rocks
These rocks are the result of the deposition of material that is insoluble (e.g. , the remains of existing rock deposited on the bottom of an ocean or lake).
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Through the application of heat and pressure, this substance is converted into rock.
The appearance of sedimentary rocks is that of layers, and they are further classed according to the major material that they contain as either calcareous (such as limestone or chalk), siliceous (such as chert or sandstone), or argillaceous (shale, etc.).
Metamorphic rock
There are two types of rocks that can be metamorphosed: sedimentary and igneous.
Metamorphic rocks are formed when sedimentary or igneous rocks are subjected to heat and/or pressure that is sufficient to alter the mineral structure of the rock.
Rock that has been manufactured typically consists of industrial byproducts such as slag (a byproduct of the metallurgical processing that is typically produced from processing steel, tin, and copper) or specialty rock that has been produced to have a particular physical characteristic that is not present in natural rock (such as the low density of lightweight aggregate).
Aggregate Production
The production of aggregates typically takes place in a quarry or mine (Figure 1), the primary purpose of which is to transform the native rock into aggregate with the desired properties.
In most cases, the rock is reduced in size by first being blasted or excavated out from the walls of the quarry, and then being processed through a succession of crushers and screens.
Some quarries also have the capability of washing the aggregate once it has been extracted.
Mineral Qualities and Traits
The kind of minerals that make up an aggregate is the primary factor that decides both its physical properties and how it performs as a material for paving.
Because of this, knowing the mineral qualities of the quarry rock can provide an excellent indication as to the suitability of the aggregate that is produced, which is something that should be considered when choosing a source of aggregate.
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It is difficult to make an accurate prediction regarding the behavior of a given aggregate source based solely on the mineral properties of that source since the interactions between mineral and physical qualities are typically highly complicated.
Chemical Qualities and Traits
The aggregate's chemical qualities are vital to the success of the pavement material, despite their relatively little significance for loose aggregate.
When it comes to hot-mix asphalt (HMA), the chemistry of the aggregate surface might influence how effectively an asphalt cement binder will stick to the aggregate surface.
Inadequate adhesion, also known as stripping, can lead to the premature failure of a structure.
In Portland cement concrete, aggregates that include reactive forms of silica have the potential to react expansively with the alkalis that are present in the cement paste.
As a result of this expansion, cracking, surface pop-outs, and spalling may occur.
It is important to keep in mind that some of the chemical properties of aggregate might change with time, particularly after the aggregate has been crushed.
It's possible that crushed aggregate that's been sitting in a stockpile for a year will have a different affinity for water than the same aggregate that's been freshly crushed and stored away.
Stripping and alkali-aggregate reaction are two examples of typical chemical properties that can be tested for aggregates.
Physical Properties
The aggregate features that are most immediately evident to the naked eye are the physical properties of the aggregate.
These properties also have the most direct influence on how well aggregate functions either as a component of a pavement material or all by itself as a base or subbase material.
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Physical aggregate properties that are commonly measured include gradation and size, toughness and resistance to abrasion, durability and consistency, particle shape and surface texture, cleanliness and harmful elements, and moisture content.
Gradation refers to the size distribution of the aggregate, while the size refers to the aggregate's overall dimensions.
These are not the only qualities of aggregates that can be measured, but rather the ones that are most frequently done so.
The majority of the tests that are used to quantify these features are empirical.
Alterations in an aggregate's physicochemical qualities are possible with enough time passing.
For example, a freshly crushed aggregate could have a higher dust content, making it less susceptible to being bound together with asphalt glue.
It is common practice to employ aggregate all by itself as an unbound base or subbase course.
When put to use in this capacity, aggregate is often characterized by the physical attributes listed above, in addition to the overall layer stiffness.
The tests that are used to define the subgrade's stiffness can also be used to characterize the layer's stiffness.
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