Construction Aggregate means
Aggregates are the important constituents in concrete.
Aggregates meaning from the Latin verb aggregare, which means to add to. As a verb it means to collect into a mass or wholehence the main function of aggregates is to give the body to the concrete such as 70 to 80 percent of the volume of concrete, to reduce shrinkage, and makes our concrete economical. Mostly they are chemically inert but some of the aggregates are chemically active. Without the study of the aggregate the study of concrete is incomplete.
Source of construction aggregate
we get aggregate from the bedrocks. Bedrocks can be of three types namely igneous rock, sedimentary rock and Metamorphic rock.
Types of Rocks
Igneous rocks are formed by the cooling of molten magma or lava at the surface of the crest (basalt or trap ) or deep beneath the crest ( granite ). Most igneous rocks make highly satisfactory concrete aggregates because normally it is hard tough and dense these rocks have entirely crystalline, massive structure or wholly glassy or in between depending on the cooling rate during formation. Igneous rocks are widely available rocks on the earth. Depending upon the percentage of silica content it may be acidic or basic.
Sedimentary rocks are formed below the sea bed and subsequently lifted from the bed. Weathering agencies such as sun, rain, and wind decompose, fragments transport and deposit the rock particle deep beneath the ocean bed where it is cemented by some of the cemented material. Cementing material could be siliceous, carbonaceous, or argillaceous in nature. These deposited rock and cemented materials are subjected to the static pressure of water and become compacted/consolidated. Deposition and consolidation takes place layer by layer beneath the ocean bed. The quality of aggregates derived from sedimentary rock depends upon the cementing material and the applied pressure.
Igneous or sedimentary rocks, subjected to high pressure and temperature which causes metamorphism. Due to extreme heat and pressure, the structure and texture of igneous or sedimentary rocks change completely. Mostly metamorphic rocks show foliated structure. The thickness of foliation may be different for different metamorphic rocks. For the production of aggregates in concrete, we use quartzite and gneiss rocks.
Classification of Aggregates
Aggregates can be classified into three types as per weight/density: The first one is Normal weight aggregate second one is Light Weight aggregate and the third one is Heavyweight aggregate. Further classification of normal weight aggregate is natural aggregates such as Sand, Gravel, Crushed rock such as Basalt, quartzite, Granite, sandstone, etc and artificial aggregates such as Broken Brick, Sintered fly ash, Air-cooled Slag, Bloated clay, etc.
It can also be classified on the basis of the size of the aggregates as coarse aggregate and fine aggregate