Aggregates for Construction – How Are They Used?
Aggregates have the important role in giving the necessary strength for concrete. A concretes transition is the interfacial region between the paste of the cement and the aggregate and is the one which is responsible in providing the strength for the cement.
Aggregates have to be round and equiangular in size and must not be flaky and irregular. The use of angular aggregates are highly advised because this kind of aggregate comes with a good interlocking effect that gives minimum surface area and will require less mortar to cover the surface.
At the time of extraction of the aggregate, care needs to be taken in order to make the aggregate undergo sieve analysis or washing before it is going to be used. Because any presence of harmful materials that involves clay, silt or acidic salts could affect the strength and the durability of concrete, which will lead to inhomogeneity in composition and in the failure of the structure if this will be subjected to eccentric loading. There are some associations that specifies four grading zones for fine aggregates that are placed in order for decreasing particle size that starts from coarse sand and ending with fine sand. It is best that you don’t use fine sand in making RCC structures because they are porous and could cause corrosions in the reinforcement.
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Fine aggregates includes crushed natural gravel, natural sand and crushed natural stones and these particles must be able to pass through sieve openings for about 4.75mm, but the ones that are completely retained in it are the coarse aggregates that includes uncrushed gravel, stone and big boulders.
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Aggregates have to be inert chemically in nature and needs to be tough sufficiently, hard and needs to have good bearing capacities.
Aggregates that are well-graded and used in a cement mixture helps to reduce the presence of air voids and also helps in providing sufficient strength and durability to the concrete.
There are some tests which are carried out to some aggregates like impact tests, abrasion tests and soundness tests of aggregates that are done through dissolving them in a certain solution of sodium and magnesium sulphate.
To provide the necessary support for concrete dams which has a huge mass, aggregates which were formed by igneous rocks are the ones that are preferred highly.
Even when aggregates are commonly known as inert fillers in concrete, various properties of aggregates are able to give a large impact when it comes to durability, strength, workability and on the economy of concrete. Various properties to which aggregates have allows designers and contractors the most flexible option for them to meet their design and the construction requirements.