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Aggregates for cocnrete

A concrete mix consists of almost 65% of aggregates. Aggregates classified into fine and coarse aggregates. Since the aggregates form the majority of a concrete mix. The quality of aggregates can greatly affect the strength and durability of concrete. Aggregates can be natural or crushed aggregates. Used aggregates should be strong, hard, and it should not contain a large amount of organic matter or harmful material that can adversely affect the strength of a concrete mix. Aggregates will be tested to determine the chemical and mechanical properties. Various tests conducted on aggregates such as sieve analysis, soundness test, flakiness index, elongation index, Los Angeles abrasion, chloride content, organic content, and others. The chemical and mechanical properties can affect concrete properties. For example, alkali aggregates can react with cement in concrete and cause severe damage to a concrete structure. Los Angeles abrasion test aims to test the hardness, toughness, and abrasion resistance of aggregates. Hard and tough aggregates will produce concrete with higher abrasion and impact resistance. 
Figure 1

In general, aggregates used in concrete should have a specific gradation. Gradation is the particle size distribution. Concrete will be made from aggregates with a specific gradation, and the maximum size of aggregates should be specified. The maximum size of aggregates can range from 10 mm to 50 mm, 20 mm is the typical maximum size aggregates. Aggregates with size bigger than 5 mm (3/16 in) classified as coarse aggregates while the aggregates with a size smaller than 5 mm classified as fine aggregates. Well-graded aggregates will contribute to enhancing concrete workability and strength. Well-grading means lesser voids, and this means more cement paste is available to act as lubricants. Also, the shape and texture of aggregates are important, and it should be considered at the time of designing the concrete mixture. Recently a new type of aggregates known as lightweight aggregates used to produce lightweight concrete. The main advantages of this type of aggregates are the lower weight compared to normal weight aggregates.  


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