Types of Aggregates Used in RCC Structures

The most commonly used aggregate size in construction is 20 mm, 40 mm and 75 mm. Aggregate size 20mm is used in RCC structures, 40mm aggregate size is used in PCC structures or mass concreting and 75mm and more size is used in retaining wall construction. Coarse-grated aggregates are all aggregates larger than 4.75 mm in size per piece. This includes boulders, cobblestones and gravel.

Fine or crushed gravel is usually 4 to 8 mm; medium or partially crushed gravel measures 8 to 16 mm; coarse-grained or uncrushed gravel measures 16 to 64 mm; pavers measure 64 to 256 mm; and rocks have anything above 256 In general, aggregate of diameter range of 9.5-37.5 mm is used in concrete work RCC. But the maximum size of the aggregate generally used on the site is 40 mm. For ease of compaction and workability, 10-15 mm aggregates are sometimes used on site. There are mainly two types of aggregates that are used in civil engineering construction work to prepare concrete. Concrete is employed for different purposes, such as foundations, pavements, etc.

About 40 to 80 percent of concrete is composed of aggregates. Therefore, the aggregates used in concrete must be free of dust, clay, organic materials such as vegetables, leaves, etc. They must be washed clearly with the aid of non-acidic water before use to prepare the concrete. Recycled concrete is a viable source of aggregate and has been successfully used in granular subbases, soil cement and new concrete. Aggregates are one of the most important components of concrete that give it body and also reduce shrinkage.

In your contract, construction or purchase agreement, the term “maximum aggregate size” refers to the smallest sieve that 100% of your aggregate can pass through. Only 15-34% of zone 1 aggregates will pass a 0.6 mm screen; 35-59% of zone 2 aggregates will; 60-79% of zone 3 will; and 80-100% of zone 4 will. It can be a single size material, typically 20 mm, 14 mm, 10 mm, or 7 mm, or a graded aggregate consisting of a single size aggregate mixture. When specifying void graded aggregates, certain particle sizes are omitted from the aggregate of the size continuum. Glass aggregate can replace some or all of the sand and gravel in concrete, for effects ranging from colorful terrazzo, to granite or marble finishes, to concrete that reflects light like a mirror. If you are looking for medium strength concrete, get 40mm aggregates, but if you are looking for high strength, 20mm is best.

The main natural resource is volcanic material, while synthetic aggregates are produced by heat or heat treatment of materials with expansive properties. Recycled concrete as an aggregate will generally have higher absorption and lower specific gravity than natural aggregate and will produce concrete with slightly higher drying shrinkage and creep. Therefore, if you are a civil engineer, you should know the different aggregate sizes while designing any structure such as a building, tunnel, bridge, or concrete road pavement. Leveling limits and maximum aggregate size are specified because these properties affect the amount of aggregate used, as well as cement and water requirements, workability, pumpability, and concrete durability. For reinforced concrete slabs such as bridge decks, deck slabs and columns and prestressed concrete elements the MSA (maximum aggregate size) is 16 to 20 mm. A mixture of all types of aggregates is suitable as a base for concrete in projects that do not require precise proportions of aggregate to cement.

However, the use of slag is no longer limited to roads but slag aggregates are widely used in all types of civil works.

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