Which size of aggregate used in RCC structure?
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Generally the most appropriate size of aggregate used in RCC structure is 20mm. It gives more strength to the structure.
In ordinary structural concrete, the agg’s occupy 65 – 75% of the vol. of hardened mass.
The coarse agg’s should be easily fit into the forms & between the r/f bars. For this purposes, it should not be longer than:
Usually 40mm, 20mm, 12.5mm, 10mm coarse agg’s are used in common practices.
Up to 20mm of aggregate is used in RCC structures, because of ease in pouring of concrete due to increase in workability.
Vibration with the help of vibrating needle must be done in a good manner if the size of aggregate is from small to medium.
This reduces the forming of honeycombing structure and reduces voids. Makes the concrete structure stiff and compact.
The constraints for Nominal Maximum Size of Aggregate (NMSA) are follows
In general 20 mm is used as NMSA but use of 40 mm provides economy for substructures. For too congested structures 12.5 mm or 10 mm is also used. For PQC 31.5 mm and DLC 26.5 mm is considered. For mass concrete dams up to 150 mm is used. For shotcretes 8 mm is used.
It depends on the structure, whether there are steel reinforcement bars provided or it is plain concrete.
For concrete slabs with reinforcement as in bridge decks, roof slabs and columns, and prestressed concrete members, 16 – 20 mm is the MSA (maximum size of aggregate).
For roads, 38 – 40 mm MSA.
For retaining walls and abutments = 75 mm MSA.
For Concrete Dams – 75 mm near the face where there steel reinforcement provided and 150 – 200 mm MSA in the rest of the dam. Here concrete is poured by cranes from concrete buckets.
If the concrete is pumped by concrete pumps, then 20–25 mm MSA.
The max size of aggregates is limited to 20mm in RCC to make better compaction and workability.
Generally the 9.5-37.5 mm diameter range aggregate are used in RCC concrete work. But Maximum size of aggregate generally on site used are 40 mm. For ease of compaction and workability sometimes on site 10-15 mm aggregate are used.
Basically in cement concrete we used 10mm to 20mm aggregate,
And and PCC we may use 40mm rarely. In damp proof course we used 10 mm for better preventions again permeability and for slab, beam and column we use mixture of 10mm to 20mm.
40mm aggregate is used for PCC in foundation or base course in rigid pavement.
In IS 456: 2000,
As per Cl 5.3.3
As per Cl 18.104.22.168