No fines concrete is one type of light weight concrete. As the name indicates, this a concrete mix without fine aggregate or sand. This type of concrete consists of only water, cement and coarse aggregate.
Important Notes on No fines Concrete
Normally coarse aggregates passing 20 mm sieve and retained on 10 mm sieve is used for production of this type of concrete.
The aggregates to cement ratio of no fines concrete generally vary from 6:1 to 10:1.
The water cement ratio is kept within the range of 38 to 0.52. Water cement ratio should be chosen very carefully considering the cohesiveness of the mixture.
Density of no fines concrete with normal aggregate vary from 1600 to 1900 kg/m3. When light weight aggregates are used density can be as low as 300 kg/m3.
No fines concrete exhibits less drying shrinkage as compared to ordinary concrete
Movement of water due to capillary action is negligible in this type of concrete.
Due to its light weight nature it is used in light weight concrete construction work.
Thermal insulating characteristic of no fines concrete is better than conventional concrete. This is why it is used in the construction of external wall.
Production of this type of concrete results in saving of material requirement. Due to absence of fine aggregate or sand, less amount of cement is needed to produce 1 m3 of no fines concrete.
The density of this type of concrete is about 25 to 30% less than the conventional concrete. Therefore it exerts less pressure on formwork.
Segregation property of this type of concrete is very low. Therefore it can be dropped from considerable height without the danger of segregation.
No special equipment is needed for compaction of this concrete. Full compaction can be achieved by simple rodding operation.
Limitations of No fines Concrete
Due to absence of fine aggregate, this type of concrete lacks cohesiveness while in plastic state. Therefore it requires long time for formwork removal.
It is more permeable than conventional concrete. Therefore walls constructed with no fines concrete needs an extra coat of mortar from durability point.
Generally reinforcement is not recommended in this type of concrete. However, if it is required to used reinforcement, then apply a thin layer of cement paste on the reinforcement before using it. This will improve the bonding of steel with concrete and also resistance to corrosion.
There exist no standard test method (such as slump or compaction factor) test to measure the consistency or workability of no fines concrete. Only by proper visual inspection and trial & error method on can judge its workability.