What is No-Fines Concrete?

What is No-Fines Concrete? .No fines concrete is a very lightweight type of concrete that does not contain fine aggregate (or sand) in the concrete mixture. This type of concrete is formed using ordinary Portland cement, water, and coarse aggregate.

In most cases, coarse, evenly sized aggregate is used to create no fine concrete between small bracket sizes. No fines concrete is becoming more popular every day due to its many advantages over traditional concrete. This type of concrete is lightweight due to the addition of large voids, and the overall appearance of No fine concrete is also aesthetically pleasing.

Read More : What Are The Types Of Concrete Finish?

Standard Mix Concrete

Standard concrete contains a mix of coarse aggregate (gravel), fine aggregate (sand) and cement.
Water is added to the mix before it is poured. After pouring, the wet concrete will normally be vibrated or tamped down to remove any air gaps or voids in the wet mix. This causes the sand and smaller fine particles to fill any gaps between the larger pieces of gravel. The mix will then set to form a dense mass of heavy, solid concrete, without visible air holes or pockets. Standard concrete containing fines, is laterally much stronger than no fines concrete.

Key Components of No-Fines Concrete

1. Cement: The primary binder used to hold the aggregates together.
2. Coarse Aggregates: Typically, gravel or crushed stone is used, ranging from 10 mm to 20 mm in size.
3. Water: Added in precise quantities to ensure adequate hydration of the cement.
4. Absence of Fine Aggregates: The exclusion of sand or other fine particles creates its porous structure.

Properties of No-Fines Concrete

No-fines stands out due to its unique properties:

• Permeability: Its open structure allows water to pass through, making it an excellent choice for drainage systems and flood-prone areas.
• Lightweight Nature: It is significantly lighter than traditional concrete, reducing load demands on foundations.
• Strength Characteristics: While its compressive strength is lower than conventional concrete, it is sufficient for non-structural and specialized applications.

Read More : What Is Self-Compacting Concrete?

Mix Proportion of No-fines 

No fines concrete is mainly made of coarse aggregate that passes through a 20mm sieve and is retained in a 10mm sieve. The density of No fines concrete is as low as 300 kg / m3 for light aggregates and typically 1600 to 1900 kg / m3 for regular aggregates. Its compressive strength can be greater than or equal to 4Mpa and less than 14 Mpa.

The aggregate-to-cement ratio of this type of concrete generally varies from 6: 1 to 10: 1, and the water-cement ratio is used in the range of 0.38 to 0.52. The water-cement ratio must be carefully selected to accommodate the cohesiveness of the concrete mixture. Unlike traditional concrete, which derives its strength primarily from the water-cement ratio, the strength of no-fines is controlled by the aggregate ratio and weight of the concrete as well as the water-cement ratio.

If the ratio of water to cement is too small, the concrete mixture will be very dry and the aggregate will not bond properly to the concrete paste and the adhesion between the particles may be reduced. If the assumed water-cement ratio is too high, the concrete binding paste will move to the bottom of the concrete, especially when vibrating, thus filling the space between the aggregates and making the bottom denser than the rest. Even in this case, the paste is very lean and the adhesion between the aggregate and the paste is very poor.

There are no standard procedures for measuring the consistency of no-fines , such as the slump test and compaction factor test. To measure the consistency of no-fines , the water-cement ratio is determined by an experienced engineer through visual inspection and trial and error.

No-fines concrete can be easily compressed with a simple tamping rod, without the need for mechanical compactors or vibration methods. The load on the formwork when casting No-fines concrete is also significantly reduced. This is because the particles do not flow and are present on the surface at specific points. Therefore, the side formwork can be removed early.

No-fine concrete has a very low adhesive strength compared to conventional concrete, so it is not used in combination with reinforcing materials. However, if the No-fines needs reinforcement, the reinforcement should be properly coated with best cement paste before being placed in the mixture to improve adhesion and prevent rust.

Read More : Concrete Hollow Blocks

Types of No-Fines Concrete Applications

1. Residential Construction: Used in non-load-bearing walls and insulation layers.
2. Road and Pavement Applications: Ideal for low-traffic roads and pedestrian paths due to its durability and permeability.
3. Drainage Systems: Often used in landscaping and stormwater management projects.

Advantages of No-fines

No-fines has many advantageous points and some of the important ones have been given below:

01 – No-fines is one of the lightweight concrete types whose density is about 25%- 30% less than that of traditional concrete due to the absence of fine aggregates.

02 – It has a low dry shrinkage value due to the absence of sand.‍

03 – The thermal insulation capacity of No-fines is superior to that of conventional concrete due to its large voids. Therefore, it is preferable to use it for the construction of the external wall.‍

04 – The lack of fine aggregate significantly reduces the surface coated with cement. This makes it more economical as it requires less cement per cubic meter of concrete.‍

05 – It can be dropped from heights without the fear of getting segregated since the quality does not get altered due to the absence of fine aggregates.

06 – No-fines concrete can be easily compacted using tamping rods.

Read More : What is Concrete Vibration and Why is it Important?

Limitations of No-fines Concrete

There are a few limitations of using no-fines that are:

01 – The lack of fine aggregate will increase the permeability of no-fines . Therefore, it is not recommended to use reinforcements in no-fines concrete, as the reinforcements are prone to corrosion due to their high permeability.

02 – Ultimately, when using No-fines , additional layers of masonry plaster are applied to make the concrete impermeable, which increases construction costs.

03 – The consistency of no-fines cannot be calculated using normal tests for concrete such as slump test and compaction factor test. Therefore, the workability of No-fine concrete is predicted by visual inspection.

04 – Due to the lack of fine aggregate in No-fines , the cohesion value of this type of concrete in the plastic state is very low. Therefore, it takes more time to remove the formwork.

No-Fines in construction

• When set, NFC contains many air pockets, which depending upon wall thickness, and inner wall lining, can provide a thermal rating similar to or better than that of a traditional, uninsulated, brick cavity wall.
• NFC is sometimes referred to as; Porous Concrete, Pervious Concrete or Permeable Concrete.
• It is generally mixed at a ratio of 6/7 parts aggregate to 1 part cement.
• No-Fines is lighter than standard concrete and therefore easier to handle if required.
• It requires moderate rodding and minimal compaction during casting. Unlike traditional concrete, it does not require significant vibration to remove trapped air.
• The height at which NFC was dropped into casting moulds determines the level of compaction and also dictates the size and quantity of air voids in the cured structure.
• No-Fines Concrete can be used to build relatively tall walls, without increased the size of footings excavation.
• The shape of the aggregate used during mixing, influences the void sizes within the cured concrete.
• No-Fines Walls up to 7.5 metres high and 18 metres long were recording in some housing structures.
• During the Inter-War and Post-War years, there were no set standards for NFC in house building, hence the quality of the finished concrete in use, varies considerably depending upon the level of workmanship.
• No-Fines is not suitable for use in reinforced concrete applications.

Read More : What Are Structural Elements of Reinforced Concrete Buildings?

FAQs About No-Fines Concrete

What is no-fines concrete used for?
It is primarily used in non-structural applications like drainage systems, pavements, and insulation layers.

Is no-fines concrete strong?
While it has lower compressive strength than traditional concrete, it is adequate for specialized applications.

How is no-fines concrete made?
It is made by mixing cement, water, and coarse aggregates, omitting fine aggregates entirely.

Related Topics

• What is Concrete Vibration and Why is it Important?

• Design Of Reinforced Concrete Structures 2nd Edition Volume 1

• Corrosion Of Steel In Concrete

• Concrete Pavement Design, Construction, And Performance 2nd Edition

• What Are Structural Elements of Reinforced Concrete Buildings?

• Concrete Beams With Openings Analysis And Design

• 7 Shocking Causes of Concrete Shrinkage You Must Know About

• The Ultimate Guide: What Are the Types of Concrete Waterstops?

• Advanced Materials And Techniques For Reinforced Concrete Structures 2nd Edition