Why is compaction factor test vital for construction?

A compaction factor test is crucial to check the workability of concrete or soil during the construction of a home or a commercial building.

If you are looking to buy a property or planning to build a house, you may hear the term “compaction factor” thrown around. The term “compaction factor” refers to the workability of concrete used in the construction of houses and buildings. When you are assessing the workability and quality of concrete, the water content and cement ratio is critical to achieving the desired strength as per design. To check if the concrete meets the required standards, it has to be done during the production phase, and the compact factor test is one of the best methods that give accurate results.

Also, the soil is frequently destroyed during construction, allowing water and air to enter. The soil compaction process removes moisture and air from the soil, resulting in a solid foundation. So, the compaction factor also plays a role in improving both concrete and soil quality. Let’s understand the significance of the compaction factor test for a home or commercial building construction.

Why compaction factor test vital? 

Compaction is a construction task that is performed on almost every housing or other type of civil project. It is required to improve concrete quality and strength and densify soil beneath the slab on the ground or compress the clay core of an earthen dam.

The compaction factor test determines the workability of fresh concrete or soil in terms of the internal energy required for thoroughly compacting it.

In the case of concrete, the complete structural stability relies on the concrete’s strength and quality. Hence, quality must be controlled during the production phase, where cement, sand, and water are mixed to build the concrete. Even small changes in water-to-cement ratio, mixing, increase in the slump, etc., can affect the required concrete strengths. Hence the compaction factor test is vital to assess the overall quality of the concrete and take remedial measures to ensure the desired strength is reached.

Learn about: What is slump test?

How to perform Compaction Factor Test?

On construction sites, you test small soil samples taken from the site to a lab. The compaction factor test is done to assess concrete or soil’s workability.

The compaction factor is the weight ratio of partially compacted concrete to completely compacted concrete. This test was first done by the United Kingdom’s Road Research Laboratory and is utilised to assess the workability of concrete mixture. 

The compaction factor is defined as the weight ratio of partially compacted to entirely compacted concrete. The compaction factor test aims to determine the maximum dry unit weight and the optimum moisture content (MOPT) of compaction. Here are the different steps carried out in the compaction factor test.

• Put the sample on the brim of the top hopper with the hand scoop, level it, and then cover up the cylinder.
• Open the door at the bottom area of the top hopper to allow concrete to drop into the lower hopper, and gently push the sample concrete attached on its sides with the rod.
• To allow the concrete to fall into the cylinder below, open the trapdoor of the lower hopper and let it fall.
• Remove the extra concrete sample above the upper level of the cylinder with trowels, level it, and then clean the outside of the cylinder.
• Weigh the cylinder with concrete to the closest 10g, and this weight is referred to as the partially- compacted concrete weight.
• Remove the sample from the cylinder and again fill it with the same concrete mix in 5 cm layers, ramming each layer heavily to achieve full compaction.
• Level the top surface of the cylinder and then weigh it with completely compacted concrete, which is referred to as the weight of completely compacted concrete.
• Then calculate the empty cylinder weight.
• The compaction factor is calculated via the formula and it usually ranges from 0.7 to 0.95

The compacting factor provides information about the workability of concrete in an indirect way. A good concrete mix has a higher compacting factor and less quality is associated with lower compaction factor. The table below shows the general values of compacting factors for various workability levels of concrete.

Tips for concrete care 

• Concrete must be coated with a protective sealant to reduce moisture & prevent stains.
• Oils and other stains damage the concrete’s looks and lead to concrete deterioration in the long run. Moreover, since concrete is porous in nature, it’s best to clean stains immediately so that the contents don’t seep into the concrete.
• Try to avoid using deicers on concrete, especially during the first year after its laid
• Coating or painting a concrete floor with an epoxy covering will improve its appearance and protect it from oil and other corrosive particles.

Practical application of Compaction Factor Test

To achieve satisfactory engineering properties such as strength, compressibility, or permeability, soil placed as fill (foundation pads, road bases) is compacted to a dense state.

Laboratory compaction factor tests provide the basis for determining the per cent of compaction and water content required to achieve the required engineering properties, as well as for controlling construction to ensure that the required compaction and water contents are met during the production of concrete.

What is the relevance of Soil Compaction in construction?

Soil compaction is an essential step in the construction process. It helps structural entities like building foundations, roads, sidewalks, and earthwork structures. Certain characteristics of a given soil type may be more or less appropriate to operate thoroughly in specific situations. In general, the pre-selected soil must have sufficient strength and be relatively incompressible so that future settlement is minimal. When the water content or other factors change, it is resistant to volume changes and should be durable and safe, with excellent permeability.

Compaction gives the structure built on top of its stability and support. The soil’s elasticity is increased as a result of this process. The details must be considered because they are critical to ensuring the proper support structure.

Soil compaction strengthens the soil while decreasing its compressibility. Soil permeability is also reduced because water flow through the soil becomes more difficult as the interval between particles decreases. As a result of this process, the soil can withstand more weight and has greater stability. It also improves its resistance to frost and deformation.

How Soil Compaction is performed? 

Soil compaction is an essential step in the construction process. It helps structural entities like building foundations, roads, sidewalks, and earthwork structures. Certain characteristics of a given soil type may be more or less appropriate to operate thoroughly in specific situations. In general, the pre-selected soil must have sufficient strength and be relatively incompressible so that future settlement is minimal. When the water content or other factors change, it is resistant to volume changes and should be durable and safe, with excellent permeability.

Compaction means the application of force to something in order to make it denser. The soil compaction factor test is used to determine the relationship between soil moisture content and dry density at given compaction energy. The amount of mechanical energy applied to the soil mass is referred to as compaction energy. 

If soil compaction is done incorrectly, the soil can settle, resulting in unnecessary renovation costs or structural failure. Therefore, mechanical compression techniques are used in almost all types of construction sites and building projects to improve soil compaction. Here are a few examples.

Smooth rollers

Smooth rollers work well on granular types of soils such as gravel and sand. These rollers compact soil via static pressure, sometimes in combination with vibration and impact. Smooth roller compactors are not the only type of rollers used, but they are most likely utilised in the final step of compaction to offer a smooth surface for the construction.

Padfoot and Tamping foot rollers

Padfoot and Tamping foot rollers are able to compact more cohesive soils. For better compaction, they utilise manipulative pressure to remove the natural bonds between the fine-grained soil particles. They have V-shaped feet to avoid fluffing the soil and reducing its ability to absorb additional water content if it rains.

Pneumatic rollers

Pneumatic rollers are effective for little to medium-sized soil-compaction jobs. Where the surface of bladed granular base materials needs to be sealed, they use staggered rubber wheels with varying air pressure. To achieve compaction goals, additional weights or ballasts can be added.

Tamping rammers

Tamping rammers are ideal for restricted work areas or small spaces because they are light and portable. They perform particularly well in cohesive soils.

What does it mean to have a Compaction Rate of 95%?

A 95 per cent compaction indicates that the soil has been compacted to 95 per cent of its maximum density using external compacting methods. The maximum dry density and moisture content is determined in the laboratory and serves as the target for field compaction. Therefore, 95 per cent is a common target compaction threshold used to ensure construction projects are built on a solid foundation. The designing engineer will provide the compact threshold, which will be based on the bearing capacity required for the final load to be structurally stable.

Conclusion 

The compaction factor test will be very helpful in determining the degree of workability of soil and concrete. Since homes and other civil structures need to be sturdy and survive many years of wear and tear due to weather and other factors, it is better to be proactive and get quality assurance through compact factor testing. As you know, concrete and soil quality can be the deciding factor when it comes to the longevity and cost of renovation needed for a home in the future. So, get a compaction factor test done and ensure the concrete and soil’s quality & strength match the required construction standards.

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