What are top 5 methods to compact concrete and the best tools to use?

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Compacting or consolidating concrete is an important step in construction projects. This step ensures that you get the highest density of concrete. The goal is to increase the packing of the coarse aggregates and reduce the internal friction between the mix components. Compaction also eliminates trapped air bubbles in the concrete mix, making the resulting concrete stronger and more reliable. In the past, concrete compaction was achieved by pruning or ramming. While these methods are still very much in use, contractors can now make use of sophisticated machinery that works in different ways to compact concrete. Here are 5 of the top methods of compaction and the tools used for them. 

  1. Rodding 

Rodding is a method of concrete compaction used for small concrete work. This method generally involves using a steel rod of about 2m long and a 16 mm diameter to poke the concrete layer until it is compacted. A flat-nosed spade can also be used for concrete rodding. The method of concrete compaction is more effective for higher-slump concrete but is not recommended for compacting reinforced concrete walls and columns. Rodding is typically used to compact the corner and edges of concrete cubes as well as precast concrete blocks.

  1. Ramming 

Ramming is a method commonly used to compact floor or roof slabs. It can also be used for pavement slabs in reinforced concrete road construction with low thickness and a smooth level finishing. It involves compacting the concrete surface using a wooden cross beam with dimensions of about 10 x 10 cm.

Ramming the concrete surface with this wooden beam helps to release any air bubbles that were trapped at the moment of placing the concrete. How the ramming will be done depends on the type of concrete slump. 

  1. Pressure and Jolting

Another method of concrete compaction is by using pressure or jolting. This compaction technique is quite effective in compacting dry concrete and is mostly used to compact hollow blocks, solid concrete blocks, and cavity blocks. 

In this method of compaction, the concrete is vibrated, pressed, and jolted to consolidate it. The combined effects of pressure and jolting help to stiffen the concrete to a dense form with stable strength and volume. 

  1. Spinning

This is a more modern method of compacting concrete and is typically used for the construction of concrete pipes such as “hume pipes” or “spun pipes). For this method of concrete compaction, the plastic concrete is spun at very high speeds. This way, the centrifugal force acting on the spinning concrete is responsible for compacting it. 

  1. Mechanical Compaction 

The more advanced way to compact concrete is by using a machine that consolidates concrete through vibration. There are different types of machines built for this purpose. Generally, machines for compacting concrete work by internal vibration or external vibration: 

Internal Vibrator

Also called immersion vibrators or needle vibrators, these are the most common types of concrete compaction machines. They consist of a metal rod vibrating end with a shaft that is driven through a flexible drive from a mortar. Internal vibrators are mostly used for large-scale construction works on flat surfaces such as floor slabs, roof slabs, reinforced concrete footing, reinforced concrete shafts, and so on. The vibrator is typically immersed at a spot until the concrete around it is fully compacted. Examples of internal vibrators include 

  • Flexible shaft internal vibrators 
  • Motor-in-hand internal vibrators 

External Vibrator

External vibrators are also known as formwork vibrators. In this type of machine, the vibrator is connected to the concrete formwork and the vibrating force of the machine is used to compact the concrete on the formwork. External vibrators are mostly used in situations where internal vibrators cannot be used. You can use them to consolidate thin concrete sections (with a thickness of up to 600mm) as well as precast concrete. Examples of external vibrators include: 

  • Roller vibrators 
  • Turbine vibrators 
  • Electric hammer 

Table Vibrator & Platform Vibrator 

A table vibrator is a special type of formwork vibrator. In this case, the vibrator is clamped to a table mounted on springs. As the table vibrates, the vibrating force is transferred to the concrete to compact it. This type of vibrator is usually used for compacting concrete cubes. Table vibrators are mostly used in labs for small and precise prefabricated reinforced concrete.

A platform vibrator is a larger version of a table vibrator. It is used for larger projects such as manufacturing concrete poles, railway sleepers, prefabricated concrete roofing elements, and so on. 

Surface Vibrator 

This type of vibrator is also known as a screed compactor or vibrator. They’re typically mounted on concrete and platforms and are used for compaction in large-scale construction projects such as bridge floors, road slabs, and so on. 

Wacker plate 

A wacker plate or vibrating plate is machinery used for compacting loose gravel or sand to create a solid base before an upper layer of concrete or asphalt is added. They are useful for a wide range of projects and come in a variety of sizes. Most construction companies offer wacker plate hire for your DIY construction projects and you get one from them. You can get a petrol-powered plate or go for an electric wacker plate hire near you depending on your preferences. 

Vibratory Roller

Vibratory rollers are used for consolidating dry and lean concrete surfaces. These types of concrete projects are called roller compacted concrete or rolled concrete. A vibratory roller typically has a dual-wheel installed on its rear end and a drum roller on the front end. The vibration from the roller helps to reorganize the concrete particles while the weight of the drum exerts pressure on specific layers to compact them. 

Conclusion 

Compaction is an incredibly important step in every construction project. Therefore, when planning  your project, you have to factor in the cost to hire a wacker plate and any other compaction tools you might need. 

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