The strength and durability of concrete depend on many factors, as listed below.
- Workability of concrete
- Water cement ratio
- A proper mix ratio of concrete
- Proper workmanship
- Compaction of concrete
Compaction of concrete is the process of consolidating fresh concrete after pouring it over the shuttering area, covering the reinforcement & making it an impermeable element. It is one of the essential properties of concrete.
Why is concrete compaction needed?
The concrete’s strength reduces up to 30% when 5% of air voids are present in concrete.
The primary purpose of the compaction is to remove the air voids which occur in the freshly mixed concrete. The voids are very harmful to the concrete element, and it impacts the concrete durability.
The compaction enhances the concrete bonding between the reinforcement & makes the concrete a substantial impermeable element.
Compaction Effect on Concrete Properties
- Permeability of concrete will increase due to the improper compaction and moisture can easily be entrapped to the steel and corrode the concrete element.
- Shrinkage cracks may appear on the concrete surface over time.
- Due to the improper compaction, the honeycomb will be formed on concrete, and chances for reinforcement corrosion.
- The concrete ingredients will be segregated improperly due to the improper concrete compaction, which results in strength reduction.
- The durability of concrete is reduced due to the cracks formed by inadequate compaction.
IS code for concrete compaction
The concrete compaction should be done as per IS code 456. The method of compaction & types of compactors has been explained below.
Methods used for Concrete Compaction
The compaction is to be done by both manual and mechanical methods.
The manual compaction method is applicable where the concrete poured location is not much more critical. The manual compaction is done by some construction tools such as
- Tamping rods
- Tamping wooden plate.
Tamping Wooden Plate
A wooden tamping plate with a size at the bottom of 10 sq cm and 2m in length will be used. The freshly poured concrete surface tamped by the wooden plate for compacting the concrete. It is mostly used to compact the PCC.
The heavy flat bottom plate rammer shall compact the foundation concrete. It is suitable mass foundation concrete and not used for roof slab, and other RCC works. You may see this method on basement filling to remove the undulations on the floor.
The tamping rod is used to consolidate the concrete where the concrete thickness is between 150mm and 200mm. The length of the rod will be a 2m long & sharp edge at the bottom.
The compaction has been done by poking of the concrete surface at random points by the rod.
Different types of mechanical vibration are mentioned below.
- Internal vibrator or Immersion vibrator
- External vibrator
- Surface vibrator
- Table vibrator
- Plate Vibrator
Generally, the fresh concrete is compacted by the internal vibrator in the slab, column & beam. The length of the needle shaft is 600mm to 2m, and the diameter of the vibration needle is 20mm to 100mm.
The needle immersed in the concrete and vibrated by the electrical charge, the concrete settled and surrounded near the reinforcement.
The external vibrator is used where the concrete thickness is very thin and the concrete congested by the reinforcement.
The external vibrators are fixed on the outer surface of the formwork. The form of work needs to be more firm to support this.
The surface vibrator is mostly used in concrete roads and large scale roof slabs or concrete floors. The vibration is given through the footplate by the electric charge to the concrete surface. The concrete depth should not exceed 250mm when using surface vibrators.
Table vibrators are used in laboratories to find the consistency of the concrete.
Plate vibrators are used mainly in road work to compact the concrete. The function of plate vibrators is similar to the earth rammer. The vibration plate beat the concrete surface to compact itself.
Happy Learning 🙂