How to thicken the concrete mix correctly?

Thickening the concrete mix should be performed during the process of concrete pouring. This is an important concrete work stage and it has an effect on the durability of ready elements. We can distinguish two methods:

• manual compaction, i.e. rodding, rolling or compaction of the mix with special rods
• mechanical compaction, by ‘vibration’, involving vibration of the mix particles

 

concrete vibration

The concrete mix is compacted mechanically, using special vibrators that remove air from the voids in the mix and cause  the aggregate to compact within the mix. It ensures that the rebars are equally wrapped and the formwork is tightly filled. Concrete becomes homogenous and obtains the nominal strength parameters. We distinguish:

• deep vibration - with the use of ‘poker-type’ vibrators, called pokers, with a diameter of 40 - 70 mm
• surface vibration - with the use of vibrating bars or floating bars, e.g. for laying of flat surfaces

 

guidelines for vibration with pokers

• the operating range of a vibration poker is 10x larger than its diameter - we select the poker depending on the size of the vibrated element
• after starting, the vibration poker is quickly immersed vertically in the concrete mix until the middle of its thickness
• after 20-30 seconds, slowly retract the poker upwards and move it to the next position without switching off
• compaction should be performed at regular distances
• immersion of the vibration poker should reach the bottom of the formwork and when concrete is laid by layers, it should be immersed to the layer that is lower by approx. 10 cm (in order to mix the layers together)
• when constructing larger elements, remember that concrete compaction should be performed in layers not thicker than 50 cm
• spacing between the points used for immersion of the vibration pole should not exceed 1.5 x the diameter of the operating range, so that vibration is ensured on the entire cross-section of the element
• overlap the zones of vibration without leaving any space to ensure that the entire element undergoes vibration

+ position of vibrator immersion

 

self-compacting SCC concrete

• compaction and venting of the mix occurs under its own weight, i.e:
  SCC concrete it is compacted under its own weight without the need for mechanical vibration, while
  ASCC is vibrated with low energy, e.g. with delicate rodding

 

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