Concrete are usually cast in forms and they take the shape of the forms into which they are cast. During the casting process, in tight forms such as columns, beams or lintels, only the part of the form through which the concrete is being cast is visible to the mason. It is expected that the concrete should be uniform, consistent and align properly with the surface of the forms across its entire surface. To get this done, the concrete is tamped through the casting surface and the body of the forms also tamped to ensure that the concrete adjust itself properly in the forms. When this is not done properly, surfaces with scattered depressions are often visible upon the removal of the forms. These are called HONEYCOMBS (see Figure 1).
Honeycombs are not healthy for concrete sections because they affect the strength of the sections and are also not palatable to sight. They also decrease the lifespan of the structure and foster rusting and corrosion of rebars. Honeycombs are caused when insufficient fine materials get into the concrete mixture due to poor mixing or use of improper aggregate or lack of proper vibration.
To avoid honeycomb in concrete,
- Use only well graded aggregate for your concrete.
- Use water proof and watertight formworks that would not allow cement slurry to escape.
- Properly compact the concrete using poker vibrator.
- Ensure that concrete mixture is done according to the mix design and that the workability is good.
- Ensure that the concrete mix is cohesive enough.
- Maintain adequate water-cement ratio.
- Don’t quickly remove formwork after casting. Allow the concrete to harden first.
- Ensure normal spacing between reinforcements to enhance proper filling of concrete against formwork.
- Ensure mixed concrete is cast in one long operation without much long breaking.
- Always have stand-by concrete mixer and vibrator when casting to avoid delay from breakdown of one.
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