HONEYCOMBS IN CONCRETE-CAUSES AND REMEDIES

Fig.1

Honeycombs are hollow spaces and cavities or voids which will happen when the concrete cannot reach the Full mass. The fig.1 shows us the honeycomb which is present outside the column. 

Below are some reasons for honeycombs in concrete,

• Improper vibration to concrete (Fig.1)
• Use of hardened concrete (i.e.,) the concrete which is going to attain its setting time.
• Less cover to the reinforcement (Fig.2)
• In places like junction of beam-column-beam because, these area contains more number of reinforcement and hence it has less cover to the rods.

Honeycombs are formed generally due to the improper vibration to concrete but, in some cases, these honeycombs wont be visible for that we have to use Ultrasonic testing,etc. 

Fig.2

Invisible cavities can be seen in Concrete Slab. These invisible cavities can be found on curing because, it causes leakage in slab. If it is not found earlier it may lead to corrosion of main reinforcement and hence causes the slab to failure.

The normal honeycombs on outer region should be strictly broken with a hammer until we get a Hard Surface and the portion should be concreted with grouting chemical to old surface but, in most of the cases normal cement slurry is used with mortar.

If proper cover to the reinforcement is provided most of this problem will be prevented. The Site Engineer should take more care towards clear cover to the reinforcement and in Junction, the beam rods should be placed in column with more clear cover to the reinforcement.

For Column=25 m

  For Beam   =25 mm

 For Slab     =12 mm

If clear cover at junction portion is unavailable, it should be bent to some extent and should be placed with proper clear cover. On concreting, the outer side of the shuttering at the junction portion can be tapped to minimize the formation of honeycombs and the concrete mix with addition of water can be increased slightly.  

For Invisible cavities, it should be broken and cleaned out and then it should be filled with waterproofing concrete.

STEEL COLUMN FORMWORK Vs PLYWOOD COLUMN FORMWORK

fig.1 Plywood Column Formwork

Many of you may seen in Small buildings, the usage of Steel Column box for casting column is more compared to Plywood. The reason behind this one is the cost difference between them. But, the absolute quality and look is always better when using Plywood box.

  fig.2 Steel Column Formwork   

In most of the small buildings, the contractors always go for steel formwork because to save few bucks but in the same sense that the steel column box will not give the desired results as expected. However, it is then covered in plastering. In some worst cases, this type of work leads to increase in thickness of plastering. Below figures shows us the effect of Steel Column Box

fig.3(a)

In fig.3(a), the top portion of column shows the deviation in actual placement of beam, this is due to the bend in the Steel Column box. To prevent such things, the Site Engineer should take more responsibility and there should be proper selection of formwork material. These types of errors should be taken more care. Each and every Steel Column Formwork should be properly checked for Right Angle at site, if it is not it must be replaced with good ones. 

In Other hand, after Unboxing of column we can also see the undulation in the surface of the column, these undulations shows the real quality difference between both the formworks. These type of errors wont happen in Plywood Column Formwork that's why we should always prefer Plywood Formwork. In High rise and Big Buildings, we wont able to see the use of Steel formwork for column why because, the cost of Plywood wont make much difference there.