Honeycomb concrete is widely used in construction and there seems to be no construction work without honeycomb concrete. It should be noted that honeycombs in concrete can cause serious problems in structures.
Let's understand the honeycomb.
What is a honeycomb in concrete
Honeycombs are the result of poor concrete compaction and the formation of voids in the concrete. Generally, honeycombs in concrete form close to the surface of the concrete.
However, due to overcrowding of the reinforcement assemblies, there is the possibility of voids forming inside them. Additionally, there is a minimal chance of internal cavities being noticed.
Causes of Honeycomb Formation in Concrete
There are many causes of honeycombing in concrete, which can be categorized depending on the type of concrete, type of structure, and environmental conditions.
In this article, we will discuss the main reasons for honeycomb in concrete. Let's see what they are.
- Poor workability of concrete
The concrete must be workable enough to be poured. If the concrete does not move or flow normally, it cannot be compacted well. Furthermore, if the concrete is more rigid, the same thing can happen.
This may result in the loss of the oil pan. Break-in is an indication of the workability of the concrete . Due to the large distance between the concreting plant and the concreting structure, the use of a wide variety of water reducing additives , etc. can lead to loss of concrete workability.
- Insufficient vibration and compression
Lack of vibration can lead to uncompressed honeycombs. Furthermore, excessive vibration can lead to honeycomb formation due to concrete segregation. This can be considered one of the main causes of honeycombs in concrete.
- Reinforcement jam
There is a risk of honeycombing in the projected areas of reinforced concrete structures. If there is not enough space for the concrete to flow, internal and external honeycombs can form in the concrete.
Poor reinforcement detailing can lead to overloading of the reinforcement.
- demarcation
Concrete can segregate due to falling height, blockages in reinforcement, excessive vibration, etc. If concrete segregates, an aggregate may separate from the mortar and be collected separately. This can be considered one of the reasons for the formation of honeycombs in concrete.
- Insufficient reinforcement coverage
If, due to the condition of the reinforcement, there is not enough space to strip the reinforcement in the coverage area, areas without concrete may appear.
Effects of honeycombs on concrete
All planners and designers should be aware of this. This way, everyone can take the necessary measures to prevent the formation of honeycombs.
- Loss of strength/reduction in static load capacity
The formation of the honeycomb structure means that there is a weak point in the concrete. Insufficiently compacted and weakly bonded aggregates will break under stress if not repaired properly.
Repair of honeycomb concrete should be carried out under strict supervision and guidance from experienced technical personnel.
If the cavity remains or the loose portion is not completely removed, structural failure of the supporting elements may occur.
- Durability issues
The Durability of concrete is the most important aspect of a concrete structure. Loss of durability can cause structures to deteriorate before their intended useful life.
The following problems have been identified as the main effects of hollow core concrete.
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- Reinforcement corrosion
- Concrete deterioration
If this Reinforced steel is exposed to the environment, it may corrode in the presence of moisture and oxygen. Additionally, small natural honeycombs in concrete also lead to Chloride reinforcement corrosion attack or Concrete carbonation .
- Water leaks from water retention structures
Honeycombs in concrete can cause water to leak through faulty concrete elements. Unidentified honeycombs on concrete surfaces cause seal damage to.
How to Prevent Honeycombs in Concrete
- Detailing the reinforcement
When detailing the reinforcement, sufficient space must be provided for the concrete to flow.
- Improve the workability of concrete
Adequate fluidity of the concrete must be guaranteed. In the situation where there is a rebar connection, Additives For example, highly effective water-reducing additives could be used.
- Maintain sufficient distance between beams
In accordance with BS 8110, a minimum distance of +5 mm aggregate size must be maintained between bars. Providing enough space for the concrete to flow can reduce the formation of honeycombs in the concrete.
- Suitable vibration and, if necessary, vibration of the formwork
Types of Honeycombs in Concrete
Concrete honeycombs can be classified according to the size or width of the honeycombs.
- The width of the honeycomb is approximately 25mm and the depth is also in the same range.
- The width and depth of the honeycomb are approximately 100 mm.
- Honeycomb width and depth are more than 100mm
The size of the honeycomb is of great importance in deciding the renovation procedure and the care required when repairing honeycomb concrete.
The larger the honeycomb, the greater the risk. Additionally, the repair can be done in several steps to minimize shrinkage.
Honeycomb Concrete Repair
The following important aspect can be highlighted and it should also be highlighted that all civil engineers should know how to treat honeycomb in concrete.
- Loose material must be completely removed.
- If the element to be repaired is stressed and the damage is significant, the repair of the cellular concrete must be carried out with due care.
- Additionally, depending on the extent of the honeycomb, external supports may be required to reduce the load on the defective structural element.
- All honeycombs must be filled with non-shrink construction mortar.
- If the size of the honeycomb in the concrete is larger (e.g. 100 mm or more), the repair must be carried out in several stages as recommended by the material supplier.
- If a larger volume is required to repair hollow core concrete, a 1:1 mixture of non-shrinkage and chipping structural mortar can be used as recommended by the mortar supplier.
- The mixing time and procedure must be specified by the supplier.
- The water content must necessarily correspond to that indicated in the mortar specification.
- Adequate healing must occur. In general, construction mortar develops a strength in the range of 50-60N/mm 2 and is a rapid process of gaining strength. Therefore, the cure must be carried out correctly.
This clarifies the question of how honeycombs in concrete are treated.
