By definition, honeycombing refers to the voids in the concrete structure due to improper compaction between the coarse aggregates and light aggregates. Although mostly, honeycombing just causes aesthetic problems (immense work has to be done before the plaster works or any related succeeding activities), it is important for quality control engineer to check the structure with the honeycombing problems as it might exist deep within the structure. Thus, reducing the durability and the structural strength of the structure.
Repairing concrete is a tremendous work which would always be best if avoided. That is why it is really essential for quality control engineer to thoroughly check the condition of formworks and the methodology prior to concrete casting. But should conditions come worst and repairing really need to be done, engineers should be equipped with the right knowledge on what to do. One cannot deny that due to time constraints, there would always be lapses like this. So, it is important that quality control engineer should be equipped with right information on how to repair concrete with shallow and massive honeycomb.
Anyhow, here is the guide to repairing concrete members with honeycomb problems.
1. Determine the depth and extent of the honeycomb
Defining the depth of the honeycomb is important as it will determine whether the member is durable and has the specified capacity as designed. This is done by simply chiseling the area to uncover the lightly casted concrete. To reveal the actual depth of honeycomb because that’s how a quality engineer decides what type of material would be used pertaining to its required thickness.
Other methods are also done such as impact-echo technique wherein an apparatus is used to determine to locate defects, voids, and flaws in a structural member.
Impact echo technique uses sound waves to graph the insides of the concrete members. This sound generated is transmitted to a device to determine internal and external imperfections of the structural member. A technician would then be able to give a report to engineers on site on the depth of the honeycomb problem needed for a better and sound decision on what to do.
2. Simply patch with similar material for shallow honeycomb problems
Light concrete honeycomb problem wouldn’t cause any structural loading problems except for the aesthetic look of the surface member. This would mean several pre-requisites works for the proceeding architectural scope such as plaster and painting works. To repair concrete with small honeycomb problems like this, thoroughly separate loose concrete until the solid concrete member is exposed. Properly clean the face of the chiseled area to be free from dust. Mix similar materials with the original member from the color to strength to promote homogeneous member. Using the same material is essential for the repaired output to be the same aesthetically. It is always best for the output to be seen as not repaired at all.
3. Cast with similar concrete material for deep honeycomb problems
For deep or massive honeycomb problems, it is important that a qualified structural engineer to determine the extent of the honeycomb problem. Some may require simple methodology as mentioned above. Some may require retrofitting and impact-echo method to check neighboring members, especially for extensive honeycomb up to the reinforcing bars.
Mostly, some qualified engineers would just cut out the faulty concrete member and replace it with sound similar concrete by means of pump, shotcrete, or other approved methodology by the consultant. Before proceeding with the cutting out (as advised by a technical person or consultant), see to it that no reinforcing bars will be cut out as well. Place and fix the formworks and scaffold rigidly to prevent any movement. In addition, use a clean and properly greased formwork sheet and tools for vibrating to prevent another honeycombing problem.
Dismantle the formworks and scaffolds at the time advised by a technical person. Taking off the formwork sheet too early would cause excessive moisture evaporation that is harmful for the newly casted concrete. Use burlap or other means of curing technique similarly as you would with other newly casted concrete.
Honeycombing complications for concreting works is a simple problem that can be avoided if the proper concreting methodology is followed. This would require a teamwork for on-site engineers. First, formwork engineer has to thoroughly check that the formwork used is properly cleaned to prevent concrete surface flaking promoting honeycomb. Concreting engineers have to strictly follow and use equipment such as vibrators during the actual concrete casting.
Quality Engineers Tips:
•It is advisable to dampen the inner side or face of the formwork before pouring of concrete to ensure that the plywood being made as formwork won’t absorb any water from concrete. Quality Engineer or consultant should give advice to the construction team to execute the dampening.
•I recommend reading the standard for concrete repairing from BSI BS EN 1504-8:2016 this is to ensure that in repairing concrete such as honeycomb is within the standard. The Quality Engineer or Consultant may require from construction team such standard to ensure repairing activity is compliant with such standard.
•It is advisable to always follow the time of formwork removal in order to prevent damage to the inner core of the concrete element due to early formwork stripping.
The main reason for honeycomb problems is improperly compacted concrete. Also, see to it the concrete vibrators are not overused as this would cause a complete separation of coarse aggregate to cement. Light and cement aggregate may settle beneath the ground line leaving the coarse aggregates in the middle portion of the structure.
Other reasons causing honeycombing that should be considered by engineers are the slow discharge of or delays of concrete supply. Delays of supply would mean cold joints, causing a slight non-uniformity of concrete mixture leaving the concrete not properly mixed, thus, honeycomb is likely to happen.
After the rectification, see to it that there is no bulging or uneven surface and that the rectified structure is good to be seen as not repaired or rectified at all. Again, preventing honeycomb would always be better than rectifying it so strictly follow concreting methodology.
Quality Engineer Tip:
The standard for “Design of Concrete Structure BS EN 1992-1:2004” is also the best read about concrete works on site. I recommend to check that out.
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