By Gert Schmidt
As a reputable concrete repair contractor, Hindle Mason Projects is well-versed in addressing all types of concrete damage, including honeycombing.
Honeycombing refers to voids or cavities in hardened concrete. This is one example of damage caused by sub-standard construction practices, such as poor concrete compaction. If incorrectly vibrated, air voids become trapped in concrete when it is placed, resulting in honeycombing. Using the wrong mix proportions can also lead to honeycombing. For example, excess water in concrete mixes makes concrete more fluid, leading to segregation and settling of course aggregates. Sub-standard formwork can also lead to honeycombing. When formwork is not sealed correctly or fit tightly, concrete will leak out creating voids and irregularities in the finished product. Shuttering avoids this by providing temporary support to the concrete until it is set. Another cause of honeycombing is sub-standard curing which prevents concrete from reaching its gains and strengths. The way concrete is placed, such as when poured from heights, can also lead to honeycombing.
Honeycombing can be small, medium and large. Small-sized honeycombs are caused by minor voids or surface irregularities that are left after concrete is placed and compacted. They are typically less than 10mm in size and, therefore, do not pose a structural risk. Medium-sized honeycombs are between 10mm and 50mm in size. They can occur due to issues such as insufficient vibration during compaction or due to poor formwork installation. These need to be addressed because they can reduce the strength and durability of concrete. Large honeycombs can significantly reduce the structural integrity of concrete. Greater than 50mm in size, they are formed by inadequate formwork and placement or compaction. They are also created when debris and other obstructions are not removed from formwork before a pour.
Honeycombing concrete repair specialist
Therefore, honeycombing in concrete is a repair that must be addressed timeously by a specialist. Bear in mind that honeycombing does not only compromise the structural integrity of concrete. It also makes concrete more susceptible to water penetration. In turn, this leads to reinforcement corrosion and other durability issues. Note that rebar corrosion is the main cause of concrete structure deterioration. It leads to cracking of concrete cover and a reduction in the cross-section rebar area. Furthermore, it causes a loss of bond strength between the corroded rebar and concrete.
However, cracking of the concrete cover poses the greatest risk of all. It does not only compromise structural integrity. Cracks provide an access point for more aggressive agents that accelerate the corrosion process.
Normally, concrete’s high alkaline environment with a pH value as high as 13,5 can sufficiently protect rebar against corrosion. This is considering the passive film of iron oxides that has been formed on the surface of the rebar. However, it is destroyed by aggressive agents such as chloride ions [Chlorides and concrete.] and carbon dioxide [https://rip.trb.org/View/2255792]. The reacted ions then change into ferrous ions and later become solid corrosion product. Rust has between two and 6,5 times more volume than virgin steel bar. It fills the concrete pores around the rebar causing them to expand and eventually cracking the concrete cover.
Concrete repair company addresses honeycombing
A skilled and experienced concrete repair company, Hindle Mason Projects successfully addresses honeycombing.
No two concrete repair projects are ever alike posing unique challenges. However, there are important principles to which concrete repair specialists will adhere to ensure that the intervention is a success.
First and foremost, we will always ensure a sound surface that is clean. Surfaces should be free of deleterious substances, such as dust, plaster, oil, paint, grease, corrosion deposits, laitance and organic growth. Our teams clean the surfaces using various methods. These include mechanical means; steam; pressure washing with clean water; grit blasting; or a combination of cleaning methods. Any remaining dust or loose material is then removed by blowing with oil-free compressed air.
The next step entails priming the concrete surface. We will first wet the surface thoroughly so that it absorbs clean water. Excess water is then removed. Repairs subject to permanent immersion will then be primed with an epoxy adhesive. An example of such an adhesive is epoxy adhesive – epidermix 344 | a.b.e.® Saint-Gobain. It is worked firmly into damp substrates with a short-bristle brush to form an intimate film with the contact area. Repairs will be undertaken immediately thereafter. If the primer dries before the mortar is applied, the area is cleaned and reprimed.
Quality concrete honeycombing repair materials
Hindle Mason Projects is an approved applicator of quality honeycombing concrete repair materials.
For shuttered repairs, we will use a cement-based non-shrink concrete reinstatement grout. A good example is dura.rep FMC | a.b.e.® Saint-Gobain. It can be applied by pouring or pumping. Select grading of aggregates and special additives ensures that there is no segregation when pouring. This is in addition to making sure that the thermal coefficient of the cured product matches that of the concrete. It also facilitates improved strength and increased impermeability. Supplied in a ready-to-mix form, the system only requires the addition of a small amount of water for easy mixing to produce fluid consistency. It is then ready to be applied into a suitable shuttered repair area at 50mm or greater thicknesses.
When we do not shutter and the minimum repair depth is 13mm, we use a polymer-modified, fibre-reinforced, cement-based mortar. This non-shrink single-component material, such as dura.rep FR | a.b.e.® Saint-Gobain, is chloride-free. In some instances, we may have to first use a wet to dry epoxy primer before applying the concrete repair system. Our preferred primer for this application is epidermix 345 | a.b.e.® Saint-Gobain.
Before mixing the repair mortar, we make sure that sufficient areas have been prepared to receive it. Hindle Mason Projects also only uses complete bags for mixes. The only exception is when the material is “dry mixed”. To avoid particle segregation, we add the required water for proportional quantities. Mixing is undertaken strictly according to the product instructions and with appropriate equipment.
Applying concrete honeycombing repair materials
The next step entails applying concrete honeycombing repair materials correctly.
Polymer-modified, fibre-reinforced, cement-based mortars are applied to the prepared and primed surface with a trowel. This while paying particular attention to packing behind and between the reinforcement, as well as ensuring thorough compaction.
In hot, humid, coastal environments and in heavy industrial areas, intervals between successive layers are kept to a minimum. In this way, we prevent possible contamination of the surface of the preceding layer with air-borne contaminants. This can result in possible inter-coat adhesion failure. When delays are unavoidable, the surface is washed down thoroughly with clean water. Only then do we proceed with the following coating.
We also completely remove sagging material before re-priming and refilling in two or more applications of mortar.
If formwork is used, it is pre-treated with a varnish to prevent moisture absorption from the repair mortar. Our teams also make sure that the positioning of the formwork facilitates good compaction. This is to avoid voids within the repair mortar.
The mortar is applied to achieve a level flush with or slightly proud of the surrounding surface. It is finished by striking off with a straight edge and then trowelled or floated depending on the circumstances. We also take care when striking off deep repair areas and to ensure that the material has set sufficiently. Striking off deep repair areas and too early may cause “hogging”, which leads to sagging cracks. We also avoid applying the repair mortar when the ambient or substrate temperature is less than 5oC or above 35oC. It also should not be applied when temperatures are 5oC on a falling thermometer. Moreover, the applied repair mortar must always be protected from freezing while drying.
Curing concrete honeycombing repair materials
The last step involves ensuring the correct curing of concrete honeycombing materials.
This must take place immediately following application of the repair mortar to any given area. Large areas of at least 0,5m2 at a time are cured as trowelling progresses. During application and curing, all work is protected against strong sunlight. We will sometimes use a general bonding and curing agent, such as dura.bond GP | a.b.e.® Saint-Gobain. This low-pressure spray applied as a curing membrane is fast drying. It is sometimes supplemented with polyethylene sheet taped around its edges.
