How to Repair Concrete Solutions Masonry Technique
Batirama.com 02/21/20087
It has indisputable qualities… but it is a living material. Concrete will therefore inevitably age… and it will be necessary, in the more or less long term, to repair it. Here are three practical cases.
Before choosing a repair technique, the diagnosis is fundamental. Indeed, and this is a golden rule in repair, you must know the cause of the problem, before proposing your solution... If repairing a parapet or a balcony does not present serious difficulties, it is not. the repair of a reinforced concrete beam, the stakes of which are not of the same order, which justifies an in-depth diagnosis. In the context of this article, it will only be a question of so-called epidermal repair concerning both horizontal and vertical structures and leaving aside structural repair to specialized companies.
Many constraints
Concrete has qualities that no other material can offer the builder, it is mouldable, economical to purchase (but still much too expensive according to some) and maintenance, resistant to compression…. But like any medal has its reverse, the concrete material has modest mechanical performance in traction and bending (around 1/ 10th of that in compression). In response to this setback, steels are positioned in all areas where there is traction or bending. However, we must not lose sight of the fact that concrete is a living material, it will undergo numerous shrinkage and expansion constraints throughout its life, when it is not a question of purely structural constraints. is not all, concrete is in constant interaction with its environment, which can be particularly aggressive. Freeze-thaw cycles, humidity, chemical attacks…are elements that will contribute to its aging. For a long time, mechanical strength was a response to this type of aggression, but for about twenty years, mechanical strength has been associated with the environment in which concrete will evolve.
A lifetime of 50 years!
Indeed, a good interaction of the concrete with its environment will guarantee a better durability of the work. If the economic durability of structures was formerly 30 years, today's concrete material can offer a lifespan of at least 50 years. Nevertheless, the best concrete will not be able to respond to a deficiency in design or implementation.
Understanding Rebar Corrosion
As we have just said, the concept of reinforced concrete is based on the presence and integrity of its steels. However, the chemical reactions, during the solidification of the concrete, will generate lime, which will protect the reinforcements – we say while the steel is passivated. This chemical protection is associated with a physical protection, called coating. The greater the coating, the better the protection of the reinforcements against external attacks. In accordance with the current BAEL (Reinforced Concrete Limit States), the coatings are as follows:
Marine environment: 5 cm
Non-aggressive medium: 3 cm
Non-wet interior: 1 cm
The passivation of the reinforcements associated with a good coating therefore constitute the two keys to guarantee the durability of a reinforced concrete structure.
Source: batirama.com / B. Lemoine
Solution #1
Repair a concrete chip
To prevent future pathologies and for aesthetic reasons, the split concrete should be repaired. Whatever the type of mortar (read the technical instructions carefully) the repair protocol is as follows:
• Prick the support, brush the dust, form if necessary
• Humidify to refusal
• Prepare the slip by mixing the mortar and a latex solution
• Apply the slip using a paintbrush or a brush on the support
• Apply the mortar by pressing firmly (pay attention to the thickness)
• Leave to firm then trowel with a trowel or polystyrene; on a stair nosing, make the coating using a walking iron
• Stripping and patching if necessary
Solution #2
1. Prick the support, brush or sand the reinforcements, form if necessary 2. Apply the passivation product generously to the reinforcements 3. Moisten the support to excess the day before installation 4. Prepare the mortar (follow the instructions scrupulously technique) 5. Apply the mortar firmly squeezing (pay attention to the thickness) 6. Leave to firm then float with a trowel or polystyrene7. Stripping and possibly patching
Solution #3
Repair cracks in paving with epoxy resin
In the case of concrete floors such as a low floor, a garage floor or a basement, it is not uncommon to be confronted with cracking.
The repair protocol is as follows:
• Open the crack frankly using a small angle grinder to a minimum depth of 10 mm
• Eliminate loose parts and dust the area
• Make sure the area is dry
• Prepare the resin in order to obtain a perfectly homogeneous mixture
• Fill the crack with resin
• Cut off excess with a spatula or trowel
• In case of additional coating, sprinkle with fine sand, let dry, sand and apply the coating
Note: immediately clean the equipment using a specific thinner.
Given the cost of the resin, packaging in a 1 kg box is preferable for one-off treatment. Wearing gloves is highly recommended.
In a hostile environment, the coating of the reinforcements becomes gangrene which will lead to the depassivation of the reinforcements, which, in the presence of humidity, will rust with the appearance of swelling ferric oxides which will cause the concrete to burst. To be complete on the subject, the corrosion of the reinforcements can also begin as soon as the concrete is cracked... Some specialists in building chemistry offer corrosion inhibitors to be mixed with the concrete in a central or spinning top or to be applied by roller on the concrete wall to be treated.
Some hostile exposures according to standard NF EN 206-1:
XC1 | low humidity |
XF1 | Freeze low thaw |
XF3 | Strong freeze thaw |
XD2 | Attack by swimming pool salts |
XS1, XS2, XS3 | Attack by sea salts |
XA1, XA2, XA3 | chemical attack |
PRACTICAL INFORMATION
Reinforced concrete
What repair mortars?
In the 1960s, there was no repair mortar on the market. Since then, the industrial offer has been considerably expanded with increasingly high-performance products.
Choosing a product depends on a certain number of parameters, among which we find the working environment (industry, sea, agri-food, etc.), the mechanical constraints, the thickness of the repair, etc. Four main manufacturers share the repair market and are present in the distribution networks intended for professionals. They all offer technical data sheets that can be easily downloaded from the internet, which allow you to choose the right product, but also to implement it in a satisfactory manner. The manufacturers, their websites and their main products are as follows (non-exhaustive list):
MAKER | WEBSITE | MAIN PRODUCTS |
Lafarge mortars | www.parexlanko.com | Concrete repair: •Mortars: 730, 731, 733, 735 (depending on the thickness of the repair) • Resin for slip: 751 • Reinforced concrete repair: – Mortars: 730, 731, 733, 735 –Passive: 760 |
Mapei | www.mapei.com | Mapegrout range |
Sika | www.sika.fr | • Two-component range: Sikatop 122 F or 121 (high performance repairs) with Sika monotop 610 AC passivator • Single component range: Sika Monotop 612 F or 650 to mix with water, passivating Sika monotop 610 1C |
Weber and Broutin | weberbroutin.com | Motex Repair range: Motex CL 230 and CL 231 |
