(It’s) a concrete solution

Mapelastic is highly effective in improving the durability of concrete structures – a fact proven through years of testing by a wide variety of associations and engineering groups globally.

Every year, incomplete concrete repairs and insufficient corrosion protection cost building owners considerable money and time. A simple, yet often overlooked critical ‘fifth step’ of concrete repair has proven successful worldwide in ensuring the integrity and durability of concrete repairs – while significantly lowering overall life cycle costs.

Factors affecting deterioration of concrete
The dynamics behind concrete deterioration are important to understand as effective repair solutions are considered. Virtually all concrete has at least small micro-cracks. It is natural, then, for chloride to penetrate – carried by moisture – through these tiny cracks, eventually reaching the rebar. As the rebar corrodes, it expands, ‘blowing’ off the cover of concrete and accelerating the cycle of deterioration.
The other key factor in concrete deterioration is carbonation. When concrete is first poured, its high alkalinity stops corrosion. However, as time goes by, and the concrete is exposed to the environment, carbonation reduces the alkalinity and breaks down the passivating barrier. In time, carbonation reaches the depth of the rebar and corrosion cells are developed.

While chloride penetration and carbonation work closely together to deteriorate concrete, other aspects – such as the quality of the concrete and design of the structure – play a pivotal role. The bottom line: even if the best available concrete repair mortar is used (i.e., high-density and dimensionally stable), carbonation and chloride penetration are working virtually 24/7 to undermine any repair effort.

Protection with MAPELASTIC against Carbonation
Thanks to its crack-bridging capability, Mapelastic protects concrete structures against the formation of cracks generated by dynamic loads, shrinkage, temperature variations, etc., even in particularly rigid weather conditions. Also, according to tests carried out by external laboratories, results show that Mapelastic are highly resistant to chemical aggression and offer efficient protection to concrete against the penetration of CO2 (carbonation) and chlorides.
Carbon dioxide (CO2) penetrates into the concrete at a parabolic rate:
x = K .t1/2

where ‘x’ is the thickness of concrete penetrated by the CO2; ‘K’ is the diffusion coefficient of CO2; and, ‘t’ is the period of exposure to an atmosphere containing CO2.
The value of K mainly depends on the characteristics of the concrete (type of cement, additives where applicable, water/cement ratio, curing time, etc.) and environmental factors (humidity, temperature, concentration of CO2, etc.), and must, therefore, be determined experimentally for each case.
Tests carried out by the Società Autostrade per l’Italia (Italian Motorways Society) research laboratories have measured the value of the diffusion coefficient ‘K’ on concrete with water/cement ratios of 0.5 and 0.6. Results gave an average K value of 7.6 for concrete with a water/cement of 0.5, and of 8.0 for concrete with a water/cement ratio of 0.6.
If we assume a thickness of concrete cover of x = 30 mm, and these values are applied in the formula, then, with x = K · t½, where we get:
tconcrete = 900 mm²/(57.76 mm² · year–1), which is ~15.6 years for concrete with a water/cement ratio of 0.5.
tconcrete = 900 mm²/(64 mm² · year–1), would be ~14 years for concrete with a water:cement (W:C) ratio of 0.6.
(Here, ‘t’ represents the time required for carbonation to penetrate through all the concrete cover).
The same tests were carried out on concrete samples protected with Mapelastic and the results showed K values of 0.25 to 0.29. If we assume an average K value for both Mapelastic of 0.27 (mm/year½) and then use the formula, then:
x = K .t1/2
where ‘x’ is their thickness equal to 2.0 mm, we can affirm that, by applying Mapelastic on the concrete surface, it is possible to increase the durability of structures by providing an efficient barrier to the penetration of CO2 for more than 50 years.

By using the same formulation, we can calculate the thickness of concrete cover with a W:C ratio of 0.5 (K = 7.6) able to ensure 50 years of protection against carbonation:
X = 7.6 • 501/2 = 54 mm.
Therefore, as far as the protection against carbonation is concerned, we can affirm that 2.0 mm – or Mapelastic – corresponds to more than 50 mm concrete cover with a W:C ratio of 0.5.
As far as aggression from chlorides is concerned, according to the Danish certification body COWI (Consultancy within Engineering, Environmental Science and Economics), a 2.5 mm thick layer of Mapelastic corresponds to a 30 mm concrete cover with a W:C ratio of 0.45.
This independent agency tested Mapelastic to determine its effectiveness in protecting concrete from carbonation. They also evaluated the test results to determine how a 2.0 mm coating of Mapelastic impacted the concrete durability:

Extract from Danish Certification body COWI

A 5-step method to repair and prevent corrosion
What, then, is the best method known today to address corroding concrete? Short of an ‘engineered’ approach that provides for sacrificial anodic or active approach involves the following repair methods as defined by the American Concrete Institute (ACI). Needless to state, any repair necessitates the involvement of an engineer who examines the structure and supervises material selection, repair methods and repair application.
ACI prescribes the following procedures:
-  Remove deteriorated concrete and profile the surface according to specifications of the repair material’s manufacturer. This includes the removal of any carbonated or chloride impregnated concrete.

There are methods available today that will remove chlorides from existing in-place concrete. These methods should be evaluated and considered by building owners and engineers. Such methods may be appropriate depending on the extent of the damage and of the desired repair.
-  Clean rebar with an appropriate method to remove all corrosion, and repair appropriately to ensure the integrity of the completed repair.
-  Coat the exposed rebar with high-performance anti-corrosion and bonding agent, such as Mapei’s Mapefer 1K.
-  Select an appropriate repair mortar with the required performance and application characteristics, such as Mapegrout T40 and Mapegrout T60. This wide range of Mapei mortars is designed specifically for horizontal, vertical and overhead repairs.

Mapei’s Mapelastic proves successful
Mapelastic’s effectiveness in halting chloride penetration was tested by an independent laboratory.  The test evaluated two specimens – uncoated concrete, and concrete coated with Mapelastic. In the test environment, both specimens were immersed in a 10 per cent solution of Sodium Chloride (NaCl) for 60 days.
According to National Italian UNI 7928 standard test method, analysis of the specimens showed that the uncoated sample exhibited chloride penetration of 35 mm, while the Mapelastic coated sample had a minimal chloride penetration depth, measuring only 1.0 mm.
The benefit of cementitious coating for repairs has been further validated by Chris Atkins, senior materials engineer within the Materials and Corrosion Engineering Section of Mott MacDonald Consulting Engineers, UK. In a published interview in the Journal of Protective Coatings and Linings, he concluded that the application of a polymer-modified cementitious coating at thicknesses over 2.0 mm (80 mils) is the best method to protect concrete structures in wastewater treatment systems.
Mapelastic has proven its effectiveness through years of testing by a wide variety of associations and engineering groups. In addition, it has been successfully used for more than a decade on such varied European applications as bridges, spillways, dams, balconies, swimming pools and numerous other structures.

Application of Mapelastic

-  Protection of renders or concrete with cracks caused by shrinkage, against the infiltration of water and aggressive atmospheric elements.
-  Protection against the penetration of carbon dioxide, of concrete pillars beams, road and railway viaducts repaired with products from the Mapegrout range, and structures with an insufficient layer of concrete covering on the reinforcement rods.
-  Protection of concrete surfaces which may come into contact with seawater, and de-icing salts, such as sodium or calcium chloride, and sulphates.
-  Flexible smoothing layer for light-sectioned concrete structures, including those subjected to minor deformation when under load (e.g. pre-cast panels).

BOX 2:
Technical Parameters of Mapelastic
Mapelastic: Two-component flexible cementitious membrane for waterproofing balconies, terraces, bathrooms, swimming pools and for protecting concrete in compliance with the requirements of EN 14891 and EN 1504-2, EN 1504-9 coating (C) principles PI, MC and IR
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