Repairing of peeled concrete due to corrosion of the steel reinforcement
I. NATURE OF THE
PROBLEM - REQUIREMENTS
Concrete protects the steel reinforcement from corrosion with its alkalinity. Due to its high pH values, a thin protective layer of stable oxides is formed on the surface of the steel, hindering the development of rust. When this protective layer of stable iron oxides is destroyed by the influence of a strong corrosive environment, the phenomenon of corrosion (rust) appears.
Corrosion of the steel reinforcement causes an increase of its volume, resulting in the creation of internal tensions and cracks in the concrete, which finally lead to its peeling.
The resulting damage:
Puts the stability of the structural element at risk.
Creates the conditions for further corrosion of the remaining steel reinforcement.
Reduces the structural element's fire resistance.
Causes problems to the structural element's appearance.
The loose and broken parts of the concrete must be removed, and the solid concrete and corroded steel rods completely uncovered. Rust must be removed from the steel by scrubbing, grinding etc. with an appropriate tool (wire brush, sand blaster, etc.), depending on the extent and level of corrosion. Next, EPOXYCOAT-AC anti-corrosive epoxy primer or FERROSEAL cement-based anti-corrosive coating is applied on the steel rods of the damaged structural elements in order to protect them from future corrosion.
Subsequently, the peeled area of the concrete is repaired by the application of MEGACRET-40 high performance patching mortar, in order to restore the monolithic nature and strength of the damaged structural element.
In detail, the repair procedure is the following:
All broken and loose particles of the peeled concrete should be removed thoroughly, and the corroded steel reinforcement is completely uncovered.
The exposed solid concrete should be roughened and cleaned from dust, rust, etc.
The corroded steel should be cleaned and scrubbed, grinded etc. with an appropriate tool depending on the level and extent of damage (e.g. sand blasting, water blasting, wire brush, etc.) in order for the rust to be removed completely before the subsequent application of the anti-corrosive layer (EPOXYCOAT-AC or FERROSEAL).
Application of EPOXYCOAT-AC: Components A (resin) and B (hardener) of EPOXYCOAT-AC are packaged in predetermined mixing proportions. The whole quantity of component B should be added to component A. The two components should be mixed for about 5 minutes with a low-revolution (300 rpm) mixer. It is important that the mixing takes place at the sides and bottom of the mixer as well, so that uniform dispersion of the hardener is achieved. The cleaned, undamaged and exposed steel rods (or the new additional steel rods that may be put in place if what remains is insufficient) should be covered with 2 coats of EPOXYCOAT-AC. The second coat is applied after the first one has dried. After the application of the second coat, and while it is still fresh, 0-0,8 mm grade quartz sand is sprinkled on it, in order to ensure the bonding of the patching mortar which will follow to the surface of the steel reinforcement.
Application of FERROSEAL: FERROSEAL is added into water under continuous stirring in proportions of FERROSEAL to water = 2,65 to 1 (volume parts) until a uniform mass is formed with no lumps. The material is applied using a brush of medium hardness in two layers. Layer thickness exceeding 1 mm per coat should be avoided because of the risk of crack appearance in the material. The second layer is applied after the first one has dried.
After 48 hours, when EPOXYCOAT-AC has been used, or after FERROSEAL has dried, the surface should be dampened thoroughly and then MEGACRET-40 high performance patching mortar is applied in order to restore the damaged area.
The content of a 25 kg bag of MEGACRET-40 is added into 4,60 lit of water under continuous stirring and mixed well until a uniform firm mass appropriate for repair work is formed. The material should be applied with a trowel or by gunning, at the desired thickness, up to 4 cm per each layer. When a second layer is required, the surface of the first layer should be roughened to achieve better adhesion. The final surface should be well protected from dehydration by covering it with wet cloths, polyethylene sheets or repeating dampening for 48 hours.
Consumption of MEGACRET-40: approx. 17,5 kg/m2/cm of layer thickness.
Alternatively, if fast work is required, RAPICRET fast-setting patching mortar may be used instead. RAPICRET is added into water under continuous stirring, until a tight, no-slump putty is formed suitable for patching or fixing works. Mixing time should not exceed 1 min. It is recommended to mix a small quantity every time, because of the short working time (about 15 min. at +200C). RAPICRET may be applied at a thickness of up to 3 cm per layer.
Consumption of RAPICRET: approx. 17,5 kg/m2/cm of layer thickness.
Temperature during application must be between +50C to +350C.
Material that has started to set should not be re-softened with water.
At high temperatures, mixing of the material with cold water is recommended, in order to avoid excessively fast setting.
At low temperature, mixing of the material with lukewarm water is recommended, in order to accelerate its setting and the development of its strength.
During the summer months, cement mortars must be dampened after application, in order to prevent their dehydration due to high temperatures.
Consult the directions for safe use and precautions written on the packaging.