Repairing of corrosion damage of reinforced concrete.

 Corrosion in RCC Element is a natural process that takes place when the steel bars within reinforced concrete structures become rusty. Scientifically concrete corrosion definition is  the “ruining of metal by chemical, electrochemical, and electrolytic reactions within its location.” It usually forms as the concrete ages.

Corrosion of reinforcing steel and other entrenched metals is the leading cause of deterioration in concrete. When steel corrodes, the resulting rust occupies a greater volume than the steel. This expansion creates tensile stresses in the concrete, which can eventually cause cracking, delaminating, and spalling of RCC structures.

                                    Corrosion in Reinforced cement concretes.

Concrete corrosion is initiated when the harmful materials to steel-like Co2 and chloride from de-icing salts start to penetrate concrete and finally reach the steel reinforcement.

This will lead to a potential difference between the anodic and cathodic areas at the surface of the steel reinforcement, which makes rust. When rust occupies a core volume than steel, it exerts inner stress which causes adjacent concrete to crack and become damaged. RCC structure must be inspected and tested on regular basis to notice and avoid corrosion, particularly when structures get older. When corrosion is found suggest appropriate treatment for the affected structure.

Repairing procedure.

The entire affected surface must be carefully cleaned and prepared. All loose particles, laitance, dust, curing compounds, oil, grease, fat, bitumen, and paint must be removed if good bond strength is to be achieved.  All laitance friable concrete should be removed by chipping, grit blasting, or scabbling until a sound base is obtained., If there is any requirement to dismantle cracked flaky portions with Hammering safety must be made by supporting and bracing of structure from places where maximum shear and bending exists, and special safety measures should be arranged for labor and supervisors. There are three steps for repairing affected structures.

    Application of Epoxy Bonding agent for the bond of old and new concretes.

1- Use of  Epoxy bonding agent for concrete repairs, bonding concrete to concrete, steel, and granolithic toppings.

Epoxy bonding agent should be applied evenly across the whole surface with a clean using a short-haired paintbrush or maybe by laying-on trowel.

Coverage of epoxy bonding materials are 1.9 to 2.9 m²/kg dependent on surface levels of porosity.

Advantages of these materials are High Strength, Nonshrink, Moisture Tolerant, Durability, and resistance against chemical attacks.

2- Second Phase includes the use of a Dual-phase Corrosion Inhibitor for Reinforced Concrete Structures, used to protect steel and concrete from corrosion. This liquid is applied at the surface with a rate of 200 Sft /Gallons using 2 to 3 coats.

The application can be done with a temperature of -17 °C to 50 °C, after the first coat second coat can be applied after 15 minutes.

3- The third Phase is Use of High performance, styrene-butadiene (SBR), latex emulsion for improving cement-based mortars. The latex consists of microscopic particles of rubber dispersed in an aqueous solution. synthetic It is used as an admixture in a mortar and concretes to improve compressive and flexural strengths, improve bond increase resistance to water penetration, improve abrasion resistance and durability. It is used with Portland cement as a reliable water-resistant bonding agent. There are achievable advantages by use of this product like Earlier hardening, improved flexibility, greatly reduces shrinkages, lower water-cement ratio, produces excellent adhesion to steel and concrete, prolong rust protection, and saves from salts.

It may be used 1 Liter /Bag of cement and 5 Liters per Bag of cement for making cement sand mortars or for cement Grouts to fill the cracks.

                                                                           SBR 

4-Last and Final stage is the application of cement sand plaster having rich ratio like (1:1), (1:2) using an admixture of SBR with a Quantity of 5 Liters /  50 Kgs of cement.

Precautions during Hammering for removal of loose concrete.

 Before the start of demolition work by hammering or by use of Hilti Drill Machine /Jack Hammer special measures should be done at the site which is as follows.

                                                              Bending and Shear Diagrams.

 1- Calculate bending moment and shear force and draw a diagram to find maximum load and stress positions and then brace the structure using scaffolding and Steel Girders.

Jacks may be used to lift the weight from affected parts. Do not start breaking from the locations where maximum shear and bending are coming at the affected structure.

Start work by gradual dismantling and repairing patterns but do not break more than 10 % of structural depth as it will increase stress in tension and compression zones of RCC sections. 

            

Safety measures should be ensured at the site because safety is always first.

 

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