Repairing Scheme for Structures

For any rehabilitation program the first step is to assess the degree of distress, the history of the structure, the environment in which the structure is standing. It is also necessary to know whether there was any change for which the structure was built for some specific function.

The assessment can be done by - visual, chemical analysis, physical properties of NDT.

Once the assessment is over, a scheme for rehabilitation is to be made with the use of various construction chemicals. Understanding the physical parameters along with compatibility tests of the chemical with the substrate is essential.

To understand the physical parameters of construction chemicals / building material the various durability factors of cement / lime based materials is also important.

As rehabilitation is an art and at the same time highly scientific and technological innovation the use of special tools and application of material plays an equal important role. Therefore, rehabilitation of structure encompasses various field of activities and failure of any activity at any step may jeopardize the rehabilitation work. However taking into consideration, the nature of distressin coastal environment with the following specification can be referred.

Detailed technical specification for the repair and corrosion protection of concrete surface

A) Repair Specification

1. Chipping off loose concrete from RCC beams, columns, walls deck slabs soffits etc., and other structural elements to expose sound concrete beneath, using light chisel and hammer, removal of rust from the exposed reinforcement as per detailed specification and also preparing the concrete surface to receive further treatment disposing the debris as directed including providing, erecting and dismantling after use of access scaffolding to all the elements being repaired using double layer H frame / pipes bracings of pipes and couplers suitable steel grated planks, all arrangements securely fixed.
2. Cleaning of surface with wire brush to removeall dirt, dust, loose particles etc.
3. Providing new reinforcement of various diameters wherever required at site in the form of Mild steel and Tor steel conforming to IS 456 and lapping and welding. After welding of reinforcement two coat of CORCHEM RE, Rust Encapsulating primer to be applied using painting brush over the new reinforcement.
4. Drilling of holes as per the required diameter and depth using electrically operated hammer drill and fixing threaded nozzles of 12mm NBMS, 75 mm long in the drilled holes using polymer modified cementitous mortar ( 1 Part Tapecrete : 1 part cement : 4 part sand ) mixed with CORCHEM 60 I, migratory organic corrosion inhibitor in the ratio of 10 : 1 ( Tapecrete : CORCHEM 60 I ).
5. Injection of cement slurry admixed with CICO non shrink polymeric grouting compound ( NSPGC ) in the ratio of 500 gms per bag of cement. The water - cement ratio of cement slurry is to be fixed as per the site requirements. The grouting pump to be used for cement slurry injection should be hand operated, freyssnet type capable of developing a block pressure of 2.5 Kg per sq. cm. After injection operation is over nozzles are to be sealed using polymer mortar.
6. Drilling of holes as per the required diameter and depth using electrically operated hammer drill and fixing threaded nozzles of 12mm NBMS, 75 mm long in the drilled holes using quick setting compound admixed with cement (CICO No. 3).
7. Widening of cracks using electrically operated cutting machine and sealing the cracks using polymer modified cementitous mortar (1 Part Tapecrete :1 part cement : 4 part sand ) mixed with CORCHEM 60 I, Migratory organic corrosion Inhibitor in the ratio of 10 : 1 ( Tapecrete : CORCHEM 60 I ).
8. Injection of low viscosity of epoxy system CICO POXY 21, using hand operated low-pressure pump through the nozzles already fixed as per Pt No. 6 & 8.
9. Polymer modified cementitous mortar made of (1 Part Tapecrete : 1 part cement : 4 part sand ) mixed with CORCHEM 60 I, migratory organic corrosion inhibitor in the ratio of 10 : 1 ( Tapecrete : CORCHEM 60 I )15 mm. The mortar is to be applied over bond coat ( made by mixing 1 part Tapecrete P151 with 2 part cement by weight ) till the coat is in tacky condition. In case the bond coat dries up before the application of the mortar another coat of bond coat is to applied.

B) Corrosion protection of concrete surface prone to atmospheric corrosion

1. Surface Preparation : The concrete surface after properly air cured shall be blast cleaned to achieve SA 2.5 profile either by means of sand blasting or sweep blasting. Any visible deposits of oil, grease or other contaminants shall be removed accordingly.
2. Priming : Priming shall not be done when ambient conditions are dusty or conductive to condensate formation on thesubstrate. The Blast cleaned surface should be primed preferably before 2 hours after blast cleaning but not more than 24 hours. Application of one coat of CORCHEM 2P, moistured cured Polyurethane Primer over the blast cleaned surface. The primed surface should also be protected so that it doesn't come into contact with rain, dust or other substances until completely hardened and coated with CORCHEM 210 I, 100% solid, high build, solvent free, aromatic, Elastomeric, polyurethane coating.
3. Coating : Application of CORCHEM 210 I, 100% solid, solventfree, aromatic, elastomeric, polyurethane coating system before the Prime coat has completely cured, not less than two hours not more than 18 hours after the prime coat has been applied by two component airless spray gun to achieve a minimum DFT of 2mm thick. The entire thickness shall be built in a single application (with number of passes).