Guidelines on Repair and Rehabilitation of Structures
Samir Surlaker & Sunny Surlaker, MC-Bauchemie India Private Limited
Since cover is the first line of defense to inhibit corrosion, repair and rehabilitation is recreation of cover with the highest protection quotient. We therefore need to use the latest technologies like polymers, fibres, etc. to lower the permeability, minimize the cracks and provide adequate bonding, to stop further deterioration. Given actual working conditions, it is difficult to create a cover that will be resistant to carbonation or chloride ingress. To remove this lacuna from the system, it is preferable to resort to protective coating that work on principles to equivalent cover to ensure durability of repairs. Therefore, the last step of Concrete Repair, which is anti- carbonation or chloride ingress resistant coating, ensures the durability of Repairs.
Cause of Deterioration
Basic Principles for the Protection and Repair of Concrete Structures
The Process of Remediation
In these steps, the choice of procedure, base pretreatment and materials for concrete repair will depend on the existing degree of deterioration, the mechanism of deterioration, its causes and anticipated future stress. A correct diagnosis must therefore be arrived at prior to repair. The reasons for evident defects or damage must be explored as thoroughly as possible. Following this a thorough QA system needs to be established to ensure the durability of repairs. To provide building owners and architects with a high level of reliability in terms of durable protection and repair work, MC has developed “Quality Assurance Systems” based on the following criteria:
- Long years of experience, professional competence and technical equipment for assessment of defects, damage and for establishment of repair measures.
- Depending on environmental or structural stress concerned and on extent of damage, protective and repair system adapted to the structure in question and involving suitable and reliable products for the repair of concrete structures will be recommended from a range of successfully tested and established materials.
- Experienced professional firms who are thoroughly familiar with the material concerned should only carry out protective and repair work. For these reason, MC passes on the experience and knowledge of its staff to professional applicators. The company will advise such firms before and during the performance of repair work.
Protection : 1
Protection : 2
The MC Concrete Repair System
Protection of Exposed Reinforcement: All exposed reinforcement cleaned to bare metal must be protected immediately after sandblasting by using Zentrifix KMH – polymer modified one component corrosion inhibitor and bond coat. In harsher conditions, a zinc rich material like MC-DUR ZKE can be used.
Treatment of Cracks: The sealing of cracks in concrete is a special measure in itself, which becomes absolutely essential in the event of the following widths of cracks: More than 0.3 mm in dry areas/rooms or More than 0.2 mm on buildings in the open or More than 0.1 mm where the structure has a high corrosion risk. Low-viscosity epoxy-resins likeMC-DUR 1264 can be used to treat fine cracks. MC-DUR 1264 produces a structurally perfect bond in the case of non-moving cracks. For bigger cracks Centricretemineral injection grout is also available. This injection must be carried out before application of the final treatment.
Concrete PCC Repair: All defective areas to be filled are first pre-treated with a bond coat. Zentrifix KMH or a mixture of Zentrifix dry mortar and a mixing liquid consisting of a polymer component, Nafufill BB 2/ Nafufill SBR and water can be used. This mixing liquid is added to the dry mortar until a grouting consistency is achieved. The resultant grout is then thoroughly brushed into the base. While the adhesive bond is still fresh, Zentrifix repair mortar is applied to it wet on wet. The Zentrifix repair, mortar can also be improve with the polymer component Nafufill BB 2/ Nafufill SBR in order to ensure good adhesion to the base, to prevent shrinkage cracking and to improve resistance to temperature changes.
Rep : 1
Rep : 2
Where conditions on site make it impossible to work wet on wet, a scud coat of suitable composition can also be applied as adhesive bond. Zentrifix mortars are applied in one operation at repair depths up to 25mm, and in several layers where such depths exceed 25mm. The fine filling described in detail below can be applied after a gap of at least 12 hours. For larger honey combs and jacketing purposes ready to use, high strength micro concretes like Emcekrete/ Expacrete/ Emcekrete Type Acan be used.
Fine Filling: To achieve a visually uniform surface and to provide additional preventive protection the repaired concrete surface should be fine-filled. This is done with a fine dry-mortar, concrete cosmetic Zentrifix FF 02/ Nafuquick, and a mixing liquid composed of water and or the polymer component Nafufill BB 2. Depending on the structure involved, it can be used in overhead work or as a fine-filler under elastic, crack-bridging systems.
Impregnation to provide Hydrophobic Qualities: As an additional, protective measure, particularly in the case of porous substrates susceptible to fractures (e.g light weight concrete), a hydrophobic impregnation agent can be applied up to saturation point to the surfaces first treated by a fine finish, using Emcephob SX/ Emcephob AC etc. This impregnation will ensure that there will be no infiltration leading to more extensive damage if hairline cracks from or if the surface protection is subjected to mechanical damage.
Concrete Surface Protection, Carbonation inhibitor, Coloured finishes: On completion of the work described above, the entire concrete surface must be provided with a final seal or final coating. This is mandatory to maintain status quo of corrosion. Such surface treatments perform several duties at the one time. Firstly, all the concrete is protected from further stress due to aggressive pollutants in the air and from progressive carbonation.
These coating systems must have to a high CO2 resistance if they are to be effective in protecting against carbonation and, on the other hand, they must not have a negative effect on the buildings water vapor diffusion rate. The Emcecolorflex/Betonflair protective system has proved itself to be particularly suitable for this purpose.
Systems on a Two- component Epoxy/ PU Resin Base: Systems based on MC-DUR reaction resins have proven to be best for structures subjected to severe chemical stress-e.g in production areas, water clarification plant, factory floors, multi-storey car parks and many other structures. It should be noted here that systems of this kind, based on two-component reaction resins, show a thermal expansion behavior different from that of concrete. Allowance must be made for this fact in the repair of structures in the open air and of objects exposed to severe stress from changes in the repair of structures in the open air and of objects exposed to severe stress from changes in temperature. MC-DUR resin systems provide important additional properties in comparison with systems bases on hydraulic binding agents – particularly where chemical or mechanical load is severe.
About the Authors
Sunny Surlaker passed his B.E. in Civil Engineering from VJTI Mumbai in 2005 and also holds a Masters in Civil Engineering from University of Michigan, Ann Arbor, USA. He is currently the Head of Admixture Division with MC-Bauchemie India Private Limited a joint venture with MC-Bauchemie, Germany manufacturing over 100 construction chemicals. He has also worked extensively in Germany and Brazil with MC-Bauchemie. Before that he was a Material Specialist with the Global Multinational AMEC Earth and Environmental, in Phoenix, Arizona, USA.