RCC STRUCTURE REPARING METHOD

MUMBAI, SURROUNDED WITH SEA.
One of the common problem here is the crack in the Rcc structure members like beams, columns etc.
Introduction:

Concrete is a composite material that consists essentially of a binding medium, within which are embedded particles or fragments of aggregates.However in cement concrete, which is relevant to RCC structures, the binding medium is the mixture of hydraulic cement and water. the Reinforced Concrete (RCC), a composite structural material, which is utilised for variety of structural uses. But, it has been observed that RCC has not proved to be durable due to large number of factors, including variations in production, loading conditions in service life and subsequent attack by the environmental factors.   Case studies reported in the literature show that many reinforced concrete structures, within a life period of 15 years or so, suffered from of durability distress. The external symptom range from cracking to spalling of concrete, which frequently involved corrosion of reinforcement. In almost all the field cases, penetration of water and /or aggressive chemicals during the service life of structures, is the primary reason for the problem. Deterioration, carbonation, chloride ingress can all lead to corrosion of reinforcement. The micro-structure of concrete material is continuously changing in response to penetration of water, CO2, oxygen and aggressive ions at a rate, which is influenced by local conditions of temperature, humidity and pressure, it would be difficult to make exact quantitative predictions of cause affecting service-life. **The above descriptions are theoretical which can be found in many books, but in  Mumbai one of the reason i see is that, the sand(fine aggregate) use in the concrete is not free from salt and organic chemicals, the other reason is that the compaction while concreting, there are some bad workmanship(there is less important to best workmanship now a days) except some reputed builders, due to this there is void left in the structure member and rain water with the chemicals in the atmosphere enters in the concrete. So the reinforcement in the structure member starts corroding and due to the corrosion the concrete expands and cracks are formed.**    Ah i think this is enough to understand why the cracks develop in concrete. My main intension is to explain how to take care of this kind of cracks in the concrete.

STRUCTURE MEMBER REPAIR
1.0 Surface Preparation of concrete: All the spalled cracked concrete or any other pre-applied mortar shall be removed by chipping to expose the reinforcing bars. The concrete shall be chipped to a minimum depth of 10mm behind the reinforcing bars. The areas to be repaired shall be profiled to get rectangular or square shape with an inward tapering edge.
1.1 Surface preparation of reinforcement: The exposed reinforcing bars should be cleaned thoroughly to remove all traces of rust, scales, etc., by using wire brush, emery paper etc. The lateral ties/stirrups shall also be cleaned in the same way. also use air blower so that smaller dust particles can be removed. After removal of corroded portion, the diameter of the reinforcement shall be checked and compared with the drawings.
1.2  Provision of additional reinforcement: If the diameter of reinforcing bars is reduced substantially (say >20%) additional bars shall be provided as per the design. This additional reinforcement shall be properly anchored to the existing concrete by providing adequate shear connectors. Weld mesh may also be provided if found necessary.
1.3 Priming of reinforcement bars: The exposed and cleaned reinforcing bar shall be provided with a coat of Epoxy Zinc Primer such that the coated film will have a dry film thickness of 40 microns. The film shall be continuous especially in the regions where pitting, imperfections etc., are present on the surface of the bars. It is important that the rear portion of the bars should not be left without coating. A second coat if needed may
be provided to achieve a uniform and continuous film. The additional reinforcement provided and also the shear connectors shall be coated with Epoxy Zinc Primer. The weld mesh if provided shall also be coated with Epoxy Zinc Primer.
1.4 Provision of Epoxy based bonding agent: The base and hardener component of epoxy resin based bonding agent must be mixed well to get a uniform grey coloured mix. Apply the material to properly cleaned and dry concrete substrate using stiff nylon brush by scrubbing it well into the substrate. The coat should be uniform and well spread on the entire surface area of the repair patch. The mixed material must be applied before the elapse of its pot life and the new repair mortar must be applied before the elapse of overlay time. As a fully dried epoxy resin coat acts as debonding layer, the repair material should be applied whilst the bonding coat is tacky. In case the applied epoxy bond coat gets dry, an extra coat should be applied before application of repair mortar.
1.5 Applying of polymer modified concrete:

•  Take  1  Kg  POLYALK  EP( sunanda's make or equivalent),  5  kg  fresh Cement,  15  Kg  Quartz  sand  (graded).(Polymer  : Cement : Quartz Sand  ratio  is 1:5:15).  This is a globally recommended composition.
•  First  dry  mix  the  cement  and  graded sand in a mixer 
•  Mix  POLYALK  EP  with  the  premixed cement-sand in the mixer.
•  Mixed well then apply with hand(wearing hand gloves) in layers to the surface.
•  fix small aggregate stone and apply again to attain the concrete level

1.6  Curing: All the repaired and encased area shall be fully cured as per standard concrete practices. Curing compound shall be used for effective curing of sides and soffits of beams. If a curing compound is applied, care shall be taken to ensure that proper surface preparation is carried out so as to remove any traces of curing compound on the surface. If this is not done, it may lead to debonding of any protective coating
applied on top.

Thanks for looking, if any suggestion or correction please leave a comment