Some frequently asked questions on structural rehabilitation are answered
What causes corrosion of reinforcement?Corrosion is caused by the oxidation of steel. Reinforcing steel when comes in contact with atmospheric carbon dioxide in the presence of moisture the corrosion process starts and spreads fast like a cancer. Ground water containing chlorides sulphates etc, rising in the capillaries of the concrete when comes in contact with the reinforcing steel the reaction between the two oxidises the steel and the corrosion process starts.
Do leakages cause corrosion?Yes leakages are the main cause of corrosion of steel. Hence a good waterproofing treatment always ensures a protective atmosphere around the steel for a long time and contributes to the longevity of the structure.
Is it safe to stay in buildings that have corrosion problems?Since the process of corrosion progresses very fast and could cause the collapse of the structure it is advisable that the repairs are carried out faster. If the sound steel is reduced to less half its original volume, then it is not safe to stay in such buildings. It could be a great risk to life and valuables stored in such buildings.
When to take up repairs?Repairs need to be taken up immediately after the first signs of the corrosion to steel are detected so that the minimum damage can be repaired economically. Any season is suitable for repairs except the rainy season.
During the rainy season difficulty will be faced by the workers on the scaffoldings to reach the area of repair and hence inefficiency. Rains cause delays and non continuity of works with the possibility of the repairs being washed away or becoming weak with the contamination with rain water. During summer holidays many tenants have a tendency to go out on holidays giving fair accessibility to the workers and less botheration to the tenants.
How to go about repairing such buildings?You need to contact a structural repair consultant to assess your building, conduct preliminary surveys and give you an initial report for which he may not charge anything. If the problem is serious the consultant highlights it in his preliminary report and suggests detailed investigation and repair or else if it is simple he will suggest ordinary means to solve it economically and may suggest economical applicators for the job. This part is generally done free of cost by the consultants.
What are the products generally used in such repaired?Materials, which are generally used in repairs, are as follows:
For non structural repairs polymer based crack fillers, mortar admixtures, waterproofing compounds, bonding agents, paint additives, water repellents, rust removers, shotcreting, guniting etc, are used at the discretion of the repair consultant keeping in view the future life of the building.
For structural repairs specialized products and services are utilised. The products basically consists rust removers, repair compound based on styrene butadiene rubber, acrylic co-polymers, plasticisers, super fluid micro concretes, epoxy bonding agents, injection grouting systems, readymade polymer plasters as per the discretion of the repair consultant.  
Which are the main products used in structural rehabilitation works?Styrene butadiene rubber and acrylic polymers (pure acrylic emulsions) are the main products which are used in a slurry form with cement as the anticorrosive coating over the steel reinforcements. Mortars modified with these products form the protective corrosion inhibiting cover concrete. These mortars show strengths in excess of the parent concrete.
As a cement modifier, which one is superior SBR or the Acrylic?          It is difficult to say but some structural repair consultants prefer SBR while some seem to prefer acrylics. Consultants generally go by their past experience with these products. All over the world, SBR has been in use for a longer time in repairs and rehabilitation works. But SBR is not resistant to ultra violet rays. Since they are not used as exterior wall paint in this type of application, this demerit does not affect the repair system and is ignored. In case the right grade of SBR is not available it is preferable to go in for an acrylic systems, like wise if a right grade of acrylic is not available it is preferable to go in for an SBR system. Perhaps this is what influences a consultant from project to project.
How to test the quality of the polymers?The quality test for polymer consists of determination of the PH and the solid content of the product to compare and verify with the data given in the product literature. Any other physical findings such as cream formed on the surface of the product or settlements at the bottom indicate a bad quality product.
What types of adulterations are possible in these products?These polymers are milky white liquids having specific gravity very close to 1. Hence if someone adds water in the ratio of 1:1 in these products common man can’t make out. Even a hydrometer test may show the specific gravity close to the specified one in the literature. Only analysis of solid contents will prove the dilution of the products. Hence it is necessary that the polymers are kept in the godown under lock and supplied to the contractor as per daily requirement. 
How do the polymers compare with the epoxy and polyurethane system?Epoxies and polyurethane are sufficiently strong and expensive products. Their mortars and coatings generally tend to be more rigid hence has a tendency to crack during movement/deflection, which the beams and roof slabs constantly face. Non-uniformity of co-efficient of thermal expansion of concrete and these products also creates the possibility of creep or lateral movement at the repair interface.  Moreover general grades of epoxy and polyurethane are not compatible with cement concrete system hence rarely used in structural rehabilitation works.                              Is it expensive to hire a repair consultant in cases of repairs?No it is not at all expensive to hire a repair consultant. Their consultancy charges vary from 3 per cent to 6 per cent of the value of the whole work for the indispensable value and quality of services they provide.
How long does it take to repair say a seven storied building?Generally it takes nine months to a year from the time the consultant is given the green signal to go ahead. 
Note: These guidelines are shared by Perma Construction Aids Pvt. Ltd. – a manufacturer of construction chemicals