1. Why do buildings show cracks after a few years?

Building show cracks because of two main reasons and hence there are two types of Cracks.

• Multi storied buildings are more of dynamic structures rather than static. They go through the normal phenomenon of settlement, deflections, vibrations and movement because of the movements of loads and wind. With time this dynamism causes some stresses, which show up in the form of cracks in the walls ceiling etc. This type of cracks are only plaster deep. These cracks are treated by, chasing them our into ‘V’ shaped groves and filling them up with good quality crack filler.
• In the reinforced concrete, water/moisture reaches the steel by leakage or because of the porosity of concrete. This water in the presence of carbondioxide oxidises the steel and causes rusting or corrosion. The volume of corroded steel puts lot of pressure on the neighboring concrete and the concrete develops cracks. The cracks due to corrosion appear on the columns and beams. These cracks are larger and generally associated with brown colored stains.

2. Are cracks dangerous and how to treat them?

Surface cracks in the plaster, and those, at the junction of the soffit of the beam and the top of brick work in a wall or those, at the junction of column and the brick work, are only plaster cracks and can be treated by the use of crack fillers

Cracks due to corrosion which are seen on the column and beams, need to be inspected by taking out the concrete to expose the reinforcement. If the reinforcing steel is corroded more than 50 % of its original volume, then it will have to be treated by replacing the lost steel and corrosion inhibition treatment done to entire steel. Then re-concreting is done, by jacketing method, using Super Fluid Micro Concretes, after removing the old concrete. If the damage to steel is less than 50 % of its original volume then the lost steel is substituted with new steel to make up the lost volume of steel, corrosion inhibition treatment is done and the broken concrete is made good by polymer modified mortar.

3. How to identify that the building has a structural problem?

Cracks in the columns and beams, cracks associated brown stains and large chunks of concrete falling off from the RCC members and cracks being very big are all signs of corrosion to indicate that the building has structural problems. Physical examination of the steel by a competent structural repair Consultant, after removal of the cover concrete establishes the degree of the problem.

4. How do we know whether reinforcement is corroded?

Brown marks associated with the cracks indicate corrosion. Bigger cracks on the beams and columns also indicate corrosion. A physical inspection after removing the cover concrete will show the corrosion if it is there. Corroded reinforcements can be separated, by picking from the fingers, as they are very weak.

5. 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 oxidizes the steel and the corrosion process starts.

6. 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.

7. 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.

8. 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 thee 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.

9. How do I 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 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.

10. What are the products generally used in such repairs?

Materials, which are generally used in repairs, are as follows

• For nonstructural repairs polymer based crack fillers, mortar admixtures, waterproofing compounds, bonding agents, paint additives, water repellants, rust removers, shot-creting, 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 utilized. The products basically consist rust removers, repair compound based on Styrene Butadiene Rubber, Acrylic Co-Polymers, Plasticisers, Super Fluid Micro Concretes, Epoxy Bonding agents, Injection Grouting Systems, ready made Polymer Plasters as per the discretion of the Repair Consultant

11. Which are the main products sued in structural rehabilitation works?

Styrene Butadience rubber and Acrylic Polymers (pure acrylic emulsions) are the main products which are used in a slurry form with cement as the anti corrosive 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.

12. 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 reapir system and is ignored. In case the right grade of SBR is not available it is preferable to go in for acrylic systems, likewise 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.

13. How do I 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.

14. 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.

15. How can we be sure that the solid contents found in the lab, are those of the polymer only and not of an adulterant?

Yes fine lightweight powders could be dissolved in these polymers, which could show a higher solid content. The laboratory will not be in a position to say whether the solid contents are of the polymer or any other cheap filler. But the sedimentation when kept in a glass for 48 hours proves the adulteration of this nature. Another method to find this out is to take small quantity of polymer in a test tube, shake well and keep it for some time. If the polymer is adulterated you will see three phases. The water settles at the bottom in the middle you will notice milky white polymer dissolved in the solvent and on top you will find the adulterated powder floating. Ethylene chloride generally dissolves most polymers.

16. 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 coefficient 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.

17. How do I proceed with the specifications?

On the basis of the preliminary survey report of the Structural Repair Consultant, if the building needs structural rehabilitation treatment then the same Structural Repair Consultant or any other Repair Consultant has to be employed to carry out detailed investigation and draw out the precise specification of the works to be carried out. The said consultant draws out detailed and precise specification for the works to be carried out, short lists materials to be used, tenders the works, collects the quotations from the approved Repair Contractors, short list them and presents it before you. Once the work is awarded to the suitable Repair Contractor, the Consultant supervises the input of materials, quality of workmanship, controls the funds flow to the contractor and helps in getting the best from the Contractor.

18. Can we hire a contractor directly for such jobs?

Yes you can hire a contractor directly for such jobs. But you could never be sure of the specification and the quality of materials utilized. When we have a health problem it preferable to go to a Doctor than to a Medical shop for consultation.

19. 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 very from 3% to 6% of the value of the whole work for the indispensable value and quality of service they provide.

20. Can I trust the rates specification and the contractor suggested by the Repair Consultant?

Yes you need to trust your Repair Consultant as you would trust your doctor or Lawyer. After all Repair Consultants are highly qualified engineers with vast experience with various structures. They ensure that the building gets the best treatment from the contractors and the best materials are utilized on the job.

21. How do I compare the rated in relation to the materials used on my buildings?

Your Repair Consultant submits to you the comparison of the various products available their merit and demerits and his own reasons for selecting a particular brand or a method of treatment.

22. 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 given by Rangshalaka, a leading Building Repairs & Paint Company for the guidance of general public in good faith and with our any prejudice. Should any one have any specific enquiry they can contact Rangshalaka though their authorized Distributors, Applicators or Rangshalaka’s technical personnel directly.