 "Practical guidelines for building repair to maximise gains")
Given below are solutions for some of the frequently asked questions pertaining to building repairs, corrosion problems, restoration of buildings and structural rehabilitation of buildings. These can provide useful guidance for customers who want to undertake maintenance or repair work of their buildings.
Why do buildings show cracks after a few years?
Buildings show cracks because of two main reasons and hence there are two types of cracks.
First, 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 out into ‘V’ shaped groves and filling them up with good quality crack filler.
Second, in the reinforced concrete, water/moisture reaches the steel by leakage or because of the porosity of concrete. This water in the presence of carbon dioxide oxidises the steel and causes rusting or corrosion. The volume of corroded steel is many times more than that of the original steel. This expanded steel puts lot of pressure on the neighbouring 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 colour stains.
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.
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.
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.
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 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 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.
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% to 6% of the value of the whole work for the indispensable value and quality of services they provide.
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 utilised on the job.
How do I compare the rates 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.
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.
____________________________________________________________________________________________________
M A Waheed is the Director of Perma Construction Aids Pvt Ltd
These guidelines are given by Perma Construction Aids Pvt Ltd, a leading manufacturer of construction chemicals for the guidance of general public in good faith and without any prejudice. Should anyone have any specific enquiry they can contact Perma through their authorised distributors, applicators, or Perma’s technical personnel directly. For details, contact at info@permaindia.com
Why do buildings show cracks after a few years?
Buildings show cracks because of two main reasons and hence there are two types of cracks.
First, 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 out into ‘V’ shaped groves and filling them up with good quality crack filler.
Second, in the reinforced concrete, water/moisture reaches the steel by leakage or because of the porosity of concrete. This water in the presence of carbon dioxide oxidises the steel and causes rusting or corrosion. The volume of corroded steel is many times more than that of the original steel. This expanded steel puts lot of pressure on the neighbouring 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 colour stains.
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.
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.
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.
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 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 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.
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% to 6% of the value of the whole work for the indispensable value and quality of services they provide.
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 utilised on the job.
How do I compare the rates 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.
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.
____________________________________________________________________________________________________
M A Waheed is the Director of Perma Construction Aids Pvt Ltd
These guidelines are given by Perma Construction Aids Pvt Ltd, a leading manufacturer of construction chemicals for the guidance of general public in good faith and without any prejudice. Should anyone have any specific enquiry they can contact Perma through their authorised distributors, applicators, or Perma’s technical personnel directly. For details, contact at info@permaindia.com