How do we Determine that Rusted Steel Bars in Concrete need to be Replaced due to Excessive Rusting?
After removal of rust scales and cleaning the reinforcement steel of old concrete, the area of the steel is measured. If the cross-sectional area reduction observed on main bars has reduced by more than 30% then additional steel bars have to be provided. Steel reinforcement used in stirrups is generally of small diameter, it is always advisable to replace this steel if rusted completely. These will however also depend on the member to member and its importance vis-a-vis the load on it and its position.
Whenever additional steel is placed, it has to be properly lapped and tied with old steel using binding wires or by welding.
Before Repairs what Type of Treatment do you Recommend for Cracks, Crevices, and Joints in a Masonry or between Masonry and RCC Framework?
Before repairs are carried out on masonry or concrete, it is important to seal all cracks, crevices, joints, and junctions properly to avoid leakages or cracking in the future.
All cracks, crevices, joints, and junctions should be properly packed with cement mortar or polymer mortar forcing the mortar to penetrate the cracks, crevices, joints, or junctions. All packed spots must be cured properly for 7 days before the final repair mortar or concrete is placed over them.
Chemical grouts and sealants can also be used. However, since they are costly, they should be used very judiciously.
Why should We Insist on the Proper Thickness of Repair Applications Over old Masonry or Concrete?
This is important on two accounts. The specified thickness within certain limitations is necessary because,
- Thickness larger than specified: This can result in pealing on or cracking of the repaired application. This can also result in additional load on the structure. Larger thickness does not necessarily mean better repairs or protection.
- Thickness smaller than specified: This will result in poor protection of old steel and concrete within it and would also result in lower strength and durability.
What is Curing? Why it is Necessary?
Whenever repairs are done using cement or cementitious materials or cement-based polymers, it is extremely important that curing is done properly to allow the cement to hydrate fully. Curing is done by continuously keeping the exposed surface wet or moist. A wet/moist exposed surface is necessary to prevent water to evaporate from the exposed surface due to hot sun, low humidity, or wind. If the exposed surface is allowed to dry, it will develop cracks which will cause seepage of moisture, corrosion, and reduction of the useful life of the structure. Curing helps improve strength, surface hardness, texture, and color, wear resistance. protection against environmental pollutants and water entry, leak-proofness, cracks resistance, and above all durability of the work executed.
Many Occupants of Offices and Flats Often do Interior Decoration and Damage the Structure. Is it true?
There are several cases in our country wherein healthy structures have even collapsed killing innocent people and destroying property worth millions of rupees mainly due to careless interior changes and structural modifications. A structure is like a human body, it can tolerate a certain amount of abuse or amputation. You can remove legs and hands from a human body, the person will be disabled but will survive. If you remove the brain, heart, lungs, or liver survival is not possible. In interior decoration, too many changes are made without consulting an Engineer or the original structural consultant who had designed the building. The structure can tolerate some changes but some changes like shifting a column, removal of reinforcement steel from beams or columns, accommodating concealed wiring or piping, removing a beam or damaging the foundation, or excavating deep pits or trenches close to the foundation of a structure or addition of mezzanine floors/masonry work are all murderous acts and the chances of building collapse cannot be ruled out.
The unfortunate part is that even after several years the persons responsible for such acts are not punished nor are any reports published to make common men and professionals aware of such acts. Therefore, these failures keep occurring year after year in many cities in our country.
During Repairs, If all Occupants Start Supervising and Instructing the Consultant or Contractor the Work will Stop or Suffer. What are your Views?
First of all, you must have faith in the Consultant and/or the Contractor you have appointed. To have proper harmony and smooth working, a committee of two or three persons from the building must be appointed to take charge and all suggestions by the occupants must be given to them. The committee should decide which ones are to be passed on to the contractor and which need not be considered. All-important instructions to the Contractor must be routed through the Consultant and properly lodged by the persons in charge.
Often under the guise of dissatisfaction with work, some occupants stop payments and cause problems for everyone. While every occupant, who pays has a right to give his individual views and opinions, the committee appointed by the occupants should be trusted and allowed to function freely whether or not they take their views into account.
Often Occupants do Costly Interiors and do not allow the Repairs in their Flat/Office. What are your Views?
It is of utmost importance that structural repairs are given priority. Costly interiors or exteriors do not ensure the safety of a building and are of no value to any occupant if the building collapses or even if the structure gradually deteriorates due to refusal to allow repairs.
What are the General Reasons for Building Collapses?
Ignorance, Carelessness, Negligence, and Greed are generally the causes of failures of structures all over the world.
It is very difficult to attribute a building collapse to just one reason. It is always a combination of several factors from its birth (construction) to its death (collapse) that cause structural failure. Some broad reasons are briefly given below:
- Bad quality materials or adulterer materials used.
- Poor construction practices.
- Poor or no supervision.
- Poor structural or architectural designs and details.
- Lack of technical knowledge of the building contractor and his supervising team.
- Poor or no supervision by the Consulting Engineer or Architect of the works which are carried out as per the drawings and specifications issued by them.
- The client (Owner/Builder) is not interested in the quality of work.
- Financial and speed considerations are given greater importance than the quality of work.
- Durability consideration not specified or followed during construction.
- Settlement of foundation.
- Chemical attacks are not envisaged earlier.
- Poor maintenance.
- Modifications (renovations) done on structural load-bearing members.
- Fire damage.
- Floods, earthquakes, storms, or other natural calamities.
- Neglect of leakages and seepages create corrosion of reinforcement steel.
- Disputes amongst occupants.
- Financial considerations for repairs/maintenance.
- Aeroplan crash or any other extraordinary impact.
- Acts, laws, and delayed legal action against guilty persons.
- After the stoppage of construction for a long period due to shortage of funds, statutory clearances, disputes, litigation, etc. when the work is restarted old surfaces including rusted steel is not cleaned properly.
- Important Questions and Answers on Building Repairs Part-1
- Important Questions and Answers on Building Repairs Part-2
- Important Questions and Answers on Building Repairs Part-3
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