Pointing out ‘structural deficiencies’ in a tower, which will be demolished at Gurgaon’s Chintels Paradiso society, a report submitted by a committee of district administration earlier this week, stated that the root cause of the collapse is attributed to the “inherent problem of excessive chloride content in reinforced cement concrete which induces and accelerates corrosion in the reinforcement and hence the reinforced cement concrete.”
The report added that there is rapid and early corrosion of reinforcement that occurred due to the presence of excessive chlorides in the concrete.
Experts from civil engineering and construction sectors said that a high chloride percentage, beyond permissible limits, in water and concrete tends to corrode reinforcements at an accelerated pace, hence the concrete starts falling.
“The problem of high chloride arises due to usage of untreated water for construction across the Delhi-NCR region. The water from hand pumps (shallow water) does not have high chloride content. However, in water from deeper acquires, especially in areas along Najafgarh drain and Yamuna, the total dissolved solids in water is very high… it is as good as seawater in some areas. As per standards, the permissible limit of chloride in construction water should not exceed 500 ppm (parts per million) while total chlorides in concrete should not exceed 0.6 kg per metre cube. However, in several areas of Gurgaon, especially near Daulatabad and along Dwarka expressway, chloride content in water is high and since untreated water is often used, it causes corrosion,” said a consultant from the construction sector.
Experts said that for construction purposes, only treated water should be used as per the norms.
“The builders and developers often engage contractors who do not employ skilled engineers and staff. Due to ignorance or convenience and lax monitoring, untreated water is often used which causes problems to structures. Excessive chloride in concrete can cause corrosion rapidly, reducing the life of concrete in 4-5 years, and hence damage to structures,” said a civil engineer, requesting anonymity.
“The corrosion in steel is an electrochemical process. For corrosion to happen, three things are essential – metal (which is available in concrete as reinforcement), oxygen and water. If anyone of these is absent, corrosion will not take place. However, when the overall environment of concrete is having an excess of chloride, it speeds up the process of corrosion, and as a result of corrosion in reinforcement and subsequent swelling of steel bars, the cover concrete starts to delaminate from the structure,” he added