SPALLING OF CONCRETE

What is it: Most of us know about it, but for the sake of repetition Spalling is concrete chunks breaking off the Structure elements due to rusting & deterioration of steel reinforcement. This is caused by rusting of Reinforcement bars as the rust is much more voluminous than steel (up to 8 times) this expansion force within concrete at first leads to cracks in concrete adjoining rusted steel and then rips the concrete apart. These concrete cracks expose steel bars to elements, accelerating the process of corrosion/ rusting of steel bars. Eventually large concrete chunks completely break away from the reinforcement steel bar, completely exposing the reinforcement. That is why Spalling is also called “concrete cancer”, since it is not noticed initially, but as the problem advances, the treatment becomes increasingly difficult and costly.  

What causes it : The most common reason is “Overall deficient site supervision,  be it during reinforcement tying, or for inspection for authorising the concrete pour or finally during concrete pour itself”, resulting in Nil or inadequate  concrete cover to the reinforcement steel or honeycombed concrete in vicinity of Reinforcement steel.

Supervision issues are: a) Mortar cover blocks crumbling due to heavy material and labour movement even before pour, though this problem is not there with PVC cover blocks, b) cover blocks far too spaced out, c) Smaller size cover block used by mistake than that required by design, d) Cover blocks are intact/ in position during initial stage Pour Card certification, but dislodged during subsequent placement of inserts/ conduits/ sleeves etc. and not inspected again just before pour start, e) Cover blocks OK although but during pour itself wheel barrow movement, head load concrete dumping impact etc. crushes mortar cover blocks, f) Honeycombed concrete cover due to leakage of slurry/ concrete due to poor shuttering joints/ or due to improper compaction/ vibration or low concrete slump for heavily reinforced sections etc.

Its Impact: Large enough concrete chunks falling off slab ceiling, Columns/ Walls in facade in buildings can lead to serious/ even fatal injuries and cause extensive property damage. It can affect water tightness of basements, other water retaining structures, where rusting can even start with Tie-rods (used for shuttering) for retaining walls, on external face. Concrete falling off, brings down with it adjoining surface finish be it false ceiling or stone/ metal/ other cladding thus requiring expensive and time consuming repairs and whole building may have to be shut down and put out of operation. Left unattended, damage to the Structure will get compounded.

 For important public infrastructure like Bridges etc. it can be disastrous. In seismically active zones like North and Western India, the Structure Stability may get compromised due to spalling. In coastal regions the Structure life may get severely shortened. Imagine the havoc it can cause, if during a Cinema show, with lights dimmed, if accoustic ceiling falls on patrons.

In recent past there have been media reports about such incidents in hospitals, residential apartments, Schools and other public buildings in Gurgaon, Noida/ Greater Noida etc.; however it would not be fair to name a few projects/ incidents here. One just needs to Google for it, to find them, as they get reported as Plaster falling from Ceiling or False ceiling falling down etc.  

It can lead to Civil & Criminal liability for Developer/ Builder/ Contractor and Supervisory staff.

How to Repair: First step is to identify problem areas, in most cases it can be easily done with keen visual inspection, after de-shuttering itself, & well before any further surface finish like plaster/ cladding etc is done. Look for tell tale signs like red rust grid pattern visible through exposed concrete surface during the concrete curing period, sometimes steel ribs can be been close to the surface. Honeycomb portions are easily noticed.

Ignore smaller rust marks for tie rods, binding wire & chair legs, as they are few in nos. and do not impact structure integrity, except for water retaining structure/ basements.

For concrete that has aged, look for cracks or more pronounced rust patterns, when in doubt, probe with a little bit of hammering/ “Takai”.

Use Ferro Detector to measure available concrete cover in potential problem areas, we used a Hilti Ferro scanner at M3M successfully (though originally procured for locating reinf steel while doing rebaring).

Repair affected areas:

• Chip away loose concrete to expose the rusted steel.
• Clean/ Scratch the rusted steel with wire brush to remove the rust.
• Sometimes additional steel reinforcement / weld-mesh may be needed if the existing steel cross section has reduced considerably.
• Apply anti-rust coating to the steel bars.
• Apply Bond-aid/ other bonding agent to the affected surface to ensure proper adhesion.
• Repair the area using polymer modified cement mortar/ micro-concrete/ shot-creting, depending upon location & extent of damage, & as per respective manufacturer.
• Cure the repaired area adequately.
• Consult/ involve Structure Design Consultant for the above.

As can be seen,  it is eminently controllable through proper supervision, but on the whole supervision levels have surely dropped over last 3 decades, though there are exceptions too.

I recall during 1988-90, in L&T, at Birla’s Cement Plant project, Satna, M.P., my Resident Engineer K. Satish Varma, was a standout Leader, being a stickler for quality and would devote considerable time at site, inspiring us. More recently, at senior level in my team Vimal Kaul & Narender Kumar (MEP) have been exceptional; & at mid & junior level there were Shantanu Mullick, Harbinder Missin, Vaibhav Setia, Raj Mor, Paramjit Thakur, Ahmad Sayeed, Sovan Sarkar, Nitin Sharma, Arvind Kuntal, Ashish Upadhyay, Vikas Kharab, Rohit Kaler, Deepak Kumar, to name some, driven by their own deep commitment. Other team members needed to be led by example, and I made it a point to visit sites frequently & extensively, down to last nook & corner; & by implication all team members would do so.

To sum up, we would have done our bit for the society and the Nation, & ourselves too if we supervise the works properly to prevent this scourge. CREDAI #credai  NAREDCO #naredco can take lead to raise awareness about this problem, and help our buildings and infrastructure become more safe & robust and less maintenance intensive. #realestate #realestatebusiness #realestateindustry  #realestateeducation