Reports are surfacing of damaged concrete in the columns holding up the condo in Miami. This explains much, and makes me wonder.
I worked for years in the concrete construction industry. The work consisted of every aspect of concrete, including the rehabilitation, and demolition of concrete exposed to salt water. The reports state the concrete was spalling, and reinforcement was exposed.
Concrete is a brittle, and dangerous construction material without reinforcement. Where the reinforcement rod can displace a load, without the "rebar", a crack can lead to the complete failure of the concrete. The failure can be as little as a chipped edge, or as severe as a structural column failing. Both damages are preventable, but the most critical step is in the initial construction. The rebar needs to be far enough into the concrete to be removed from the exposure of the elements. Normally, this is one and one half inch, but in extreme environments, it's increased to three inches.
The spalls in the reports indicate only one thing: The rebar was exposed to moisture and started rusting, Eventually the rust became so severe, the swelling of the rust caused the concrete to spall away from the reinforcement, and the exposed rebar lost structural integrity without the concrete for stiffening.. With structural components, this is a sign of a possible catastrophic failure, and a wise engineer will inform the owner of the necessity of removing enough of the concrete in a small area to determine the structural capability of the rebar. If there is enough deterioration, the load rating of the structure is lowered to accommodate the reduced strength. This is good for bridges, but with a tall building, the structure itself is the major load, and a sufficient reduction in the concrete strength requires removing occupants until the building can be rehabilitated (probably too expensive) or demolished.
There are multiple ways to repair concrete, but only two basic methods:
One method is to remove the spalled concrete, clean the rebar with only surface rust, and applying a coat of repair grout. This method is costly, since the removal requires small chipping guns, abrasive cleaning, and preparation of the good substrate for new cementitious material. That, and the expensive methods to gain access to the damaged concrete. Some areas might be at ground level, but others may require scaffolding, or barges. The repair grouts are expensive, and can cost over a thousand dollars a cubic yard.
The other method, which is required for severely damaged concrete, requires removing the damaged concrete, removing and replacing the damaged rebar, and placing a fiberglass jacket around the concrete. The oversized jacket is then filled with either a high strength grout, special designed concrete, or and epoxy that has a sand filler. Usually, the jacket remains in place. If there is no clearance to allow this construction, false work has to be placed, the damaged structural component is removed, and a new concrete structure is placed. Retrofitting in this environment is a nightmare, and has an unreasonable cost. With the expensive materials added, such repairs are usually only performed on exposed concrete structures, such as a dock.
There are variations of both types of repairs, and combinations of both. The best construction methods prevent the corrosion by the application of coatings on the concrete. The coatings, which some only allow moisture and block salt, let the concrete "breathe". The elastomeric coating doesn't allow salt to penetrate the barrier, while allowing the moisture to transfer through the membrane. The best coatings are flexible, and don't crack with the movement of the concrete. All add costs, and are avoided, unless absolutely required.
The report of exposed rebar, and spalling concrete would have concerned me, if I was asked my opinion. Without being able to determine the extent of the damage, and the fact people were living above this damaged column, if I was asked for my suggestions, I doubt they would have acted on my suggestion, and evacuated the building, since the lost revenue would have been astounding.
So, how did the building get to this level of disrepair without someone raising a red flag? That's the big question, since the failure led to multiple fatalities. Was the city informed? Were those informed aware of the danger, and if so, why didn't they act to prevent this disaster?
If I had to guess, there were a lot of people crossing their fingers, and hoping for the best. The owner would hope they could keep on collecting revenue, and eventually sell the property. The city officials would hope their head turning would allow them to retire in the future, and the engineering firm would hope their inaction, or sloppy inspection, would never come to light. My experience tells me this is probably what happened, since that's what usually does happen.
I have to add to this post to add information that is now becoming available.
According to newest news reports, the HOA was informed of the damages, and the property owners have dragged their feet, due to the tremendous costs involved. The wait, and further analysis of dangerous conditions, allowed the damage to reach the point of failure.
One report said that a remediation contractor refused to repair some damage after preliminary work exposed structural members corroded beyond repair. I can understand their concern, since the change requires a detailed new engineering analysis, a new bid, and the consent of the owners for the work. Such things usually take months, if not years, and the slow monster of the city has to approve everything.
What I don't understand is how the building was allowed to be occupied after the contractor pulled off the job. At that point, the danger was not theorized, and became apparent. Failing to act, or hiding the information, is unconscionable.
