Many people are familiar with construction. What people may not know is how important it is for these projects to […]
Many people are familiar with construction. What people may not know is how important it is for these projects to be completed to NZ standards. Even the slightest mistake can result in costly repairs, going over schedule and budget, or even having to start again from the beginning. CSI Ltd are on the investigative side of construction. We have been called into hundreds of extremely varied projects. Hence we come across projects that show us the dark side of construction.
We recently worked on a sizable apartment building with a car park below. This building is around 10 years old and has a modern design. We were called in to investigate some water damage to certain shotcrete walls located in the underground car park. When we got there, it was evident there was much efflorescence in the concrete.
The picture above shows calcium and rust deposits leaking to the surface. You can also see the extent of the corrosion. Structures should be able to survive decades without experiencing any compromised concrete or reinforcement.
We first performed carbonation tests to determine the condition of the concrete (shotcrete). This test allowed us to see how much calcium carbonate was present; which can indicate a risk of reinforcement corrosion. The results showed that the protective properties of the concrete had become compromised. We then performed various breakouts to confirm our results. This was no easy feat as water began to rush out! It became clear there was severe shadowing within the concrete that helped facilitate water ingress. This accelerated the corrosion of the reinforcement tremendously.
When reinforcement begins to corrode, the resulting rust takes up more volume in the concrete. This leads to cracks and spalling which can affect the structural integrity. With the rebar exposed, we began a half-cell test to determine the condition of the reinforcement. Since corrosion is an electrochemical process, its behaviour can be characterized by measuring its half-cell potential. The greater the potential, the higher the risk. The results can not only determine which areas are likely to continue corroding, they can also allow us to conclude whether further investigation is needed or if repair is required.
The results from the works we completed were bitter sweet. We could give the client a comprehensive report on the issues, however, it was disheartening to see such damage to a reasonably new structure because of poor construction. Replacing the walls seems to be the best option, which would be at a very high cost to the client. It was great we were contacted when we were because if this issue continued unchecked, it would have resulted in an even bigger problem for the client. Expert diagnostic testing accurately identifies the remedial works required.
If you have an issue that you need help with, contact Concrete Structure Investigations at
0800 33 77 67 or email us at Info@csiscan.nz