Expert: Roger Zona - 5/15/2009

Question
QUESTION: Any techniques to stop/retard rebar corrosion before spawling is noted aside from coating concrete with impervious material?  Anybody consider using low voltage d.c. similar to marine use applications to avoid use of Zinc bars on hulls and machinery.

ANSWER: Hello David,

Years ago, when a rebar inspection was made, the rebar had to be clean and free of rust, grease, oil, paint, etc.  That meant wire brushing each bar and applying a de-greaser.

Thank goodness those days have passed!  Now the Inspector looks for proper concrete coverage, ties, laps, etc. and the condition of the steel is overlooked.

I have seen demolition of reinforced concrete where the rebars were very nearly rusted away.  Especially here in Florida where the water table is very high and the rainfall saturates the ground.

The life expectancy of a building is much shorter than when our ancestors built monuments.  Especially with the trend for "green" buildings.  Any building over 10 years old is inefficient and causes pollution.  And for that matter, not many new buildings are "green".  It's less expensive to demolish and re-build than to retrofit.

I'm not familiar with the use of low-voltage electricity to delay or stop rebar deterioration.  I'll research the method.

Thanks for your inquiry.

Roger

---------- FOLLOW-UP ----------

QUESTION: So, I guess one just waits until spawling is evident and then do something about it or just let the structure disintegrate?

Answer
Hi David,

There are so many factors that can effect a building - weather conditions at the time of construction, typical weather conditions (freezing, rain, humidity, exposure to sun, etc.), soil conditions, natural forces (earthquake, settlement, sink holes, etc.), design criteria, local codes, contractor experience, competency of workman-and the list goes on and on.  

Yes, it is better to use clean rebar steel - but try and find any! A great amount of our rebar steel is imported and the quality is poor. And then there is the developer (or building owner) - get the building up as quickly as possible for the least amount of money.

I'm not entirely clear about why you asked the question.  Are you having problems?  Are you a builder?

There has been an interesting series on TV's History Channel about what happens to our cities when people are gone.  Computer enhancement shows what happens to a neglected building.  It's very interesting.

Roger