Florida DOT Concrete Batchman/Operator Practice Exam

What type of admixture is used to inhibit corrosion of embedded reinforcing steel?

1. Calcium Chloride

2. Calcium Nitrite

3. Silica Fume

4. Lime

The correct answer is: Calcium Nitrite

The correct answer is calcium nitrite, which is a specific type of corrosion-inhibiting admixture used in concrete. It works by providing a passivation layer on the reinforcing steel, effectively reducing the rate of corrosion caused by exposure to chlorides and other aggressive agents typically found in concrete environments. Calcium nitrite reacts with both the zinc in the steel and the chloride ions present, forming protective compounds that safeguard the steel from rust and deterioration. By doing so, it helps enhance the longevity and durability of structures by extending the lifespan of the embedded reinforcing steel. In contrast, while other options such as calcium chloride can serve as accelerators to enhance the setting time of concrete, they do not provide the corrosion protection that calcium nitrite offers. Silica fume is utilized to improve the density and strength of concrete and enhances its durability in terms of permeability but does not specifically target corrosion inhibition. Lime primarily affects the pH levels within concrete but lacks the specific chemical action needed to prevent corrosion on rebar.