A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
for epoxy-coated bars, they extended the time taken for cracking to occur
when compared with galvanized steel bars.
The best corrosion resistant reinforcement among all is stainless steel. In
particular, austenitic stainless steel stayed uncorroded even there was
chloride contamination in concrete in the experiment. Reference is made to
K. W. J. Treadaway (1988).
14. Does the presence of rust have adverse impact to the bond
performance of bar reinforcement? (SR4)
In fact, the presence of rust in bars may not have adverse impact to the
bond performance and it depends on the types of bar reinforcement under
consideration.
For plain round bars, the rust on bars improves the bond performance by
the formation of rough surfaces which increases the friction between steel
and concrete.
However, for deformed bars, the same theory cannot apply. The presence
of rust impairs the bond strength because corrosion occurs at the raised
ribs and subsequently fills the gap between ribs, thus evening out the
original deformed shape. In essence, the bond between concrete and
deformed bars originates from the mechanical lock between the raised ribs
and concrete. On the contrary, the bond between concrete and plain round
bars derives from the adhesion and interface friction. With such differences
in mechanism in bonding, the behaviour of bond between deformed bars
and plain round bars in the presence of rust varies. Reference is made to
CIRIA Report 147.
15. What is the difference in bonding performance to concrete
between epoxy-coated bars and galvanized bars?
Based on the findings of CEB Bulletin 211 [11], the bonding of galvanized
bars to concrete is lower in early age owing to hydrogen release when zinc
reacts with calcium hydroxide in concrete and the presence of hydrogen
tend to reduce the bond strength between galvanized bars and concrete.
However, bonding will increase with time until the full bond strength of
ungalvanized bars is attained.
For epoxy-coated bars, there is a 20% decrease in bond strength for bars
placed at the bottom of concrete sections while for bars placed on the top
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