Critical Study on Bond Behaviour of Steel and Concrete with Pull-Out Test

This investigation presents the influence of protective coating on bond strength development of steel
with concrete. Pull-out test was conducted in the 1000 kN capacity Universal Testing Machine as per
procedure outlined in Indian Standards. The tested rebar includes rusted (uncoated) rebar as
available in the site, acid pickled rebar (Rust free rebar) and cement polymer anticorrosive coated
rebar obtained from a single source. Concrete of M25 grade were used and totally 18 specimens were
tested. The loads at the free end slip of 0.025 mm, 0.25 mm, loaded end slip of 0.25 mm and ultimate
pull out load were observed. The load-versus slip behaviour was studied at the free end and loaded
end using precision dial gauges. The bond stress corresponding to the lowest load value of 0.025 mm
FE slip and 0.25 mm LE slip was considered as the usable bond strength. The test results revealed
that a well defined correlation exists between Load at 0.025 mm free end slip and 0.25 mm loaded
end slip. It was found that presence of rust and cement polymer anticorrosive coating in the steel
concrete interface appreciably increases the bond strength of the order of 16%, 35% respectively for
16mm diameter bars as compared to rust free rebar. For 20 mm dia. bars, marginal reduction in bond
strength for rusted rebars and significant increase in bond strength for coated bars as compared to
uncoated bars were observed. It is concluded that presence of rust influences in reduction / increase
in bond strength depending on the nature of rust at the interface in the initial ages. Application of
cement polymer coating improves the bond strength of the order of 30 – 35% due to excellent
compatibility at the steel concrete interface, satisfies the codal requirements of Indian Standards.