The effect of using natural pozzolan-based cement concretes on zinc phosphated rebars corrosion

Abstract

Studies on using zinc phosphating in reinforced concrete (RC) field are still in the early stages. Use of natural pozzolan (NP) as cement replacement is growing rapidly in the construction industry due to its economical, ecological and technical benefits. Four phosphating baths were prepared; Zn phosphate (P-Zn), Zn-Ni phosphate (P-Zn-Ni), Zn-Cu phosphate (P-Zn-Cu) and Zn-Mn phosphate (P-Zn-Mn) respectively. Ø14 mm reinforcing steel bars were treated at 55-60 °C for 15 min in the phosphating baths. Concrete specimens were produced with different levels of NP; 0% (control specimen), 10 %, 20% and 30%, respectively. The effectiveness of using both NP and P-Zn coatings in retarding rebar corrosion has been investigated using an accelerated test after 28 and 90 days concrete curing. In addition, the bond strength between the concrete and the rebar was investigated by the pull-out test. Test results revealed that the concretes containing higher replacement levels of NP and rebars treated in bi-cationic baths exhibited corrosion initiation periods several times longer than the control specimens with uncoated steel and a zero NP content. Moreover, the results showed that the bond strength was not affected by adding NP and P-Zn coatings. SEM analysis was employed, as well.