Durability performance of rebar embedded in chloride admixed blended cement concretes

Abstract

In concrete structures, permeation of chloride ions either through the pores or by visible/microcracks or contamination of chloride along with the fine and coarse aggregates increase the availability of chloride ion at the rebar level. The reduction of OH⁻ ions by pozzolanic reaction and by replacement of cement by mineral admixtures may reduce the chloride ion tolerable limit of rebar in blended cement concretes. In the present investigation, the corrosion rate of rebar in 0·5 and 1% chloride admixed concrete was assessed periodically up to a period of 1765 days using electrochemical impedance spectroscopic technique. Ordinary Portland cement (OPC), pulverised fuel ash cement (PFAC) and blast furnace slag cement (BFSC) were evaluated in 20, 30 and 40 MPa concretes. The high R_p value of rebar obtained in blended cements indicates that the additional calcium hydrates maintains the pH and also contributes significantly to the inhibitive effects at the steel/concrete interface thus maintaining the passivity of rebar. The results reveal that the high chloride ion complexing ability and microstructural changes by the formation of additional calcium hydrates in the PFAC and BFSC concrete matrix enhancing the corrosion resistance of rebar by a factor of five times than that of OPC concrete in 0% chloride added concrete and three times in 1% chloride contaminated concrete. The reduction of OH⁻ ions did not decrease the chloride tolerable limit of rebar in PFAC and BFSC concrete; moreover they had 1·4 times higher chloride tolerance than that of OPC concrete.

Keywords:

• Blended cements
• Pozzolanic reaction
• Polarisation resistance
• Chloride
• Threshold value