Effect of clay pozzolana on the corrosion behaviour of steel reinforcement in concrete.

ABSTRACT

This study investigated the corrosion resistance of steel reinforcement in two types of concrete mixtures – ordinary Portland (OPC) used for concrete and clay pozzolana cement (CPC) used for concrete. These two concrete types were exposed to 3% and 5% (W/V) of Sodium Chloride (NaCl) and 3% (W/V) Calcium Hypochlorite (Ca(OCl)2) that acted as corrosion media. Mechanical properties and electrochemical analysis were performed over 1, 7, 15 and 23 days. The results indicated that concrete mixtures that contained clay pozzolana cement recorded an average compressive strength of 15.17 MPa while that which contained ordinary Portland cement was 22.75 MPa. Pull – out forces recorded for steel embedded concrete samples that contained clay pozzolana cement in the corrosion media recorded average values of 71, 65.33, 57.7 and 54.67 MegaNewtons (MN) over 1, 7, 15 and 23 days respectively as compared to 80, 70.1, 61, and 49 MN over the same period for concretes without clay pozzolana. Values of corrosion rates obtained from anodic and cathodic curves from Tafel plots revealed that samples exposed to 5%(W/V) NaCl had higher corrosion rates followed by those exposed to 3%(W/V) NaCl and 3% Ca(OCl)2 in that order. XRD analysis showed high presence of Alite (3CaO.SiO2) in all concrete types, however concrete containing clay pozzolana, had higher amounts of alumina – silicates. The XRD also showed low intensity peak for sodium chloride (NaCl) in pozzolana containing concretes and relatively higher intensity peak for ordinary Portland cement (OPC) concretes. SEM showed shallow to deep corrosion pits on steel rods embedded in OPC containing concrete. No corrosion pits were found on steel rods embedded in CPC containing concretes, even though some surface corrosion activities were visible.