Corrosion of rebar in concrete structures is one among the various causes impairing its long-term durability. Precise assessment of corrosion rate (CR) is of prime importance to evaluate the structural safety as well as for estimation of service life of concrete structures. Among the electrochemical techniques, Galvanostatic Pulse Technique (GPT) is very promising for field mapping due to its rapidity. The reliability of GPT in determining the CR under passive and active state of rebar has been carried out using small size laboratory specimens and large scale aged concrete structures. The CR determined by the GPT is compared with the CR obtained by Electrochemical Impedance Spectroscopy Technique (EIST) and weight-loss method. The study reveals that an anodic pulse of 100 碌A with a pulse duration of 10 seconds is able to determine the CR from 1-663 碌m/y (from negligible to higher corrosion activity) on the rebar network more precisely even up to 65 mm of cover concrete. For instance the rebar corroding at higher rate, the CR predicted by GPT is very close to the CR by weight-loss method whereas it is 20 times less by EIST. In the case of passive state of rebar, the CR predicted by EIST is very close to weight-loss method whereas GPT predicts 10 times higher. In aged structures, the change in microstructure of concrete and loss of moisture from the concrete make the potential of rebar and resistivity of concrete more unpredictable and mislead the status of rebar embedded inside the concrete.
Critical tolerable limit of chloride for steel in Ordinary Portland Cement (OPC), Portland Pozzolona Cement (PPC) and Portland Slag Cement (PSC) extracts in the presence and absence of nitrite inhibitor were studied by cyclic polarization technique. Studies also carried out in composite (binary and ternary) cement extracts. The re-passivation potential (E rep ) is an important parameter to characterize the corrosion resistant property of cements and the efficiency of inhibitor. Blended cements (PPC and PSC) have higher tolerable limit of chloride than OPC. Binary cements increase the tolerable limit of chloride than individual cements. The passivity of steel maintained by ternary cement was found to be less than 45000 ppm of chloride along with 5000 ppm of nitrite (pitting occurred at 45000 ppm). This chloride level is more than that of chlorides in natural sea water (35000 ppm). Hence the use of composite cement especially in marine atmosphere increases the corrosion resistance of steel in concrete.
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