Executive Summary : | India has a very long coastal line, that adversely affects the service life of the reinforced cement concrete (RCC) structures by causing corrosion in the metallic reinforcement. In general, it is believed that the off-shore structures are susceptible to chloride-induced corrosion. But in actuality, carbonation plays a major role in initiating corrosion in the off-shore structures (due to a favourable relative humidity of 60 – 70%). In brief, carbonation-induced corrosion is the process in which the atmospheric CO2 gets diffused into the concrete pores and reacts with the various hydration products and forms carbonates, bicarbonates, and carbonic acid, which lowers the pH of the cover concrete and depassivate the embedded steel. The service life of the RCC structures can be enhanced by delaying the corrosion initiation period, which can be achieved by using a good quality cover concrete and corrosion inhibiting chemical admixtures.
The limestone calcined clay cement (LC3) based cementitious systems have the potential to enhance the service life and reduce the life cycle cost of the RCC structures. Because, the LC3 based cementitious systems not only exhibit low CO2 emission and cost-effectiveness, but also possess higher electrical resistivity and excellent transport properties that inhibit the ingress of chloride ions, and delay the onset of chloride-induced corrosion. But the recent studies showed that the LC3 based cementitious system tends to carbonate much earlier than the ordinary portland cement system, which makes them more vulnerable to carbonation-induced corrosion. It is the major drawback in the LC3 based cementitious system and that has to be overcome with a viable solution. Therefore, the proposed research work attempts to study the carbonation-induced corrosion resistance of the quenched self-tempered (QST) steel embedded in the LC3 based cementitious systems made with and without bipolar corrosion inhibitors (at the water binder ratio of 0.35 and 0.45).
The parameters such as the pH threshold, thickness, and atomic concentration of the passivating film will be assessed on the QST steel. Whereas, the compressive strength, depth of water penetration, oxygen permeability index, carbonation depth, and carbonation coefficient will be measured on the LC3 concrete. For evaluating the above-mentioned parameters, the following experiments such as transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy-dispersive x-ray spectrometry (EDS), x-ray photoelectron spectroscopy (XPS), accelerated carbonation (at 3% CO2), half-cell potential (HCP), linear polarization resistance, (LPR) electrochemical impedance spectroscopy (EIS), compressive strength, water permeability, and oxygen permeability tests will be conducted. With the recorded experimental results, a nomogram will be developed to design the LC3 concrete system for the desired service life. |