Journal Nov 2020

Corrosion measurements in concrete structures and interpretation of data Carmen Andrade

The measurement of the corrosion demands certain specialization as the best techniques are of electrochemical nature. The most common techniques used for the corrosion assessment are based on corrosion potential, resistivity, and polarisation resistance. The use of the galvanic current is not approached because, it does not give better information than the polarization resistance technique in most cases. Corrosion potential provides information about the corrosion risk, and resistivity is directly related to the moisture content/humidity level in concrete. Among these, the polarisation resistance is the only technique that can quantify the loss of metal. In present paper, their fundamentals are briefly described, together with some general guidance on the meaning of their values and where those ranges can be found. The methods that enable the correct measurement of the corrosion rate in large structures are also described. These measurements can be made using probes that are embedded in or attached onto existing structures. Finally, a model of prediction of the corrosion propagation is discussed.

The corrosion behavior of rebar in metakaolin and red mud blended concrete exposed to chloride and sulfate solutions U. Raghu Babu, B. Kondraivendhan

The effect of chloride (NaCl), sulfate (MgSO4), and combined chloride plus sulfate on rebar corrosion in blended concrete was evaluated in this study. Two water to cementitious material ratios (w/cm) and three different cementitious materials namely Ordinary Portland Cement (OPC), OPC blended with Metakaolin (MK), and OPC blended with Red Mud (RM) were adopted for the experimental investigation. The corrosion performance was measured by corrosion current density (icorr), half-cell potentials, and Ohmic drop (IR) compensated concrete resistivity. To overcome the problems regarding the distribution of electrical signal over reinforcement and ohmic drop, guard ring setup was adapted to measure icorr values with IR compensated linear polarization resistance technique. The superior performance was observed in the case of concrete blended with MK, in terms of lower icorr and higher IR compensated resistivity. Further, it was observed that the MgSO4 along with chlorides, increase the corrosion activity. Finally, Two-way ANOVA test with interaction was used to evaluate the effect of cementitious materials and w/cm ratio on corrosion data.

Corrosion inhibitor for preventing carbonation induced rebar corrosion Kulwinder Kaur, Sorabh Saluja, Shweta Goyal, Bishwajit Bhattacharjee

The adverse weather conditions, particularly the raised CO2 level in air leads to reduction in service life of reinforced concrete structures. In the present study, the retardation in carbonation induced corrosion was attempted with the use of organic based migrating type corrosion inhibitors. The carbonation acceleration of the specimen was achieved by using carbonation chamber maintained at a temperature of 30 ± 2ºC and having 5 ± 0.5% CO2 concentration by volume. The experimental results show that the inhibitor treated specimens had lower carbonation depth as well as corrosion current density and nobler half cell potential as compared to the control specimen.

Performance evaluation of organic bipolar corrosion inhibiting admixture P. N. Ojha, Puneet Kaura, Piyush Mittal

Reinforcement corrosion is the most important durability threat and cause of premature failure of reinforced concrete structures. Ingress of chlorides and atmospheric CO2 are the two important phenomena promoting the reinforcement corrosion. Various corrosion prevention techniques are available to delay, decrease or control the corrosion of reinforcement in concrete; however, the most common is the use of inhibitors. The aim of this paper is to evaluate the performance of nine numbers of commercially available admix type organic bipolar corrosion inhibitors through short term and long-term test. Short term tests like JIS Z1535, immersion test (as per ASTM G1) and accelerated chloride induced corrosion test using polarization technique were conducted to investigate the effectiveness of inhibitors and evaluate their corrosion inhibiting efficiency. For long term performance study, RCC slabs were exposed to field environment and laboratory environment, after a conditioning regime of two years during which the specimens were kept in sheltered environment. One set of RCC slabs with and without corrosion inhibitor were kept under laboratory exposure i.e. 3.5% NaCl solution for another one year and corrosion rate for these slabs were measured at an interval of two months. Similarly, another set of RCC slabs with and without corrosion inhibitor were exposed to field environment for one year and corrosion rate for these slabs were also measured at an interval of two months as well. Other short-term test like electrical resistivity and half-cell were also carried out to supplement the corrosion rate results. The test results indicate good relationship between corrosion rate of concrete samples exposed to field and accelerated laboratory environment. This study also exhibits a linear relationship between short term corrosion inhibiting efficiency and long-term corrosion inhibiting efficiency.

Enhancing service life of prestressed concrete structures by using fly ash and corrosion inhibitors Dyana Joseline, Radhakrishna G. Pillai

Seven-wire strands in pretensioned concrete (PTC) structures can undergo chloride-induced localized corrosion. The corrosion products occupy the space between the wires of the strands and do not exert expansive stresses onto the surrounding concrete. Hence, propagation of such corrosion cannot be identified/detected on time using visual observation of concrete surfaces and can lead to catastrophic failure. This scenario necessitates technologies to significantly enhance the chloride-resistance and corrosion-resistance of PTC systems. This paper quantifies the role of pulverised fuel ash (PFA; fly ash) and corrosion inhibiting admixtures (CIAs) in enhancing the probabilistic service life. For this, lollipop specimens with embedded prestressing steel (five in each category) were prepared and subjected to wet-dry exposure using simulated concrete pore solution containing 3.5% NaCl, and the chloride threshold (Clth) was determined. Also, the synergistic effects of chloride diffusion coefficient (DCl) and Clth on the corrosion-free service life of PTC systems are demonstrated. The paper also demonstrates the need for specifying both strength and durability requirements (say, “Mx-Dy” concrete). Such an approach can aid engineers and designers in making informed choices of materials to achieve protection of PTC systems against chloride-induced corrosion and to achieve service life of 100+ years with minimal maintenance/repair cost.

Service life of reinforced concrete (RC) systems with cement-polymer-composite (CPC) coated steel rebars E. K. Arya, Alan Verghese Ittyeipe, Deepak K. Kamde, B. S. Dhanya

Cement-Polymer-Composite (CPC) coating is used to coat steel rebars in anticipation of delaying the initiation of corrosion in reinforced concrete (RC) systems. However, CPC coating is sometimes inadequately applied on rusted steel. This paper investigates the effect of such inadequate application of CPC coating on service lives of RC systems. For this, a total number of 30 macrocell specimens with following steel surface conditions were cast with and without CPC coating (a) rusted (b) mechanically cleaned with wire-brush and (c) sand-blasted, and tested for corrosion current, half-cell potential, and chloride threshold. The corrosion initiation time of RC system with inadequate quality construction practices was found to be 40% less than the design life.

Performance of galvanized steel rebars in concrete M.S. Haji Sheik Mohammed, V. Roopa

In this experimental investigation, the performance of galvanized steel rebars was assessed for its use in construction. The corrosion control efficacy of galvanized steel reinforcement (rebars) and the influence of galvanization on mechanical properties of steel rebars were studied. The tests were conducted following the Indian / ASTM standards and procedures followed by earlier researchers. It was noticed that galvanization provides adequate sacrificial protection to steel rebars in the chemical resistance test, open circuit potential test, and macrocell corrosion test in the tested duration. The performance of the galvanized rebars was 1.75 to 2.60 times higher than the uncoated rebars in the highly accelerated electrochemical corrosion conditions. The bond strength values for galvanized rebars were similar when compared with uncoated rebars. Impact and adhesion test results also indicate that galvanized rebars comply with the codal requirements of Indian and ASTM Standards. The coating damage of 1% did not adversely influence the corrosion resistance properties of galvanized rebars.

Corrosion-induced cracks in concrete exposed to 1D and 2D chloride ingress Ze Gyang Zakka, Mike Otieno

In this paper, 12 steel reinforced concrete specimens made of fly ash and slag concrete are exposed to 1-directional (1D) and 2-directional (2D) chloride ingress. The specimens were cracked before they were exposed to chloride over a period of 110 weeks. The steel mass and cross-sectional area loss, corrosion pit depths, and corrosion-induced cracks in the concrete were assessed. The corrosion-induced cracks, steel reinforcement bar mass and cross-sectional area loss in specimens that were exposed to 2D chloride ingress were significantly higher than that of specimens exposed to 1D chloride ingress.

Hybrid anodes for accelerated cathodic protection of corroding concrete structures Naveen Krishnan, Zameel D. V., Dhruvesh Shah, Haixue Liao

Patch repairs can lead to the formation of incipient anodes in the zones adjacent to a repaired area. Presently, in India, cathodic protection using alkali-activated galvanic anodes are widely used to prevent the formation of any corrosion cells at the interface of new and old concrete. Newer addition in the field of cathodic protection of the concrete system is the two-stage hybrid anodes that can supply a high amount of charge and passivate the steel in a relatively short period compared to galvanic anodes. However, there are fewer field data available on the performance of these anodes. This paper presents the results of the performance assessment test conducted on installed two-stage hybrid anodes in a heritage structure in India. It was observed that the installed hybrid anodes satisfied the ISO EN 12696:2016 recommended criteria throughout the testing period and were able to passivate the steel rebar within ? 100 days after installation.

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