Bulu Pradhan

Role of Steel and Cement Type on Chloride-Induced Corrosion in Concrete

This paper reports the findings of a comprehensive experimental investigation where the corrosion performance of different types of steel and cement were studied in different concrete mixtures contaminated with admixed chloride. Three different types of steel, namely cold twisted deformed (CTD) bars and two varieties of thermo-mechanically treated (TMT) bars have been used as steel reinforcement. Three types of cement used in this investigation are ordinary portland cement (OPC), portland pozzolana cement (PPC), and portland slag cement (PSC). Corrosion current density, half-cell potential values, and the relative concrete resistivity have been measured together with free and total chloride concentrations and pH values of the concrete mixtures. From the study, it was concluded that PSC performed best in increasing the corrosion initiation period while PPC performed best in extending the propagation period among the cement types. Similarly, Tempcore TMT steel performed best both in the initiation and propagation period than the other two types of steel.

Corrosion Behavior of Reinforced Concrete Exposed to Sodium Chloride Solution and Composite Sodium Chloride-Sodium Sulfate Solution

The present paper presents the findings of an experimental work that was undertaken to investigate the effect of aggressive ions such as chloride ions and sulfate ions on rebar corrosion in concrete. In the present work, reinforced concrete specimens were prepared with Portland pozzolana cement and Tempcore TMT steel bar at w/c ratios of 0.45, 0.50 and 0.55. The reinforced concrete specimens were exposed to sodium chloride solutions and composite solutions of sodium chloride and sodium sulfate. Corrosion tests such as half-cell potential measurement and linear polarization resistance technique for corrosion current density measurement were carried out on the specimens after a specified exposure period. From the obtained results of potential values and corrosion current density, behavior of reinforced concrete subjected to chloride and composite chloride-sulfate solutions has been assessed.

Empirical approach to predict leached nutrients from landfill site

An empirical approach is made in this investigation to predict the leached concentrations of sodium (Na), calcium (Ca), and potassium (K) in the effluents from a landfill site. Water at certain predetermined inflow filling rate is applied to a specific ponding depth, at the top of an experimental column filled with landfill refuse soil at the top (upper layer) and normal local soil at the bottom (base layer). The water infiltrates into the upper layer soil, percolates through the pores in upper and base layers, and in the process leaches the nutrients from the soils that are collected at the bottom of the column. The experimentations were for different combinations of heights of upper and base layer soils, water ponding depth, and inflow filling rates. The nutrient concentrations in the outflow leachates are measured using flame photometer. The observations showed mixed responses of leaching and trapping of nutrients in the soil layers for the various combinations. The experimental observations also inferred that the nutrient leaching is more for cases involving higher ponding depths and higher inflow filling rates. Empirical relationships with respect to the geometrical parameters, to predict the leached concentrations of Na, Ca, and K, are developed from the experimental observations using nonlinear least squares regressive techniques. Exponential equations gave the best empirical fit among various nonlinear relations in the regression technique. The empirical models also predicted well for each subcategory of independent variables that are substantiated by high correlation coefficients.

Durability of Fly Ash Added Reinforced Concrete in Chloride and Composite Chloride–Sulfate Environment

This work reports the corrosion performance of steel reinforcement in OPC and OPC with 20% fly ash concrete mixes exposed to chloride (5% NaCl) and composite chloride–sulfate solutions (5% NaCl + 2% MgSO4 and 5% NaCl + 4% MgSO4). The reinforced concrete specimens were exposed to these solutions for a period of 12 months with alternate wetting–drying cycles. Compressive strength and corrosion parameters were measured on concrete cube specimens and reinforced concrete specimens, respectively. The half-cell potential test and linear polarization resistance measurement (LPR) were performed to evaluate the corrosion parameters of steel reinforcement. From the results, it is observed that the compressive strength of the OPC concrete mix was higher as compared to OPC with 20% fly ash. From the results of corrosion parameters, it is observed that the addition of magnesium sulfate in composite solutions reduced the probability of occurrence of steel reinforcement corrosion and corrosion current density till the exposure period of 12 months. The replacement of the OPC with fly ash improved the performance of concrete mix against corrosion of steel reinforcement. Further, mostly there was less probability of occurrence of steel reinforcement corrosion and lower corrosion current density at lower w/b ratio as compared to that at higher w/b ratio.

Corrosion Performance of Steel in Self-compacting Concrete Exposed to Chloride Environment

The objective of this paper is to investigate the durability performance of self-compacting concrete (SCC) in terms of corrosion performance of steel reinforcement. The corrosion performance was evaluated by half-cell potential measurement, which provides information about the probability of occurrence of steel reinforcement corrosion and determining the corrosion current density by linear polarization resistance (LPR) measurement, which indicates the corrosion rate of steel reinforcement. Keeping this in view, in the present work prismatic reinforced concrete specimens with a centrally embedded steel bar were made from SCC mixes. Ordinary Portland cement (OPC) was used as a binder, and two w/c ratios of 0.40 and 0.43 were used for the preparation of concrete mixes. The fresh properties of SCC were evaluated by conducting slump flow, T50cm time, V-funnel flow time, L-box, and sieve segregation tests, and the compressive strength was determined for the hardened property. The prismatic reinforced concrete specimens were exposed to sodium chloride solutions for 180 days with alternate wetting–drying cycles. The fresh concrete test results revealed satisfactory filling ability, passing ability, and segregation resistance at both the water–cement (w/c) ratios. From results of corrosion parameters, it is observed that higher concentration of chloride ions increased the corrosion current density at longer exposure period. Further, higher corrosion current density was observed at w/c ratio of 0.43 as compared to that at w/c ratio of 0.40 at the longer exposure period.

Electrochemical Behaviour of Steel in Contaminated Concrete Powder Solution Extracts

The main cause of reinforced concrete degradation is the corrosion of reinforcing steel. This paper reports the influence of chloride and sulfate ions on steel reinforcement corrosion. In the present work, concrete specimens were admixed with sodium chloride, sodium sulfate and magnesium sulfate. The concentration of sodium sulfate and magnesium sulfate is fixed at 3 % whereas the concentration of sodium chloride is varied as 3, 5, and 7 %. Tempcore TMT steel, Portland pozzolana cement (PPC) and w/c ratio of 0.5 were used in the present experimental investigation. Concrete powder was obtained by crushing concrete specimens those were admixed with different concentrations of chloride and sulfate ions. The electrochemical behaviour of steel has been evaluated by conducting potentiodynamic polarization study on steel in contaminated concrete powder solution extracts. On the basis of the results obtained, ranges of potential for different zones of corrosion of steel reinforcement in concrete powder solution extracts contaminated with composite chloride and sulfate ions have been obtained.