M. Shameem

Comparison of properties of steel slag and crushed limestone aggregate concretes

Abstract Steel slag is produced as a by-product during the oxidation of steel pellets in an electric arc furnace. This by-product that mainly consists of calcium carbonate is broken down to smaller sizes to be used as aggregates in asphalt and concrete. They are particularly useful in areas where good-quality aggregate is scarce. This research study was conducted to evaluate the mechanical properties and durability characteristics of steel slag aggregate concrete in comparison with the crushed limestone stone aggregate concrete. The durability performance of both steel slag and crushed limestone aggregate concretes was evaluated by assessing water permeability, pulse velocity, dimensional stability and reinforcement corrosion. The results indicated that the durability characteristics of steel slag cement concretes were better than those of crushed limestone aggregate concrete. Similarly, some of the physical properties of steel slag aggregate concrete were better than those of crushed limestone aggregate concrete, though the unit weight of the former was more than that of the latter.

EFFECT OF MOISTURE, CHLORIDE AND SULPHATE CONTAMINATION ON THE ELECTRICAL RESISTIVITY OF PORTLAND CEMENT CONCRETE

When reinforcement corrosion is under resistive control, the chloride-contamination level is known to influence the electrical resistivity of concrete and hence the kinetics of reinforcement corrosion. While some data exist on the relationship between moisture content on electrical resistivity of concrete, very little research has been conducted to evaluate the effect of chloride and sulphate ions on the conduction of electricity through concrete. This study was conducted to evaluate the effect of chloride and sulphate contamination on the electrical resistivity of concrete. Results indicate that both moisture, chloride and sulphate contamination influence the electrical resistivity of concrete. At higher salt concentrations, moisture content has very little influence on electrical resistivity. This indicates that in near dry concrete, high salt concentrations could sustain reinforcement corrosion. The reduction in the electrical resistivity in sulphate-contaminated concrete increases the rate of reinforcement corrosion in carbonated concrete.

Effectiveness of concrete inhibitors in retarding rebar corrosion

Abstract The effect of inhibitors on the corrosion of steel reinforcements in concrete was evaluated by using anodic polarization, electron spectroscopy for chemical analysis (ESCA) and Auger electron spectroscopy (AES). The reinforcement corrosion in uncontaminated concrete specimens was evaluated by impressing +4 V anodic potential for accelerated corrosion of the steel bar and measuring the time-to-cracking of the concrete specimens. The effectiveness of the inhibitors in retarding reinforcement corrosion in the contaminated concrete specimens was evaluated by measuring the corrosion potentials and corrosion–current density. Results indicated that the time-to-cracking in uncontaminated concrete specimens incorporating inhibitors M2 and R2 was higher than that in the control concrete specimens. While the increase in the time-to-cracking in the concrete specimens incorporating M2 was marginal, a significant improvement in the corrosion-resisting characteristics of concrete incorporating R2 was indicated over the control specimens. The data on time-to-cracking in the uncontaminated concrete specimens and the corrosion rate of steel in the contaminated concrete specimens indicated the usefulness of corrosion inhibitor R2 in retarding reinforcement corrosion. The electrochemical test results and surface analysis results using ESCA and AES techniques showed the better performance of inhibitor R2 compared to inhibitor M2 in retarding corrosion of steel in an environment of saturated calcium hydroxide in the presence of chloride ions.

Durability of proprietary cementitious materials for use in wastewater transport systems

Abstract Several methods and materials, such as high performance coatings, fiber glass reinforced linings, special mortars, brick or ceramic linings, etc., are used to protect concrete from sulfuric acid attack in a sewage environment. Two proprietary high alumina cementitious lining materials, CC and SC, are recent additions to the list of protective materials used in the Arabian Gulf. This paper documents the findings of a laboratory study under accelerated conditions as well as a two-year field study of CC and SC in a wastewater lift station in Jubail, Saudi Arabia. In the laboratory investigations, 50 mm cube mortar specimens prepared using: (1) SC, (2) CC, (3) Type I+8% silica fume cement, (4) Type I+20% fly ash cement and (5) Type I cement were exposed to 2% sulfuric acid for 150 days. The laboratory specimens were tested for weight reduction, compressive strength, sulfate content, and alkalinity. In the field, the walls and ceiling of a wastewater manhole were coated using the proprietary lining materials, SC and CC, and were exposed to a normal sewage service environment. Performance of the liner materials was monitored for sulfate content and alkalinity after 6, 12 and 24 months of exposure. The analysis and evaluation test data generated from the accelerated laboratory study and the field study, which lasted for 24 months, showed that SC performed better than other materials tested in this investigation.

Efficiency of generic and proprietary inhibitors in mitigating Corrosion of Carbon Steel in Chloride-Sulfate Environments

The efficiency of generic and proprietary corrosion inhibitors (based on nitrite, amine carboxylate or amino alcohol) in corrosion mitigation of carbon steel, which is exposed to concrete solutions with different amounts of chloride as well as sulfate, was studied. The corrosion protection provided by the selected corrosion inhibitors was investigated by performing a potentiodynamic polarization study. In addition, the surface morphological properties of carbon steel samples exposed to the electrolyte mixed with or without inhibitors was also evaluated by scanning electron microscopy. The potentiodynamic polarization measurements showed that the evaluated inhibitors decreased the corrosion current density by 1.6 to 6.7 times depending on the type of inhibitor and the level of sulfate concentration in the electrolyte. The performance of inhibitors based on nitrite was better than that of inhibitors based on amine carboxylate or amino alcohol. The possible mechanisms of the inhibition in the chloride plus sulfate environments are also elucidated.