Mohammed Maslehuddin

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 Magnesium Sulfate and Sodium sulfate on the Durability Performance of Plain and Blended Cements

In this investigation, mortar specimens made with two plain cements, Type I and V, and blended cements, made with fly ash, silica fume, and blast furnace slag, were exposed to sodium-sulfate and magnesium-sulfate solutions. The performance of these cements, in both the environments, was evaluated by measuring expansion and determining reduction in compressive strength. The data indicate that while the performance of all blended cements, particularly those made with silica fume, was generally excellent in the sodium-sulfate environment, their performance in the magnesium-sulfate environment was not satisfactory. A similar trend was observed in mortar specimens made with a water-cement ratio of 0.35. The type of cement did not have any significant influence on the performance of either plain or blended cements in both environments. The deterioration of plain and blended cements in sodium-sulfate and magnesium-sulfate environments is attributed to the initial reaction of sodium sulfate and magnesium sulfate with calcium hydroxide. The reduction of calcium hydroxide in blended cements provides an opportunity to magnesium sulfate to react more directly with the primary and secondary calcium silicate hydrate due to the destabilization of these phases by magnesium hydroxide. Comparatively, lower deterioration of blended cements exposed to the sodium-sulfate environment is attributed to the reduced calcium hydroxide, which significantly mitigates the sulfate attack in these cements.

Effect of coarse aggregate quality on the mechanical properties of high strength concrete

Abstract This paper reports results of a study conducted to evaluate the effect of four types of coarse aggregates, namely calcareous, dolomitic, quartzitic limestone, and steel slag, on the compressive and tensile strength, and elastic modulus of high strength concrete. The highest and lowest compressive strength was obtained in the concrete specimens prepared with steel slag and calcareous limestone aggregates, respectively. Similarly, the split tensile strength of steel slag aggregate concrete was the highest, followed by that of dolomitic and quartzitic limestone aggregate concretes. The lowest split tensile strength was noted in the calcareous limestone aggregate concrete. The type of coarse aggregate also influences the modulus of elasticity of concrete. Weaker aggregates tend to produce a more ductile concrete than stronger aggregates do.

Sulfate resistance of plain and blended cements exposed to varying concentrations of sodium sulfate

Concrete deterioration due to sulfate attack is the second major durability problem, after reinforcement corrosion. This type of deterioration is noted in the structures exposed to sulfate-bearing soils and groundwater. Though concrete deterioration due to sulfate attack is reported from many countries, the mechanisms of sulfate attack have not been thoroughly investigated, particularly the effect of sulfate concentration and the cation type associated with the sulfate ions on concrete deterioration. This study was conducted to evaluate the performance of plain and blended cements exposed to varying concentrations of sodium sulfate for up to 24 months. Four types of cements, namely Type I, Type V, Type I plus silica fume and Type I plus fly ash, were exposed to five sodium sulfate solutions with sulfate concentrations of 1%, 1.5%, 2%, 2.5% and 4%. These concentrations are representative of the sulfate concentration in highly saline soils. The sulfate resistance was evaluated by visual examination and measuring the and reduction in compressive strength. The maximum deterioration, due to sulfate attack, was noted in Type I cement followed by silica fume and Type V cements. The performance of Type V, Type I plus silica fume and Type I plus fly ash was not significantly different from each other. The enhanced sulfate resistance noted in the Type I cement blended with either silica fume or fly ash indicates the usefulness of these cements in both sulfate and sulfate plus chloride environments.

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.

ROLE OF CHLORIDE IONS ON EXPANSION AND STRENGTH REDUCTION IN PLAIN AND BLENDED CEMENTS IN SULFATE ENVIRONMENTS

Abstract The deterioration of concrete due to sulfate salts in soils, groundwater and marine environments is a well-known phenomenon. While it is known that the use of low-C3A cements can provide protection against sulfate attack, the combined effect of chloride and sulfate salts on such a deterioration is highly debated and inconclusive. Moreover, the use of blended cements incorporating supplementary cementing materials, such as natural pozzolan, fly ash, blast furnace slag and silica fume, is becoming common these days. The performance of these cements in environments characterized by the conjoint presence of chlorides and sulfates, however, is not well documented. In this investigation, the effect of sulfate and sulfate-chloride environments on the expansion and reduction in strength of mortar specimens due to sulfate attack was evaluated. Results indicated that the presence of chloride ions in the sulfate environments mitigated the sulfate attack in plain and blended cements. The performance of plain cements was better than that of all blended cements. However, the performance of blended cements was observed to depend on the type of mineral admixture used, both in the sulfate and the sulfate-chloride environments.

Long-term effect of sulfate ions and associated cation type on chloride-induced reinforcement corrosion in Portland cement concretes

This paper reports the influence of sulfate concentration on chloride-induced reinforcement corrosion in Portland cement concretes (with C3A varying from 3.6% to 9.65%). The concrete specimens were exposed to mixed chloride and sulfate solutions for a period of 1200 days. The chloride was fixed at 5% NaCl for all solutions, while the sulfate concentration was varied to represent that noted in the sulfate-bearing soil and ground water. The study included an assessment of the effect of cation type associated with sulfate ions, namely Na+ and Mg2+, on chloride-induced reinforcement corrosion, an important factor that has received little attention. Reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density at regular intervals. The results indicate that the presence of sulfate ions in the chloride solution did not influence the time to initiation of chloride-induced reinforcement corrosion, but the rate of corrosion increased with increasing sulfate concentration. Further, the rate of chloride-induced reinforcement corrosion in the concrete specimens exposed to sodium chloride plus magnesium sulfate solutions was more than that in the concrete specimens exposed to sodium chloride plus sodium sulfate solutions.

EFFECTIVENESS OF CORROSION INHIBITORS IN CONTAMINATED CONCRETE

Abstract Four types of corrosion inhibitors (calcium nitrite at two dosages, calcium nitrate at three dosages and two organic inhibitors at their recommended dosages) were evaluated at five different levels of contamination, i.e., 0.8% chloride; 0.8% chloride plus 1.5% SO3; seawater; brackish water; and unwashed aggregates. Concrete specimens were used to assess the effect of corrosion inhibitors on the compressive strength of concrete and reinforcement corrosion. The results indicated that the corrosion inhibitors investigated in this study did not adversely affect the compressive strength of concrete. Furthermore, calcium nitrite was efficient in delaying the initiation of reinforcement corrosion in the concrete specimens contaminated with chloride, while both calcium nitrite and calcium nitrate mitigated the corrosive effects of chloride plus sulfate salts or sea water. In the concrete specimens prepared with brackish water or unwashed aggregates, all the inhibitors were effective in reducing the rate of reinforcement corrosion. The type and dosage of corrosion inhibitor were observed to be dependent on the nature and level of contamination.

Mechanical properties and durability characteristics of polymer- and cement-based repair materials

This study was conducted to evaluate the mechanical properties and durability characteristics of nine polymer- and cement-based repair mortars. Mechanical properties, such as compressive, tensile and flexural strength, elastic modulus, shrinkage and thermal expansion were studied. The durability characteristics of the repair materials were evaluated by measuring: (i) chloride permeability, (ii) electrical resistivity and (iii) carbonation depth. The mechanical properties of the selected repair mortars did not vary very significantly from each other. The elastic modulus of the polymer-based repair mortars was less than that of the cement-based repair mortars. This will lead to a reduced drying shrinkage cracking in the former repair mortars compared to the latter. The electrical resistivity of polymer-based repair mortars was more than that of cement-based repair mortars. Such a trend was not noted in the chloride permeability data. The chloride permeability in all the repair materials was very low according to ASTM C 1202 criteria. Enhanced carbonation was noted in some of the polymer-based repair mortars.

Effectiveness of concrete surface treatmentmaterials in reducing chloride-induced reinforcement corrosion

Abstract The effectiveness of concrete surface treatment materials, such as silane, siloxane, acrylic coating, etc., in reducing chloride-induced reinforcement corrosion was investigated. Two sets of reinforced concrete specimens were cast. In the first set, reinforcement corrosion was accelerated by impressing an anodic potential of 2 V and the time to cracking was monitored. The second set of concrete specimens were immersed in the chloride solution and reinforcement corrosion was monitored by measuring corrosion potentials and corrosion current density. Among the surface treatment materials investigated, silane, silane/siloxane with top coat and acrylic coating were effective in reducing the rate of reinforcement corrosion. Furthermore, the data developed in this investigation indicated that the performance of coatings can be quickly evaluated using impressed current technique.