Abdullah A. Almusallam

Effect of reinforcement corrosion on bond strength

Abstract The effect of reinforcement corrosion on the bond strength between steel and concrete was investigated. The bond behaviour of reinforced concrete elements, including the ultimate bond strength, free-end slip, and the modes of failure in precracking, cracking and postcracking stages was studied. Also, the effect of different crack widths and the rib profile degradation for various degrees of corrosion on the bond strength were evaluated. In order to establish different levels of corrosion, a calibration curve establishing a relationship between the duration of the impressed current and the corresponding degree of corrosion was prepared. The magnitude of corrosion was measured as gravimetric loss in weight of the reinforcing bars. The results indicate that in the precracking stage (0–4% corrosion) the ultimate bond strength increases, whereas the slip at the ultimate bond strength decreases with an increase in the degree of corrosion. The degradation of bond results from the crushing of concrete keys near the bar lugs. When reinforcement corrosion is in the range of 4 to 6%, the bond failure occurs suddenly at a very low free-end slip. At this level of reinforcement corrosion, a large slip was noted as the ultimate failure of the bond occurred due to the splitting of the specimens. Beyond 6% rebar corrosion, the bond failure resulted from a continuous slippage of the rebars. The ultimate bond strength initially increased with an increase in the degree of corrosion, until it attained a maximum value of 4% rebar corrosion after which there was a sharp reduction in the ultimate bond strength up to 6% rebar corrosion. Beyond the 6% rebar corrosion level the ultimate bond strength did not vary much even up to 80% corrosion. In terms of the effect of rib profile, a sharp reduction in the bond strength was initiated when its degradation exceeded 25%. This decrease in bond strength continued up to 45%. Thereafter, there was no significant effect of the rib profile degradation on the bond strength.

Effect of degree of corrosion on the properties of reinforcing steel bars

Abstract This paper reports results of a study conducted to assess the effect of degree of corrosion of reinforcing steel bars on their mechanical properties. Reinforcing steel bars, 6 and 12 mm in diameter, that were corroded in reinforced concrete specimens were removed and tested in tension. Results indicated that the level of reinforcement corrosion does not influence the tensile strength of steel bars, calculated on the actual area of cross-section. However, when the nominal diameter is utilized in the calculation, the tensile strength is less than the ASTM A 615 requirement of 600 MPa when the degree of corrosion was 11 and 24% for 6- and 12-mm diameter steel bars, respectively. Furthermore, reinforcing steel bars with more than 12% corrosion indicates a brittle failure.

Effectiveness of surface coatings in improving concrete durability

This paper reports results of a study conducted to evaluate the durability of concrete coated with concrete surface coatings representing five generic types. The durability of the uncoated and coated concrete specimens was evaluated by assessing water absorption, chloride permeability and chloride diffusion. The chemical resistance was evaluated by immersing the uncoated and coated mortar specimens in 2.5% sulfuric acid. The results indicated that epoxy and polyurethane coatings performed better than acrylic, polymer and chlorinated rubber coatings. However, noticeable variation in the performance of the same generic type procured from different manufacturers was noted. Therefore, the selection of coatings should be done after conducting trial tests rather than basing it solely on the generic type.

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.

Factors affecting threshold chloride for reinforcement corrosion in concrete

Three cements with variable C3A contents were mixed with different levels of chloride, alkali and sulfate contents to study the effect of these parameters on pore solution composition. Effect of exposure temperature was also studied by curing the chloride-treated specimens at 20 ° and 70 °C. Pore solution was extracted using a high pressure pore solution extrusion device and analysed for chloride and hydroxyl ion concentrations. Threshold chloride for onset of reinforcement corrosion was computed using threshold [Cl−OH−] ratio of 0.3. The results showed that C3A content and exposure temperature have very strong influence on threshold chloride content. Alkali content of cement has marginal effect whereas presence of sulfates along with chlorides has moderate effect on the threshold chloride content.

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.

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.

Effect of environmental conditions on the properties of fresh and hardened concrete

Abstract The effect of varying environmental conditions, at the time of casting on the properties of fresh and hardened concrete was evaluated. The influence of air temperature, wind velocity, and relative humidity on plastic shrinkage, compressive strength, pulse velocity and pore structure of concrete was investigated. Results indicate that exposure conditions at the time of casting significantly affect plastic shrinkage of concrete. As expected elevated temperature affected porosity, compressive strength, and pulse velocity of concrete. Casting of concrete at elevated temperature decreased its compressive strength. Similarly, the pulse velocity of concrete cast at 45°C was less than that of cast at 30°C. The volume of total pores in the concrete specimens cast at 45°C was more than that of cast at 30°C. The lower pulse velocity and increased pore volume in the concrete cast at 45°C than that cast at 30°C may be attributed to the coarse pore structure formed in the former than the latter. Other weather parameters, such as relative humidity and wind velocity, also influence the properties of fresh and hardened concrete.

EFFECT OF MIX PROPORTIONS ON PLASTIC SHRINKAGE CRACKING OF CONCRETE IN HOT ENVIRONMENTS

Abstract The effect of mix proportions, i.e. cement content and water–cement ratio, on plastic shrinkage cracking of concrete in hot and arid environments was investigated. The cumulative effect of these parameters on plastic shrinkage of concrete was assessed by measuring the rate of bleeding, water evaporation, and time and intensity of cracks. The results indicated that cement content and water–cement ratio significantly affect the parameters controlling plastic shrinkage of concrete. Lean-stiff concrete mixes cracked earlier than the rich-plastic concrete mixes. The intensity of cracks in the former was, however, less than that in the latter. Plastic shrinkage cracking occurred when the rate of evaporation was in the range of 0.2–0.7 kg m−2 h−1, as against a value of 1 kg m−2 h−1 suggested by ACI 305. The rate of evaporation and bleeding was the least in a lean-stiff concrete mix made with a cement content of 300 kg m−3 and a water–cement ratio of 0.40, indicating that this mix composition can be beneficially utilized in hot environments to minimize plastic shrinkage cracking.