Ahmad S. Al-Gahtani’s research while affiliated with King Fahd University of Petroleum and Minerals and other places

The effect of reinforcement corrosion on the flexural strength of a uniformly loaded and simply supported one-way slab was investigated. In addition to the flexural strength, the effect of different degrees of reinforcement corrosion on the deformational behavior ductility, and the mode of failure of the slabs were also evaluated. The critical level of reinforcement corrosion that renders the strength contribution of steel negligible was evaluated by comparing the strengths of slabs with highly corroded reinforcement with the strengths of plain concrete slabs. In order to induce different levels of reinforcement corrosion, a calibration curve establishing a relationship between the duration of the impressed current and reinforcement corrosion was prepared. The magnitude of reinforcement corrosion was measured as gravimetric loss in weight of the steel bars. The results indicate a sharp reduction in the ultimate flexural strength of slabs with an up to a 29% reinforcement corrosion; thereafter, the strength decreased at a somewhat reduced rate with further increase in reinforcement corrosion. The ultimate deflection of the slabs decreases with an increase in the magnitude of reinforcement corrosion, leading to a marked and progressive reduction in the ductility of the slabs. Furthermore, the strength of plain-concrete slabs and those reinforced with Steel bars of less than 60% corrosion was almost similar.

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.

Performance data based on accelerated corrosion-monitoring and exposure site tests indicate that cement type, reflecting particularly the C3A content, significantly affected concrete durability with respect to corrosion of reinforcing steel. On average, Type I cement (C3A = 9.5 percent) performed 1.7 times better than Type V cement (C3A = 2.8 percent) in terms of time of initiation of corrosion. Accelerated sulfate-resistance tests show that a 20 percent microsilica blended with Type I 14 percent C3A cement performed 1.4 times better against sulfate attack than a Type V portland cement with 1.88 percent C3A. Also, sulfate deterioration data indicate that, in addition to the C3A content, the C3S/C2S ratio of the cement has a significant effect on the sulfate resistance of the cement. Additional study results are discussed.

Adverse geomorphic and climatic conditions as well as defective construction practices control concrete performance in the Arabian Gulf area. Condition surveys on structures located in Eastern Saudi Arabia show an alarming degree of deterioration within the short span of 10 to 15 years. Data show that this deterioration is attributable in decreasing order of importance to corrosion of reinforcement, sulfate attack, and environmental cracking. The mechanisms of these causal factors are discussed with respect to the environmental conditions of the Gulf coast.