خصائص الاعمدة الدائرية الخرسانية المسلحة المستدامة المعرضة لمياه البحر

Characteristics of Sustainable Reinforced Concrete Circular Columns Exposed to Sea Water

Abstract

Reinforced concrete structures in marine environments face severe environmental challenges due to constant exposure to chloride and sulfate ions present in seawater, which contribute to concrete deterioration and accelerate the corrosion of reinforcing steel, reducing service life and increasing maintenance costs. To address this problem, research is directed toward developing sustainable concrete mixes using fine admixtures such as mineral powders and pozzolanic materials, which improve density, reduce permeability, and resist harmful chemical reactions.
This study aims to evaluate the performance of reinforced concrete columns made from mixes containing secondary materials that partially replace cement, such as glass powder, ceramic powder, and marble powder, as well as cement additives such as carbon black powder and graphite powder.
These materials were incorporated in the concrete mixes either as additives specifically carbon black and graphite powders at ratios of 0.5%, 1%, and 1.5% by weight of cement or as partial cement replacements, including glass, ceramic, and marble powders at replacement levels of 5%, 10%, and 15%. A total of sixteen concrete mixes were investigated in this study, comprising five different powder-based cement replacement materials, each tested at three replacement or additive ratios, in addition to a reference mix without any supplementary materials.
The tested specimens were subjected to a comprehensive experimental program that included mechanical, structural, and durability evaluations. Mechanical tests involved measuring compressive strength, splitting tensile strength, and density. Structural behavior was assessed through ultimate load capacity, ductility, and toughness indices. For durability assessment, the specimens underwent chloride ion penetration testing, water permeability under pressure, and half-cell potential measurements to evaluate the likelihood of reinforcement corrosion. The structural tests were conducted on two groups of specimens: the first group was unexposed to corrosion, while the second group underwent accelerated corrosion through the application of an electric current.
The enhanced mixtures incorporating fine powders demonstrated a notable improvement in the structural capacity of concrete columns. The mixture containing 15% ceramic powder recorded the highest increase in ultimate load, with an improvement of 19.16% compared to the reference mix. This was followed by the glass powder mixture 10% with a 17.69% increase, graphite powder 0.5% with 11.69%, marble powder 10% with 11.36%, and finally carbon black 0.5% with an 8.93% increase. These results reflect the positive influence of the added powders in enhancing axial load resistance and improving the internal cohesion of concrete.
Under accelerated corrosion conditions, several modified mixtures exhibited a smaller reduction in ultimate load compared to the reference mix, which lost 19.6% of its structural capacity. The best performance in terms of durability was achieved by the graphite powder mix 0.5%, with only a 3.6% decrease in load capacity, followed by 0.5 % carbon black 3.73%, 10% marble powder 12.39%, 10% glass 16.69%, and 15% ceramic 18.64%. These findings highlight the effectiveness of certain powders, particularly graphite and carbon black, in mitigating the adverse effects of corrosion on structural behavior.
Several modified mixtures also showed reduced water permeability under pressure relative to the reference mix, indicating improved resistance to fluid and contaminant ingress. The 10% glass powder mixture exhibited the highest reduction at 76.92%, followed by 15% ceramic powder 68.46%, 0.5% graphite powder 33%, 10% marble powder 31.54%, and 0.5% carbon black 24.62%. This improvement is attributed to both the physical and chemical roles of the powders in reducing porosity and enhancing particle packing.
Regarding chloride ion penetration resistance, all mixtures outperformed the reference mix, reflecting a positive impact on corrosion resistance. The graphite powder mix 0.5% achieved the greatest reduction in chloride ingress at 76.27%, followed by 0.5% carbon black 45.76%, 15% ceramic powder 34.58%, 10% marble powder 33.05%, and 10% glass powder 30.51%. These outcomes indicate that the powders, especially graphite powder, enhance reinforcement protection in chloride-rich environments.
The non-presentation of the remaining mixes does not imply poor performance; rather, the highlighted mixes demonstrated improvements across all tests, unlike the others, which showed either slight decreases or marginal improvements in certain aspects.
The study recommends selecting precise and well-thought-out additive ratios based on the physical and chemical properties of the materials while avoiding excessive use of highly conductive materials until their homogeneous distribution is ensured. It also emphasizes the importance of conducting a comprehensive assessment of mechanical and structural properties when designing concrete mixes intended for aggressive environments to ensure long-term performance sustainability.