Stainless Steel Rebars Research Articles

Galvanic Coupling Between Carbon Steel and Stainless Steel Reinforcements

Galvanic corrosion is a potentially major concern associated with the application of stainless steel reinforcement which is in direct (electrical) contact with carbon steel reinforcement in concrete structures. Judicious use of stainless steel rebar in both new construction and rehabilitation of older structures is a viable, cost effective option for extending service life and reducing maintenance costs. Questions, however, have arisen about the possibility of increased corrosion due to galvanic effects. This paper investigates the galvanic coupling behaviours of three different types of stainless steel and carbon steel. Tests were performed both in electrochemical cells and with specimens in concrete inside an environmental chamber. The results show that oxygen reduction on stainless steel is the rate determining factor for galvanic coupling of these two metals. It is much lower than that of passive carbon steel. As a result, the galvanic coupling of stainless steel with carbon steel will not increase the risk of corrosion of carbon steel reinforcement.

Threshold Chloride Concentrations of Selected Corrosion-Resistant Rebar Materials Compared to Carbon Steel

Abstract The threshold chloride concentration for solid Type 316LN (UNS S31653) stainless steel, Type 316L (UNS S31603) stainless steel clad, 2101 (UNS S32101), Fe-9%Cr, and carbon steel rebar (ordinary ASTM A 615M) was investigated using potentiodynamic and potentiostatic current monitoring techniques in saturated calcium hydroxide (Ca[OH]2) + sodium chloride (NaCl) solutions. There is general consensus in this study and the literature that the chloride threshold for carbon steel is less than a chloride to hydroxl (Cl−/OH−) molar ratio of 1. Solid Type 316LN stainless steel rebar was found to have a much higher chloride threshold (i.e., threshold Cl−/OH− ratio > 20) than carbon steel (0.25 < Cl−/OH−< 0.34). Type 316L stainless steel clad rebar possessed a chloride threshold expressed as a Cl−/OH− ratio of 4.9 when cladding was intact. However, surface preparation, test method, duration of period exposed to a passivating condition prior to the introduction of chloride, and the presence of cladding defects all affected the threshold chloride concentration obtained. For instance, the presence of mill scale on any of the more corrosion-resistant materials reduced the chloride threshold to approximately that of carbon steel. The chloride threshold for Type 316L clad rebar was highly dependent on any defects that exposed the carbon steel core. At best, it was similar to that of solid stainless steel. However, when defective, it was equal to that of carbon steel rebar in the potentiostatic method used here. A model was implemented to predict the extension of the Cl− diffusion time period until corrosion initiation would be expected using rebar materials with a higher chloride threshold concentration than carbon steel. Model results confirmed that corrosion-resistant rebar materials in a pickled condition may increase time until chloride-induced breakdown of passivity and onset of corrosion to 100 years or more.

Stainless steel rebars, a cost effective and sustainable solution to the corrosion of structures

Civil engineering structures may suffer accelerated damage from the corrosion of their carbon steel reinforcement bars. This corrosion originates from the carbonatation of concrete that lowers the pH and from the diffusion of chlorides through the concrete. It generates heavy maintenance and repair costs and it significantly reduces the service life of the structures. These consequences can be avoided with the general or partial use of stainless steel reinforcement bars. This solution affords many advantages: Significant reduction of the maintenance costs. Increased sustainability. Reduced service costs. Improved safety. Optimized concrete thickness. The limited extra cost of stainless steel rebars over carbon steel rebars is quickly overcompensated for by the savings that they allow on maintenance costs.

Stainless steel rebar: the choice of service life

Use of stainless steel rebar for concrete reinforcement is increasing worldwide. The enhanced properties of stainless steel prove to be a viable solution when life cycle costs of the structures are taken into account. Austenitic and duplex stainless steels are used as rebar because they present an excellent combination of corrosion resistance in concrete, high strength and good ductility. Stainless steel reinforcements are compared with conventional carbon steel reinforcements to point out the specificities and advantages of the stainless steel solution. The influence of the fabrication method (hot or cold rolling) on microstructure, strength and ductility is also discussed. The resistance to pitting corrosion of various stainless steels has been evaluated in the laboratory by electrochemical tests. This helps to select the most suitable grade according to the environment in which the concrete structure is located and the risks of exposure to aggressive atmospheres and attack during its life. The studied grades are: 1.4301, 1.4311, 1.4404, 1.4429, 1.4362 and 1.4462. The tests were carried out at pH between 8 and 12 in chloride-containing solutions to simulate the concrete pore liquid in a seawater environment or penetration by road de-icing salts. A classification of the selected austenitic and duplex grades was created.

GALVANIC COUPLING BETWEEN CARBON STEEL AND STAINLESS STEEL REINFORCEMENTS

Galvanic corrosion is a potentially major concern associated with the application of stainless steel reinforcement which is in direct (electrical) contact with carbon steel reinforcement in concrete structures. Judicious use of stainless steel rebar in both new construction and rehabilitation of older structures is a viable, cost effective option for extending service life and reducing maintenance costs. Questions, however, have arisen about the possibility of increased corrosion due to galvanic effects. This paper investigates the galvanic coupling behaviours of three different types of stainless steel and carbon steel. Tests were performed both in electrochemical cells and with specimens in concrete inside an environmental chamber. The results show that oxygen reduction on stainless steel is the rate determining factor for galvanic coupling of these two metals. It is much lower than that of passive carbon steel. As a result, the galvanic coupling of stainless steel with carbon steel will not increase the risk of corrosion of carbon steel reinforcement.

Performance of galvanized and stainless steel rebars in concrete under macrocell corrosion conditions

In the recent past, the damage caused by rebar corrosion in concrete structures has been considered as one of the major durability problems affecting the service life of concrete structures. In order to prevent corrosion of steel reinforcement, various types of protective methods have been adopted. One of the protective measures is using galvanized reinforcement in concrete to enhance the service life. In the present study various types of galvanized rebars namely bare – Cold Twisted Deformed (CTD), bare – Thermo Mechanically Treated (TMT), galvanized – Cold Twisted Deformed, Galvanized – Thermo Mechanically Treated, galvanized and chromated – Cold Twisted Deformed, galvanized and chromated – Thermo Mechanically Treated and stainless steel rebars have been evaluated for their corrosion resistance in M30 grade concrete under macro cell corrosion condition over a period of one year. From the studies it has been observed that TMT bars performed better when compared to CTD bars. Among the rebars tested, stainless steel rebar has shown negligible corrosion in chloride contaminated concrete.

Mechanical properties and corrosion behaviour of stainless steel reinforcing bars

Austenitic stainless steels have recently been used as reinforcing bars in special civil constructions in order to increase their expected life in corrosion environments. The complete mechanical characterization of two kinds of austenitic stainless steel rebars, 304LN and 316LN grades, obtained after hot and cold rolling schedules, was performed. Their mechanical properties and the influence on these of the rib region were obtained, as well as determining the fracture behaviour of these bars by means of their J– R curves. The experimental work was completed with the study of the corrosion behaviour of all the bars in a saline environment. All the results have been justified taking into account the fabrication method employed in each case.

Bridge using stainless steel rebar to last 120 years

Bridge using stainless steel rebar to last 120 years

Prevention of Chloride-induced Corrosion Damage to Bridges.

The annual direct cost of bridge infrastructure corrosion to the U.S. economy is estimated at $8.3 billion, with indirect costs approximately 10 times higher. Of the approximately 600000 bridges in the U.S., between 15% and 20% are listed as “structurally deficient”, frequently due to corrosion damage. Five technologies are presented for reducing the cost of chloride-induced corrosion damage: (1) conductive coating anodes for cathodic protection of existing reinforce concrete bridges, (2) epoxy-coated rebar (ECR), (3) stainless steel rebar, and (4) high-performance concrete for extending the service life of new structures, and (5) metalizing to provide economical, long-term corrosion protection of steel bridges. Conductive coating anodes and stainless steel rebar represent ongoing work by the Oregon Department of Transportation with final verdicts not expected for years. The ECR and metalizing technology have longer track records and are better established in the bridge construction and protection industry. Application of these technologies is guided by a thorough understanding of their performance, of characteristics of the bridge and its environment, and of the results that are sought.

Pullout Tests on Deformed and Plain Rebars in Cement-Stabilized Rammed Earth

Stabilized rammed earth offers a low energy durable alternative to conventional building materials, such as masonry and processed timber, for low-rise residential projects. To date, rammed earth construction has mainly been used in the developing world, particularly Africa and Asia. Despite recent applications in Australia and the United States, further development of rammed earth in these countries has been hindered by a lack of data on important aspects of material performance. In this paper, work undertaken to assess bond of rebars embedded in rammed earth is described. A variety of cement-stabilized rammed earth pullout test samples were fabricated with deformed, galvanized deformed, plain, and stainless steel rebar. Pullout bond resistance is shown to be a function of rammed earth compressive strength, rebar type, embedment length, and the method of specimen preparation.

Corrosion resistance of stainless steel in chloride contaminated concrete

The results of an investigation of the performance of 2-year-old stainless steel reinforced concrete specimens which were previously placed in an aggressive aqueous solution containing chlorides are presented. This study consisted of corrosion rate testing of reinforced concrete samples with normal reinforcing steel and stainless steel rebars by means of the a.c. impedance spectroscopy. The equivalent circuit simulation analysis method was applied in the data interpretation. The performance and effectiveness of stainless steel in preventing corrosion in chloride contaminated concrete was evaluated.

The performance of a 12% chromium steel in concrete in severe marine environments

3CR12, essentially a 12% Cr steel, was used in two series of exposure programmes to assess its performance as reinforcing in concrete. In the first exposure programme, steel and 3CR12 in the pickled and passivated condition were exposed in a specially designed marine climate simulator. Comparative performance after 4 1 2 years exposure confirmed 3CR12 as a viable durable reinforcing material for concrete. In the second exposure programme, steel, 3CR12, 316 and 304 stainless steel were exposed in the hot rolled condition (scale intact). Galvanised steel and powder epoxy coated rebar were also exposed. Exposures were carried out at a severely corrosive marine site and in the simulator. Within 2 years, the results from this programme emphasized the need to remove all hot-roll scale from the 3CRI2, the 316 and 304 stainless steel rebars before being used as reinforcing in concrete. Galvanized steel rebars performed poorly. Powder epoxy coated rebars showed severe under-rusting and corrosion. By comparison steel rebars performed extremely badly. Despite the highly alkaline conditions (i.e. the absence of carbonation), chloride penetration caused severe corrosion; the chloride front penetrating through 25 mm of good concrete cover within 2 years.