The repair and rehabilitation of corroding infrastructure systems consumes significant resources. It is well documented that significant value is gained by using durable materials that exhibit long-term, repair-free performance. In the US, most state highway agencies (SHAs) are approached by material producers and requests are made to evaluate the material for possible use in the infrastructure system. SHAs have limited resources and are in need of new evaluation methods that are reliable, fast, and cost-effective. This research evaluated four different accelerated test methods for evaluating the corrosion performance of steel in cementitious materials. Results were compared with results from the commonly used standard ASTM G 109 test method. The corrosion performance of conventional bars, stainless steel bars, galvanized bars, and epoxy-coated bars were evaluated using concrete and mortar mixtures with different water-cement ratios and containing different amounts of a corrosion inhibitor. The effectiveness, time requirements, complexity, and costs of the new test methods were compared with the ASTM G 109 method. This research found that the Rapid Macro-cell Test (RMT) is relatively simple to perform and provides reasonable results for most products in a reasonable time frame with minimal relative cost.

This CD contains 10 papers presented at the ACI Spring Convention, Dallas, TX, March 2012, and sponsored by ACI Committee 222, Corrosion of Metals in Concrete. The papers cover a variety of subject areas, including mechanism of corrosion of reinforcing steel in concrete; identifying, investigating, and quantifying corrosion; corrosion control measures for new and existing structures; and innovative materials and testing techniques. Engineers, scientists, researchers, inspectors, technicians, academics, materials manufacturers, and suppliers will all benefit from this SP. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-291

This paper presents the preliminary results of a study examining the stress vs. strain behavior, stress relaxation, and corrosion resistance of six candidate high-strength stainless steels (HSSSs) for potential use as corrosion-resistant prestressing reinforcement in concrete structures. Austentic grades 304 and 316; duplex grades 2101, 2205, and 2304; and a precipitation hardened martensitic grade 17-7 were selected for the investigation and cold drawn to diameters of approximately 4 mm (0.16 in). Tensile strengths of 1290 to 1550 MPa (185 to 225 ksi) were achieved in the cold-drawn HSSS wires. 1000-hr stress relaxation of all candidate HSSSs was predicted to be between 6 and 8 % based on the results of short-term relaxation tests conducted at 70% ultimate tensile capacity. Cyclic polarization testing for chloride-induced corrosion resistance determined that in alkaline pore solutions, 2205 and 2304 exhibited low corrosion susceptibility and 304 exhibited moderate corrosion susceptibility at 0.5 M chloride concentrations. When exposed to carbonated pore solutions with 0.5 M chloride, grades 2205 and 2304 exhibited low and moderate corrosion susceptibility, respectively. Duplex grade 2205 exhibited superior corrosion resistance in all cases. Based on these results, optimal HSSSs were identified as duplex grades 2205 and 2304.

Electrochemical polarization and Raman spectroscopy were used to investigate the passive film formation of four grades of stainless steels in concrete and synthetic concrete pore solutions. Steels tested were austenitic grades UNS S24100 and UNS S31603, and duplex grades UNS S32101 and UNS S32304. These techniques have identified both similarities and differences in the protective films. The air-formed Cr2O3 film is not stable on any of the steels at potentials more anodic than approximately -100 mV SCE. In its stead, CrO3 and mixed spinels form at more anodic potentials. The manganese-bearing grades (S24100 and S32101) exhibited Raman peaks attributed to manganese-bearing spinels, indicating that these steels form unique passive films. These films show similar stability and breakdown behaviour in chloride-free pore solutions; studies in chloride-bearing solutions are on-going.

This paper describes a prototype passive sensor that can be powered and interrogated in a wireless manner to monitor the conditions inside structural concrete members. The term “passive” is used because the sensors do not include any on-board processing capabilities or sources of power (batteries). The sensors are designed to be embedded in the concrete during construction and interrogated sporadically over the life of the structure. The response of an embedded sensor is determined by measuring the impedance of an external reader coil that is magnetically coupled to the sensor. To date, the research has focused on detecting the initiation of corrosion within concrete structures. Accelerated corrosion tests were used to evaluate the reliability of the passive sensors. Sensors were embedded in reinforced concrete prisms and successfully detected the onset of corrosion in the reinforcement. Unlike the traditional measurements, such as half-cell potentials, the passive sensor readings did not fluctuate with changes in the temperature or moisture content of the concrete.