International Concrete Abstracts Portal

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 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 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.

The title of this paper borrows from the 1981 book by Harold Kushner entitled “When Bad Things Happen to Good People”. In his book, Kushner attempts to explain why a universe created by a deity who is of a good and loving nature still holds so much pain and suffering for good people. In the context of this paper, the title is meant to be an epigraph that suggests that although a building may be meeting its intended structural purpose, bad things, at least as they are perceived, can happen during design, construction and service of the building that bring its safety into question. One of the main circumstances that can bring into question the integrity of an unbonded post-tensioned building is corrosion of the strands and anchorage components. This paper will highlight the unnecessary demise of a modern high-rise post-tensioned structure due to corrosion, and contrast that outcome to several existing unbonded post-tensioned buildings that experienced corrosion and were successfully repaired and continue to function.

Accurate determination of the locations and sizes of actively corroding areas on embedded steel reinforcement in concrete is rather challenging using the standardized half-cell potential mapping technique. In this research, it is hypothesized that half-cell potentials on the surface of the concrete can be used, beyond their originally intended purpose, to identify the locations and sizes of anodic and cathodic sites on the steel reinforcement by means of inverse modeling algorithms. The problem, simply put, is a boundary identification problem: given the potential measurements on the surface of the concrete, identify the anodic and cathodic boundaries on the surface of the reinforcement. To this end, a conjugate-gradient based inverse modeling algorithm is developed to assimilate standard half-cell potential measurements on the concrete surface and to calculate the potential distribution on the surface of the reinforcement. The performance of the inverse model is demonstrated with various configurations of corroding systems with single and multiple anodes using identical twin numerical experiments. The results show that the developed inverse modeling algorithm is robust and can be used as a starting point to investigate more practical cases for which the number of observation points on the surface of the concrete is limited.