International Concrete Abstracts Portal

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.

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.

The purpose of this report is to compare the corrosion resistance of several proprietary combinations of stucco and wire reinforcing mesh (lath) to enhance corrosion protection against chloride environments. The lath is produced by spot welding galvanized steel wire and was tested pre-welding, post-welding and after a post-weld chromate treatment. The effect of the weld joint and the chromating on the initial rapid corrosion, typical of zinc embedded in cement-based materials, was first investigated. Despite the loss of zinc at the welds, there was little difference in corrosion rates of the non-welded and welded specimens. The chromating, however, was found to be highly beneficial in eliminating the initial rapid corrosion. A second set of tests investigated the comparative corrosion behavior of the lath in OPC-based stucco and a commercial calcium-aluminate-based stucco (Stucco A) in chloride solution. The study showed the Stucco A to provide less protection than the OPC stucco. Addition of lime to Stucco A, which is not recommended by the manufacturer, resulted in greater corrosion protection.