Journal of Performance of Constructed Facilities

Teaching through failure case studies complements and integrates the traditional civil engineering topics that are introduced with the lecture-based method. This paper describes the development of a course on failures at Worcester Polytechnic Institute with particular reference to the implementation of case study instruction and structuring of the course. The topic of failures is used to assess the decision-making process that underpins the life cycle of a facility, and the variables that affect the performance of this process. The primary objective of the case study method is to enhance learning through students' active participation in case presentation and discussion. The method is effective in blending real world situations and applications of theoretical and scientific principles.

The purpose of this paper is to describe the settlement behavior of posttensioned slab-on-grade. The two case studies illustrate that the amount of damage to the structure depends on how the posttensioned slab-on-grade deforms. For the first case study, about one-half of the posttensioned slab-on-grade was unaffected by soil movement and remained relatively level, whereas the remaining one-half of the slab settled. This caused the development of a slab crack and hinge point, where moderate damage occurred in the area parallel to the slab crack. The Skempton and MacDonald settlement criteria and the severity of damage versus foundation deformation parameters were applicable for this case. For the second case study, which was the settlement of deep fill, there was a tendency for the posttensioned slab-on-grade to tilt uniformly (no hinge point). This resulted in substantially less damage than the first case study, even though the maximum differential settlement was greater for the second case. The severity of damage versus foundation deformation parameters were not applicable for this case. One advantage of posttensioned slab-on-grade that was common for both cases was that the slab cracks were relatively small, due to the posttensioning (compression) effect, which enabled the slab to resist the tension forces due to fill settlement.

A bonded concrete overlay (BCO) is a concrete pavement rehabilitation method used to extend the life of an existing concrete pavement. The BCO should bond fully with the existing concrete, leading to a thicker composite pavement section, a much stiffer pavement, and a considerable decrease in pavement stresses. For one project, cost estimates for a BCO were half as much as for full-depth replacement of a pavement. In some cases BCOs have delaminated shortly after construction. This paper proposes a framework for identifying the causes of early age delamination in BCOs. The early age behavior of newly constructed BCOs is examined. The factors affecting the long-term performance of the BCO are the quality of the surface preparation, the materials used in the BCO, and the curing of the BCO. Weather monitoring during BCO construction is recommended. Methods of detecting and mapping delaminations are discussed. Several BCO delamination case studies are analyzed using this framework. The model is useful not only for investigating BCO performance but also for understanding and preparing BCO construction specifications.

Tilting of phosphoric acid storage tanks in the Chemical Fertilizer Factory in Aqaba, Jordan, was noticed a few years after the plant had been put to work. The amount of tilt continued to increase beyond the allowable limit and threatened to hinder the operational procedure of the factory. Field monitoring indicated an increase in the amount of tilt with time. Laboratory studies revealed that the tilt was due to a differential upheaval of the foundation soil resulting from the chemical reaction taking place between the acid that had leaked and the subgrade soil. Based on this study, solutions to rectify the current problem and minimize potentially similar problems have been presented.

Chloride extraction and realkalization are nondestructive, electrochemical treatments to halt and prevent corrosion in chloride-contaminated and carbonated concrete, respectively. The process actually removes chloride ions from the contaminated concrete by the principle of ion migration while at the same time raising the pH of the carbonated concrete through electro-osmosis. Concrete to be treated is first tested to determine the level of chloride contamination. Then, after preparing the surface, a steel or titanium mesh electrode is attached to the structure. The electrode is embedded in a nontoxic biodegradable electrolytic media. Next, electric contacts are established between the attached electrode and the steel reinforcement bars (rebars) inside the concrete. When an electric field is applied, chloride ions migrate away from the rebars and towards the externally attached electrode, eventually ending up in the temporary electrolytic media, which is then discarded. Simultaneously, alkali ions migrate from the electrolyte into the concrete, raising its pH to the original levels. The passivating layer of the rebars is thus reestablished to protect them from corrosion.

Since the discovery of the Australian continent by Europeans, the development of the country has been closely linked with the development of water resources. At the end of the 19th century, several arch dams were built in New South Wales, four of which are described in this paper. The four dams (Moore Creek, Gap, Korrumbyn Creek, Quipolly) had similar features, i.e., water supply storage with thin concrete arch wall. Despite their technological sophistication at the time, they became fully silted very quickly, with each one being used for less than 25 years. Although their structural design was advanced, the design of the reservoir systems (dam, lake, and catchment) was a failure. The designers did not take into account correctly the soil erosion and sediment transport processes, and no soil conservation practice was considered. The experience gained from these failures may be of use today to prevent practicing engineers from making similar mistakes.

Results of two recent questionnaires, one in 1993 and the other 1996, reveal that state Departments of Transportation are beginning to shift their priorities to emphasize inspection and rating of infrastructure. Specifically, the use of nondestructive evaluation (NDE) as a tool for maintenance decisions is increasing. In 1993, 94% of the state highway agencies responded to the survey; in 1996, 86% responded. The 1993 survey determined that steel is the material most often inspected with NDE and that concrete NDE techniques need further development. In the 1996 questionnaire, specific inspection information was acquired regarding both steel and concrete members as well as scour. In response to survey results, use of an ultrasonic imaging method for inspecting concrete structures is proposed. Finally, research directions are presented for future NDE development.