International Concrete Abstracts Portal

A study of concrete water tanks in the Province of Ontario indicated an unusually high rate of deterioration. The different types of tanks in existence are described, and observed defects and possible related mechanisms are discussed. Particular attention is directed to freeze-thaw cycles and internal ice formations, and methods for estimation of these effects are proposed. Criteria and recommendations for the design of reinforced concrete storage structures in both freezing and nonfreezing environments are discussed.

Describes deterioration of concrete in the chambers and the culverts of Eisenhower Lock that were observed soon after the lock was completed in 1958. Investigators from the U.S. Army Engineer Waterways Experiment Station postulated that the most probable cause of deterioration was pressure created by freezing water in critically saturated concrete that was not mature enough to withstand the pressure. Slow strength gain of the concrete was believed due to the use of natural cement. The investigation conducted prior to repairs performed at Eisenhower Lock in the winter of 1985-86 suggested that poor durability of the in-place concrete may have been caused to a large extent by inadequate control over concrete operations during construction works. Therefore, all precautions have been taken to assure that the newly placed concrete will perform adequately under severe service conditions. The only operation that caused concern was adding hot water at the project site to the dry concrete mix containing portland cement.

Concrete bridge decks have long been a problem for the design and construction industry. They have a tendency to crack and/or spall over time. The deicing process then creates problems because of salt intrusion into cracks. These cause spalling and ultimate deterioration of the reinforcing steel and the load-carrying ability of the concrete slab. The author wrote specifications concerning methods to produce a bridge deck that should be relatively crack free and thus enhance the long-term durability of the slab. Some items specified included long-term wet-mat curing, better concrete quality control, and a reduction of the water-cement ratio by 20 percent below standard specifications. He further discusses the utilization of retarders and high-range water reducers to accomplish the objective. The author then covers other methods in the literature such as epoxy-coated reinforcing bars as part of the overall process to produce a bridge deck that is relatively maintenance free over the long term.

Presents a simple design aid for predicting long-term (up to 50 years) movements in reinforced concrete columns and bridge beams made of normal and lightweight aggregate concrete. The method is based on the principle of superposition using a creep factor chart, which takes into account varying sizes of members, age at loading, exposure conditions, and the percentage of reinforcement, and it requires only a knowledge of the concrete strength and the loading history of the member. The method is developed from the study of in situ movements in two reinforced concrete structures subjected to increment loading. The shrinkage strains in columns are predicted using a shrinkage chart, which requires only a knowledge of elastic modulus of concrete at 28 days. The predicted load-induced and basic strains show excellent agreement with measured strains in the two structures, and the method shows good agreement with literature. The paper demonstrates how the simple method of predicting long-term movements in buildings and bridges can be utilized by the structural engineer as a designer's tool.

In seismic zones, severe earthquakes occur within a certain period. However, the important functions of a concrete structure must be maintained after the earthquake. Hence, structures must be designed for safety during the earthquake and serviceability after the earthquake. The acceptable level of damage can be varied in accordance with the type and importance of the structure. When a reinforced concrete structure suffers significant plastic deformation, residual deformation and large crack opening in the structure are impaired. A new and rational seismic design method was proposed. The peculiarity of the concept of the design method is as follows: Seismic design should be performed to fulfill required serviceability after the design earthquake as well as required safety during the earthquake. High magnification factor due to dynamic response was introduced according to actual observation in the earthquakes. Reduction factor referred to the acceptable level of damages in the structure after the earthquake was introduced. The importance of design details was emphasized. Furthermore, the influence of axial compressive force on the ductility was pointed out.