The durability of concrete structures is related not only to design and materials but also to construction. Construction quality is highly variable, and in severe environments any deficiencies will soon be revealed. To a certain extent, a probability approach to the durability design can take the high variability into account. For concrete structures in severe environments, construction quality and variability are key to any rational approach to more controlled durability. Performance-based concrete quality assurance during construction, along with proper documentation, is essential. Examples of recent applications are summarized.

The Sitra bridges are part of a causeway linking the main island of Bahrain to the island of Sitra, forming one of the most strategic road links in the Kingdom. The causeway is located in the aggressive marine environment of the Arabian Gulf. After just 30 years in service, the structural condition of the concrete bridges deteriorated so significantly that it was not economically feasible to maintain or repair them. At a cost of $280 million, the existing causeway is being replaced. This article presents some aspects relevant to the specification and execution of structural concrete on this project to satisfy the client’s stringent requirements for durability in the aggressive environmental and climatic conditions of the Middle East.

Asian Concrete Federation

Structural concrete in the Americas—a a timely event.

The 6th International Structural Concrete in the Americas Workshop was held March 19-20, 2010, in Chicago, IL. Eight sessions were held, with topics

including: Historical and Modern Concrete Structures in Latin America, Differences in Application of ACI Building Code in Latin America, Bridges and Modern Concrete Structures, Current and Future ACI Documents, and Concrete Structural Wall Systems.

The ACI Construction Liaison Committee (CLC) and the American Society of Concrete Contractors (ASCC) Education and Training Committee teamed up in 2005 to reach out to students interested in construction. As part of these efforts, the committees created the Concrete Construction Competition, a contest that requires students to take on a task that is very similar to one a Project Manager or a Field Engineer might face on a real construction project. Because ACI’s conventions are held at various locations in North America, each competition’s specific task has been and will continue to be structured around the location of the convention, with specific consideration of its climate, common project types, or regional materials. The task developed for the Spring 2010 Convention in Chicago, IL, had a sustainability theme.

This article is an introduction to a series of articles based on a technical session sponsored by ACI Committee E702, Designing Concrete Structures. This series is intended to build on that session. While the target audience is primarily young engineers in professional practice, the series will also be of use to more experienced engineers as a basic review. Numerous types of reports cross the desk or the computer screen of the practicing engineer on a daily basis. Reports can help engineers design correctly, monitor the progress and quality of construction, resolve construction problems, and provide a concise written record of events. The benefits gained from a report are limited by its quality and timing, so it is important to know what to request and when to ask for it.

A geotechnical report is the written summary of a geotechnical investigation—the process of boring, sampling, and testing to establish subsurface profiles and the relative strength, compressibility, and other characteristics of the various strata encountered within depths likely to have an influence on the design of the constructed environment. A geotechnical report can include soil classification, bearing capacity, lateral pressures, and the elevation of the ground water table. The report will also include recommendations on possible foundation designs suitable for the site and on the geotechnical aspects of site preparation.

Project specifications, including those that cite ACI 301, “Specifications for Structural Concrete,” and ASTM C94, “Specification for Ready-Mixed Concrete,” state time limits for the discharge of concrete.

1. When I told a contractor that concrete could resist a single cycle of freezing after its compressive strength reached 500 psi (3.5 MPa), he surprised me by saying that the testing laboratory found that his concrete had reached 500 psi (3.5 MPa) prior to the completion of finishing. He then wondered if that meant no protection against freezing was needed. What was the testing laboratory measuring and is it related to the resistance to frost damage of the concrete?

2. We’re placing columns and walls using a concrete mixture containing portland cement, fly ash, and slag cement. Our vertical forms don’t support formwork for slab or beam soffits, and we want to cycle them as quickly as possible.