International Concrete Abstracts Portal

Recent literature suggests that there is considerable potential for reduction in the emission of CO 2 to the environment through the manufacture of new types of cement that do not rely on the calcination of limestone (and accompanying release of CO 2). The 1988 1-billion metric t worldwide production of cement accounted for 1 billion metric t of CO 2 release, i.e., 5 percent of the 1988 world CO 2 emission (human activity only). This is equivalent to the CO 2 emission of all Japanese activity. The use of lesser amounts of calcium-based cements could be achieved through their partial replacement by alkali-activated alumino-silicate materials, which do not release large quantities of CO 2 in their manufacture. The fostering of low-CO 2 high-alkali-based cements will mean a dramatic change in the research and development presently carried out in the USA and other countries. Alkalies are generally thought of as the cause of deleterious alkali-aggregate reaction. As a result, the tendency has been to avoid any addition of alkali portland cement products, often requiring cement manufacturers to supply low-alkali cements. The use of MANSMR spectrography for the determination of composition of alkali-activated cements, in combination with ASTM C 227 bar expansion, allows the prediction of potential for alkali-aggregate reaction. A preliminary study involving Al and Si MANSMR spectroscopy revealed that the alkali-activated alumino-silicate cements are the synthetic analogues of natural pozzolans that are known to effectively suppress alkali-aggregate reaction. These cements, even with alkali contents as high as 9.2 percent, do not generate any deleterious alkali-aggregate reaction, according to the ASTM C 227 bar expansion test. Industrial experience based on the use of alkali-activated slags in Eastern Europe since 1964, associated with the commercially produced alkali-activated cements in the US since 1988, suggest that high-alkali cements will ultimately improve the concrete used in buildings and highways, and also serve global need by reducing emission of CO 2 and reducing energy consumption during cement manufacturing. In terms of a 5 percent growth scenario, the predicted business as usual (BaU) world cement production for the year 2015 equals 3500 million metric t. Based on an amount of blended portland cement production on the order of 1850 million metric t (1000 portland + 560 slag + 290 fly ash) in the 21st century, the need for novel alkali-activated cementitious materials could be in the range of 1650 million metric t.

The future of the concrete industry appears to be bright from projections based on current trends in population growth, and increasing industrialization and urbanization. However, this optimism must be tempered with changing attitudes in society on ecological issues such as conservation of natural resources, durability of engineering materials, and environmental pollution. Due to increasing public concern with durability of concrete as a construction material, this subject is discussed in detail with reference to deficiencies in the science of concrete durability, methods of testing for quality assurance and service-life prediction, and education in concrete technology.

In the August, 1971 issue of the ACI Journal, the report of the ACI Board Committee on "Concrete--Year 2000" was published. That committee concluded that looking ahead 30 years in 1971 was as difficult as it was in 1900 to look ahead 70 years to 1970 because of the accelerating rate of change. That acceleration has not altered. It is believed that the least amount of progress has occurred in the area of cooperation under what, in 1971, the committee termed "advancements in attitude." It seems that there is more rather than less conflict and litigation among participants in concrete technology. One of the most significant improvements waiting to be made is in the area that some are calling "conflict resolution." In the 21st century, concrete technology will be alive and well, and continuing to make progress in some ways that cannot now be predicted.

Durability criteria for major bridges differ from those of most other structures in that, currently, major bridges are designed to serve for 100 to 125 years. Challenging this longevity are not only the normal physical and chemical attacks on the concrete itself and on the reinforcement, but also the intentional application of salts to highway bridge decks and, in the case of railroad and floating bridges, the accumulation of internal damage (fatigue) due to cyclic dynamic loading. Great progress has been made recently in identifying causes and finding preventive and mitigating measures aimed at specific phenomena. Advanced laboratory technology and equipment have been combined with field observations to describe the processes, prescribe tests for early diagnosis, and develop appropriate countermeasures. A number of tests of specific parameters have recently been developed and are now being implemented as mandatory criteria for concrete in major bridges designed for lives in excess of 100 years. Ever more refined linear elastic finite element analyses are being employed to reveal areas of probable cracking due to structural response. Rigid enforcement of specified quantitative criteria, focused on specific parameters, ignores the interactive complex processes involved. Excessive reliance on such criteria impedes rather than helps construction progress, and may on occasion be counterproductive to durability. What is required, instead, is a holistic systems approach that addresses not only individual processes and phenomena but their interaction.

The authors have been involved in concrete technology in the field over the past half-century. While there have been many beneficial advances, there have also been subtle, but important, regressions. To gain full advantage of concrete's potential, the undesirable effects of those regressive aspects must be corrected through a series of paradigm shifts. Performance requirements are changing, accentuating the need for new and advanced technologies. Concrete qualities other than 28-day strength must be recognized when durability is considered. High strength does not assure high durability. However, the characteristics that improve durability will generally produce higher strength than that required for structural purposes for concrete exposed to an aggressive environment. When this occurs, strength based on durability must be a deciding strength factor. Standard concrete practices are not always in the best interest of quality and constructability. These conditions are traced and solutions are offered. The principal concern is that most engineers are no longer trained to provide broad concrete industry leadership, as in the past. A major technical void has developed between design and construction teams. Just as geotechnical engineers took over foundation design, concrete engineers must be trained to lead concrete design and construction into the 21st century.