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Concrete for the twenty first century can be much stronger, more durable and at the same time cost and energy efficient. However, this will not be possible unless we understand this material better. In spite of its wide spread use, compared to other structural materials there is very little well organized expenditure on research and development of concrete. One critical gap in our understanding is relating microstructure with macroscopic properties, and relating what happens at the ionic level to the response of concrete structures. Integrating the understanding of microstructure with processing and engineering properties is one of the major goals of our Science and Technology Center for Advanced Cement-Based Materials in the United States, established in 1989. Interactions with Industry have flourished due to the coordinated multidisciplinary and multi-institutional approach of the center. The Industrial Affiliates Program has eighteen members representing a wide range of internationally active corporations who provide invaluable input regarding the commercial significance of the Center's research. An overview of some of our new research results will be presented. The center has made significant progress in (1) characterizing pore structure, (2) developing experimental tools and computer models to relate evolving pore structure with permeability and conductivity, (3) understanding rheology, (4) designing a new class of organo-silicate composites, (5) untlerstanding fracture process zone, and (6) high performance fiber reinforced composites.

Fly ash, a by-product from the coal-burning power generation process, is often used, for its pozzolanic properties and its fineness, to enhance the strength and durability of concrete and high-strength concrete. The quality assurance of fly ash is frequently questioned since its properties tend to vary depending on the source of coal, type of boiler, pulverizing equipment, and the removal efficiency of the air pollution control devices. Since fly ash is cornmonly used as one of the main components in the development of high-performance concrete, a closer look at the effects of fly ash on the properties of high-performance concrete is critical. In this study, two types of fly ash, dry and wet bottom ashes of different particle size distributions, were used. Physical and chemical properties of these fly ashes were tested and compared with the original feed fly ashes received directly from the utility. The effects of these fly ashes on the strength of concrete were studied when used as 15, 25, 35, and 50 percent cement replacement by weight of cement. The results show that fly ash, when proportioned properly, can enhance the properties of concrete. The chemical composition of fly ash of different particle size distributions varies slightly. For the same type of fly ash, the finer the particle, the higher the specific gravity. The smaller fly ash particle has a faster reactivity rate than the coarser one. The compressive strengths of several selected mixes of fly ash concrete are equal to, or higher than, the control concrete before the age of 28 days. For fly ash with large particle size distribution, the fly ash concrete reaches only 85 percent of the control concrete strength at the age of 180 days. It was also found that fly ash concrete exhibits excellent acid resistance when compared to conventional concrete.

This paper discusses recent research on high performance concrete with a focus on cemenentitious materials designed for durability. A major key to suchp erformance originates with the concrete microstructure. Recent advances in optimizing cement and concrete materials by using calculated packing diagrams offer the promise of superior products achieved by increased packing efficiency. A high packing density coupled with adequate processing and cement binder characteristics makes possible the formation of a fine microstructure. In turn, this fine microstructure results in a low permeability and therefore provides a resistance to aggressive forces from the environment, which together enhance its long term durability. The favorable interaction among physical and chemical phenomena gives rise to better long term performance, whether the application is structural, or chemical, such as in waste management.

Flowable concrete has been used for a long time in Thailand and has been known as tremy concrete for bored pile construction. For this type of concrete, strength may be less important in early development, but workability must satisfy the performance in construction. In the second stage of development, research has concentrated on high strength concrete. Even though higher strengths have been achieved, workability of the concrete may be slightly poor. Several studies have emphasized utilization of concrete here high strength can be an advantage. The structural members were both reinforced concrete and prestressed concrete; and the emphasis was placed on flexure, shear, and compression. In recent development, both workability in the fresh state and strengths in the hardened states have been considered so as to satisfy the performance in workability, strengths, serviceability, and durability. Efforts have been concentrated on constituent materials for high performance concrete, mix proportions, and concrete properties. Satisfactory structural behaviors for compression, flexure, and shear in reinforced and prestressed concrete members have been reported. Various developments to suit particular applications such as bored pile, mass concrete, structural concrete, and durable concrete have been made for the construction industry. Demands of HPC are growing, further development and utilization are expected.

Taiwan, with a population of over 21 million and situated within only 36,000 sq km of land, has achieved miraculous economic growth in the last 20 years. This economic achievement has transformed the national image from one of underdeveloped work force to that of a global economic power. The mass volume of concrete construction which has occurred during the transition period has resulted in the near exhaustion of natural resources such as limestone, river gravel, and river sand. Diminishing supplies of limestone for the manufacture of cement and aggregate for making concrete have resulted in serious shortages over the last four years. In response to the crisis, the Architecture and Building Research Institute (ABRI) of the Ministry of Interior initiated a research program in 1991 to investigate all concrete-related industries in the private sector. A team of six professors and ten graduate students from five prominent universities were asked to examine these problems and to draft a national strategy to resolve the crisis at hand. The program was completed in June, 1992 and the final report is being used to guide the process of bolstering the domestic concrete industry. This aper presents an overview of current problems existing in the concrete related industries, methods used in investigations, and suggested topics for current and future research. The proposed research programs were subsequently divided into three term stages with the objective of avoiding possible delays with the on-going Six-Year National Construction Plan and laying down a sound foundation for the development of high performance concrete (HPC) technologies in Taiwan. With the support from governmental agencies, high performance concrete has been successfully used in the construction of a few major highway bridges and an 85- story high-rise building that is currently under construction in Kao-Hsiung, the second largest city in Taiwan.