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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 14 Abstracts search results
September 1, 1993
N. Hasan, E. Faerman, and D. Berner
Underwater repairs to, and rehabilitation of, existing reinforced concrete velocity caps of the circulating water intake structure at St. Lucie Powerplant, Fort Pierce, Florida were made utilizing high-performance in a marine environment. Use of this repair technique avoided the necessity of constructing a cofferdam for repair work in the dry, and thus minimized interruption to plan operation, and resulted in considerable savings. Mix proportions for the high-performance concrete included cement, fly ash, silica fume, and antiwashout admixtures as well as high-range water-reducing and set-retarding admixtures. The mix proportions were tested extensively in the laboratory and field conditions to optimize the slump and the initial setting time of concrete while assuring early compressive strength requirements for conformance with the specified requirements. Large scale mock-up tests, utilizing both tremie and pumping methods, were conducted to simulate under water placement in the surf zone and to select the actual concrete placing method, rate of placement, and to identify surface preparation and protection requirements. Construction procedures for the new reinforced concrete slabs involving approximately 3000 yd 3 precast and tremie concrete utilizing a barge-mounted concrete batch plant; quality control and post-placement inspection measures are also discussed.
Editor: Paul Zia
Many recent innovations in advanced concrete materials technology have made it possible to produce concrete with exceptional performance characteristics. Recognizing the need to encourage the development of such high performance concrete technology and to expedite its transfer into practice, the ACI Technical Activities Committee formed a Subcommittee on High Performance Concrete (THPC) in 1992. High performance concrete is defined by THPC as concrete which meets special performance and uniformity requirements that cannot always be achieved routinely by using only conventional materials and normal mixing, placing, and curing practices. The requirements may involve enhancements of placement and compaction without segregation, long-term mechanical properties, early-age strength, toughness, volume stability, or service life in severe environments.The Symposium on High Performance Concrete in Severe Environments held at the ACI Fall Convention in Minneapolis, Minnesota on November 9, 1993, is the first formal activity organized by THPC. Co-sponsored by RILEM, the symposium emphasizes field applications. This volume contains 14 papers, of which 13 have been scheduled for presentation at the symposium.
M. R. Hansen, M. L. Leming, P. Zia, and S. Ahmad
Three types of High Performance Concrete (HPC) for highway applications were investigated: Very Early Strength (VES), High Early Strength (HES) and Very High Strength (VHS). Two of the objectives of the research were to measure the chloride permeability of these concretes and explore an alternate method using AC impedance. Many of the concretes had coulomb values of 4000 and higher, placing them in the "high permeability" category as specified by AASHTO T 277 - Rapid Chloride Permeability Test (RCPT). Coulomb values were also found to decrease with concrete age and with increased silica fume content. Coulomb values were found not to vary significantly with dosage of calcium nitrite used as accelerator, up to 6 gal/yd 3 (29.7 l/m 3). The AC impedance test results (ohms) were found to correlate well with the RCPT results (coulombs) and were sufficiently accurate to place the concretes in the proper chloride permeability category. The advantages of the AC impedance test are that it is faster and less expensive than the RCPT and it avoids the potential heating problem sometimes encountered in the RCPT. AC impedance was found to increase with concrete age and with increased silica fume content and decrease with increased calcium nitrite dosage.
J. Le Bris, P. Redoulez, V. Augustin, J. M. Torrenti, and F. de Larrard
The cable-stayed bridge which is being built across the Elorn river near Brest (western France) will have the world's longest span (400 m, or 437 yd) in this range of full concrete bridge. Besides a normal-strength concrete (C 35/6,500 psi), a lightweight concrete (LC 32/4,600 psi) is extensively used in the deck, in order to minimize the effect of dead load on the overall stability. But the most significant part of the loads to be carried by the bridge is due to the wind, with a maximum accounted speed (in the design) of 210 km/h (130 mph). Furthermore, the bridge is located about 3 km (2 miles) from the sea; thus, the wind will carry a large amount of chlorides. This is why the term serve environment seems to be appropriate for the Elorn bridge. Two grades of high-strength concrete--namely C60/ psi and C80/ psi--are used in the towers. For the first time in France--and perhaps in the world--a strength of 80 MPa (11,600 psi cylinder strength) has been used in the design of a bridge. Details on the concrete mix proportions, producing facilities, placing techniques and testing of samples are given in this paper. A special emphasis is put on the thermal curing aspects. As the thickness of the towers walls is 1.10 m (3.5 ft), the temperature can reach more than 80 C in the pylons. The effect of heat of hydration on the long-term strength and modulus was investigated. Also, finite-element calculations were performed, in order to predict the stresses induced by thermal gradients, and to choose the most appropriate curing (thermal insulation, time of form removal, and so on).
N. Miura, N. Takeda, R. Chikamatsu, and S. Sogo
In Japan, a new super-workable concrete, which has higher flowability and filling capacity, has attracted attention as being effective in rationalization of concrete execution. It can be applied for simplifying placing work while securing high quality of reinforced concrete structures. Especially in case of heavily reinforced structures, it is highly applicable because of its excellent filling capacity or lower consolidation effort. For several years, the authors have studied improvements of workability of some special concretes, such as anti-washout underwater concrete, expansive grouting concrete for inverted placement, and ultra high-strength in-site concrete, and have consequently succeeded in developing super-workable concrete, suitable for rapid placing or perfect filling without consolidation. The authors also have established a new evaluating method for segregation resistance of mortar and aggregate, that is useful to design mix proportion, or keep high quality of super-workable concrete in site. Recently, opportunities to apply super-workable concrete to several actual structures with difficult construction conditions have arisen. One is the LNG (liquefied nitrogen gas) in-ground storage tank, which has much complicated reinforcement at the junction of base mat and side wall, another is a tall, thin reinforced concrete wall, which must be placed from upper point, 6 to 8 m in height. This paper describes the basic properties of super-workable concrete, the new method of quality control, and a summary of applications to reinforced concrete structures mentioned.
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