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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
January 1, 1987
Some of the problems experienced while placing concrete at the Ontario Hydro Darlington Nuclear Generating Station, located on the north shore of Lake Ontario, are described. Also presented are the novel placing methods and procedures used to overcome the placing problems to obtain the resultant quality concrete. Most of the concrete can be considered mass concrete because of its large dimensions. Placements in narrow walls have particular congestion problems and also require a slow placing rate due to formwork design limitations. Methods of achieving good consolidation and controlling time of set are described.
E. K. Schrader
Roller-compacted concrete (RCC) is rapidly becoming a popular material for dam construction, heavy-duty paving, and mass fill applications. Its economy comes primarily from being able to transport and place it in large quantities with minimal time and labor by using earthmoving or conveyor equipment. The no-slump mix is spread with bulldozers and compacted into a solid mass with large vibratory rollers. The effect of compaction methods, water content, and other variables on density, pore pressure, practical construction problems, and permeability are discussed.
D. Whiting, G. W. Seegebrecht, and S. Tayabji
Concretes were prepared at degrees of consolidation varying from 100 to 85 percent. Mixtures were typical of those used for pavement applications with cement factors ranging from 520 to 610 pounds per cubic yard (308 to 360 kg/m3) and air contents ranging from 5 to 9 percent. Additional concretes were intentionally overvibrated to the point of incipient segregation. Test specimens were cast for determination of compressive strength, bond of reinforcing steel to concrete, permeability of concrete to chloride ions, and resistance of concrete to freezing and thawing in water. Results show that compressive strength is reduced by about 30 percent for each 5 percent decrease in degree of consolidation. Bond stress is reduced even more dramatically, suffering a loss of approximately 50 percent for 5 percent reduction in degree of consolidation. Overconsolidation has little apparent effect on compressive strength, and may increase bond strength by virtue of displacement of air in these air-entrained concretes.
Makaoto Kagaya, Hiroshi Tokuda, andMakoto Kawakami
Adequate consolidating condition of concrete is generally judged by experiential observation, and even in such condition the internal composition differs from one in a specified mix partially as introduced in several papers and books. Furthermore, there are a number of unclarified points regarding this phenomenon, such as the relationship between consolidating condition and internal composition in fresh state and the properties in hardened state. This study was carried out to clear the adequate consolidating condition quantitatively based on the variation degree of internal composition measured by mix analysis and of mechanical properties. The vertical distributions of air content, water-cement ratio, unit contents of materials, compressive strength, tensile strength, and modulus of elasticity were measured in the prismatic test piece casted with changing the vibrating time. A parameter to evaluate the consolidating condition was proposed from the time-dependent variations of these distributions. The adequate condition is judged from this parameter, and the method for determining this one in situ was proposed also.
Fiber reinforced concrete is reinforced by a small amount of short fibers randomly dispersed into cement concrete, and this composite material is superior to normal plain concrete, with respect to flexural strength, impact resistance, and ductility. But the consistency of fiber reinforced concrete is extremely decreased by adding fiber so that, in some cases, it becomes difficult to place and mold by the ordinary method. These phenomena are observed irrespective of kinds of fibers used. The effects of compaction methods on the strength of fiber reinforced concrete with poor consistency and containing a fairly large amount of fibers were investigated. Conventional steel fiber and alkali-resistant glass fiber were used. Test specimens (10 x 10 x 60 cm) of plain and fiber reinforced concretes were compacted by external vibration with temporary or continuous compressive loading, and were tested in flexure. The mechanism of compaction effects was discussed. Test results indicate that the compaction with compressive loading increases the flexural strength of both types of fiber reinforced concretes and also does extensibility of glass fiber reinforced concrete, although the improvement is made within a certain limit of compaction loading.
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