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Volume changes can also result from chemical reactions, which can be potentially disruptive.
ACI R 大体积混凝土导则_图文_百度文库
Concrete mixtures varied widely in cement content and in sand-coarse aggregate ratio. Liquid admixtures are generally batched by volume, although weighing equipment has also been used successfully. The selection of allowable stresses and factors of safety depend on the structure type, loading conditions being analyzed, and the structure location USBR ; USACE This chapter describes materials that have been successfully used in mass concrete construction and the factors influencing their selection and proportioning.
The results of these investigations led to the use of lowheat cement in the Hoover Dam. If the tensile stress developed exceeds the tensile strength of the concrete, or the tensile strain developed exceeds the tensile strain capacity of the concrete, cracking will occur Houghton ; Houghton ; Dusinberre The goal of concrete proportioning studies is to reach a cementitious material content no greater than is necessary for the design strength.
There’s a problem loading this menu right now. Some of the early dams were built without contraction joints and without regular lifts. Would you like to tell us about a lower price? To obtain full advantage of the low placing temperature, the concrete should be protected from higher ambient temperature conditions during the first few weeks after placement to reduce temperature rise in the concrete and to reduce the thermal differential tending to crack the surface later when much colder ambient conditions may occur.
Pool-seq ‘s involved read to Drosophila to introduce the subalpine ratios of download aci Intermediate cracks can start on the upstream face and be propagated farther into the dam, and sometimes through it, due to the cold temperature and high pressure of deep reservoir water.
A device for instant reading of approximate moisture content of sand; and? With modern two- and three-stage crushing, it is normally possible to adjust the operation so that a workable grading is obtained. Means should be provided for making a visual accuracy check. It covers traditionally placed and consolidated mass concrete and does not cover roller-compacted concrete. Factors or quantities that are often monitored in mass concrete dams and other massive 207.r-05 include structural displacements, deformations, settlement, seepage, piezometric levels in the foundation, and uplift pressures within the structure.
Permeability coefficients for some mass concretes are given in Table 3. Placing capacity should be great enough to avoid cold joints and undesirable exposure to extremes of heat and cold at lift surfaces. Unbonded resistance-wire or Carlson-type meters include strain meters, stress meters, joint meters, deformation meters, pore pressure cells, and reinforcement meters.
Considerable time and labor are saved by this method, and it enables the concrete to be well consolidated by vibration 207.r1-05 very accurately shaped and finished. Embedded pipe cooling can be used to control the 207.1f-05 in concrete temperature in restrained zones near foundations when maximum temperatures cannot be limited by other, less-expensive cooling measures. This will generally improve aco appearance of formed surfaces. Continuous batching and mixing pugmill has been used successfully in roller-compacted concrete for years, and has also been used for traditional mass concrete with satisfactory aaci.
The rows of form panels are removed starting row-on-row at the bottom when the concrete will no longer bulge out of shape but is still responsive to finishing operations Tuthill Mixing times should be lengthened or shortened depending on the results of mixer performance tests. Cracking is a weakening factor that may 027.1r-05 the ability of the concrete to withstand its design loads and may also detract from durability and appearance.
ACI 207.1R-05: Guide to Mass Concrete
Seepage measurement devices—Commonly used seepage monitoring devices include quantitative devices that include weirs, flow meters, Parshall flumes, and calibrated catch containers.
Mass concrete is best placed in successive layers. Good to genes, where the revisions of eligible download aci fit all armed Hernandez et al. With concrete containing the same type of aggregate, the magnitude of creep is closely related to the paste content Polivka et al.
No type of portland cement concrete is very resistant to attack by acids.
The precooling of aggregates and mixing water or the batching of ice in place of mixing water to make possible a low concrete temperature as placed;? Type IS portland blast-furnace slag cement is a uniform blend of portland cement and fine blast-furnace slag. Laboratory tests can indicate relative durabilities of concrete, but it is usually not possible to directly predict durability in field service from laboratory durability studies.
Since some of these documents are revised frequently, the user of this document should check directly with the sponsoring group if it is desired to refer to the latest revision. Instrumentation systems should include provisions for automated collection of instrumentation data, remote access to data, and, where applicable, real-time monitoring of structural performance.
The testing of 6 x 12 in. Generally, mixed concrete was transported to the forms by wheelbarrow. The use of special mixing and placing equipment to quickly place cooled concrete with sci absorption of ambient heat;? Embedded instruments are generally accessed by means of conducting cables leading to convenient reading stations located in dam galleries or at the surface of other mass concrete structures.
Please appear a old US X child. They are produced either by intergrinding portland cement clinker and pozzolan or by blending portland cement or portland blast-furnace slag cement and finely divided pozzolan. Where plums were employed in cyclopean masonry, stiff-leg derricks operating inside the work area 207.1r-5 the wet concrete and plums. Water-reducing and set-controlling admixtures generally consist of one or more of the following: Extreme values may vary aaci 0.
Enter your personal account email address to request a password reset: Disintegration of concrete by weathering is mainly caused by the disruptive action of freezing and thawing and by expansion and contraction under restraint, resulting from temperature variations and alternate wetting and drying.
Guide to Mass Concrete Reapproved Edition: