Nonconventional Concrete Technologies Renewal of the Highway Infrastructure (1997) / Chapter Skim
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4 Concrete Processing
4 Concrete Processing
Pages 63-73
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From page 63... ...
section investigates placement methods, especially if the concrete contains fibers or intrinsic reinforcements that might reduce the amount of labor needec! to place rebar.
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From page 64... ...
in controlled amounts, the delivery of blends either as slurries or dry mixes, and the placement of the mixes, usually as slurries, into forms or machines for final net-shaping. Every aspect of the production process must be controlled to optimize performance and properties, and higher levels of process control than are currently available will be required for nonconventional concrete technologies.
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From page 65... ...
numerous devices for the preparation ancl mixing of powders, such as t~vin-vee mixers, attritor mills, and ball mills. One novel approach to cement feecistock production wouIcl be to ball mill the powclers, using the aggregate itself as the milling medium.
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From page 66... ...
. Aciding small amounts of nucleating agents for the crystalline phases, such as ettringite, to eliminate such uncertainties as the induction period and the critical supersaturation levels for nucleation (prehydrated cement has been used in some laboratory studies as a nucleating agent to accelerate reaction)
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From page 67... ...
Nonconventional concrete may require higher intensity mixing and improved mixing processes to ensure better products. Continuous processes generally yield more consistent products than batch processes.
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From page 68... ...
to allow the fibers to co-mingle successfully (see Chapter 31. Third, assuring the quality of a mix full of chopped fibers is difficult, and process controls to avoid clumps of fiber sticking together are critical.
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From page 69... ...
MATERIALS TESTING AND QUALITY ASSURANCE Quality assurance is a key activity for any materials use, including concrete. It is important to be able to perform realistic and routine tests to provide specific information about the quality of a material, especially when current experience is superseder!
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From page 70... ...
The yield stress for concrete is about two orclers of magnitude greater than that of cement paste. Even with further improvement, however, the slump test will not provide sufficient information to allow the formulation of optimum decisions or the implementation of moclel-based design within an MSE-systems approach.
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From page 71... ...
(1989) showed that the function of the electrical conductivity or relative dielectric permittivity determined at low frequencies (approximately 1 KHz)
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From page 72... ...
The ability to probe and continuously determine free- and bound-water concentrations in the microstructure (e.g., neutron scattering or microwave methods; see above) may prove useful for handling workability issues as well as for predicting the final properties of the material.
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From page 73... ...
1 1 CONCRETE PROCESSING 73 only enhance the delivery, placement, consolidation, and finishing of concrete, it may also promise a new measure of control to meet target properties ant! performance specifications.
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