Influence of transport parameters on the fresh and hardened characteristics of ready-mixed concrete Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/xp68km78k

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  • Most specifications for ready-mix concrete (RMC) limit mixing time to 90 minutes and/or truck drum revolution counts (DRC) to 300 before discharge. These specifications have been in place for many years with the objective of ensuring the quality and performance of the finished concrete product. However, limited research has been performed to determine the validity of these limits. These limits could increase construction costs without increasing benefits. This is especially the case for concrete mixed for more than 300 truck DRCs and/or longer than 90 minutes that exhibits similar performance as those mixed for less than these limits. Because there have been significant changes in chemical admixtures and mixing equipment since these limits were first implemented in 1935, research is needed to assess whether these limits are still applicable. The objectives of this research program are to evaluate whether existing specifications for mixing concrete are applicable for today’s materials and equipment and if not, to identify key indicators that can be used for determining the acceptance of concrete mixtures. This study evaluated the influence of mixing time and truck DRC on fresh and hardened characteristics of concrete for several different concrete mixtures. Results from this research indicate that mixing time and truck DRC have no detrimental effects on the mechanical properties and durability characteristics when the mixtures exhibited good workability and castability. This research indicates that workability can be used as a key indicator for determining the acceptance of concrete and that time and truck DRC limits are not directly related to hardened concrete properties.
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