Effects of extended discharge time and revolution counts for ready-mixed concrete.
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Effects of extended discharge time and revolution counts for ready-mixed concrete.

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  • Abstract:
    Specifications for ready-mixed concrete limit drum revolution and mixing time to 250 drum revolutions and/or

    1.5 hours 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, these limitations could potentially increase

    construction costs without additional benefits, especially when longer transport distances are required. Because

    there have been significant changes in concrete constituent materials (e.g., chemical admixtures) and equipment

    since these limits were first implemented, research is needed to assess the effects of time to discharge and drum

    revolution counts on concrete performance. The objective of this research program is to evaluate and verify

    whether existing specifications for mixing and transporting concrete are applicable for today’s materials and

    equipment and if not, to identify key variables or tests that can ensure adequate placeability and good mechanical

    and durability characteristics. This study evaluated the influence of coarse and fine aggregate, supplementary

    cementitious materials quantity and type, chemical admixtures, temperature and mixing time and drum revolution

    on the mechanical and durability characteristics of concrete. Results indicate that existing specifications may be

    appropriate due to loss of workability. However, mixing time and drum revolution counts had no significant effects

    on the majority of mechanical properties and durability characteristics of ready-mixed concrete and results from

    this research indicate that existing specification limits are very conservative.

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