Study on Quality Control Methods for High Performance of Extremely Dry Concrete

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The aim of this study is to discuss how to control the quality of extremely dry concrete. Compaction in the field is carried out using heavy vibratory rollers which can reduce the porosity of roller compacted concrete to relatively low values. Low porosity concrete leads to high strength and long term durability and thus it is important to optimize compaction procedures so that the compacted material is adequately packed.In this research, a compactibility test method developed by the authors is used to assess the efficiency of compaction and to evaluate the optimum mix proportion. The evaluation of the compaction character of extremely dry concrete show that maximum compaction is achieved by vibrating the concrete over 2.5 G of minimum acceleration. The relationship between compaction effort and filled volume ratio of a same mixture of extremely dry concrete is constant even if vibrating condition is different, and a compaction function is proposed. The optimum sand aggregate ratio is … More able to be selected by assessing the compaction effort attain 98% of filled volume ratio and the value is coincided to that from hammer test and VB test. The effects of fine aggregate and fly-ash as admixture on the compactibility is discussed as well as unit content of mixture too.Compaction mechanism of surface vibrator is discussed on laboratory medel test. The acceleration transmitted to compacting layr from surface vibrator decreases, and the frequency seems to be constant. But depending on a consistency of concrete and vibrating conditions the response of acceleration in the compacting layr diminish occasionally. As this lack of response of acceleration occurs when the exciting force of vibrator is over its weight, a heavier vibrator is advantage to effective compaction. Rigid support makes steeper distribution of acceleration and density in compacting layr but the porosity of upper layr is low. On the other hand springy support makes small difference in acceleration and density between upper and bottom layr.Mix proportion of precast concrete units manufactured by instance deform method is evaluated by comparing the results of compactibility test. Less