Studies on Compaction Mechanism and Judging Compaction Degree of Extremely Stiff Consistency Concrete

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The extremely stiff consistency and lean six concrete was placed into prismatic specimen moulds and compacted by surface vibrator. The compaction process was observed through a transparent side panel of the mould and the cement paste pressure was measured simultaneously by pore water pressure gauge embedded in the bottom part. On the other hand, unit contents of internal constituent materials and compressive strength in each position in the vertical direction were measured. The conclusions are as follows.(1) Cement paste moved downward at early compaction stage, subsequently the moving direction changed to upward and spaces between aggregate particles were filled up thoroughly by cement paste.(2) The pressure in cement paste increased gradually with compaction periods and reached the maximum value just at the time the spaces were filled up, and then turned to decrease.(3) The air content in each position decreased with increase in compaction periods, and the content in lower position was about 1% higher than that in upper position. Water cement ratio in lower position was higher than that in upper position up to certain compaction periods, and after these periods the reversed trend could be observed.(4) The periods taking to reach the maximum pressure were nearly equal to those corresponding to the maximum compressive strength. Therefore, compaction degree could be judged by measuring the pressure. Still more, the gauge attached to the end of steel pipe was embedded in the large scaled specimen, and after compaction effort the pipe could be pulled out easily and be reused.