Judgement of Compaction Degree of Extremely Stiff Consistency Concrete by Pore Water Pressure Gauge

Abstract

This research was carried out to develop a simple method to judge the compaction degree of roller compacted dam concrete. For this purpose, the extremely stiff consistency and lean mix concrete was placed into prisms and large scaled specimens, and compacted by surface vibrator. The compaction process was observed through a transparent side panel of the specimen mould and the cement paste pressure was measured simultaneously by pressure gauge embeded in the bottom part. On the other hand, compressive strength was measured at the age of 28 days. 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. The pressure in cement paste increased only a little at early compaction stage, subsequently increased rapidly and attained to the maximum value at a certain compaction level, and then turned to decrease. The periods taking to reach to the maximum pressure were nearly equal to those corresponding to the maximum compressive strength. Therefore, the adequate compaction degree could be judged by measuring the cement paste pressure from embeded pressure gauge during compaction process. It was observed that this method could be also applicable to the concrete with maximum size of 80mm coarse aggregate. Still more, the gauge attached to the end of steel pipe was embeded in the large scaled specimen, and after compaction effort the pipe could be pulled out easily and be reused.