FUNDAMENTAL EXPERIMENTS ON COMPACTION DEGREE OF EXTREMELY STIFF CONSISTENCY CONCRETE INFLUENCED BY PLACING AND COMPACTING METHODS

Abstract

The following experimental facts regarding the compaction process of prismatic concrete specimen compacted by surface vibrator were clarified. Cement paste moved downward at early compaction stage, after this time the moving direction changed to upward and the interstitial spaces between aggregate particles were filled up thoroughly by cement paste. The pressure of cement paste near the layer bottom increased gradually with compaction periods and reached the maximum value just at the time the spaces were filled up. On the other hand, the periods taking to reach the maximum compressive strength were nearly equal to that corresponding to the maximum pressure. Accordingly the compaction degree could be evaluated by measuring the pressure. Subsequently the following facts were found. The propagation of compacting effect to lower part was difficult with increase in specimen height. The methods of concreting one lift by dividing into several layers and compacting each layer up to the certain compaction degree were more successful than those of concreting and compacting the lift at a time, and thin mortar layer placed on joint before concreting was also useful to make effective compaction. Combining the frequency and amplitude of surface vibrator appropriately was more successful than increasing its weight to make effective compaction. Especially combining high frequency and low amplitude was the most effective practically.