2. Compacting concrete test block by mechanical vibration method. Fill the concrete mixture with a trial mold at a time, preliminarily tamp it with a vibrating rod to make it higher than the trial mold, put it on a vibrating table, hold the trial mold with one hand, put pressure on the upper surface of the concrete with an iron trowel with the other hand, and constantly control and wipe it back and forth. To determine the vibration time according to the slump of concrete, it is necessary to ensure that the stick can be compacted. When the vibrating time is coming to an end, use an iron trowel to scrape off the excess concrete on the surface and smooth the surface. The vibration time of each block in the same group should be the same.
thirdly, manually tamp the test block. The concrete mixture is divided into two layers, each layer is about 1/2, and the number of tamping in each layer is generally 2 5 times. When tamping, it should be carried out evenly from the edge to the center on the whole area of concrete. When tamping the bottom layer, the tamping rod should reach the bottom surface of the trial mold, and when tamping the top layer, the tamping rod should be inserted 2-3 c m below the bottom surface of the layer. After tamping the surface layer < P >, it should be rammed several times along the four-sided mold wall with a trowel, so as to eliminate the bubbles at the interface between the concrete L and the trial mold, and avoid the phenomenon of honeycomb and pits. Then, the float should be used to scrape off the excess coagulation on the surface and polish the surface to make the concrete slightly higher than the trial mold. After standing for half an hour, the test block is plastered for the second time, and the test block is carefully polished and smoothed, so that the size error of the test block is controlled < P >. After the test block is formed, cover the surface with wet cloth, leave it at room temperature of 1 62 for less than one day and night, but not more than two days and nights, and then dismantle the test block. After the test block is dismantled, it should be numbered immediately, and the concrete strength grade, representative engineering parts and production date should be clearly written on the test block.