1956年,美国材料试验协会发表的研究报告指出:只要在混凝土拌和物能回复到塑性状态这样的时间间隔范围,甚至只要振捣器能插入混凝土拌和物内,二次振捣就能增加其强度。报告指出,无加气剂的混凝土拌和物间隔4 小时后进行第二次振捣,其7 天令期的抗压强度可增加36％;其28无令期强度和90天令期强度分 In 1956, a study published by the American Society for Testing and Materials pointed out that as long as the vibrator can be inserted into the concrete mix, the vibrator can increase its strength as long as the concrete mix can return to the plastic state. . The report pointed out that the concrete mixture without air-entraining agent was shaken for a second time after 4 hours, and its 7-day stress strength could be increased by 36%; its 28 no-strength and 90-day strength scores.