终凝是指水泥加水拌和到水泥浆完全失去可塑性并开始产生强度的时间。
硅酸盐水泥的初凝时间不得早于45分钟，终凝时间不得迟于390分钟。
The initial setting time of Portland cement shall not be earlier than 45 minutes, final set time not later than 390 minutes.
产生原因：振捣后没有用拖板、刮尺抹平；混凝土未达终凝就在上面行人和操作。
Reasons: No scraping work after vibration; People walks or works on concrete before final set.
指出了商品砼的优点，详细分析了砼终凝前和砼终凝后出现裂缝的原因，并提出相应的控制措施。
The article points out the advantage of commercial concrete, expounds the cause of the crack before and after concrete coagulation, and presents the corresponding control measures.
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