水泥有初凝时间和终凝时间。一般初凝时间不得早于45min，硅酸盐水泥终凝时间不得长于6.5h，其他五类水泥终凝时间不得长于10h。
由于施工程序的原因，进行超声检测的基桩混凝土龄期往往不足28天。
Due to the process of the construction, the life-span of the stake-base concrete being detected by the ultra-sound is usually less than 28 days .
利用概率的方法，确定开裂概率和临界开裂风险来评价混凝土结构的早龄期开裂的可能性大小，并在混凝土挡土墙工程中应用。
The probability of concrete structure cracking at early age is estimated by cracking probability and critical cracking risk with probabilistic method for a real case of concrete wall.
利用概率的方法，建立分析早龄期混凝土开裂的数学模型，并利用一实际的混凝土挡土墙工程观测结果进行验证。
A mathematic model is set up by probabilistic method for analyzing concrete crack in early age, which is tested by the observation results of a concrete retaining wall case.
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