超低温储罐基础大体积混凝土施工质量控制研究

Research on quality control of mass concrete construction for ultra low temperature storage tank foundation

液化天然气(LNG)超低温存储罐基础浇筑属于大体积混凝土施工,由于混凝土体量大、温度控制要求高、施工温差大等特点,质量控制关系到项目的成败,施工过程中应通过专家论证,确定合适的质量控制目标.实际施工表明:储罐外罐底板下加设适当厚度轻质混凝土隔离层,防止储罐泄漏时超低温液化天然气对混凝土基础的瞬间冻伤;混凝土施工阶段内部温升应不大于50℃,表里温差应小于25℃,降温速率应小于2℃/d;浇筑采用"分段定点,同步进行,一个坡度,分层浇筑,循序渐进,一次到顶"的斜面浇筑方法,一次浇筑到位,严格控制坍落度;混凝土的养护以保温保湿为主,初凝前喷雾养护,浇筑完成后12h内覆盖保温层;保温层应分层逐步拆除,当混凝土表面与环境最大温差小于20℃时,可全部拆除,并及时回填土;浇筑施工前,应根据混凝土热工计算结果和温度控制要求,编制测温方案,监测混凝土的入模温度、表里温差、降温速率及环境温度.各项技术措施以及质量控制要点取得了较好的施工效果.

The foundation construction of liquefied natural mass concrete construction. The quality control is related gas （LNG） cryogenic storage tank equipment belongs to to the success or failure of the project because of the large quantity of concrete, the high requirement of temperature control and the great difference in the temperature of the construction. In the eourse of construction, the appropriate quality control targets should be determined through expert demonstration. The actual construction shows that a suitable thickness light concrete isolation layer should be installed under the bottom plate of the external tank to prevent the instantaneous frostbite of the concrete foundation caused by ultra-low temperature LNG during the leakage of the storage tank. The internal temperature rise of concrete during construction shall be no more than 50 ℃, the temperature difference in the case shall be less than 25 ℃, and the cooling rate shall be less than 2 ℃/d. In the process of concrete pouring, a pouring gradient should be set, the concrete should be casted in layers and sections, and the slump should be strictly controlled. The curing of concrete is mainly heat preservation and moisture preservation, spray curing before initial setting, and covering the insulation layer within 12 hours after pouring. The thermal insulation cover layer should be dismantled step by step. When the maximum temperature difference between the concrete surface and the environment is less than 20 ℃, it can be completely removed. At the same time, the excavation should be backfilled in time. Before pouring construction, according to the results of concrete thermal calculation and temperature control requirements, the temperature measurement scheme should be worked out to monitor the concrete entry temperature, surface temperature difference, cooling rate and environmental temperature. And all the technical measures and quality control points have achieved good construction effect.