【作者】 刘杨；

【导师】 董事尔；

【作者基本信息】 西南石油大学 ， 结构工程， 2011， 硕士

【摘要】 大体积混凝土浇筑完成初期,由于水泥水化放热引起混凝土内部温度急剧攀升而导致其表里温差超限,加之表层混凝土水分散失而造成的干缩变形,从而可能产生危害性极大地贯穿性裂缝。由混凝土干缩与自收缩所引发的表层裂缝虽不影响结构的安全性能,但部分超出规范要求的表层裂缝会降低结构的耐久性、防水性和整体性以致引起钢筋锈蚀等不良后果。因此,无论是有碍观瞻的表层裂缝还是危及结构安全的有害裂缝都是工程施工中必须严格加以控制的。本文以某核电站核岛底板大体积混凝土工程实例为背景,主要针对以下几个方面进行了深入地探讨与研究：(1)阐述大体积混凝土裂缝的成因与发展机理；(2)在施工方案期间,基于热传导基本原理将有限差分法与MATLAB软件结合,对核岛底板大体积混凝土温度场展开预测性计算,准确地实现早期混凝土内部温度场的可视化,得到核岛底板温度及温升曲线走势图；(3)分析不同入模温度与计算模型差异分层厚度情况下的温度场发展规律,确定早期混凝土温度场发展的主要受制因素；(4)在得到核岛底板温度场基础之上,运用地基长墙模型测算出底板在外约束作用下的温度应力值,验算基于抗裂标准的温度应力极值,提前优选出最佳的混凝土入模温度,为科学地制定各项施工方案及养护布置提供理论依据与指导；(5)讨论混凝土入模温度选择值的经济合理性以及其他施工措施的辅助作用；(6)针对裂缝产生的原因及特点,制定有效的应对措施是成功控制裂缝形成与发展的关键所在。本文在实际的裂控方案中,从构造设计与现场施工两大方面入手,总结与分析出一系列行之有效的技术措施,与此同时,提出了多种应对温度应力与温度裂缝的新工艺与经改善的施工方法。具体的方法与思路包括优选原材料、科学制定配合比、提高混凝土的浇筑质量、严控混凝土温度及温升峰值、减缓混凝土温降梯度、抑制混凝土收缩变形、提高混凝土抗拉强度值、释放或解除混凝土所受约束以及加强温度与温度应力监测等；(7)将预测计算得出的结论与实测情况进行比对分析,检验预测计算的可靠性,总结出了大体积混凝土温度场与温度应力随龄期演变的基本脉络,并据此提出一些关于大体积混凝土裂缝控制的建议与意见。更多还原

【Abstract】 At initial stage of pouring completion of mass concrete, due to the sudden temperature rise of concrete resulting from the cement hydration heat, the temperature difference inside and outside of concrete excesses its limit. In addition, moisture dissipation on surface layer of the concrete results in shrinkage deformation, and then generates hazardous penetrating crack. Surface cracks caused by drying shrinkage and autogenous shrinkage of concrete though dose not affect the safety performance of the structure, some of them exceed the requirements of Specifications will reduce the durability, waterproofing and integrity of the structure which bring about steel corrosion and other adverse consequences. Therefore, whether they are unsightly and unharmful surface cracks or the harmful cracks which endanger the structural safety must be strictly controlled in construction.Taking the nuclear island basemat of a nuclear power plant as an example, mainly carrying out the following aspects research and discussion:(1) Describing the causes and development mechanisms of mass concrete cracks;(2) Combining finite difference method with MATLAB software bases on the heat conduction principle, carrying out predictive calculation for the nuclear island basemat mass concrete temperature field, achieving the visualization of early concrete internal temperature filed accurately, receiving the temperature curve chart and temperature rise during the period of construction program;(3) Analyzing the temperature development law in the condition of different placement temperature and layer thickness, to determine the main restricted factors of temperature field development;(4) Using the model of a long wall on the foundation to calculate the temperature stress of basemat under the external constraints on the basis of temperature field, checking the temperature stress extremum according to crack resistance standard, obtaining the optimal placement temperature of concrete in advance. These prophase efforts provide a theoretical basis and guidance for formulating construction programs and curing arrangement scientifically;(5) Discussing the economic rationality of concrete placement temperature as well as the supplementary role of other construction measures;(6) For the reason and characteristics of cracks, drawing up effective response measures is the key to control the formation and development of cracks. This paper elaborates the actual crack control scheme, mainly involves structure design and site construction, summarizes and analyzes a series of effective technical measures, at the same time proposes a variety of new technology and improved construction methods to control temperature stress and temperature cracks. The specific methods and ideas include the selection of raw materials, formulating mixing proportion scientifically, improving the quality of concrete placement, and strictly controlling the temperature rise and the temperature peak, delaying the cooling rate, inhibiting concrete shrinkage, increasing concrete tensile strength value, releasing or discharging constraints suffered by nuclear island basemat concrete and strengthening the monitoring of temperature and temperature stress.etc;(7) The article compares the predicted results with measured situation, tests the reliability of the prediction calculation, summarizes the basic context with age evolution of mass concrete temperature field and temperature stress. And thus proposes some suggestions and advice about crack control of mass concrete.更多还原