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首页> 外文期刊>ANCOLD Bulletin >THERMAL CRACKING IN LARGE CONCRETE PLACEMENTS: THEORY AND APPLICATIONS
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THERMAL CRACKING IN LARGE CONCRETE PLACEMENTS: THEORY AND APPLICATIONS

机译：大型混凝土中的热裂：理论与应用

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Large concrete placements such as those encountered in dam construction are subjected to severe stress conditions at early age due to the heat generated in the process of hydration of cement. These thermal stresses can be higher than those experienced by the structures during its service life. Being young concrete, its tensile strength is much lower than that of hardened concrete. Consequently if measures are not taken, thermal stresses could lead to the cracking of concrete. In the traditional approaches, the criterion of limiting the maximum temperature rise (in some cases both average and differential) is specified as the sole criterion to avoid thermal cracking. However, practical experiences has shown this approach to be superficial, being either conservative or unconservative depending on the conditions. This is due to the fact that thermal cracking occurs when thermal stresses exceed the current tensile strength of the concrete and accordingly temperature limits have no direct relevance. Also, traditional deemed-to-satisfy criterion of limited maximum temperature rise, based on experience(s) at past projects, would not be valid for today's conditions where cement types and construction techniques are very different. Consequently, some modern design and construction practices, such as Japanese standards, permit or require designers and contractors to develop their own procedures/criteria with respect to thermal crack control in concrete structures. A method involving the calculation of a thermal cracking index (ratio of thermal stress/tensile strength) would be a better and more rational approach. However, this method needs to consider structural, hydration, material, thermal and exposure parameters. As early-age concrete is in a semi-plastic state with the involvement of many interactive parameters such as creep, temperature, ambient conditions, strength gain etc., the evaluation of the thermal cracking index entails complex procedures. This paper presents the details of a numerical procedure (THERMAL) developed to predict the time-history of thermal cracking index. Examples are also presented to show where this procedure has been successfully applied.
机译：由于水泥水化过程中产生的热量，大型混凝土浇筑物（例如在水坝建设中遇到的混凝土浇筑物）在早期就承受严峻的应力条件。这些热应力可能会比结构在使用寿命期间承受的热应力高。作为年轻混凝土，其抗张强度远低于硬化混凝土。因此，如果不采取措施，热应力可能导致混凝土开裂。在传统方法中，限制最大温升的准则（在某些情况下是平均和差分）被指定为避免热裂纹的唯一准则。但是，实践经验表明，这种方法是肤浅的，根据情况可能是保守的或不保守的。这是由于以下事实：当热应力超过混凝土的当前抗拉强度时，就会发生热裂纹，因此温度极限没有直接关系。同样，基于过去项目的经验，传统的公认的最大温升限制标准也不能令人满意，对于当今水泥类型和施工技术差异很大的情况而言，该标准是无效的。因此，一些现代设计和施工实践（例如日本标准）允许或要求设计师和承包商制定有关混凝土结构热裂缝控制的程序/标准。一种涉及计算热裂纹指数（热应力/拉伸强度之比）的方法将是一种更好，更合理的方法。但是，此方法需要考虑结构，水合，材料，热和暴露参数。由于早期混凝土处于半塑性状态，并涉及许多相互作用参数，例如蠕变，温度，环境条件，强度增益等，因此，热裂指数的评估需要复杂的过程。本文介绍了用来预测热裂解指数的时程的数值程序（THERMAL）的细节。还提供了一些示例，以说明在哪里成功应用了此过程。

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