Evaluation of Fracture Properties of Various Concretes

作为研究工作的第一步，基于混凝土的断裂力学，对高强混凝土、自密实高性能混凝土等各种混凝土的断裂性能进行了评价。自密实高性能混凝土是一种非常有前途的新型混凝土，因为它在浇筑过程中不需要压实。然而，从断裂力学的角度来看，由于自密实高性能混凝土中含有的粗集料数量显著减少，从而提供了足够的流动性，因此与传统混凝土相比，它提供的断裂能更少。另一方面，由于高强混凝土中粗骨料的含量与普通混凝土没有显著差异，所以高强混凝土的断裂能呈现出与普通混凝土相同的趋势。作为第二步，对测定混凝土拉伸软化曲线的试验方法进行了广泛的研究。拉伸软化曲线是混凝土断裂力学的重要参数之一。本研究提出了一种确定混凝土拉伸软化曲线的新方法。在该方法中，考虑了弹性应变能的释放。此外，基于对纵向应变分布的测量，可以准确地评估虚拟裂纹的扩展。虽然这种新方法与反分析方法相比非常简单，但它可以相当准确地预测混凝土的拉伸软化曲线。最后，基于所获得的断裂特性，对使用不同混凝土的结构混凝土的尺寸效应进行了数值预测。

As the first step of this research work, fracture properties of various concretes, such as high strength concrete, self-compacting high performance concrete, etc. have been evaluated based on the fracture mechanics of concrete. Self-compacting high performance concrete is a very promising new concrete because it does not need the compaction during casting. However, from the viewpoint of the fracture mechanics, it is found that it will provide less fracture energy compared with conventional concrete because the amount of coarse aggregates included in self-compacting high performance concrete is remarkably reduced to provide the sufficient flowability. On the other hand, the fracture energy of high strength concrete shows the same tendency as conventional concrete because the content of coarse aggregates in high strength concrete is not significantly different from conventional concrete.As the second step, the experimental method to determine the tension softening curve of concrete has been investigated extensively. The tension softening curve is one of the most important parameters for the fracture mechanics of concrete. In this research, the new method to determine the tension softening curve of concrete has been proposed. In this new method, the release of elastic strain energy is taken into account. Moreover, the extension of the fictitious crack can be evaluated accurately based on the measurement for longitudinal strain distribution. Although this new method is quite simple compared with inverse analysis, it can predict the tension softening curve of concrete with reasonable accuracy.Finally, the size effect of structural concrete using various concretes is numerically predicted based on the obtained fracture properties.