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测定了在不同轴向压力下,混凝土中各种直径的粗集料与水泥砂浆之间界面裂缝宽度的变化发展规律,表明水化硬化时,粗集料上下界面抵抗裂缝出现及扩展的能力差别极大。混凝土受压后,裂缝首先在粗集料下界面形成并迅速扩展,其裂缝宽度发展的突变点与混凝土宏观力学行为中的初始应力σ_i相应。上界面裂缝宽度趋于极大;或上界面不开裂而下界面裂缝宽度趋于极大,此时的应力水平则与混凝土的临界应力σ_(cr)相应。试验表明,粗集料粒径的大小对混凝土的临界应力大小有明显的影响,而对初始应力σ_i值则稍有影响。粗集料粒径小,可明显提高混凝土的临界应力,因此一般混凝土工程应尽可能使用粒径较小的粗集料。
The variation regularity of the interface crack width between coarse aggregate and cement mortar of various diameters in concrete under different axial pressures was measured. It was shown that the ability of the upper and lower interfaces of the coarse aggregate to resist the appearance of cracks and their ability to expand during hydration hardening great. After the concrete is compressed, the cracks first form at the interface under the coarse aggregate and rapidly expand. The sudden change of the crack width corresponds to the initial stress σ_i in the macroscopic mechanical behavior of the concrete. The upper boundary crack width tends to be extremely large; or the upper interface does not crack and the lower boundary crack width tends to be extremely large, and the stress level at this time corresponds to the critical stress σ_(cr) of the concrete. Experiments show that the size of the coarse aggregate has a significant influence on the critical stress of the concrete, but slightly influences the initial stress σ_i value. The coarse aggregate has a small particle size and can significantly increase the critical stress of the concrete. Therefore, in general, a coarse aggregate with a relatively small particle size should be used for the concrete project.