骨料粒径对混凝土灾变破坏影响的试验研究

发布时间：2018-04-19 19:30

本文选题：混凝土 + 尺寸效应　；参考：《燕山大学》2014年博士论文

【摘要】：混凝土是由水泥砂浆和石子等粗骨料组成的非均匀、各向异性的工程复合材料。由于其成本低廉，便于运输、施工和容易浇筑成任何形状，又具有良好的抗冻性、耐腐蚀性和较强的抗压强度，所以混凝土材料被广泛的应用在工业和民用等建筑中。但是，在一些重大的事故如地震中房屋的倒塌、一些堤坝的过早破坏等事件中，人们发现除去个别因施工质量等因素外，混凝土材料均没有达到设计时的强度就已发生破坏。后来经过研究发现，之所以混凝土结构的构筑物远低于设计值便发生灾变破坏，是因为人们没有考虑尺寸效应的影响。以往各国学者对混凝土的各种尺寸效应研究了很多，本文主要从混凝土试件的不同表面状态、不同骨料粒径这两种尺寸效应来研究它们对混凝土试件破坏的影响。本文研究手段主要是借助试验的方法。不同表面状态的试件分为浇筑表面的试件和切割表面的试件，浇筑表面试件为在试模里直接浇筑形成，试件外层主要为砂浆层。切割表面试件为由一大块混凝土试件切割而成，试件外层露出很多粗骨料。不同骨料粒径的试件为混凝土试件中骨料粒径分别为5-10mm、5-15mm、5-20mm。先对不同的试件进行了静压试验，对静压试验后试件的强度值、应变值进行了对比，并计算出了各个试件的吸收能。通过这些数值的对比，发现浇筑表面的试件无论是在强度值、应变值还是在吸收能上均大于切割表面状态的试件。不同表面状态下不同骨料粒径的试件在这三个参数的对比上也得到了一致的规律，，即最大骨料粒径较小的试件均大于最大骨料粒径较大的试件。接下来用白光散斑法分析了试件表面变形场的不同。文中用应变场涨落来定量分析混凝土试件应变场的局部化程度。试验后对比发现，不同的表面状态和不同的骨料粒径对试验后试件的应变涨落有着明显的影响，试件的局部化程度也不同，最终试件发生破坏的方式也不同。又对不同种类的试件进行了疲劳加载的试验。试验采集中分别借助了白光散斑法、超声法、声发射和低场核磁共振扫描的方法。通过白光散斑法的采集计算，得到了不同试件加载过程中的应变场。通过对比发现，这两种尺寸效应对混凝土试件的位移场及应变场的演化、剪切应变场的演化也有明显的影响，不同试件会有不同的破坏。用超声波法对疲劳后的试件进行了内部探伤，发现试件表面状态不同，骨料粒径不同，试件内部的损伤量是不一样的，即尺寸效应对试件的内部损伤产生了不同的影响。用声发射法分别对静压加载和疲劳加载的试件进行了采集。试验发现在这两种加载形式下，得到了与前述试验方法大致相同的尺寸效应影响试件破坏的规律。为了进一步分析不同试件内部的孔隙破坏情况，对疲劳后的试件进行了核磁扫描。通过核磁扫描后分析得到的T2谱图、孔径分布图、孔隙度以及成像图等，发现不同骨料大小以及不同表面状态的试件疲劳后，内部所表现出的孔隙破坏特征与之前所用试验方法总结得到的规律一致。这也进一步验证了本文总结的两种尺寸效应对混凝土灾变破坏影响规律的准确性。
[Abstract]:Concrete is an uneven, anisotropic engineering composite made of coarse aggregate such as cement mortar and stone. Because of its low cost, easy transportation, construction and easy pouring into any shape, it has good frost resistance, corrosion resistance and strong compressive strength. The concrete material is widely used in industry and civil and so on. However, in some major accidents, such as the collapse of the buildings in the earthquake, and the premature destruction of some dikes and dams, it is found that the strength of the concrete material has not been destroyed when the quality of the concrete is not reached to the design, and it is found that the construction of the concrete structure is far lower than that of the concrete. The design value will suffer catastrophic damage because people do not consider the effect of size effect.
In the past, many scholars have studied various size effects of concrete. This paper mainly studies the effect of the two size effects of different surface state of concrete specimen and different aggregate size on concrete specimen damage. The main method of this paper is to use the method of experiment. The test parts of different surface states are divided into pouring table. The test parts of the surface and the cutting surface are tested directly in the test die. The outer layer of the specimen is mainly the mortar layer. The cutting surface specimen is cut by a large concrete specimen, and the outer layer of the specimen shows a lot of coarse aggregate. The size of the specimen with different aggregate size is 5-10mm, 5-15mm, 5, respectively. -20mm.
The static pressure test of different specimens is carried out first. The strength value and strain value of the specimens after the static pressure test are compared, and the absorption energy of each specimen is calculated. Through the comparison of these numerical values, it is found that the specimen on the surface of the pouring is in the strength value, the strain value or the specimen in the absorption energy which is larger than the cutting surface. In the contrast of the three parameters, the specimens with different aggregate sizes are also consistent, that is, the specimen with the smaller size of the largest aggregate is larger than the larger size of the aggregate. Then the difference of the surface deformation field of the specimen is analyzed by the white light speckle method. The quantitative analysis of the concrete specimen by the strain field fluctuation is used in this paper. The degree of localization of strain field. After the experiment, it is found that different surface state and different aggregate size have obvious influence on the strain fluctuation of the test specimen, the degree of localization of the specimen is different, and the way of final specimen damage is also different.
The tests of fatigue loading of different kinds of specimens were carried out. In the test collection, the methods of white light speckle, ultrasonic, acoustic emission and low field magnetic resonance were used respectively. The strain field in the loading process of different specimens was obtained by the acquisition and calculation of white light speckle method. Through comparison, these two kinds of size effects were found to be concrete. The evolution of the displacement field and strain field, the evolution of the shear strain field also have obvious influence, the different specimens will have different damage. The internal test of the specimen after fatigue is carried out by ultrasonic method. It is found that the surface state of the specimen is different, the size of the aggregate is different, and the damage amount inside the specimen is different, that is, the size effect is inside the specimen. The damage of the Ministry has had a different effect.
The specimens of static pressure loading and fatigue loading are collected by acoustic emission method. It is found that under these two kinds of loading forms, the law of damage of the specimen with the same size effect as the experimental method is obtained.
In order to further analyze the void damage in different specimens, the specimens after fatigue were scanned by NMR. The T2 spectra, pore size distribution, porosity and imaging of the specimens were analyzed after the NMR scanning, and the characteristics of the internal pore damage were found after the fatigue of the specimens with different aggregate size and different surface states. It is consistent with the rules obtained by the previous method, which further validates the accuracy of the effect of the two size effects on the damage of the concrete.

【学位授予单位】：燕山大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU528

【参考文献】